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Home , Brazing, CuproBraze, Gunmetal, Pickling, Solderability, Solder alloys

Soldering and of and copper alloys Contents

1. Introduction 4 5. Quality assurance 47

2. Material engineering fundamentals 9 6. Case studies 48

2.1. Fundamentals of copper and copper alloys 9 6.1 Hot-air levelling of printed circuit boards 48 2.2 Filler materials 10 6.2 Strip tinning 49 2.2.1 Soft solder 11 6.3 Fabricating heat exchangers from copper 49 2.2.2 Brazing filler 13 6.4 Manufacture of compact high-performance 2.3 or brazing pure copper 16 from copper 49 2.4 Soldering / brazing copper alloys 18 2.4.1 Low-alloyed copper alloys 18 7. Terminology 50 2.4.2. High-alloyed copper alloys 22 8. Appendix 51 3. Design suitability for soldering/brazing 26 References 57 4. Soldering and brazing methods 29 Index of figures 58 4.1 The soldering/brazing principle 29 4.2 Surface preparation 30 Index of tables 59 4.3 Surface activation 32 4.3.1 Fluxes 33 4.3.2 Protective atmosphere / Shielding gases 35 4.4 Applying the solder or brazing filler 36 4.5. Soldering and brazing techniques 37 4.5.1 Soldering with 38 4.5.2 Dip bath soldering or brazing 38 4.5.3 Flame soldering or brazing 40 4.5.4 soldering or brazing 40 4.5.5 Electric resistance soldering or brazing 43 4.5.6 Induction soldering or brazing 44 4.5.7 Electron beam brazing 45 4.5.8 Arc brazing 45 4.5.9 Laser beam soldering or brazing 46

2 | KUPFERINSTITUT.DE List of abbreviations

Abbreviations

Nd:YAG laser. Neodymium-doped yttrium garnet laser SMD Surface-mounted device PVD Physical vapour deposition RoHS Restriction of (the use of certain) Hazardous Substances EG Europäische Gemeinschaft EC European Community MIG Metal inert gas process TIG Tungsten inert gas process DVGW German Technical and Scientific Association for Gas and Water [Deutsche Vereinigung des Gas- und Wasserfaches]

Chemical elements and compounds

Ag Al Aluminium Ar Be C

CO2 Cr Cu Copper

H2

H2O Water HF Hydrofluoric acid Mn Ni

O2 Oxygen P Pb S Sulphur Sb Antimony Si Sn Te Tellurium Zn Zr

KUPFERINSTITUT.DE | 3 1. Introduction

Copper is a material that has been used by man for thousands of years because of its special properties. As a native metal, i.e. one that is also found naturally in its pure me- tallic form, copper was used early in human history because of its good malleability and formability and because of its colour. Copper thus became man’s first working metal.

With increasing industrialisation, other technique to be used, the choice of filler This booklet aims to reflect the current properties of copper became important, material and any preparative or state of soldering and brazing copper and such as its excellent electrical and thermal after-treatment procedures, need to be copper alloys in industrial applications, but conductivity and its resistance to carefully selected on the basis of the does not claim to be complete. As research atmospheric , and its generally materials to be joined. The factors that and development work in this field is high resistance to chemical attack. influence the solderability or brazeability of continuing, enquiries should be directed to Copper can form alloys with many a material are shown in figure 1 and need the German Copper Institute or corre- different metals and a large numbers of to be taken into account both individually sponding organisations. systems are now available that enable and in combination. mechanical and technological properties, A component is considered solderable or such as hardness, tensile strength, brazeable if the parent material is suitable strength, chemical resistance, resistance to for soldering or brazing, and one or more wear, to be modified in a controlled way. soldering or brazing techniques can be If their particular physical and mechanical applied, and if the parts to be joined are characteristics are taken into account, designed so as to facilitate the soldering/ copper and the majority of copper alloys brazing process and to ensure that the show a high degree of solderability or soldered/brazed part is safe under the brazeability. Fabrication process variables, conditions in which it is to be used [1]. such as the particular soldering or brazing

4 | KUPFERINSTITUT.DE Chemical and metallurgical Physical properties properties Mechanical properties

· Chemical composition · Wettability · Strength and formability · Oxidation behaviour · Solidus · Residual stresses · Corrosion behaviour · · Diffusion and solubility characteristics · , · Ability to undergo precipitation heat treatment specific heat capacity · Microstructure

Material suitability for soldering/brazing

Solderability or brazeability of a workpiece

Manufacturing suitability Design suitability for for soldering/brazing soldering/brazing

· Dimensional stability of the parts to be joined · Location of soldering/brazing seam or zone · Condition of surfaces · Cross-sectional ratios · Surface coating · Notch effect · Shape and size of the assembly gap or · Seam irregularities the gap/joint to soldered or brazed · Static or dynamic loads · Stresses in the region of the soldered/brazed joint · Location of inserted solder/ and air vents · Loading rate · Fastening of parts to be joined · Loading temperature · Solder or brazing filler metal · Load-transfer medium · Materials and methods of removal · Soldering or brazing cycle · Soldering/brazing rate · Post treatment · Joint clean-up · Joint testing

Figure 1 – Definition of solderability/brazeability (see [2])

KUPFERINSTITUT.DE | 5 Like , soldering and brazing are Soldering and brazing do not involve any The following points should, however, be important methods of thermally joining melting of the parent material, i.e. of the noted: the strength of a soldered or brazed materials, typically metals. As it is the surfaces to be joined. Instead, the joint is typically not as great as that of the resulting joint – irrespective of the method workpieces are joined by introducing an parent material; the parent metal and the used to make it – that ultimately deter- additional molten metal, the ‘filler metal’, solder/braze metal have different chemical mines the properties of the part being possibly in combination with a and/or potentials; there is a risk of chemical fabricated, the two methods are classified in a protective gas atmosphere [4]. corrosion due to the presence of flux (see e.g. [3]) in terms of the chemical residues; design restrictions may be nature of the joint, the chemical composi- Some of the advantages of soldering or relevant because of factors such as narrow tion of the parent metal (or metals) and brazing compared to other joining soldering/brazing gaps and tight dimen- the type of filler material used, if any. Both methods are: [5] sional tolerances at the joint. Extensive welding and soldering/brazing lead to the · soldering/brazing enables dissimilar preparatory and after-treatment proce- formation of a metallic joint, however the materials to be joined; dures are often required, such as degreas- chemical composition of these joints differ. ing, etching, removal of flux residues, etc. [6]. Whereas a welded joint has the same · as less heat is applied in the joining The related joining techniques of soldering chemical composition as that of the two process, soldered or brazed parts tend and brazing are distinguished in the identical parent metals being joined, the to exhibit greater dimensional accuracy DIN ISO 857-2 standard by the liquidus use of a filler alloy in a soldering or brazing and less distortion; temperature of the filler metal used. In procedure means that the soldered or · multiple soldered/brazed joints can soldering, the liquidus temperature of the brazed joint has a different chemical be created on a single workpiece in a filler metal is below 450 °C; in brazing it is composition to that of the parent single operation; above 450 °C. Up until February 2007, materials. A soldered or brazed joint · intricate assemblies can be soldered/ high-temperature brazing (at comprises the heat-affected parent brazed without damage; above 900 °C) was defined in the earlier materials, the diffusion/transition phase and now withdrawn DIN 8505 standard. · soldered/brazed joints exhibit good and the solder/braze metal. The solder Today, high-temperature brazing is thermal and electrical conductivity; and metal or braze metal can be formed by the classified simply as brazing. action of heat either with or without a · as soldering/brazing directs less heat filler material. into the joint than welding, there is less residual stress and distortion in the component.

Brazed joint

Brazing seam Ag72Cu28 brazed metal Brazed metal zone

Cu Ag

Diffusion zone

Heat-affected zone

Figure 2 – Example of a brazed copper-silver joint. (Note that no filler metal was used; the alloy Ag72Cu28 is formed by diffusion during the brazing process.)

6 | KUPFERINSTITUT.DE Both physical and chemical processes are Heat is applied to melt the filler metal and σ involved in soldering/brazing. Soldering/ any flux being used. The method used to 1,2 1 brazing joints are created through surface heat the parts to be joined will depend on chemical reactions and diffusional processes the type of join to be created (see ϑ σ1,3 σ2,3 2 of the liquid filler metal and the solid parent Section 4.3). Fluxes serve to activate the material. The soldering/brazing mechanism surfaces to be joined. The molten filler comprises the following steps: [7] metal will only be able to wet the surfaces 3 1. Heating of the parts to be joined to be joined if they are clean and free from oil, grease and other surface deposits. The 2. Surface activation, e.g. by a flux or a wetting process is also influenced by 1 Surrounding vapour phase shielding gas capillary action of the molten filler, 2 Molten filler 3. Flow of filler metal and wetting – the adhesion and diffusion processes between 3 Parent material ϑ Contact angle molten filler metal flows into the gap the liquid phase and the parent material. between the mating surfaces or spreads figure 3 shows the wetting of the surface σ1,2 Surface tension between molten filler and the across the surface by the molten filler metal. The contact surrounding atmosphere σ 4. angle ϑ is determined by the interaction 1,3 Surface tension between the solid base metal and Formation of the solder/braze metal the surrounding atmosphere through (physical and chemical) inter- between the three surface tensions σ2,3 Surface tension between molten filler and solid action between the molten filler and involved in the wetting process: σ1,2 base metal the parent material (vapour-liquid surface tension), σ1,3 (vapour-solid surface tension) and σ2,3 Figure 3 - Wetting of a metallic surface with a 5. Solidification of the liquid solder/braze (liquid-solid surface tension). liquid filler metal [7] metal.

Perfect wetting Adequate wetting Dewetting

ϑ = 0° ϑ ≤ 30° ϑ > 90°

Table 1 – Relationship between contact angle and degree of wetting [7]

The smaller the contact angle, the better does not melt, a diffusion zone is (the ‘holding time’) should be as short as the wetting of the surface. Table 1 defines established in the wetted area. An alloying possible to prevent extensive alloying the three regimes ‘perfect wetting’, element in the parent material and at within the parent metal or the formation ‘adequate wetting’ and ‘dewetting’ in terms least one of the alloying elements in the of brittle phases in the transition zones. of the corresponding contact angle. filler alloy combine to form a solid To achieve optimum strength in the solution, a or an soldered/brazed joint, the filler metal After soldering or brazing, alloying compound. Phase diagrams needs to remain in its liquid phase for elements from the filler metal can be can be consulted prior to soldering/ several seconds so as to create a found in the parent material and alloying brazing to determine whether any sufficiently deep diffusion zone [1] [6] [9]. elements from the parent metal are diffusion will occur between the metal detectable in the filler metal. This change pairs. Diffusion is both time- and in the chemical composition is referred to temperature-dependent. The time spent as diffusion. Although the parent material at the soldering/brazing temperature

KUPFERINSTITUT.DE | 7 Figure 4 depicts the cross-section of a locally heated soldered/brazed joint. The parent material was heated only in the region of the joint, as would be the case in torch brazing or torch soldering. This localised heating can increase the level of residual stress within the part. If the whole assembly is heated, as in furnace brazing or furnace soldering, the result is lower residual stress and less distortion. In this case, the entire assembly is heated and cooled uniformly, which means that the heat-affected zone covers the entire structure (i.e. all of the parent material). An advantage of this approach is that soldering/brazing can be carried out at the same time as heat treatment (e.g. precipitation hardening) of the workpiece.

1 2 3 A B 4

t

j

1 Parent material 2 Parent material affected by the soldering/brazing process 3 Diffusion zone / Transition zone 4 Solder/braze metal A Soldering/brazing seam B Heat-affected zone W t Component thickness 1 2 3 B j Effective joint width W Overlap or lap length

Figure 4 - Schematic diagram of a soldered/brazed joint [10]

8 | KUPFERINSTITUT.DE 2. Material engineering fundamentals

2.1 Fundamentals of copper and Copper alloys may be classified in terms of Copper alloys are also classified as copper alloys the treatment they have undergone: alloys, wrought alloys (e.g. strip, , Copper is a non-ferrous metal with a · Precipitation hardening alloys tubing, ) and sintered alloys. Some 3 of 8.94 kg/dm . Copper has a (e.g. CuBe alloys) and of the best-known copper alloys are face-centred cubic (fcc) crystal lattice (copper-zinc alloys) and structure and as such retains its excellent · Work-hardened alloys (=cold-worked (copper-tin alloys), but alloys of copper ductility and cold-working capacity down alloys), with nickel, manganese, aluminium, iron, to low temperatures. Cold working copper or in terms of their chemical composition: beryllium, chromium and silicon are also causes an increase in hardness (‘strain · Single-phase materials ((e.g. pure Cu) common. It should be noted that the terms hardening’, ‘work hardening’). or alloys that exist as a solid solution ‘’, ‘’, ‘Gunmetal’ and ‘nickel Copper also exhibits high electrical and of the elements (e.g. CuNi alloys, sing- silver’ are not standardised, though these thermal conductivity (the ratio of le-phase brass) and designations are still common commer- electrical to thermal conductivity is cially and elsewhere. constant) and shows good corrosion · Multiphase materials (e.g. two-phase resistance to a wide variety of chemical brass alloys) [11]. media.

Material group Coefficient of Electrical Thermal conduc- 0.2 % yield Tensile strength Elongation after

expansion conductivity tivity at 20 °C strength Rp0.2 Rm min. fracture 10-6/K [MS/m] W/(m∙ K) approx. N/mm² N/mm² A min. %

Cu 17,0 59,1 393 40 … 90 200 … 360 max. 42 CuZn 18,0 … 20,5 15,0 … 33,3 117 … 243 60 … 500 230 … 560 4 … 50 CuNiZn 16,5 … 19,5 3,0 … 5,0 27 … 35 220 … 660 360 … 800 8 … 45 CuSn 17,1 … 18,5 8,7 … 11,5 62 … 84 140 … 1000 360 … 1000 30 … 65 CuNi 14,5 … 17,6 2,04 … 6,4 21 … 48 90 … 520 290 … 650 10 … 40 CuAl 17,0 … 18,0 5,0 … 10,0 40 … 83 110 … 680 350 … 830 5 … 50 Unalloyed 12,0 5,5 … 7,0 48 … 58 175 … 355 290 … 630 18 … 26

Additional information on these materials is available from the DIN Handbooks 456-2 and 456-3 and from the corresponding material data sheets issued by the German Copper Institute (www.kupferinstitut.de)

Table 2 - Comparison of the physical and mechanical properties of copper, important copper alloys and unalloyed steel

KUPFERINSTITUT.DE | 9 2.2 Filler metals Phase diagrams can be consulted in order chemical composition (72 % silver, 28 % Copper can form alloys with numerous to determine key temperatures (melting copper). The eutectic alloy solidifies like a metallic elements. Many of these alloys are points, eutectic temperature), the mutual pure metal, i.e. there is no solidus sold commercially as semi-finished solubility of the elements and the phases temperature and no liquidus temperature, products or brazing and soldering filler present (solid solution, eutectic phases). It the molten mixture undergoes an metals. Filler metals are available in a is important to realise that the phase instantaneous phase transition from the variety of forms: , strips, preforms diagrams only apply under equilibrium liquid to the solid state. Solidification at (see figure 5), powders, pastes, etc. conditions. The phase diagram for the 780 °C is significantly below the melting Copper-based filler metals are character- binary silver-copper system is shown in points of the pure elements in the alloy (Cu ised by their good flow properties, good figure 6. The phase diagram has a number and Ag). When the eutectic mixture gap-filling ability and good ductility. of different phase fields that are separated solidifies, numerous crystal nuclei are from one another by phase boundary lines. formed that hinder each other’s growth Important phase boundary lines are the resulting in a uniform, finely divided liquidus and the solidus curves. The microstructure with good mechanical liquidus curve separates the higher lying properties. This is the reason why eutectic region L, which represents the homogene- alloys, such as Ag72Cu28, are frequently ous liquid phase and the liquid-solid phase used in technical and engineering lying below. The solidus line represents the applications [13]. boundary between the solid phase and the liquid-solid phase. The phase diagram for the copper-silver binary system also shows that there is a eutectic point at one specific Figure 5 – Filler metal preforms [11]

Composition (weight percentage) The filler metals are classified as soft or brazing filler metals depending 10 20 30 40 50 60 70 80 90 100 on the liquidus temperature. There are a 1200 number of criteria that can be used when 1084,87°C selecting a suitable filler metal: · Type and physical/mechanical 1000 961, 93°C L properties of the parent material · Dimensions and manufacturing Ag Cu 800 780°C tolerances of the workpiece · Stresses at the soldered/brazed joint · Operating temperatures and pressures 600 · Ambient conditions at the soldered/ [°C] Temperature brazed joint (e.g. aggressive media) · Cost-efficiency 400

· Work safety

· Soldering/brazing method [6]. 200 0 10 20 30 40 50 60 70 80 90 100 Ag Composition (atomic percentage) Cu

Figure 6 - Silver-copper phase diagram (from [14])

10 | KUPFERINSTITUT.DE 2.2.1. Soft crystals (diameter: approx. 1 µm; length: The filler metals used for soldering melt at several millimetres) that can cause short temperatures below 450 °C. The low circuiting and thus damage to electronic strength of soft solder alloys and of the components. These crystals grow very resulting soldered joint make these filler slowly so that they may take years to materials suitable for applications that are appear. Possible reasons for whisker subjected to low mechanical loads. They growth include residual stresses in find most frequent use in electrical and layers due to the presence of organic electronic applications. Soft solder alloys inclusions/contamination, and mechani- can be selected using the cally induced stresses when tinned DIN EN ISO 9453 (2014) or the DIN 1707- materials are processed. Lead-free 100 (2011) standards. alternatives for soft solders include tin-copper, tin-silver and tin-copper-silver In the past lead solders were often used to alloys. It should be noted that the price of solder copper pipes and tubing. The the solder increases the more silver it presence of lead improves the flow contains. In its technical application note characteristics of the solder, produces GW 2, the German Technical and Scientific bright smooth surfaces and requires only Association for Gas and Water (DVGW) moderate soldering temperatures. stipulates the use of the solders Sn97Ag3 However, lead is environmentally harmful and Sn97Cu3 for drinking water applica- and a recognised . Since 1 July tions. Antimony-free solders are used for 2006, the inclusion of lead in solders has fine soldering applications, antimony-con- been prohibited by the RoHS Directive taining solders and low-antimony solders 2002/95/EC of the European Parliament are used for coarse soldering work in, for and of the Council on the restriction of the example, the manufacture of condensers use of certain hazardous substances in and cooling units, in the electrical industry electrical and electronic equipment (later or for and installation work. superseded by Directive 2011/65/EU in Zinc-based and -based soft 2011). At present, exceptions exist that solders are used but are less common. permit the use of high-lead solders in Unlike brazing filler materials that contain certain sectors, such as medical, security cadmium, cadmium-containing solders are and aerospace technologies. In the not prohibited. However, as cadmium is electronics industry, lead-free tin solders regarded as harmful to health, the accident are now frequently used as a an alterna- prevention regulations (as published in tive. There is, however, a risk of the Germany by the relevant employers’ formation of tin whiskers on the surface of liability insurance associations) must be the metal. Whiskers are filiform single observed [15].

KUPFERINSTITUT.DE | 11 Group Alloy designation in acc. with Melting range Average chemical Preferred Areas of use (solidus/ liquidus) composition soldering method in °C DIN DIN EN ISO 1707-100 9453 (2014) Sn Pb Cu T I H D Part 100 (2011) Sn50Pb49Cu1 Electrical, – 183/ 215 50 bal. 1,4 X (162) electronics – S-Sn60Pb40Cu 183/190 60 bal. 0,15 X Electrical, Soft solders Sn60Pb39Cu1 electronics, – 183/190 60 bal. 1,4 X X with copper (161) PCBs Installation of copper Sn97Cu3 – 227/310 bal. 0,07 3 X X X X piping/tubing, metal (402) goods Sn Pb Ag – S-Sn50Pb46Ag4 178/210 50 bal. 3,5 X X Electrical, electronics, – S-Sn63Pb35Ag2 178 63 bal. 1,4 X X X PCBs Sn96,3Ag3,7 – 221/228 bal. 0,07 3,7 X X X X (701) Installation of copper piping/tubing; Sn97Ag3 – 221/224 bal. 0,07 3 X X X X electrical (702) Ag Cd Zn – S-Cd82Zn16Ag2 270/280 2 bal. 16 X X Electrical, Soft solders – S-Cd73Zn22Ag5 270/310 5 bal. 22 X X with silver electric motors – S-Cd68Zn22Ag10 270/380 10 bal. 22 X X Ag Pb Others Pb98Ag2 Sn Electrical, – 304/305 2,5 bal. X X (181) 0,25 electric motors Pb95Ag5 Sn for high operating – 304/370 5,5 bal. X X (182) 0,25 temperaturesr Sn Electrical, – S-Pb95Sn3Ag2 304/310 1,75 bal. X X 2,0 electric motors bal. for high operating – S-Cd95Ag5 340/395 5 0,1 X Cd temperatures Sn Pb P – S-Pb50Sn50P 183/215 50 bal. X Soft solders – S-Sn60Pb40P 183/190 60 bal. X Electronics, PCBs, with particularly drag, phosphorous – S-Sn63Pb37P 183 63 bal. X wave and dip soldering – S-Sn60Pb40CuP 183/90 60 bal. X

Sn Pb Others Sn50Pb32Cd18 Fine soldering – 145 50 bal. Cd18 X X X X Other soft (151) and cable solders – S-Sn80Cd20 180/195 bal. 0,05 Cd20 X X X Electrical engineering Sn95Sb5 – 235/240 bal. 0,07 Sb 5 X X X Industrial (201)

D-Dip soldering; H-Hot-iron soldering; I-Induction soldering; T-Torch soldering Table 3 - Soft solders for copper and copper alloys as classified in the DIN EN ISO 9453 (2014) and DIN 1707-100 (2011) standards

12 | KUPFERINSTITUT.DE 2.2.2. Brazing filler metals As an alloying element, phosphorous of the parent copper to yield copper The filler metals used to braze copper and shows low solubility in copper and is metaphosphate. By chemically reducing copper alloys are typically copper-based, present mainly as the intermetallic the oxide layer in this way, the surface of silver-based and brass-based alloys that compound copper(I) phosphide (Cu3P). The the parent copper becomes wettable. are suitable for fabricating joints able to mechanical properties of copper-phospho- Silver alloy filler metals and copper-phos- withstand higher levels of mechanical rous filler metals are determined by size, phorus filler metals with the appropriate stress. Brazing temperatures are usually shape and arrangement of the Cu3P DVGW or RAL quality mark are used for within the approximate range 500– particles, whose precipitation is a function brazing gas and water pipes. Silver alloy 1000 °C. DIN EN ISO 17672 (2010) divides of the phosphorous content. If the filler metals have relatively low melting brazing filler metals into classes. The filler phosphorous content of the filler metal is temperatures and exhibit good wettability metal classes suitable for brazing copper above 7 %, the brazed structure cannot be and adequate corrosion resistance in a are: ‘Class Cu’ (copper), ‘Class CuP’ cold worked. However, at temperatures of variety of media. Silver-copper-phospho- (copper-phosphorus), ‘Class Ag’ (silver about 300 °C and above, all copper-phos- rus filler metals are particularly well suited alloy) and ‘Class Au’ ( alloy). phorus brazing filler metals exhibit for brazing copper, Gunmetal, copper-tin Copper-zinc brazing filler metals are excellent formability. Filler metals with a and copper-zinc alloys. Up until 2011, recommended for brazing pure copper and wide melting range (e.g. CuP 179) can be cadmium was added to brazing filler high-melting copper alloys. As the amount used for brazing assemblies with large metals to further lower the melting of zinc in the brazing alloy rises to about joint clearances. As phosphorus has a temperature. Since December 2011, the 40 %, the melting temperature decreases deoxidising effect, copper-phosphorus use of cadmium-containing filler metals while the strength of the material filler metals tend to be self-fluxing and for brazing applications has been increases, which is why brass filler rods can therefore be used to braze copper and prohibited by EU (Regulation (EU) typically have a zinc content not exceeding to a certain extent bronze (CuSn6) 494/2011). They may only be used for 40 %. Small amounts of silicon (0.1 % to surfaces without requiring the use of a safety reasons or for defence or aerospace 0.2 %) are often added to avoid the forma- flux. This is because at high temperatures applications. tion of voids in the joint caused by zinc the phosphorus in the copper reacts with vaporisation and hydrogen absorption. the oxygen in the air to form phosphorus Torch brazing (also known as ‘flame pentoxide, which itself then reacts with brazing’) is carried out using a slightly the Cu(I) and Cu(II) on the surface oxidising flame of moderate intensity [16].

Figure 7 – Torch brazing a copper tube joint [12]

KUPFERINSTITUT.DE | 13 Average chemical Melting range in °C Designation in acc. with composition Brazing Usage notes (mass fractions in %) temperature in °C

DIN EN 1044 DIN EN ISO DIN EN ISO Application of (1999; previ- Sol. Liq. Parent material Gap width 17672 (2010) 3677 (1995) filler metal ous standard) Copper-based brazing filler metals Cu-Zn-alloys

B-Cu60Zn narrow Cu 470a Cu 301 60Cu; 0,3Si; Rest Zn 875 895 (Si)-875/895 Copper and or wide copper alloys hand-fed or 1 2 with a solidus B-Cu60Z- 58* Cu/ 60* Cu; inserted n(Sn)(Si) 0,175*1 Si/0,275*2 temperature narrow or Cu 471*1 Cu 304*2 870 900 (Mn)- Si; 0,35Sn; 0,15Mn; above 950 °C wide 870/890 bal. Zn Copper-phosphorus brazing filler metals CuP-alloys B-Cu92P- CuP 182 CP 201 bal. Cu; 7,8 P 710 770 Preferentially 710/770 copper, Gunmetal, B-Cu93P- hand-fed or CuP 180 CP 202 bal. Cu; 7P 710 820 copper-zinc narrow 710/820 inserted alloys (brasses), B-Cu94P- copper-tin alloys CuP 179 CP 203 bal. Cu; 6,2P 710 890 710/890 (bronzes) Copper-phosphorus brazing filler metals Ag-CuP-alloys B-Cu80AgP- CuP 284 CP 102 15Ag; 5P; bal. Cu 645 800 Copper, narrow 645/800 Gunmetal, B-Cu89AgP- copper-zinc hand-fed or CuP 281 CP 104 5Ag; 6P; bal. Cu 645 815 645/815 alloys (brasses) narrow or inserted and copper-tin B-Cu92AgP- wide CuP 279 CP 105 2Ag; 6,3P; bal. Cu 645 825 alloys (bronzes) 645/825 Silver alloy brazing filler metals Ag-Cu-Zn-alloys B-Cu48ZnAg(Si) 12Ag; 48Cu; 40Zn; Ag 212 AG 207 800 830 narrow -800/830 0,15Si Copper and hand-fed or B-Cu55ZnAg(Si) 5Ag; 55Cu; 40Zn; copper alloys narrow or inserted Ag 205 AG 208 820 870 -820/870 0,15Si wide

Table 4 - Selection of copper-based filler metals for brazing copper and copper alloys

14 | KUPFERINSTITUT.DE Average chemical Designation in acc. with composition (mass Melting range in °C Usage notes fractions in %)

DIN EN 1044 DIN EN ISO DIN EN ISO Application of (1999; Vor- Sol. Liq. Parent material Gap width 17672 (2010) 3677 (1995) filler metal gängernorm) Ag-Cu-Zn-Sn-alloys B-Ag56CuZ- 56Ag; 22Cu; 17Zn; narrow hand-fed or Ag 156 AG102 620 655 Copper alloys nSn-620/655 5Sn inserted B-Ag45CuZ- 45Ag; 27Cu; 2,5Sn; Ag 145 AG 104 640 680 nSn-640/680 25,5Zn B-Ag40CuZ- 40Ag; 30Cu; 2Sn; Ag 140 AG 105 650 710 nSn-650/710 28Zn B-Cu36AgZ- 34Ag; 36Cu; 2,5Sn; Ag134 AG 106 630 730 nSn-630/730 27,5Zn B-Cu36ZnAgSn- 30Ag; 36Cu; 2Sn; Ag 130 AG 107 665 755 665/755 32Zn Copper and B-Cu40ZnAgSn- 25Ag; 40Cu; 2Sn; copper alloys Ag 125 AG 108 680 760 680/760 33Zn B-Ag44CuZn- Ag 244 AG 203 44Ag; 30Cu; 26Zn 675 735 675/735 B-Cu38Z- Ag 230 AG 204 30Ag; 38Cu; 32Zn 680 765 nAg-680/765 B-Cu40Z- Ag 225 AG 205 25Ag; 40Cu; 35Zn 700 790 nAg-700/790 Ag-Cu-Zn-Ni-Mn-alloys B-Ag50CuZn- Ni-660/705 hand-fed or Ag 450 660 750 Copper alloys narrow 50Ag; 20 Cu; inserted 28Zn Zinkfreie Ag-Cu-Lalloys (without zinc) B-Ag- Copper and Ag 272 AG 401 72Ag; 28Cu 780 780 narrow inserted 72Cu-780 copper alloys

Table 5 - Selection of silver alloy filler metals containing more than 20 % silver for brazing copper and copper alloys

KUPFERINSTITUT.DE | 15 2.3. Soldering or brazing pure copper Copper is very well suited to both soldering and brazing. Care must be taken to ensure that the oxide layers on the surfaces to be joined have been properly removed by mechanical or chemical cleaning. The most commonly used cleaning agents are: isopropanol, ethanol, acetone, aqueous cleaner and nitric acid. The soldering/brazing (or tinning) process should take place immediately after the surfaces have been prepared. Table 6 presents a selection of copper metals that are particularly well suited to soldering or brazing.

Suitability for soldering/ Designation Material number Composition [%] Area of use brazing Cu O P min. max. Oxygen-containing copper Soldering: v. good; Cu-ETP CW004A 99,9 0,04 – Brazing: good (not for Electrical torch brazing) Deoxidised copper (with phosphorus), oxygen-free 99,95 – 0,002- Soldering: v. good; Cu-HCP CW021A Electrical, cladding 0,007 Brazing: v. good 99,90 – 0,015- Soldering: v. good; Construction, Cu-DHP CW024A 0,040 Brazing: v. good piping/tubing Oxygen-free copper, non-deoxidised Soldering: v. good; technology, Cu-OFE CW009A 99,99 – – Brazing: v. good electronics

Additional information on these materials is available from DIN CEN/TS 13388 and from the corresponding material data sheets issued by the German Copper Institute (www.kupferinstitut.de)

Table 6 - Selected types of copper

16 | KUPFERINSTITUT.DE Soldering Components of electric motors that are refrigeration applications. In some cases, Electronics is one of the main areas of subjected to high temperatures during the strength of a soldered lap joint between application of copper soldering. The solders operation should be preferentially soldered two tubular parts is greater than that of a most commonly used for soldering using soft solders that have a higher solidus brazed joint, as the brazing process can electronic components are the tin-based temperature. Soldered joints made with reduce the strength of the copper parent filler alloys as defined in DIN EN ISO 9453 these solders usually tend to show a higher metal. Soldered joints that will be subjected (2014) and DIN 1707-100 (2011). The filler shear strength than those made with to higher temperatures should be made alloys used for electrical and electronic tin-lead solders. The short-term shear with lead-free, thermally stable solders that soldering applications are usually unleaded. strengths of lap joints made with these can withstand permanent temperatures of Lead-containing solders may only be used solders have been shown to be about 20 N/ up to 120 °C without damage. in exceptional cases, as listed in the Annex mm². Lead-free soft solders are also Like wrought copper, copper casting alloys to ‘Directive 2011/65/EU of the European preferred when joining copper piping that as defined in DIN EN 1982 (2008) can be Parliament and of the Council of 8 June carries drinking water (see DVGW technical soldered without difficulty. 2011 on the restriction of the use of certain application note GW 2) or when the hazardous substances in electrical and soldered joint will be exposed to low electronic equipment’ (RoHS). temperatures, e.g. in industrial

Designation Specific examples Selected areas of use Flux

Pb88Sn12Sb Manufacturing of condensers 2.1.1 Antimony-containing solders Sn60Pb40Sb and cooling units 2.1.2 2.1.3 Pb60Sn40 Tinning, plumbing, Low-antimony solders 2.2.2 Sn60Pb40 galvanised thin sheet 2.2.3 1.1.1 Electrical and Antimony-free solders Sn60Pb40E 1.1.2 Electronics 1.1.3 Sn99Cu1 1.1.2 Lead-free solders for electronic Sn96Ag4 Electrical and electronics 1.1.3 applications Sn96Ag3Cu1 1.2.3 Sn95Ag4Cu1 Pb93Sn5Ag2 1.1.2 High-lead, RoHS-compatible For operating temperatures Pb98Sn2 1.1.3 soft solders up to 200 °C Pb98Ag2 1.2.3 Drinking water piping 2.1.2 Lead-free solders for drinking Sn97Ag3 Other important applications in 3.1.1 water pipes Sn97Cu3 the DVGW regulations 3.1.2 Sn95Sb5 Lead-free solders for low- Sn97Ag3 Industrial refrigeration 3.1.1 temperature applications Sn95Ag5

Table 8 – Filler metals suitable for brazing copper

KUPFERINSTITUT.DE | 17 Brazing content of the parent copper when to form water. As Brazing is used if the joint will be selecting the brazing method. Brazing is more likely to occur in torch brazing or subjected to high mechanical and thermal oxygen-containing copper can cause when brazing in a reducing atmosphere, stresses. When brazing copper, the filler hydrogen embrittlement, i.e. the formation induction brazing or vacuum brazing are metals of choice are brass brazing alloys, of cracks and voids after contact with preferred. If torch brazing has to be copper-phosphorus and silver brazing hydrogen-containing gases. Types of performed, the parent metal should be an alloys. Silver brazing filler metals have copper susceptible to this problem include oxygen-free and/or deoxidised copper in lower brazing temperatures, which reduces those used in electrical and electronic order to avoid hydrogen embrittlement. the risk of coarse grains and applications. At high temperatures (above enables faster brazing speeds 500 °C), hydrogen diffuses into the copper It is important to consider the oxygen and reacts with the oxygen in the copper

Specific examples as defined in Brazing filler metal class Notes Example flux DIN EN ISO 17672 (2010) · suitable for drinking water pipes Ag 244 Silver alloy brazing filler metals · composed primarily of Ag, Cu, Zn Ag 134 FH10 (Class Ag) · Brazing temperature: approx. Ag 145 650–830 °C CuP 182 · no flux necessary due to CuP 180 presence of phosphorus Copper-phosphorus brazing CuP 179 · recommended joint clearance for – filler metals (Class CuP CuP 284 P content of 5 %: 0.125 mm CuP 281 · Brazing temperature: approx. CuP 279 650–730 °C Cu 470a · suitable for brazing solid structures Brass brazing filler metals Cu 470 · composed primarily of Cu and Zn FH10 (Class Cu) Cu 680 · Brazing temperature: approx. 870–920 °C Cu 681

Table 8 – Filler metals suitable for brazing copper

2.4. Soldering / brazing copper alloys to -200 °C. Copper alloys not included in can be improved not only by suitable heat A copper alloy consists of copper and at this group are CuZn5, CuSn2, CuSn4, treatment (precipitation hardening), but least one other metal. Alloying produces a CuSn5, CuAl5As and CuNi2, as these are also by cold working. In contrast, the new material with new properties. Some of classified as belonging to the copper-zinc, strength of the non-heat-treatable the most well-known copper alloys include copper-tin, copper-aluminium and wrought copper alloys, such as CuAg0,10, brass, , bronze and Gunmetal. copper-nickel alloy groups. The composi- CuSi1 and CuSn0,15, can only be achieved tions of low-alloyed are specified by cold working [17]. Further information 2.4.1. Low-alloyed copper alloys in DIN CEN/TS 13388 (2013). A distinction on low-alloyed copper alloys is available in Low-alloy coppers contain up to about is made between heat-treatable/hardena- the DKI monograph i8 (2012). 5 % of alloying elements. One characteris- ble and non-heat-treatable/ hardenable tic feature of these alloys is their wrought copper alloys. In the case of behaviour at low temperatures, with no heat-treatable alloys, such as CuBe2, embrittlement observed even down CuCr1Zr and CuNi1Si, material strength

18 | KUPFERINSTITUT.DE Cold-worked (work hardened) alloys brazing should be kept as small as possible Copper-lead so that any in material strength The CuPb1P (CW113C) alloy contains between Copper-silver is localised, though it is very important to 0.7 % and 1.5 % lead to improve its Copper-silver alloys such as CuAg0,10 make sure that the brazing temperature is machinability. A trace phosphorus content in (CW013A) and CuAg0,10P (CW016A) are attained across the entire area to be the range 0.003 % to 0.012 % ensures a high characterised by their high electrical and brazed. level of deoxidation in the material and thermal conductivity values. These alloys safeguards against hydrogen embrittlement. are particularly well suited to applications Copper-iron CuPb1P has a very high electrical conductiv- in which they are subject to continuous The copper-iron alloy CuFe2P (CW107C) ity. It is often used instead of pure copper loads at high temperatures, as is the case contains between 2.1 % and 2.6 % of iron whenever both good machinability and good in many electrical engineering applica- as well as the alloying elements phospho- electrical conductivity are required, such as tions. The presence of silver raises the rus and zinc. This material exhibits high when fabricating - products alloy’s softening temperature (to about thermal and electrical conductivity as well from a high-conductivity material. The 350 °C in an alloy with 0.1 % Ag) without as high tensile strength and a high presence of lead means that this alloy shows having a detrimental effect on electrical softening temperature. CuFe2P is therefore only limited weldability. CuPb1P is also not conductivity. Copper-silver alloys are mainly used for electrical applications and well suited for brazing, but it can be soldered standardised in DIN CEN/TS 13388 (2013) large quantities are used in the fabrication of successfully. and are very well suited to both soldering lead frames in chip packages (see figure 8). and brazing. As is the case with pure copper, soldering is carried out using tin-lead soft solders Soldering is best carried out with containing between 40 % and 60 % tin. lead-free, tin-based solders (e.g. Sn99Cu1). Class 3.1.1 fluxes are recommended. For Suitable fluxes for electrical applications electrical applications, lead-free tin-based are those in the classes 3.1.1, 2.1.1 and 1.1.1 solders are used in combination with and 1.2.3. Because of the high softening non-corrosive fluxes (e.g. 1.1.2 or 1.1.3). temperature of the parent metal, soldering, if performed correctly, does not have a If brazing cannot be avoided, it is recom- detrimental effect on the high strength mended that a silver alloy brazing filler metal achieved through cold working. with a low brazing temperature (e.g. Ag 156) is used together with a flux of type FH10. Brazing, however, is carried out at higher temperatures and thus produces a Copper-Sulphur significant reduction in the strength of The copper-sulphur alloy CuSP (CW114C) work-hardened copper-silver alloys. contains between 0.2 % and 0.7 % sulphur Oxygen-free deoxidised alloys such as to improve the machinability of the alloy CuAg0,10P (CW016A) containing 0.001 % Figure 8 – Lead frames [17] while maintaining the material’s high to 0.007 % of phosphorus or another electrical conductivity. The phosphorus deoxidising element, like , are the content of between 0.003 % and 0.012 % most suitable parent metals for brazing Soldering can be carried out using tin-cop- makes the alloy resistant to hydrogen applications. Generally speaking, brazing per solders that conform to DIN EN ISO embrittlement. can be carried out with most silver alloy 9453:2014, such as Sn99.3Cu0.7, and using brazing filler metals using a flux such as fluxes in class 3.1.1. For information on solders, see section on FH10. If the electrical conductivity of the copper-silver. brazed joint is particularly crucial, fluxless For brazing applications, silver alloy, brazing can also be carried out using the copper and phosphorus brazing filler Silver alloy filler metals in combination filler metal Ag 272 (Ag72Cu28) under metals may be used in combination with with FH10 fluxes are recommended for vacuum or in a reducing atmosphere. No FH10 fluxes. brazing applications. Brazing reduces the flux is required when brazing with a strength of the cold-worked copper-sul- phosphorus-containing brazing filler phur alloy back to that of the material in metal. The heating zone created when its original not cold worked condition.

KUPFERINSTITUT.DE | 19 Copper-tellurium Heat-treatable/hardenable alloys Where possible, brazing should be carried The copper-tellurium alloy CuTeP (CW118C) If cold-worked wrought copper alloys are out between the solution treatmentstage with 0.4–0.7 % tellurium and 0.003–0.012 % brazed, they tend to suffer some loss of and the precipitation hardening (heat phosphorus has the same properties as the material strength in the region that is treatment) stage. In most cases, low-melt- copper-sulphur alloy described above. heated. In the case of heat-treatable/ ing silver alloy filler metals with low hardenable alloys, in contrast, certain brazing temperatures in the range For information on solders, see section on types of brazing can be used without 650–670 °C, such as Ag 156, are used in copper-silver. having a negative impact on the material’s combination with low-melting fluxes that mechanical properties. In fact in furnace contain high-activity fluorides. In order By adding tellurium to the alloy composition, brazing, the brazing step and the heat not to compromise the later precipitation the temperature at which tempering causes treatment can be combined into a single hardening stage, the brazing joint must be a loss of strength in the material (stress operation. heated rapidly (it may even be necessary relaxation resistance) can be raised to about to cool the areas surrounding the joint) 300 °C. If soldering is performed correctly, it Copper-beryllium and the part quenched once the filler is possible to avoid any significant reduction The copper-beryllium alloys CuBe 1.7 metal has solidified. Rapid brazing is in the strength of the cold-worked alloy. (CW100C) and CuBe2 (CW101C) with essential, as even a brazing time exceeding 1.6–2.1 % beryllium exhibit average 30 seconds will impair the ability of the Brazing is usually carried out using silver electrical conductivity, very high tensile parent material to respond to precipitation alloy filler metals and a type FH10 flux. strength in their hardened state and a high hardening. High-melting brazing alloys, However, brazing reduces the strength of the degree of thermal stability. Copper-beryl- such as Ag 272 (Ag72Cu28) which melts at worked-hardened parent metal back to that lium is used in a wide variety of applica- 780 °C, are available for special cases. of the material in its original untreated state. tions, such as in the manufacture of Though high, the melting temperature is membranes, wear-resistant components always within the solution annealing Copper-zinc and non-sparking tools. Parts that are to be range. Because of the greater propensity The alloy CuZn0.5 (CW119C) contains soldered or brazed should be free of grease for oxidation at these temperatures, between about 0.1 % and 1.0 % zinc and up and cleaned by acid pickling. Once the brazing under a shielding gas with a flux is to 0.02 % phosphorus. CuZn0.5 exhibits high parent alloy has been prepared, soldering or recommended. In order to ensure that the electrical conductivity, has excellent cold brazing should be carried out immediately material can undergo subsequent working properties, is resistant to hydrogen before the surfaces to joined become precipitation hardening, the brazed parts embrittlement and is also well suited for both tarnished. If it is not possible to solder or are held at about 760 °C until the filler welding and brazing. Its main area of braze the parent material immediately, the metal has solidified and are then quenched application is therefore surfaces to be joined should be plated with in water. technology where the alloy is used for a thin protective coat of copper, silver or tin manufacturing lead frames. As the alloy also that acts as a compound layer and improves Copper-beryllium-lead exhibits good deep- capabilities it surface wettability. The alloy CuBe2Pb (CW102C) has also finds frequent use in the production of properties similar to those of CuBe2. The hollow ware of all kinds and of heat Soldering is always carried out after the presence of lead does, however, improve exchanger elements. hardening stage using solders with a flow the machinability of the alloy. CuBe2Pb temperature below the typical softening can be soldered and brazed in a manner For information on solders, see section on temperature of the copper-beryllium analogous to the copper-beryllium alloys. copper-silver. parent metal. Soldering is typically carried Rapid soldering does not lead to any out using the lead-free solder Sn60P- softening of the cold-worked parent b39Cu1. Copper-containing solders such material. as Sn97Cu3 can also be used. Depending on the nature of the surfaces to be joined, Brazing is usually carried out with silver alloy fluxes of type 3.2.2 or 3.1.1 can be used. filler metals and a type FH10 flux. Pre-tinned parts can be soldered using rosin-based (colophony-based) fluxes of type 1.1.2 or 1.1.3.

20 | KUPFERINSTITUT.DE Copper--beryllium are also being used increasingly for to avoid the time-dependent softening of The alloy CuCo2Be (CW104C) with between connector plugs in the automotive the parent metal at the elevated tempera- 2.0 and 2.8 % cobalt and 0.4 to 0.7 % industry. tures used in brazing. beryllium is a highly conductive cop- per-beryllium alloy. Compared with the Here, too, soldering temperatures are Copper-zirconium binary copper-beryllium alloys, CuCo2Be is below the precipitation hardening The copper-zirconium alloy CuZr of slightly lower strength but exhibits temperature so that soldering does not (CW120C), which contains between 0.1 % more than double the electrical conductiv- have any appreciable effect on the and 0.3 % zirconium, is insensitive to ity while also having a significantly higher mechanical properties of the parent annealing in a hydrogen-containing thermal stability. This alloy is used mainly material. Suitable solders are tin-lead atmosphere. The alloy exhibits a very high to manufacture electrically conducting solders used in combination with fluxes electrical conductivity and stress and thermally stressed springs, as well as in class 3.1.1. relaxation resistance as well as superior components for the plastic processing strength and creep rupture strength. At industry and resistance welding elec- It is recommended that brazing is carried high temperatures, however, there is a risk trodes. out using low-temperature silver brazing of oxidation due to the high affinity of alloys together with fluxes of type FH10. zirconium for oxygen. The information on soldering and brazing The strength of the parts being brazed copper-beryllium alloys applies for the can be detrimentally affected at high No special aspects need to be taken into most part also to copper-cobalt-beryllium. brazing temperatures or if brazing times account when soldering this alloy. As the If it is important to retain the strength of are long. alloy has a high softening temperature, the precipitation hardened state, high-melting solders can be used. If fluxes low-melting silver alloy filler metals should Copper-chromium-zirconium of type 3.2.2 are not permitted because of be used and soldering/brazing times kept The alloy CuCr1Zr (CW106C) contains corrosion, a flux of type 2.1.2, 2.2.2 or 1.1.2 short. 0.5–1.2 % chromium and 0.03–0.3 % should be used. zirconium. In contrast to the binary Copper-nickel-beryllium copper-chromium alloy, copper-chromi- If brazing is performed with a filler metal Shortages in the supply of cobalt led to um-zirconium shows higher notch whose melting temperature is above the the development of the alloy CuNi2Be strength at elevated temperatures and is softening temperature of copper-zirconium, (CW110C), in which the cobalt in cop- often now preferred in applications in brazing times must be kept short to avoid per-cobalt-beryllium alloy is replaced by which CuCr1 (CW105C) was formerly used. reducing the strength of the hardened nickel. The mechanical and physical The alloy exhibits high strength at room parent metal. The softening temperature properties of this alloy are equivalent to temperature, has a high softening rises the more zirconium is present in the those of CuCo2Be. In terms of soldering temperature and improved creep rupture alloy; with 0.2 % zirconium, the softening and brazing, the two alloys behave very strength, even at elevated temperatures. temperature is around 575 °C. similarly. The advantage of a CuNi2Be alloy compared with a CuCo2Be alloy is that the As the heat-treated (i.e. precipitation former exhibits slightly higher electrical hardened) parts have a high stress and thermal conductivity values. relaxation resistance, soldering can normally be carried out without any loss of Copper-nickel-silicon material hardness. Suitable solders include Copper-nickel-silicon alloys, such as the tin-lead solders, but more common CuNi1Si (CW109C), CuNi2Si (CW111C), solders are the lead-free varieties, such as CuNi3Si (CW112C) with between 1.0 and Sn95Ag5 , Sn97Ag3 or Sn95Sb5 in 4.5 % nickel and 0.4 to 1.3 % silicon, combination with a flux of type 3.1.1. are materials that have average electrical conductivity values but high For brazing applications, low-melting silver tensile strengths. They are used brazing filler metals are used with type primarily for the production of , FH10 fluxes. The brazing heating cycle bolts and overhead line hardware. They should be kept as short as possible in order

KUPFERINSTITUT.DE | 21 Copper-chromium Copper-zinc alloys (Brasses) brittle when the parts to be joined are The copper-chromium alloy CuCr1 Of all the copper alloys, the copper-zinc wetted with liquid solder. The risk of (CW105C) contains between 0.5 % and alloys (commonly known as ‘brasses’) are soldering embrittlement is particularly large 1.2 % chromium. It is a wrought copper the most common and the most widely when the parts to be soldered are worked alloy that because of its reduced notch used. The ubiquity of these alloys is due to or reshaped while they are being wetted strength at elevated temperatures has now the appealing colour, the ease with which with the molten solder. The binary been largely replaced by the copper-chro- they can be processed and their favoura- copper-zinc alloys with a pure α phase mium-zirconium alloy described above. The ble physical and strength properties. (alpha brasses), e.g. CuZn30 (CW505L), are soldering and brazing properties of the Copper-zinc alloys are classified into more susceptible to liquid metal embrittle- two alloys are very similar. The copper ment (LME) than those with an α+β · binary copper-zinc alloys (containing casting alloy CuCr1-C (CC140C) continues structure, e.g. CuZn37 (CW508L). If in no other alloying elements), to be used, however, as it has proved very doubt, the stresses present in the parent difficult – if not impossible – to produce · copper-zinc-lead alloys that contain metal should be relieved by annealing the copper-chromium-zirconium casting added lead and cold-worked parts before soldering. alloys. The copper-chromium casting alloy · complex (multi-element) copper-zinc Experience shows that this effectively is rarely soldered or brazed, but its alloys that contain a number of additi- eliminates the risk of LME. suitability for soldering and/or brazing is onal alloying elements. no different to that of the wrought alloy. Soldering is carried out using fluxes in Copper-zinc alloys are available as both classes 3.1.1, 3.1.2, 2.1.2 and 2.2.2. The alloy can be soldered with lead-tin wrought and casting alloys. solders or with higher melting lead-free Copper-zinc wrought alloys containing solders in combination with a flux without Soldering additional alloying elements (special brasses) detrimentally affecting the strength of the Despite the fact that the elements zinc and can be soldered without difficulty. One parts being joined. tin are incompatible in solders, both binary exception to this rule is the aluminium-con- Brazing is typically performed with and lead-bearing copper-zinc alloys (brass taining copper-zinc alloys where the higher low-melting silver alloy filler metals. If the and leaded brass) can be soldered without oxygen affinity of the aluminium (propensity filler alloy Ag 156 is used and if brazing difficulty. If possible, copper-zinc alloys to form oxide films) can cause a number of times are kept short, the loss of strength is should be soldered using low-antimony problems. However, fluxes can be used to relatively small. solders (containing no more than 0.5 % remove these aluminium oxide films. antimony). If solders with a higher amount Brass casting alloys are rarely soldered. 2.4.2. High-alloyed copper alloys of antimony are used, tensile stresses in the Their ability to be soldered is very similar to Copper alloys that contain more than 5 % soldered structure may lead to the that of wrought copper-zinc alloys of of alloying elements are referred to as formation of brittle antimony-zinc crystals comparable composition. high-alloyed coppers. They are standard- causing solder embrittlement in both the ised in DIN CEN/TS 13388 (2013). Examples joint and the parent material. Depending on include the copper-zinc alloys (brasses), the particular application, tin-lead, lead-tin, copper-tin alloys (bronzes) and cop- tin-copper and tin-silver solders can be per-nickel-zinc alloys (nickel silvers). used. The solders Sn97Ag3, Sn95Ag5 and Sn97Cu3 can be used for soldering applications in the industry, e.g. brass fittings and taps for copper drinking water systems. In contrast to pure copper, cold-worked brasses tend to exhibit soldering embrittlement if extended soldering (or brazing) times are used or if large amounts of solder (or brazing alloy) are applied. If there is a non-uniform distribution of stresses at the joint to be made, the parent material may become

22 | KUPFERINSTITUT.DE Brazing Phosphorus-containing filler metals flow Copper-tin alloys (Bronzes) Brazing is used to join brass workpieces freely on pure copper. When used to braze Copper-tin alloys (commonly known as that are subjected to greater mechanical brass, however, these filler metals need to ‘bronzes’) are important materials in the and thermal stresses. The risk of liquid be combined with a flux. Leaded cop- electrical engineering (e.g. electrical springs) metal embrittlement can, however, be per-zinc alloys, particularly those with a and mechanical engineering (e.g. slide avoided by stress relief annealing, by using lead content above 3 %, are harder to bearings, bearing linings, membranes). They low-melting brazing alloys and by braze than the binary alloys and may well are classified into wrought alloys and casting minimising external stresses. The brass exhibit brittle joints. With certain alloys. brazing filler metals Cu 470a and Cu 680 limitations, leaded brasses can be brazed are suitable for brazing binary copper-zinc using low melting silver brazing alloys and Soldering alloys with low zinc content, as their a flux of type FH10. Copper-zinc alloys Like pure copper, copper-tin wrought alloys brazing temperatures are below the solidus containing aluminium can be brazed can be soldered with little difficulty, temperatures of the parent metals. without difficulty. If the alloy contains although surface wetting is not as rapid. In Low-melting silver brazing alloys may also more than 1 % aluminium, fluxes of type some situations (e.g. wave soldering), it is be used depending on the brazing FH11 must be used. Brazing can be carried proves expedient to tin the surfaces to be temperature and the required ductility at out with low-melting filler metals. If the joined beforehand with the lead-free solder the joint. As a result of the heat generated parts are likely to be subjected to a Sn99Cu1. Soldering is normally carried out during brazing, the strength of the brazed corrosive environment, silver brazing alloys using lead-free solders, such as Sn96Ag3Cu1 joint is lower than that of the parent with a higher silver content should be or Sn99Cu1. metal. If the amount of overlap between used. For parts exposed to a marine the surfaces being brazed is large enough, environment, brazing filler metals with a For fine soldering applications, fluxes in the embrittlement will not be located at the silver content of about 40–56 % are classes 1.1.2, 1.1.1 or 1.1.3 may be used. joint but in the peripheral annealed area recommended. Suitable filler metals For general soldering applications, fluxes in (heat affected zone). In plumbing include Ag 140, Ag 155 and Ag 244. The classes 3.1.1 and 3.1.2 should be used. installations, fittings made from cop- VG 81245-3 (1991) standard lists all Bronze casting alloys are hardly ever per-zinc alloy are typically brazed to non-ferrous heavy-metal filler metals for soldered, however, their solderability is very copper pipes using the filler metals welding and brazing that are suitable for similar to that of wrought copper-tin alloys CuP 279, CuP 179, Ag 145, Ag 134 or use in shipbuilding or in the construction of comparable composition. Ag 244 in combination with a flux of type of other floating equipment [19]. The FH10. US-AWS 5.8 specification recommends the Brazing use of the nickel-bearing silver brazing Brazing copper-tin wrought alloys also tends alloy BAg-3 (50 % silver) for marine to cause softening in the joint. The filler applications. However, BAg-3 contains metals of choice are low-melting silver cadmium, which is prohibited in the brazing alloys, such as Ag 156. For capillary European Union by EU Regulation brazing applications copper-phosphorus filler 494/2011. A cadmium-free alternative is, metals such as CuP 179 or CuP 182 are used. for instance, Ag 450. The brazing of If other filler metals are used, there is a risk copper-zinc casting alloys is carried out in of localised melting of the parent material the same way as brazing the correspond- and associated embrittlement through the ing wrought alloys. formation of coarse grains. For brazing temperatures below 800 °C fluxes of type Selected areas of use FH10 are appropriate; above 800 °C, fluxes of Figure 9 – Metallographic longitudinal section through a Soldered/brazed components made from type FH20 are preferred. Castings from brazed joint between a pipe and a pipe fitting copper-zinc alloys are fabricated in very copper-tin alloys that do not contain more (filler alloy: Ag-CuP) [18] large volumes for a very wide range of than 1.5 % of lead are well suited to brazing applications in the electrical and automo- with silver brazing filler metals. For parts tive industries, communications and exposed to marine environments, the same domestic appliance technologies, and for recommendations apply as for copper-zinc electrical and mechanical systems. alloys (see section on the brazing of copper-zinc alloys above).

KUPFERINSTITUT.DE | 23 Copper-nickel-zinc alloys (Nickel silvers) Copper-nickel alloys (Cupronickels) copper as the filler metal. Generally, Copper-nickel-zinc wrought alloys (also Copper-nickel alloys (also known as however, copper-based filler metals, such known as ‘nickel silvers’) are used in ‘cupronickels’) are some of the most as Cu 470a to Cu 680 or Cu 681, are used electrical engineering applications (for corrosion-resistant copper materials in combination with fluxes of type FH21, springs), in the construction industry, in known. The wrought alloys are important or silver brazing alloys are used with fluxes precision engineering e.g. as spectacle materials in marine construction (particu- of type FH10 that prevent oxidation at the temples and hinges, in the arts and crafts larly for condensers and undersea piping), brazing surfaces. The filler metals should sector, and for . The casting alloys in the plant construction sector and in the be phosphorus-free in order to avoid are used, for instance, for marine electrical engineering sector (e.g. as embrittlement. For iron-bearing cupronick- hardware, fixtures and fittings, and cast resistance wire). In addition to marine els, brazing is usually carried out with the ornamental ware. The solderability of the applications, casting alloys are filler metals Cu 773 and Ag 244. copper-nickel-zinc casting alloys is very used in the mechanical engineering and CuNi13Sn8 is a CuNiSn alloy with higher similar to that of the corresponding chemical industries. nickel and tin content that is used for wrought alloys. manufacturing high-quality, thin Soldering lightweight spectacle frames with Soldering The solderability of these alloys is similar excellent flexibility and is brazed using Soldering is best carried out either with to that of pure copper. The somewhat silver alloy filler metals. For marine lead-tin solders or with lead-free Sn97Ag3 sluggish wetting of these alloys with soft applications, the brazing filler metal or Sn95Ag5 solders, as they have better solders can be improved by the addition of should have a silver content of about 40 % bonding and wetting characteristics. The a flux. In particularly difficult cases, the to 56 %. The VG 81245 Part 3 (1991) temperatures reached during soldering are surfaces to be joined should be pre-tinned. standard ‘Filler metals for welding and not high enough to cause any softening of Suitable solders are the lead-free tin-silver brazing applications in shipbuilding and the work-hardened parent material. For and tin-copper solders, such as Sn95Ag5, the construction of other floating wetting to be successful, the joint to be Sn97Ag3 or Sn97Cu3. Compared to the equipment’ [19], specifies the use of the soldered must be free of grease and leaded tin solders used previously, the silver brazing alloys Ag 140, Ag 155 and oxides. To facilitate optimum wetting, the lead-free solders exhibit improved Ag 244 as defined in the ISO 17672 (2010) surfaces to be soldered should be prepared hardness, higher corrosion resistance and standard. For marine applications, the by very careful acid pickling (e.g. with a greater temperature stability. Fluxes of US-AWS 5.8 specification recommends the 10 % sulphuric acid solution) and type 3.2.2 or 3.1.1 are appropriate. In use of the nickel-bearing silver brazing degreased. Strongly activating fluxes of electrical applications, copper-nickel alloys alloy BAg-3 (50 % silver). BAg-3 is a type 3.2.2 or 3.1.1 should be used.. are frequently pre-tinned or pre-silvered, cadmium-containing brazing filler metal; then soldered with rosin-based (colopho- the cadmium-free alternative is the filler Brazing ny-based) fluxes of type 1.1.2 or 1.1.3. The metal Ag 450 as defined in DIN ISO 17672 Copper-nickel-zinc alloys can be brazed alloy CuNi9Sn2 (CW351H), which is used (2011). A brazing flux of type FH11 is with silver-bearing brazing filler metals. particularly for the fabrication of spring recommended. The brazeability of the The most commonly used brass filler metal components, exhibits excellent tarnish cupronickel casting alloys is similar to that Cu 681 has the same silver-grey colour as resistance and therefore very good of the copper-nickel wrought alloys of the copper-nickel-zinc parent metal. solderability even after storage for a long comparable composition. Suitable fluxes are those of type FH10. If period. Higher-melting solders are used for the parts are brazed in a furnace, there soldering electrical resistors that are may be some deterioration in the hardness exposed to elevated temperatures. The characteristics achieved through prior cold cupronickel casting alloys are rarely working of the material. Leaded nickel soldered. silvers have a tendency to crack when annealed, particularly if they have been Brazing significantly cold worked prior to brazing. The solidus temperature of the cop- These alloys should therefore be brazed per-nickel alloys is higher than that of using low-melting silver alloy filler metals copper. This is the reason why cop- and heating should be carried out per-nickel alloys, particularly those with a gradually. high nickel content, can be brazed with

24 | KUPFERINSTITUT.DE Copper-aluminium alloys Copper-tin-zinc casting alloys Brazing and soldering of copper and (Aluminium bronzes) (Gunmetal) copper alloys to themselves and to Copper-aluminium alloys (also referred to The copper-tin-zinc casting alloys other materials as ‘aluminium bronzes’) exhibit an (‘Gunmetal’) exhibit low friction and good There are many practical applications in exceptionally high resistance to cavitation anti-seizure properties, as well as high which copper and copper alloys are joined erosion and are some of the most resistance to cavitation, wear and to other metals. One of the most common corrosion-resistant copper alloys known. -water corrosion. Typical uses include procedures involves brazing copper-based Both the wrought and casting alloys are water taps, valve and pump housings, materials to steel. As and nickel therefore indispensable materials in the fittings and sliding bearings. Depending on alloys can both form brittle phases, they chemical and mechanical engineering the particular application, Gunmetal can be cannot be joined together by brazing with industries. Brazing and soldering of soldered with selected tin-lead solders a CuP filler metal. The choice of brazing copper-aluminium alloys always requires containing at least 60 % tin. Fluxes from filler metal is determined by the parent the use of fluxes to remove the highly the flux classes 3.1.1 and 3.1.2 are material of lower brazeability. When chemically resistant oxide films. Cop- appropriate. In the plumbing sector, fittings designing the joint and the soldering/ per-aluminium casting alloys are rarely and tap components used in drinking water brazing method to be used, the different soldered or brazed, however, their piping systems are soldered using lead-free properties of the materials to be joined solderability or brazeability is very similar and antimony-free solders. Castings that (e.g. thermal conductivity, thermal to that of wrought copper-aluminium contain less than 1.5 % lead can be brazed expansion, specific heat capacity) must be alloys of comparable composition. effectively using silver alloy brazing filler taken into account. metals containing at least 30 % silver and The increasing significance of metal/ Soldering fluxes of type FH10. Brazing of copper composites in industrial applica- Copper-aluminium alloys are rarely tubing with flanges made of Gunmetal is tions has led to the study of these material soldered, as the wettability of the parent common in the equipment manufacturing combinations and has driven the develop- metal deteriorates as the amount of sector. Undersea piping is subject to the ment of appropriate soldering and brazing aluminium in the alloy increases, making regulations of the classification societies, solutions. Copper and alumina (Al2O3) can bonding difficult and necessitating the use which stipulate, for instance, that the now be brazed using active filler metals or of special fluxes. If soldering is performed, brazing filler metals used must have a soldered with tin-lead solders. Active filler it can be carried out using the solders silver content of around 50 %. If Gunmetal metals generally contain the metal Sn97Cu3 or Sn97Ag3; for applications in fittings are used in the copper piping for , which reacts at the interface which the parts will be subjected to higher drinking water supply systems, the filler between the filler metal and the ceramic, temperatures, CdAg5 can be used. metals CuP 279 or CuP 179 in combination making the surface more amenable to Cadmium-containing solders are, however, with a flux of type FH10 are recommended. wetting [9]. no longer readily available as they are regarded as a health risk. Special fluxes for Copper-lead-tin casting alloys aluminium alloys belonging to flux classes (High-leaded tin bronzes) 2.1.2 or 2.1.3 can be used. The leaded tin bronzes are important engineering and bearing materials that are Brazing rarely joined by brazing or soldering. Brazing can be carried out without Soldering can be performed using tin-lead difficulty provided that appropriate fluxes solders with 50–60 % tin and a flux of are used. Suitable brazing filler metals are class 3.1.1 or 3.1.2. Brazing is possible using the silver brazing alloys with low to low-melting silver brazing alloys (e.g. medium brazing temperatures, such as Ag 156) and a flux of type FH10, though Ag 156. For parts exposed to marine the brazeability of leaded tin bronzes is environments, the same recommendations limited. If alloys with a higher lead content given for copper-zinc alloys apply (see are brazed, very significant diffusion section on brazing copper-zinc alloys should be expected. above).

KUPFERINSTITUT.DE | 25 3. Design suitability for brazing

Design suitability for brazing is concerned In normal (‘narrow-gap’) brazing, the gap between the surfaces to be joined (the ‘faying’ or with design characteristics that influence ‘mating’ surfaces) should not be more than 0.5 mm. If the distance between the surfaces is the brazing process, such as the shape and larger, the joining technique is referred to as braze welding. Braze welding uses a larger structure of the joint and the forces acting quantity of filler metal than normal brazing. Braze welding frequently involves single-V, on it. This requires giving consideration to and double-V butt joints The gap/joint widths for different joining techniques are shown in the the operational stresses involved, the type following figure: of parent material to be joined and the brazing technique to be used. A distinction (Narrow-gap) brazing, gap < 0.5 mm Braze welding, gap > 0.5 mm is made between the brazing techniques Manual braze used to join materials and those used for welding surface cladding work (also known as (flux-assisted) hardfacing). Brazing joining techniques are Manual further classified into normal brazing (flux-assisted) (i.e. ‘narrow-gap’) brazing and braze welding. Machine brazing (flux-assisted)

Brazing in a protective gas atmosphere

Vacuum brazing

0 0,1 0,2 0,3 0,4 0,5 Gap width [mm] (Narrow-gap) brazing A narrow gap between the parts to Figure 10 - Difference between ‘narrow-gap’ brazing and weld brazing be joined is filled with filler metal by capillary pressure. At room temperature, the gap between the components to be brazed is known as the ‘assembly To ensure that the joint gap is filled gap’. The term ‘brazing gap’ is the gap between the components to be brazed at the brazing uniformly, the liquidus temperature temperature. It may differ from the assembly gap due to the different degrees of thermal of the filler metal can be exceeded expansion exhibited by the materials to be joined. by 20–50 °C [9].

bM bN b

Braze welding A wider gap between the parts to be joined, which is filled with filler Assembly gap Brazing gap Brazing seam metal primarily by gravitational Narrow, mainly parallel gap Narrow, mainly parallel gap May be wider than the spreading [9]. between the components to between the components to assembly gap due to The liquid braze metal is held inside be brazed, measured at be brazed, measured at the surface melting. the joint by surface tension. room temperature [10]. brazing temperature [10].

Table 9 - Difference between standard (narrow-gap) Table 10 - Distinction between the terms ‘assembly gap’, ‘brazing gap’ and ‘brazing seam’ brazing and braze welding

26 | KUPFERINSTITUT.DE 200

The gap widths should be designed to be as narrow as possible in order to fully exploit the capillary effect when brazing 150 (see figure 11). The capillary effect is a surface tension phenomenon. It produces a force that draws the flux and the molten filler metal into the gap between the 100 components to be joined.

Capillary pressure [mbar] 50

0 0,05 0,1 0,2 0,3 0,4 0,5 Gap width [mm]

Figure 11 - Capillary pressure as a function of gap width [12]

500

The gap width for normal brazing should be 400 between 0.05 mm and 0.5 mm. In addition to the width of the brazing gap, the cross-sec- tional area of the gap (see figure 12) also affects the capillary pressure and thus the 300 quality of the resulting brazed joint. An open has a capillary pressure 4.5 times greater than in a parallel flat gap [9]. 200

100 Capillary pressure [mbar]

Figure 12 - Capillary pressure as a function of gap geometry [12]

KUPFERINSTITUT.DE | 27 When designing the assembly to be be configured so that the flux can flow Other factors that need to be taken into joined, the direction of flow of the filler out again and any air can escape. In account when designing a soldered or metal should be considered. There should general, the solders and filler metals used brazed joint are the detailed shape of the be no discontinuities in the gap that and the solder/braze metal in the finished gap and the condition of the mating surfa- would prevent the filler metal from joint are not as strong as the parent ces. Score marks and grooves on the flowing and filling the joint area. The material. The joining surface should surfaces to be joined are generally region around the joint should be therefore be as large as possible in order undesirable. If there is scoring on the designed so as to minimise stress concen- to achieve a strong, secure join. This is surface, it is important that the score tration factors, bending loads and frequently achieved by designing a lap or marks are aligned with the direction of geometric notch sensitivity factors. Shear insertion joint. Other geometrical variants flow of the molten filler metal. Any stressing of soldered/brazed joints is of soldered/brazed joints are listed in component after-treatment procedures beneficial. If a flux is used, the gap must table 11. should also be taken into account when designing the brazing joint and/or assembly. Any residual flux, binder or solder mask should be readily removable. α = 0° / 180° 0° < α < 90° α = 90° 90° < α < 180° As with welded joints, the fatigue strength of a brazed or soldered joint is enhanced Square butt joint Inclined joint T-joint Inclined joint when there are no sharp changes in the cross-section and the joint is smoothly contoured (e.g. by forming a concave fillet). The rules governing the symbolic · Suitable for Angular or Angular or Angular or representation of brazed and soldered soldering/ corner joint corner joint corner joint joints can be found in DIN EN 22553 brazing and Possible (1997) [6]. soldered/brazed braze welding joints · Relatively small joining · Suitable for · Suitable for · Suitable for surfaces soldering/ soldering/ soldering/ brazing and brazing and brazing and braze welding braze welding braze welding · Relatively small · Relatively small · Relatively small joining surfaces joining surfaces joining surfaces

Lap joint Insertion joint

Parallel or fully overlapping joint

· Suitable for Preferred soldering/ · Large soldering/brazing surfaces soldered/brazed brazing and ensure a strong joint joints braze welding · Large joining surfaces can be achieved · Preferred joint type for sheet metals and tubing

Table 11 – Geometric configurations of common soldered/brazed joints [6]

28 | KUPFERINSTITUT.DE 4. Soldering and brazing methods

4.1. The soldering/brazing principle figure 13 illustrates the characteristic The reflow temperature of the solder/braze Melting the solder or brazing filler metal temperatures and times during soldering/ metal corresponds roughly to the melting requires the uniform application of brazing and the terminology as defined in temperature of the solder/filler metal thermal energy to the entire soldering/ DIN ISO 857-2 is explained in Section 6. applied. If the soldered/brazed assembly brazing zone. A specific temperature-time The thermal profile shown below is typical will be subjected to high service stresses, a profile is followed that consists fo the of that observed during furnace soldering higher reflow temperature is desirable in following sequence of steps: [6] or furnace brazing. order to optimise the quality of the 1. Melting the flux soldered/brazed joint. This can be achieved For reasons of cost, the holding time at by significantly extending the holding 2. Activating the surface the soldering/brazing temperature is temperature, which to a diffusi- 3. Melting the solder or filler metal usually restricted to the time needed to on-driven change in the chemical 4. Wetting of mating surfaces by the achieve a uniform temperature in the composition of the solder/braze metal and molten solder or filler metal assembly. After a relatively short holding thus to a shift in the solidus and liquidus time, the assembly is allowed to cool in temperatures of the solder/braze metal. 5. Flowing of solder or filler metal into the still air at room temperature or under The soldered/brazed joint can then be soldering/brazing gap defined cooling conditions. During this subjected to diffusion annealing at the 6. Filling of soldering/brazing gap by the period the soldered/brazed metal solidifies. soldering/brazing temperature [1]. solder or filler metal.

Soldering/brazing temperature

Dwell temperature Temperature [°C] Temperature

Dwell time Holding Heating time time Cooling time

Soldering/brazing time

Total time Time Figure 13 - Characteristic temperatures and times during soldering/brazing [20]

KUPFERINSTITUT.DE | 29 4.2. Surface preparation and other auxiliary materials; the structure Table 13 contains recommendations for In order to achieve a high quality soldered/ and condition of the mating surfaces; and pickling the surfaces of copper and brazed joint between metallic materials, heat transfer during the soldering/brazing copper alloys. The surfaces must always the mating surfaces need to carefully process. Soldering/brazing should be be degreased prior to pickling and rinsed prepared. Surface preparation can involve carried out as soon as possible after the thoroughly afterwards. Further recom- chemical, mechanical or thermal cleaning surfaces have been prepared. Once mendations regarding surface prepara- procedures or a combination thereof (see cleaned, the parts should be protected tion techniques are described in the DVS table 12 for a list of available procedures). from recontamination and from contact technical leaflet 2606 (2000) [21]. The parts to be soldered or brazed must be with sweaty hands. Parts should be stored clean and free from any residues that preferentially in an inert and dry atmos- might inhibit wetting, such as oxides, oil, phere. The following procedures can be grease, dirt, rust, paint, cutting fluids, etc. used to prepare the surfaces of copper and (see figure 14). Furthermore, the wetting copper alloys. Which procedure(s) to adopt behaviour of the solder or brazing filler will depend on the type and extent of the metal also depends on the following contamination, the cleanliness requirements factors: the properties of the parent and the geometry of the surfaces to be material, the solder or brazing filler metal cleaned [21].

Cleaning procedure Example

Degreasing with commercially available solvents (e.g. isopropanol, acetone); Steam degreasing with hydrocarbons and chlorinated hydrocarbons; Chemical cleaning Cleaning with aqueous alkaline solutions; emulsion cleaning using mixtures of hydrocarbons, fatty acids, wetting agents and surface activators; Pickling treatments using acids, acid mixtures or (see table 13)

Grinding, filing, abrasive blasting, Mechanical cleaning Caution: Steel wire brushes must not be used to clean the surfaces of copper or copper alloys! Cleaning in a reducing atmosphere, e.g. of hydrogen and hydrogen fluoride at Thermal cleaning temperatures above 800 °C

Table 12 - Cleaning procedures for copper and copper alloys [21]

30 | KUPFERINSTITUT.DE Parent material Notes Formulation

With hot sulphuric acid (H2SO4); sequential dipping in two solutions:

I. 65 ml 96 % sulphuric acid ( H2SO4) diluted Copper-chromium alloys with water to give 100 ml of solution; solution used while hot

II. 3 ml 96 % sulphuric acid (H2SO4) diluted with water to give 100 ml of solution

a) 5 ml 96 % sulphuric acid (H SO ) diluted Prior mechanical removal of oxides may be 2 4 with water to give 100 ml of solution Copper and copper alloys required (copper or brass wire brush, b) 50 ml 65 % nitric acid (HNO ) diluted with emery cloth) 3 water to give 100 ml of solution

Sequential dipping in two solutions: I. 2 ml 40 % hydrofluoric acid (HF) with 3 ml 96 % sulphuric acid (H2SO4) diluted with water to give Copper-aluminium alloys Pre-coating of surfaces may be necessary 100 ml of solution II.2 g sodium dichromate (Na2Cr2O7) and 5 ml 96 % sulphuric acid (H2SO4) diluted with water to give 100 ml of solution

With hot sulphuric acid (H2SO4); sequential dipping in two solutions: Eintauchen in zwei Lösungen Prior mechanical removal of oxides may be I. 65 ml 96 % sulphuric acid (H2SO4) diluted with Copper-nickel alloys required (copper or brass wire brush, emery water to give 100 ml of solution; solution used cloth) while hot II. 3 ml 96 % sulphuric acid (H2SO4) diluted with water to give 100 ml of solution

Sequential treatment using the following two solutions: I. 5 ml 65 % nitric acid (HNO3) diluted with water to give 100 ml of solution Prior mechanical removal of oxides may II. 2 ml hydrofluoric acid (HF) and 3 ml 65 % nitric Copper-silicon alloys be required acid (HNO3) diluted with water to give 100 ml of solution

III. 2 g sodium dichromate (Na2Cr2O7) and 3 ml

65 % nitric acid (HNO3) diluted with water to give 100 ml of solution

Sequential dipping in two solutions: I. 5 ml 96 % sulphuric acid (H SO ) diluted with Prior mechanical removal of oxides may be 2 4 water to give 100 ml of solution Copper-zinc alloys required (copper or brass wire brush, II. 2 g sodium dichromate (Na Cr O ) and 3 ml emery cloth) 2 2 7 96 % sulphuric acid (H2SO4) diluted with water to give 100 ml of solutio

Table 13 - Recommended pickling solutions for copper and copper alloys that will undergo fluxless brazing [21]

KUPFERINSTITUT.DE | 31 4.3. Surface activation take place. This process is known as Proper contact between the solder or surface activation. Some of the most brazing alloy and the surface of the common methods of surface activation parent metal is an essential requirement are the use of fluxes, soldering/brazing in in any high-quality soldered or brazed a reducing atmosphere or soldering/ joint. However, sufficient contact brazing in a vacuum. Other techniques between the molten solder or filler metal include soldering/brazing under an inert and the surface is not always established shielding gas, arc brazing, and soldering in all cases. Figure 14 represents a methods involving mechanical activation realistic cross-sectional view through the of the faying surface, as in ultrasonic surface of an engineering metal. The dirt, soldering or abrasion soldering. Surface contamination and adsorbed layers activation always involves the absorption present on the surface have to be of solid, liquid and gaseous layers. removed before soldering or brazing can

Particulate contamination approx. 104–105 nm (dust, abraded metal particles)

Contamination approx. 3 nm (grease, oil)

N Adsorbed layers approx. 0.3–0.5 nm O O H 2 2 Me (HCs, CO , H O) Me Me Me

Reaction layers approx. 1–10 nm

(MexO, MexOH, MexN)

Parent material with up to approx. 5000 nm modified microstructure

Parent material with undisturbed microstructure

Figure 14 - Schematic cross-section of the surface of an engineering metal [22]

32 | KUPFERINSTITUT.DE 4.3.1. Fluxes about 50 °C below that of the solder or Solder fluxes (classified according to According to DIN ISO 857-2 (2007), a flux brazing filler metal as this ensures that DIN EN 29454-1 (1994) is defined as a ‘non-metallic material the surface has been activated before it is A flux is normally required for soldering which, when molten, promotes wetting by wetted and before the solder or filler operations. Solder fluxes are classified in removing existing oxide or other metal starts to flow. As there is no terms of their chemical composition [4]. detrimental films from the surfaces to be universal flux, the composition of the flux joined and prevents their re-formation must be carefully selected for the In practice, solder fluxes area also during the joining operation’ [10]. Fluxes proposed joining operation [1]. A categorised according to their chemical are available as powders, pastes, liquids distinction is made between fluxes for function. or as solder-flux mixtures. soldering DIN EN 29454-1 (2004) and The melting range of the flux should be fluxes for brazing DIN EN 1045 (1997).

Flux type Base Activator Form Areas of use

[1] With rosin Electrical, [1] Resin [1] Without activator Electronics [2] Without rosin [2] Halide activator (other activating agents [1] Water-soluble are available) Electrical, Electronics, [2] Organic [3] Non-halide activator [A] Liquid Metal goods [2] Not water-soluble [B] Solid [1] With ammonium Plumbing applications chloride Cu and Cu alloys [1] Salts [3] Inorganic [2] Without ammonium Ni and Ni-alloys [C] chloride Precious metals [1] Phosphoric acid Cr, Cr-Ni-alloys [2] Acids [2] Other acids Stainless steels [1] Amines and/or [3] Alkaline

Table 14 - Solder fluxes (classified according to DIN EN 29454-1 (1994) (1994) [23]

Functional class Key chemical constituent Mode of action

Flux residues cause corrosion in copper and copper alloys (pitting); workpieces must be Corrosive fluxes Zinc chloride washed after soldering with hydrochloric acid and then rinsed repeatedly with water Residues can remain on the workpiece or can Non-corrosive fluxes Zinc bromide be rinsed off with water If the temperature is controlled correctly, the flux will evaporate completely leaving a clean surface. Non-corrosive, residue-free fluxes Organic amines and hydrobromic acid Subsequent cleaning of the workpiece is not required.

Table 15 - Chemical function of solder fluxes [24]

KUPFERINSTITUT.DE | 33 Brazing fluxes (classified according to and tungsten. Fluxes in DIN EN 1045 (1997) class FL are used when brazing light The DIN EN 1045 (1997) standard metals, such as aluminium and aluminium classifies brazing fluxes into two classes: alloys. Only class FH fluxes should be FH and FL. Class FH fluxes are used in the used for brazing copper and copper brazing of heavy metals, such as steels, alloys. stainless steels, copper and copper alloys, nickel and nickel alloys, precious metals,

Effective Type Brazing temperature Description / Areas of use After-treatment temperature range

contains compoundsand Residues are corrosive; FH10 approx. 550 – 800 °C > 600 °C simple and complex fluorides; remove by washing or pickling multi-purpose flux

contains boron compounds and simple and complex fluorides Residues are corrosive; FH11 approx. 550 – 800 °C > 600 °C and chlorides; mostly used for remove by washing or pickling copper-aluminium

contains boron compounds, elemental boron and simple and Residues are corrosive; FH12 approx. 550 – 850 °C > 600 °C complex fluorides; mostly used for remove by washing or pickling stainless steels, high-alloy steels and

contains boron compounds and Residues are corrosive; FH20 approx. 700 – 1000 °C > 750 °C simple and complex fluorides; remove by washing or pickling multi-purpose flux

contains boron compounds; Residues are not corrosive; FH21 approx. 750 – 1100 °C > 800 °C multi-purpose flux remove mechanically or by pickling

contains boron compounds, phos- phates and silicates; Residues are not corrosive; FH30 > 1000 °C mostly used together with copper remove mechanically or by pickling and nickel filler metals

contains chlorides and fluorides; Residues are corrosive; FH40 approx. 600 – 1000 °C boron-free; used when presence of remove by washing or pickling boron is not permitted

Table 16 - Brazing fluxes (classified according to DIN EN 1045 (1997) [25]

34 | KUPFERINSTITUT.DE Table 17 lists substances that are contained covered by the legislation, boric acid will be cation and labelling rules for brazing fluxes in a number of fluxes and which, since generated in the brazing torch flame and containing boric acid, pentahydrate 1 December 2010, are classified as will deposit on the workpiece and in the or boron trioxide is available (in German) in Category 1B reproductive toxins if present workplace. Boric acid deposits are toxic. For the DVS technical leaflet 2617 [26]. Table 17 in the amounts given in the table. Products this reason, brazing operations involving a also specifies the concentrations above affected must be marked with the symbol product containing trimethyl borate are which the product is classified as hazardous. ‘T’ and the R phrases R60 and R61. subject to the same regulations that apply Although products containing trimethyl to brazing fluxes that contain boric acid borate (EC No.: 204-468-9) are not directly [26]. Further information on the reclassifi-

Substance EC Number Hazard classification cut-off

233-139-2 Boric acid ≥ 5,5 % 234-343-4

Boron trioxide 215-125-8 ≥ 3,1 % 215-540-4 Borax anhydrate 235-541-3 ≥ 4,5 % 237-560-2

Borax decahydrate 215-540-4 ≥ 8,5 % Borax pentahydrate 215-540-4 ≥ 6,5 %

Table 17 - Concentration levels for hazard classification purposes [26]

4.3.2 to be joined or to prevent the re-formation and increases process productivity as Protective atmosphere / Shielding gases of such films on surfaces which have fluxes no longer need to be applied and According to DIN ISO 857-2 (2007), a previously been cleaned ’ [10]. A protective flux residues removed. Using a protective protective atmosphere for soldering or atmosphere of shielding gas(es) improves atmosphere is, however, associated with brazing is the ‘gas atmosphere or vacuum the quality of the soldered/brazed joint, higher process and equipment costs. round a component, either to remove oxide enables precise control of soldering/brazing Table 18 contains examples and definitions or other detrimental films on the surfaces temperatures and soldering/brazing times, of the various protective atmospheres used in soldering and brazing operations.

Atmosphere Shielding gas Vacuum

reducing inert

‘Pressure sufficiently below atmospheric so that the ‘Gas which prevents the formation of oxides will be prevented to a degree Definition from DIN formation of oxides ‘Gas which reduces oxides’ [10] sufficient for satisfactory soldering or brazing, ISO 857-2 (2007) during the soldering or because of the low partial pressure of the brazing process’ [10] residual gas’ [10] Exothermic gas atmosphere (‘exogases’) formed by incomplete combustion of gases in air with a high air-to-gas ratio; endothermic Example Argon, helium Low (rough), medium, high, ultrahigh vacuum gas atmosphere (‘endogases’) for- med by partial combustion of gases in air with a low air-to-gas ratio; dissociated ammonia atmosphere

Table 18 - Protective atmospheres used in soldering/brazing operations

KUPFERINSTITUT.DE | 35 4.4. Applying the solder or brazing by dipping the parts into the molten filler filler metal material, or by positioning filler metal In addition to selecting the correct method preforms where the joint is to be made. of surface cleaning and surface activation, Filler metals are available in a variety of choosing the most suitable way to forms (e.g. wire, rod, strip, film, paste) and introduce the filler metal into the joint is sizes to suit the design and dimensions of also an important aspect of the soldering the soldering or brazing gap. or brazing process. In most cases, the application of the filler metal is dictated by Table 19 shows a number of different ways the design of the assembly. The solder or of introducing the filler metal to the joint. brazing alloy can be introduced manually,

Soldering or brazing with filler metal applied to the joint Process during which the components are heated up to the soldering or brazing temperature in the area of the joint, and the filler metal is brought to its mainly by contact with the components to be soldered or brazed. gebracht.

Soldering or brazing with filler metal deposited or inserted in the joint Process during which the filler metal is placed in the area of the joint before heating, and is then heated to the soldering or brazing temperature together with the components to be soldered or brazed.

Dip soldering or brazing Process during which the components to be soldered or brazed are dipped in a bath of molten filler metal.

Soldering or brazing with components coated with filler metal Process during which the filler metal is applied before soldering/brazing by coating (e.g. roll cladding, , vapour deposition or tinning).

Table 19 - Different ways of introducing the filler metal to the soldering or brazing joint (based on [10]

36 | KUPFERINSTITUT.DE 4.5. Soldering and brazing techniques · method of application of the filler Soldering and brazing techniques can be metal (e.g. dip soldering/brazing, classified in different ways, such as by the soldering/brazing with filler metal heating method (energy source) used (see applied to the joint) table 20). Other classification schemes are · method of fabricating the joint (e.g. based on the: manual, partially automated or fully · nature of the soldering/brazing joint automated soldering/brazing) (cladding, (narrow-gap) soldering/braz- ing, braze welding) · method of oxide removal (e.g. soldering/brazing in a protective gas atmosphere, vacuum soldering/ brazing, flux-assisted soldering/brazing)

Process Energy source Name of technique

Soldering using a solid heat source ∙ Soldering with soldring iron

∙ Dip soldering Soldering using a liquid heat source ∙ Wave soldering ∙ Drag solderingn Soldering Soldering with a gaseous heat source ∙ Flame soldering

Soldering using an electric current ∙ Induction soldering in air

Furnace soldering ∙ Furnace soldering

Brazing using a liquid heat source ∙ Dip brazing

Brazing using a gaseous heat source ∙ Flame brazing

∙ Manual brazing with an electric arc Electric arc brazing ∙ MIG, TIG, Plasma

∙ Laser beam brazing Brazing using radiation ∙ Electron beam brazing Brazing ∙ Induction brazing ∙ Induction brazing in a protective gas atmosphere ∙ Indirect resistance brazing Soldering using electrical heating ∙ Direct resistance brazing ∙ Furnace brazing in a reducing atmosphere ∙ Furnace brazing in an inert gas atmosphere ∙ Furnace brazing in a vacuum

Table 20 - Classification of soldering/brazing processes (based on [10])

KUPFERINSTITUT.DE | 37 4.5.1. Soldering with soldring iron tion of the parts and greater erosion of Hot-iron soldering is a soldering technique 4 the parent material. The workpiece is in which the thermal energy is supplied by 3 typically immersed for between 20 and a solid medium. 2 60 seconds. Dipping speed needs to be The joint is heated and the solder is melted 1 carefully controlled. It should be selected by applying heat from a hot iron that is so that the workpiece reaches the controlled either manually or by a soldering or brazing temperature during machine. Hot-iron soldering is not suitable all stages of the dipping process. A visible for fabricating narrow-gap joints with sign that the correct dipping speed has large overlap zones. been chosen is the presence of a concave 1. Conductor 2. Printed-circuit board meniscus at the interface of the molten Most soldering irons are equipped with a 3. Tip of soldering iron 4. Flux-cored solder solder of filler metal and the workpiece. built-in electrical heating element or with Large parts should be preheated prior to Figure 15 - Example of hot-iron soldering on a a small tank containing a combustible gas printed-circuit board (based on [10]) dipping to avoid too great a drop in the such as natural gas, or propane. bath temperature when the workpiece is The heat capacity and the shape of the immersed. Dip brazing is typically used in soldering iron and its tip (also known as the manufacture of condensers, cooling Advantages the ‘bit’) must be suitable for the assembly units and metal vessels [16]. · Low cost to be soldered. The more pointed the tip is, · Reproducible the easier it is to access the joint, though · Suitable for hard-to-access heat losses are also higher. Soldering iron 1 joints tips have masses ranging from about 20 g 3 · Suitable for temperature- 2 to 1 kg and used to be almost exclusively sensitive components made of copper due to its excellent · Good for single soldered joints thermal conductivity and good wettability. In high-volume soldering work, these Disadvantages copper tips would eventually dissolve in · Scaling on the iron tip due to the tin solder and the tips would need to high-temperature oxidation be reconditioned or replaced. For this · Operators must have a high reason, copper-containing solders and tips degree of skill and manual dexterity plated with other materials were devel- oped. When soldering with lead-free 1. Workpiece 2. Concave meniscus solders, the hot iron needs to be removed 3. Bath of molten solder or brazing filler metal Table 21 - Advantages and disadvantages of from the joint more quickly than with hot-iron soldering Figure 16 – Dip soldering/brazing (based on [10]) leaded solders to prevent spiking or solder pull-out, as the lead-free solders in use today have different flow characteristics 4.5.2. Dip soldering or brazing Advantages than the SnPb solders used previously. The he parts to be soldered or brazed are · Fully automated melting range of lead-free solders is mechanically cleaned and placed into · Application and melting of solder narrower than in lead solders so that position. Flux is then applied before the or filler metal in a single step solidification occurs more rapidly [6]. assembly (‘workpiece’) is dipped into a · Cost-efficient bath of molten solder or filler metal. The The soldering time is usually less than temperature of the dipping bath should Disadvantages 60 seconds. Depending on the specific be between 60 K and 100 K above the · Can cause high thermal stressing soldering application to be performed, liquidus temperature of the solder or filler of workpiece between 15 W and 2000 W of thermal metal. Higher temperatures will lead to · High maintenance energy needs to be applied. The tip of the increased oxide formation on the surface iron can reach temperatures in the range of the bath. Higher temperatures are also 200–600 °C [6]. associated with a greater risk of distor- Table 22 - Advantages and disadvantages of dip soldering or dip brazing

38 | KUPFERINSTITUT.DE Wave soldering source, the high reflectivity (up to 96 %) Wave soldering is chiefly used to solder of the shiny metallic components is not electronic components onto printed conducive to heating and needs to be circuit boards. taken into account when designing the process. The actual soldering stage The process comprises four stages with a occurs when the PCB assembly is conveyor transporting the printed circuit transported through the solder wave board (PCB) to the different zones. The zone. The final stage involves cooling the process begins with flux being applied to PCB assembly in the cooling zone, either the PCB assembly. In the second stage, naturally under ambient conditions or by the PCB assembly is pre-heated using a forced cooling. [27]. Experience has convection heater or an infrared lamp to shown that the PCB assembly is best compensate for the different heat drawn across the surface of the solder capacities and thermal expansion inclined at an angle of 7° [10]. coefficients of the materials on and in the PCB. PCBs contain epoxides, which as Drag soldering is a variant of wave poor conductors of heat make it difficult soldering. In drag soldering, the solder is to raise the temperature of the assembly. applied not by contact with the solder The PCB laminate therefore acts to cool wave, but by immersion in a static solder the surrounding metal components bath. The angle at which the assembly making it impossible to heat the assembly enters and exits the bath is typically uniformly up to the soldering tempera- between 8° and 10°, and the immersion ture. In addition, hot flux vapour causes a depth is usually about half the thickness rise in temperature of the tempera- of the PCB. A rigid strip is used to remove ture-sensitive electronic components. If the oxides (‘dross’) from the surface of infrared radiation is used as the heat the solder bath [10].

1 =7°

2

3

1. Printed-circuit board 4 2. Dryer 3. Solder bath with solder wave 4. Wave fluxer or foam fluxer 7° Conveyor angle

For the advantages and disadvantages of wave soldering, Figure 17 – Wave soldering (based on [10]) see the section on dip soldering or brazing.

KUPFERINSTITUT.DE | 39 4.5.3. Flame soldering or brazing work is available in the technical application reducing thermal stresses and distortion in Flame soldering or brazing (or Torch notes GW 2 and GW 7 issued by the the workpiece. The temperature-time soldering/brazing’) can be performed by German Technical and Scientific Association profile is relatively easy to control. hand or by machine. The heat is applied by a for Gas and Water (DVGW). For example, Workpieces with complex shapes and large flame of combustible gas (e.g. acetylene). drinking water installations are subject to numbers of joints can be soldered or The gas is fed to the torch head through a special requirements: copper piping larger brazed without difficulty. Additionally, pressure regulator. The choice of torch than 28 x 1.5 mm must only be joined by heat treatment and soldering/brazing can depends on the workpiece, material and gas brazing [28] [29]. be carried out in a single operation. The being used. The first stage involves applying solder or brazing filler metals should have 2 flux to the surfaces to be joined. The joint 1 a narrow melting range in order to prevent gap must be dimensioned accordingly. The and erosion [6]. parts to be soldered or brazed must be fixed in position to prevent them from slipping. Furnace soldering or brazing carried out in The workpiece should be pre-heated at the a controlled atmosphere (using inert gases location of the joint and its immediate such as argon, helium or , or vicinity so that the solder or filler metal can reducing gases like hydrogen or carbon flow easily. If the area to be soldered/brazed monoxide) is well suited to high-volume is not hot enough, the solder or filler metal 3 soldering or brazing jobs in which multiple will contract when it comes into contact joints need to be made, such as the with the cold surface and no wetting will 1. Components to be joined fabrication of condensers, cooling units, occur. Pre-heating is done with a neutral or 2. Flux and solder 3. Flame heat exchangers and in automotive with a reducing or slightly reducing flame. Figure 18 – Torch soldering (based on [10]) construction [6].

The solder or filler metal is fed to the joint Advantages A variety of furnace types are available, in the form of a rod or wire. If the solder or · Process can be easily mechanised including retort-type, batch-type and filler metal is to be inserted into the joint · Low equipment costs continuous-type . The tempera- (e.g. as a pre-form), consideration must be ture in the furnace should be approxi- given to the right type of solder or filler Disadvantages mately 50 °C above the relevant soldering metal and to the design of joint. In general, · Working with a naked flame or brazing temperature. It is important the soldering time or brazing time should · Components need to be held in that the surfaces to be joined are not exceed three minutes. The flame should place with a jig thoroughly cleaned prior to furnace not be aimed directly at the joint as this · Time-consuming preparation soldering or brazing. Furnace soldering or could damage the flux. Most fluxes need to and after-treatment of the brazing of brass components is only be removed once the soldering or brazing workpiece possible if a flux is used [6]. process is finished. Copper-copper joints are best made with phosphorus-containing Soldering or brazing in a vacuum furnace Table 23 - Advantages and disadvantages of solders or filler metals, as no flux is then torch soldering or torch brazing is a flux-free method of joining compo- required. Appropriate solders can be found nents that need to meet exacting quality in the following standards: DIN EN ISO 4.5.4. Furnace soldering or brazing specifications. It is commonly used in the 17672 (2010) for brazing filler metals; DIN Furnace soldering or brazing is nearly aviation, aerospace, electronics, automo- 1707-100 (2011) and DIN EN ISO 9453 always carried out either in a protective tive, machine tool, plant equipment (2014) for soft solder alloys. Torch soldering gas atmosphere or in a vacuum; it is rarely construction, and power engineering and brazing are used in numerous industrial done in an air atmosphere. industries. Vacuum furnaces also come in sectors, including refrigeration and a variety of types. Examples include air-conditioning, mechanical construction It offers a number of advantages over radiation-heated glass vessels, resist- of small-scale and large-scale equipment, other soldering or brazing processes. If ance-heated and induction heated plumbing and heating installations, and gas due consideration is given to the materials furnaces. Soldering or brazing is usually and water installations. Information and workpiece geometries used, uniform carried out under a low to moderate pertaining to gas and water installation heating and cooling can be achieved, thus vacuum (1 mbar to 10-3 mbar) or high

40 | KUPFERINSTITUT.DE vacuum conditions (10-3...10-7 mbar). In Medium Vacuum Reducing gas Inert gas Flux the majority of cases, the heating power of a vacuum furnace lies between 50 kW and 500 kW. Before any soldering or brazing Flux X X X can take place, the heating chamber needs to be cleaned and the components Reducing gas X carefully positioned within it. The temperature of the furnace is then Inert gas O X increased rapidly to about 50 °C below the solidus temperature. The furnace is then Vacuum X held at this temperature for a short time to facilitate temperature equilibration. This is followed by rapid heating to approximately X – can be used simultaneously 20–30 °C above the soldering or brazing O – can be used sequentially temperature of the solder or brazing filler Table 24 - Surface activation in furnace soldering or brazing metal. Depending on the work being carried out, the soldering or brazing temperature must be held for a period of 5–20 minutes. Process times can be shortened by heating and cooling under a 3 4 5 6 7 8 protective gas atmosphere. In such cases, 2 the vacuum in the furnace chamber is 9 generated at higher temperatures [6]. 1

10

1. Infeed 2. Extractor hood 3. Exit port for protective gas 4. Pre-heating zone 5. tube port 6. Soldering/brazing zone 7. Cooling water 8. Cooling zone 9. Exit 10. Entry port for protective gas

Figure 19 – Vacuum soldering/brazing furnace [30] Figure 20 - Schematic diagram of a continuous-feed furnace with an inert gas atmosphere (based on [6])

Another means of classifying furnace soldering or brazing processes is in terms of the process consumables used, such as: Advantages Disadvantages · Uniform heating and cooling ensures · All areas of the workpiece are · Flux low-stress and undistorted components subjected to heat treatment · Flux and protective gas · Soldering/brazing of complex assemblies · Long soldering/brazing times · Soldering/brazing and heat-treatment · High equipment costs · Reducing protective gas (e.g. hydrogen) can be performed in a single step · Inert protective gas (e.g. argon, helium) [6]. · Process can be readily controlled · Multiple joints can be made in a single step

Table 25 - Advantages and disadvantages of furnace soldering or brazing

KUPFERINSTITUT.DE | 41 of solder pastes containing, for example, Reflow soldering is an important SnAgCu or SnAg alloys. In a reflow oven, technique in the electronics industry. It is the solder in the solder/flux paste melts a common method of attaching surfa- creating a material bond between the ce-mounted components to printed electronic components and the circuit circuit boards. The technique makes use board (see figure 21).

Figure 21 - Surface-mounted component shown before the solder in the solder paste melts [31]

Condensation Radiation Convection Conduction (vapour phase)

Infrared Laser Air Nitrogen

Simultaneous X X X process Simultaneous X X batch process

Sequential X process

Heat transfer to Partially PCB assembly Large energy Very large energy inhomogeneous if Homogeneous Homogeneous Homogeneous (inter- density density no planar contact comparison) to component

Maximum T can be T can be control- achievable T can be control- P T is limited by the P P controlled P led precisely temperature Temperature can Temperature can led very precisely choice of medium very precisely (max. hot-plate relative to the slightly exceed T slightly exceed T (max. gas temp. (max. temp. P P (max. gas temp. temperature temperature T on ≤ 350 °C) ≤ 260 °C) P ≤ 350 °C) ≤ 350 °C) the PCB assembly

Flexibility in controlling the High Low Very high Very high Medium Medium to low temperature profile

Component Solder paste and Requires a flat, Special specifications No substrate must No No bare contact requirements must be taken be suitable surface into account

The following heat sources may be used: light/radiation (e.g. infrared), convection (e.g. hot Table 26 - Comparison of the different reflow nitrogen), vapour-phase condensation (latent heat) and conduction. Table 26 lists some of soldering heating modes [31] the characteristic properties of the various heat sources.

42 | KUPFERINSTITUT.DE Convection reflow soldering in a nitrogen controlled externally by fans, blowers and soldering can also be done under vacuum. atmosphere has gained in importance in injector nozzles. As can be seen in figure 22, Nevertheless, soldering faults can still recent years. The nitrogen partially a convection reflow oven has multiple arise, such as solder skips, tombstoning displaces the air from the reflow oven thus process zones that can be controlled (unbalanced solder melting and wetting reducing the oxygen content in the individually [31]. behaviour at the mounting pads on chamber. As nitrogen itself does not react different sides of the component), solder chemically with the other elements present, No matter which type of reflow soldering bridges and solder balls [15] [31]. it effectively prevents oxidation on the oven is chosen, the reflow process is metallic surfaces to be soldered and always composed of the following steps: therefore improves the solder wetting pre-heating, solder reflow, and cooling. To process. The convection of the hot gas is achieve pore-free soldered joints, reflow

Pre-heating Peak Cooling

Figure 22 - Schematic diagram of a convection reflow oven [31]

4.5.5. brazing: direct resistance soldering/brazing, Electric resistance soldering or brazing in which the electric current flows directly Advantages Typical parent metals are copper, brass, through the joint, and indirect resistance · Heat is applied only in the unalloyed steel and aluminium, but all other soldering/brazing, in which the current is region of the joint, neighbouring metallic materials can be soldered or brazed introduced to the part to be joined via an areas remain unaffected by this technique. electrode without flowing through the · Short soldering/brazing times joint [6]. · Suitable for temperature- The solder of filler metal is applied to or F sensitive parts placed in the assembly gap before soldering or brazing begins. The electrodes (made, for Disadvantages example, from tungsten) are used to press · Geometry of assembly must be the mating surfaces together. The electric taken into account current flowing in the secondary circuit of 2 the transformer generates intense heat at Table 27 - Advantages and disadvantages of electric the point of contact between the parts to resistance soldering or brazing be joined and causes the solder to melt. Depending on the particular application, a 1 flux or a controlled atmosphere can be 3 used. Soldering or brazing times range from a few milliseconds to a few seconds. There are two types of resistance soldering/ F

1. Workpiece 2. Joint to be soldered 3. Electrodes Figure 23 – Direct resistance soldering (based on [10])

KUPFERINSTITUT.DE | 43 4.5.6. Induction soldering or brazing Table 29 shows how the heat penetration Induction soldering or brazing can be depth (or ‘skin depth’) in copper and brass used to join all types of metal and varies with frequency. It is readily apparent typically uses a flux in an air or that lower frequencies are more suited to controlled atmosphere. The technique is heat generation at greater depths, while primarily used, however, for copper, higher frequencies are better for processing brass, steel and aluminium. The solder or at the workpiece surface. brazing filler alloy selected should have a narrow melting range or a fixed Material Temperature [°C] Skin depth [mm] at the following frequencies: melting point and good flow properties. 50 Hz 500 Hz 10 kHz 1 MHz The cleaned joint is surrounded by a single-turn or multi-turn water-cooled Copper 600 17 5,5 1,2 0,12 induction coil. The induction coil must be shaped appropriately to fit the form Brass 600 26 8,5 1,8 0,18 of the workpiece. The technique is Table 29 - Skin depth as a function of operating frequency [32] therefore particularly well suited for rotationally symmetric parts. An AC Induction soldering/brazing offers a number temperature-sensitive parts. Drawbacks current flows in the coil, generating an of advantages over other soldering/brazing include the creation of an electromagnetic alternating magnetic field that induces techniques. There is no exposure to high field during the soldering/brazing process electric currents and therefore heat in levels of light, heat or noise at the workplace, and the high initial cost of the equipment, the part being soldered or brazed [6]. systems can be readily which makes the technique more suited to mechanised or automated, the process is the mass production of assemblies [6]. The technique requires a medium- energy efficient, heating is fast and localised, 4 frequency or high-frequency generator. which is beneficial when dealing with 3

Medium frequency High frequency 1

Frequency 1000 – 10.000 Hz 0.1 – 5 MHz 2 Size of copper parts t = 4 – 12 mm t = 0.3 – 3 mm [thickness t] 1. Components to be joined 2. Brazing joint 3. Induction coil 4. Generator Figure 24 – Induction brazing [10] (above) Output power 20 – 300 kW 2 – 30 kW Table 30 - Advantages and disadvantages of induction soldering or brazing (below)

Soldering or brazing time 0,5 – 4 min 5 – 60 sec Advantages · Contactless process Precision engineering, · Short soldering/brazing times Appliance manufacturing, electrical engineering, tool Areas of application · High-quality soldered/brazed joints automotive engineering fabrication, aerospace · Uniform heating of the engineering components

Coupling gap between Disadvantages the coil and the part to be 2 – 4 mm for Cu: 1–2 mm · High investment cost soldered or brazed · Joint must be accessible to induction coil 0.05–0.25 mm (for narrow gaps in a controlled atmosphere; · More suited for rotationally Gap width in all other cases: flux required) symmetric components · Electromagnetic field Table 28 - Characteristic features of induction soldering or brazing [6]

44 | KUPFERINSTITUT.DE 4.5.7. Electron beam brazing 4.5.8. Arc brazing Electron beam brazing is carried out in a Advantages Electric arc brazing can be performed as medium or high vacuum environment. It is · Highly localised heating of a MIG or TIG process. The arc is created characterised by high power and parent material between a wire electrode and the parts a small beam diameter. The electrons are · Good reproducibility to be brazed, transforming electrical thermally emitted from the cathode and · Minimal distortion of components energy into heat at the brazing joint. The accelerated by the strong electric field that · No complex preparation or filler metal is typically a copper-based results from the high voltage (15–75 kV) after-treatment required alloy wire or rod whose melting range is applied between the cathode and anode. below that of the parent metal. The The electron beam exits the beam Disadvantages solidus temperature of common filler generator through a hole in the anode. · Process carried out in a vacuum metals of this type is in the range 830 °C When the tightly bundled electron beam · Potential x-ray hazard to 1060 °C. Electric arc brazing is impacts the target material, the kinetic · Requires use of filler metal generally used for braze welding energy of the fast-moving electrons is preforms or pre-coated parts applications. The most important filler converted into thermal energy, generating metals are listed in table 32. heat in the material. In electron beam brazing, the parts to be joined must be Table 31 - Advantages and disadvantages of electron pre-coated with filler-metal or filler metal beam brazing preforms must be inserted at the location of the joint. Electron beam brazing is used DIN EN ISO 17672 Filler metal alloy DIN ISO 24373 (2009) for applications in which the joints have (2013) tight dimensional tolerances, where high-power, highly localised heating is Designation Material number Material number required, or where heating has to be Silicon bronze CuSi2Mn1 Cu 6511 Cu 521 achieved extremely rapidly [6]. Silicon bronze CuSi3Mn1 Cu 6560 Cu 541 2 1 Tin bronze CuSn6P Cu 5180A Cu 922 Tin bronze CuSn12P Cu 5410 Cu 925 4 CuAl7 Cu 6100 Cu 561 3 6 5 Aluminium bronze CuAl10Fe Cu 6180 Cu 565 8 7 9 Manganese bronze CuMn13Al8Fe3Ni2 Cu 6338 Cu 571

Table 32 - Overview of important filler metals used in laser and electric arc brazing

In recent years MIG brazing with consuma- ble wire electrodes and plasma brazing have grown in importance, particularly when joining zinc galvanised sheet steel 10 11 (thickness: less than 3 mm) in the automo- tive industry. Figure 26 shows a continuous 1.Vacuum chamber 2. Cathode 3. Anode peripheral MIG brazing seam on a motor 4. Power source connector terminals bike fuel tank [33]. 5. Beam deflection system 6 . Focusing lens 7. Hartlötkammer 8. Electron beam 9. Brazing joint 10. Device for moving/ positioning workpiece 11. Components to be joined

Figure 25 – Electron beam brazing [10] Figure 26 - Fuel tank from a Honda VT 1300CX with CuAl8 brazing filler metal [33]

KUPFERINSTITUT.DE | 45 Studies have shown that when electric 1 arc brazing is carried out under a Advantages shielding gas, the commonly used · High productivity 2 3 7 copper-based (bronze) filler metals cause · Little preparation or after-treatment 5 diffusion and partial dissolution to occur required (no flux involved) 4 at the interface of the parent metal and · Minimal distortion of components the coating and filler metals. The metal · Can be readily mechanised surfaces that come into contact with the · High brazing speed brazing filler alloy should be clean and · Low investment costs bare so as to facilitate metallurgical · Optically well-finished joints 6 interaction between the parent metal and 1. Power source 2. Laser beam 3. Focusing lens the wetting filler metal. Fluxes are not Disadvantages 4. Shielding gas 5. Brazing joint required as the surfaces are activated by · Precision electrode feeding required 6. Components to be joined 7. Filler wire the burning arc. The DVS technical leaflet · Arc blow may need to be taken Figure 28 – Laser beam brazing (based on [6]) 0938-1 (2012) contains further informa- into account tion on the principles and details of the Laser brazing is commonly used in the process as well as the equipment automotive industry to join zinc galvanised requirements. Application notes on arc Table 33 - Advantages and disadvantages of electron body panels, as it enables high brazing arc brazing brazing are available in DVS technical speeds to be achieved while the small heat leaflet 0938-2 (2005). One of the 4.5.9. Laser beam soldering or brazing affected zone minimises panel distortion advantages of electric arc brazing While both laser beam soldering and issues [36]. The images in table 34 show a compared with laser beam brazing is brazing techniques are used, most of the roof seam fabricated using laser brazing the lower capital investment costs applications in the automotive industry and a CuSi3Mn1 silicon bronze filler. Filler [6] [34] [35]. involve laser beam brazing. The technique metals that are suitable for use in electron enables high temperatures to be reached beam brazing (see table 32) can also be so that high-melting copper-based filler used for laser beam brazing [37]. metals can be processed without difficulty. A highly focused laser beam generates 1 high power densities but only a small heat-affected zone. A particularly suitable radiation source for copper-based filler metals is a Nd:YAG solid-state laser as it generates laser radiation at a wavelength of 1.06 µm by the filler alloy. It is Laser-brazed roof seam Laser-brazed roof seam on a Volkswagen Passat on an AUDI Q5 (2008) important that the parts to be joined are CC (2008) 2 5 pre-coated with filler metal or that the Table 34 - Examples of a laser brazed seam [33] (above) 3 filler metal is precisely positioned. Laser Table 35 - Advantages and disadvantages of laser beam 4 beam soldering and brazing techniques are brazing (below) used primarily in the electrical, automotive and precision engineering sectors. Very short soldering or brazing times are Advantages · Very high productivity 1. Wire electrode (filler metal) 2. Shielding gas possible. For example, single soldering · Minimal preparation or after-treatment 3. Arc 4. Brazing joint 5. Power source times in the millisecond range are possible for surface mounted electronic compo- required (no flux involved) Figure 27 - Electric arc brazing (MIG) (based on [6]) · nents [6]. Can be readily mechanised · Minimal distortion of components · High brazing speed Disadvantages · High capital investment costs · Positioning and feeding of filler wire has to be done very precisely

46 | KUPFERINSTITUT.DE 5. Quality assurance

Quality assurance is one of the main contains all of the relevant standards and data are, however, essential when the elements of a quality management system DVS technical leaflets relating to soldering soldering or brazing process is mechanised and is concerned with verification. The aim and brazing. or fully automated, such as in a completely of quality assurance is to prevent the encased continuous-feed furnace. production or supply of defective products. In addition to the standards, the German As in welding, the quality of a brazing or Welding Society DVS (Deutscher Verband Another important aspect when assessing soldering process depends on the skill and für Schweißen und verwandte Verfahren the quality of a soldered or brazed experience of the operator. Soldering and e.V.) also issues technical leaflets and connection concerns of the geometry and brazing are physicochemical processes in guidelines. There are fewer rules and metallurgical structure of the joint. which a material bond is created through accepted methods of quality assurance for Dimensional and visual inspections are interactions between the solid parent soldering and brazing than for welding. The obligatory. The presence of cracks and material and the molten solder or filler primary criteria are: appropriate qualifica- pinholes (pores) are typically demon- metal. Phenomena such as capillary action tion and training of operating personnel; strated using dye penetration and and surface wetting are exploited in production monitoring; checking on magnetic particle inspection techniques. If soldering and brazing processes. If the assessing the quality of the joints made. soldering or brazing defects are to be parent material and solder or filler alloy are assessed and the wetted joint area properly matched, and if the joint is The objective is to fabricate a high-quality determined, x-ray and ultrasonic testing properly designed and made, a soldered or soldered or brazed joint in a reproducible are used. The different materials and the brazed joint can provide a more reliable join fashion while taking cost efficiency factors thicknesses of the parts must be taken than that achievable by welding [38]. This into consideration. The need for well- into account if these non-destructive section aims to provide an overview of trained and skilled personnel is important testing methods are deployed. Metallo- quality assurance issues but does not claim not only for producing well-executed graphic sections are prepared in order to be complete. soldered or brazed joints, but also for fixing check the condition of the microstructure, The following faults and defects can arise in or jigging the components of the soldered the transition zone, the seam width and a soldering or brazing process: or brazed assembly. The following any erosion. If brazing is used in the · flux burning when the temperatures guidelines and standards govern the construction of tanks, containers and used are too high, procedures to be followed in training piping, pressure and leak testing is courses: DVS Guideline 1183 (2004), DIN required [6]. Destructive testing methods · inadequate wetting by the solder or ISO 11745 (2011) and DIN EN ISO 13585 suitable for evaluating soldered joints are filler metal alloy, (2012). set out in the standard DIN 8526 (1977); · wrong choice of solder/filler or flux, those used to assess brazed joints are · no preparation or improper preparation By identifying and, where necessary, described in DIN EN 12797 (2000). of the mating surfaces, correcting workflow irregularities early, Non-destructive testing methods must monitoring procedures play an important conform with DIN EN 12799 (2000). · de-wetting caused by oxidation at the role in ensuring that the soldering or joint because soldering/brazing times brazing process meets the required quality Other defects that can occur include were too long. specifications while remaining cost-effec- cracking, lack of fusion, and voids.The DIN It is therefore important to produce and tive. Monitoring involves capturing key EN ISO 18279 (2004) standard provides a maintain quality assurance documentation. process parameters (e.g. temperature time comprehensive classification system for The documentation should provide profile is) and observing the state of listing imperfections in brazed joints. safeguards against potential claims and soldering is, the filler alloys and other Permissible defects and imperfections are provide the necessary proof that a fault or auxiliary materials and consumables. detailed in DIN 65170 (2009). This standard defect could not have occurred during the Manual processes, such as hot iron also specifies permissible wetted joint fabrication or production process. soldering, demand highly trained operators areas, which are an important criterion for Important recommendations are contained with good manual dexterity as, in most assessing the quality of a brazed joint [6]. in the standards governing quality cases, devices measuring and displaying the management systems: DIN EN ISO 9001 temperature at the workpiece are not used. (2008) and ISO/TS 16949 (2009). The Measuring instruments that can monitor DIN-DVS Manual 196 (Parts 1 and 2) also process parameters and record process

KUPFERINSTITUT.DE | 47 6. Case studies

Quality requirements in soldering and/or brazing

Operational and Fabrication / Testing / Personnel administrative aspects Production Assessment

Quality management system Qualification testing Soldering and brazing Non-destructive DIN EN ISO 9001 (2008) of operators processes DIN EN 12799 (2000) ISO/TS 16949 (2009) DIN ISO 11745 (2011) DIN ISO 857-2 (2007) Destructive DIN EN 13585 (2012) DIN 8526 (1977)DIN EN 12797 DVS-Richtlinie 1183 (2004) (2000) Defects / Imperfections DIN EN ISO 18279 (2004) DIN 65170 (2009)

Table 36 - Summary of a number of important quality requirements

6.1. Hot-air solder levelling of ensure uniform reproducible results, solder printed circuit boards analyses should be conducted at regular Hot-air solder levelling (also: hot-air intervals. These analyses are generally levelling – HAL) is used to coat exposed carried out free-of-charge by the solder copper surfaces on a PCB with solder. To supplier [39]. make sure that the copper is wettable, it is crucial that all dirt or tarnish is removed from the PCB before HAL is performed. HAL process After pre-cleaning, the flux is applied at the fluxing station. To restrict flux ∙ Fluxed PCB is dipped into a bath of hot solder contamination in the HAL system, the ∙ Board withdrawn after a short period amount of flux applied should kept to the vertical ∙ Excess solder is blown off by jets of hot air (‘hot-air knives’) minimum needed. In semi- and fully ∙ Result: some plated-through holes missed and non-uniform solder automated systems, the solder application thickness on the PCB, horizontal HAL method is therefore preferred process can be carried out with the PCB oriented vertically or horizontally (see Wave tinning Roller tinning table 37). The horizontal process can be further classified into wave tinning ∙ PCB travels at constant speed ∙ PCB is accelerated after systems, in which the solder is applied over the entire length of the passing through the fluxing zone when the PCB passes through a solder HAL machine ∙ PCB guided through up to wave bath, and roller tinning systems, in PCB is pulled though a solder three pairs of rollers horizontal ∙ which the PCB passes through a set of wave bath ∙ Excess solder blown off pinch rollers [39]. ∙ Excess solder removed by hot-air knives If lead solders are used in the HAL process, ∙ Contact time with molten the choice of solder is critical, as solders solder longer than in roller with a copper content of more than 0.3 % tinning will result in uneven soldered surfaces. To

Table 37 - Process steps in vertical and horizontal HAL systems

48 | KUPFERINSTITUT.DE 6.2. Strip tinning Tinned strips of copper or copper alloys The adapter tube on a CuproBraze® process joints are created are the raw materials for plug-in can be fabricated by brazing a flexible by brazing with the filler alloy CuNiSnP. connectors that are used in a wide inner copper tube with a protective Once the tubes and fins have been variety of applications, such as connec- woven bronze shield using fluxless fabricated, a filler metal paste is applied tors for vehicle wiring looms, for electric arc brazing (TIG). Appropriate to them. Once brazed, the elements are computers and other electronic devices. filler materials are the high-tin bronze then assembled to make the heat Component miniaturisation has placed rods, such as CuSn12P. In TIG brazing, exchanger and held in position by a jig. increasingly tough demands on the the arc burns above a sharp-tipped Brazing paste is then applied again and quality of the strip tinning process. tungsten rod and the filler metal is fed the assembly is brazed in a conti- Meeting these quality specifications to the joint by hand. Well-executed nuous-feed furnace. There is no need for requires the strip to be hot-dip tinned brazes have a visually appealing fluxes and subsequent rinsing proce- with non-corrosive, no-clean fluxes (see appearance [33]. dures [40] [41]. table 15), which have to be carefully selected for the particular strip tinning line and for the copper alloy being tinned. Corrosive fluxes are rarely selected, as customers who use tinned strips frequently demand a chloride-free tinning process. Layer thicknesses can be adjusted individually to satisfy customer specifications [24].

6.3. Fabricating heat exchangers from copper Figure 29 – Heat exchange tube [33] Thanks to their good thermal conductiv- ity and their high mechanical stability, heat exchangers made from copper/ Figure 30 – Compact high-performance [12] brass are commonly used for air-condi- tioning systems in utility vehicles, for 6.4. Manufacture of compact radiators in construction machinery, or high-performance radiators for industrial cooling equipment. They from copper are manufactured in four steps. The The CuproBraze® process is used to initial stage involves machine-tinning manufacture compact high-performance brass strip by hot-dipping in a tinning heat exchangers from copper and bath and then drawing into tubes. The non-ferrous metals. The compact highly tubes are then brazed with copper fins efficient design of these heat exchan- in a furnace. Dip brazing is then used to gers makes them particularly well suited join the tubes to the tube sheet. Finally, for applications in the automotive and the water tank is manually brazed to the aviation industries, but also for coolers, tube sheet. Non-corrosive or no-clean condensers or evaporators in the fluxes are preferred for all steps of the refrigeration and electrical engineering production process. To achieve the best sectors. One of the advantages of possible brazing results, the fluxes are radiators made from copper or copper selected for the particular brazing alloys over those made from aluminium operation. Corrosive fluxes are only used is that they prevent biofouling and thus in exceptional circumstances as they eliminate the bad odours that would require additional rinsing operations that otherwise be generated by and drive up process costs [24]. in the cooling channels. In the

KUPFERINSTITUT.DE | 49 7. Terminology

Cooling time Holding time Design suitability for soldering/brazing Time span during which the joint cools down Time during which the joint is kept at the Property of the design that is determined in from the soldering/brazing temperature to soldering or brazing temperature [10]. equal measure by the material and the ambient temperature [10]. manufacturing process [2]. Capillary attraction Heating time Force, caused by surface tension, which Closed joint Time during which the soldering/brazing draws the molten filler metal into the gap Joint in which the gap is filled principally temperature is reached. It includes the between the components being joined, even by capillary action with filler metal, i.e. equalising (preheating) time and can also against the force of gravity [10]. either a butt joint or a lap joint between include other times, e.g. the degassing parallel faces of the components to be time [10]. Liquidus temperature soldered or brazed [10]. Temperature above which a material is Wetting completely liquid. Soldering or brazing temperature Spreading and adhesion of a thin continuous Temperature at the joint where the filler layer of molten filler metal on the surfaces of Solderability/Brazeability metal wets the surface or where a liquid the components being joined [10]. Property of a component that enables it to be phase is formed by boundary diffusion and produced by soldering or brazing so as to there is sufficient material flow [10]. Diffusion zone / Transition zone meet the requirements of its intended use [2]. Layers formed during soldering or brazing Soldering or brazing time with a chemical composition that is different Material suitability for soldering/brazing Time period for the soldering or brazing from that of the parent material(s) and that Property of a material that is influenced by cycle [10]. of the solder or braze metal [10]. the manufacturing process and, to a lesser extent, by its design [2]. Filler material Equalising temperature Added metal required for soldered or brazed Temperature at which the components being Solder metal or braze metal joints, which can be in the form of wire, joined are held so that they are uniformly Metal formed by the soldering or brazing inserts, powder, pastes, etc [10]. heated through [10]. process [10]. Soldering or brazing paste Equalising temperature Soldering / Brazing Metal powder combined with a binder and in Time during which the components to be Joining processes in which a molten filler some cases a flux. Soft solder pastes are soldered or brazed are held at the equalising/ material is used that has a lower liquidus used, for example, in reflow soldering; preheating temperature [10]. temperature than the solidus temperature brazing pastes are used, for example, in the of the parent material(s), which wets the brazing of pipes made of copper or De-wetting surfaces of the heated parent material(s) galvanised steel. Separation of solid filler material which, and which, during or after heating, is drawn although it had spread over the surfaces of into (or, if pre-placed, is retained in) the Solidus temperature the components to be joined, had failed to narrow gap between the components being Temperature below which there is no bond to them because of e.g. inadequate joined [10]. liquid phase cleaning or fluxing [10]. Manufacturing suitability for Parent material affected by the soldering/ Soldered or brazed assembly soldering/brazing brazing process Assembly formed by soldering or brazing Property of the manufacturing process that Material with properties different from those two or more components together [10]. is primarily influenced by design factors and of the parent material due to the influence of less by the material itself [2]. the soldering/brazing process [10]. Total time Period which includes the heating time, the Soldering or brazing seam Heat-affected zone holding time and the cooling time [10]. Region of the joint comprising the solder/ Zone of parent materials affected by the braze material and the diffusion/transition soldering/brazing process [10]. Parent material zones [10]. Material being brazed/soldered [10]. Effective temperature range Temperature range within which a flux or a protective atmosphere is effective [10].

50 | KUPFERINSTITUT.DE 8. Appendix The tables below present a selection of standards and guidelines relating to soldering and brazing

Standard Title / (Year of publication)

DIN 8514 Brazeability, solderability (DIN 8514:2006-05)

General Welding and allied processes – Vocabulary – Part 2: Soldering and brazing processes DIN ISO 857-2 and related terms (ISO 857-2:2005)

Graphical Representation of Welded, Soldered and Brazed Joints – Concepts and Terms for DIN 1912-4 Soldered and Brazed Joints and Seams (DIN 1912:1981)

Welding and allied processes - Symbolic representation on drawings - Welded joints Engineering desig DIN EN ISO 2553 (ISO 2553:2013); German version EN ISO 2553:2013

Aerospace – Brazed and high-temperature brazed components – DIN 65169 Directions for design (DIN 65169:1986) Processes / DIN EN 14324 Brazing – Guidance on the application of brazed joints (German version EN 14324:2004) Manufacturing Copper and copper alloys – Compendium of compositions and products DIN CEN/TS 13388 (DIN CEN/TS 13388:2013

Filler metals for soft soldering, brazing and brazewelding– Designation DIN EN ISO 3677 (ISO 3677:1992; German version EN ISO 3677:1995

DIN EN ISO 17672 Brazing – Filler metals (ISO 17672:2010; German version EN ISO 17672:2010

DIN 1707-100 Soft solder alloys – Chemical composition and forms (DIN 1707-100:2011-09) Parent materials / Soft solder alloys – Chemical compositions and forms (ISO 9453:2014; Solders and filler DIN EN ISO 9453 metals / Fluxes German version EN ISO 9453:2014) Brazing – Fluxes for brazing – Classification and technical delivery conditions DIN EN 1045 (German version EN 1045:1997)

Soft soldering fluxes – Classification and requirements – Part 1: Classification, DIN EN 29454-1 labelling and packaging (ISO 9454-1:1990; German version EN 29454-1:1993)

Soft soldering fluxes – Classification and requirements – DIN EN ISO 9454-2 Part 2: Performance requirements (ISO 9454-2:1998; German version EN ISO 9454-2:2000)

Brazing – Qualification test of brazers and brazing operators (ISO 13585:2012; DIN EN ISO 13585 German version EN ISO 13585:2012)

DIN EN 13134 Brazing – Procedure approval (German version EN 13134:2000)

Brazing for aerospace applications – Qualification test for brazers and brazing operators – DIN ISO 11745 Brazing of metallic components (ISO 11745:2010; DIN ISO 11745:2011-01)

DIN EN 12797 Brazing – Destructive tests of brazed joints (German version EN 12797:2000)

DIN 8526 Testing of soldering joints – Gap soldered joints, shear test, creep shear test (1977) Test procedures DIN EN 12799 Brazing – Non-destructive examination of brazed joints (German version EN 12799:2000)

Brazing – Imperfections in brazed joints (ISO 18279:2003; DIN EN ISO 18279 German version EN ISO 18279:2003) (2004)

Aerospace series – Brazed and high-temperature brazed metallic components – DIN 65170 Technical specifications; Text in German and English (2009)

Specification and qualification of brazing procedures for metallic materials – DIN 1900 Procedure test for arc brazing of steels (DIN 1900:2010-04)

Table 38 - Selected standards covering soldering and brazing processes

KUPFERINSTITUT.DE | 51 Regulations / Technical guidelines / Technical leaflet

Berufsgenossenschaftliche Vorschrift für Sicherheit und Gesundheit bei der Arbeit BGV D1 [Accident prevention regulations governing welding, cutting and allied processes; published by the German Employers’ Liability Insurance Association] (04/2001)

Löten in der Hausinstallation – Kupfer – Anforderungen an Betrieb und Personal Richtlinie [Technical guidelines: Soldering/ brazing in domestic installation work – Copper – Requirements to be met DVS 1903-1 by companies and their employees] (10/2002)

Löten in der Hausinstallation – Kupfer – Rohre und Fittings – Lötverfahren – Befund von Lötnähten Richtlinie [Technical guidelines: Soldering/brazing in domestic installation work – Copper – Pipes and fittings – Soldering/brazing DVS 1903-2 procedures – Inspecting soldered/brazed joints] (10/2002)

Merkblatt Lichtbogenlöten – Grundlagen, Verfahren, Anforderungen an Anlagentechnik DVS 0938-1 [Technical leaflet: Electric arc brazing – Principles, methods and technical requirements] (08/2012)

Merkblatt Lichtbogenlöten – Anwendungshinweise DVS 0938-2 [Technical leaflet: Electric arc brazing – Application notes] (05/2005)

Merkblatt Hartlöten mit der Flamme DVS 2602 [Technical leaflet: Torch brazing] (04/2011)

Merkblatt Öfen für das Hart- und Hochtemperaturlöten unter Vakuum DVS 2604 [Technical leaflet: Furnaces for brazing and high-temperature brazing under vacuum] (02/2008)

Merkblatt Hinweise auf mögliche Oberflächenvorbereitungen für das flussmittelfreie Hart- und Hochtemperaturlöten DVS 2606 [Technical leaflet: Information on surface preparation methods for flux-free brazing and high-temperature brazing] (12/2000)

Merkblatt Prozesskontrolle beim Hochtemperaturlöten DVS 2607 [Technical leaflet: Process control during high-temperature brazing] (02/2008)

Merkblatt Reparatur von Hochtemperaturlötverbindungen DVS 2608 [Technical leaflet: Repair of high-temperature-brazed joints] (02/2008)

Merkblatt Visuelle Beurteilung von Weichlötstellen – SMD auf Leiterplatte – Kriterien im synoptischen Vergleich DVS 2611 [Technical leaflet: Visual assessment of soldered joints – SMDs on printed-circuit boards –Comparison criteria] (05/1993)

Merkblatt Flussmittel für das Weichlöten in der Elektronik – Hinweise für den Praktiker DVS 2612-1 [Technical leaflet: Fluxes for electronic soldering applications – Information for soldering operators]

Neueinstufung und Etikettierungsvorschriften für Flussmittel zum Hartlöten, die Borsäure, Merkblatt Boraxpentahydrat oder di-Bortrioxid enthalten DVS 2617 [Technical leaflet: Reclassification and labelling rules for fluxes containing boric acid, borax pentahydrate or boron trioxide] (09/2012)

Verbinden von Kupfer- und innenverzinnten Kupferrohren für Gas- und Trinkwasser-Installationen DVGW innerhalb von Grundstücken und Gebäuden GW 2 (A) [Technical application note: Joining copper pipes and internally tinned copper pipes for gas and drinking water installations in buildings and property] (2012)

Flussmittel zum Löten von Kupferrohren für Gas- und Wasserinstallationen DVGW GW7 [Technical application note: Fluxes for soldering/brazing copper pipes in gas and water installations]

Table 39 – Regulations, technical guidelines and leaflets covering soldering and brazing processes

52 | KUPFERINSTITUT.DE Temperature in acc. with DIN Process Filler materials Soldering / brazing method Example applications ISO 857-2 (2007)

Manufacture of condensers, Soft solders mostly Hot-iron soldering, cooling units and metal tin-based; commonly used in ≤ 450 °C Soldering wave soldering, vessels; Electronics; combination with a flux: dip soldering Fabrication of PCBs; joint strength is relatively low Tinning

Refrigeration and air-conditioning; Typically used with a flux; Gas and water installations; suitable brazing filler Mechanical construction metals (BFMs) are: of small-scale and silver-based BFMs, brass Torch brazing, large-scale equipment; BFMs, copper alloy BFMs; induction brazing, > 450 °C Brazing Plumbing and heating copper and copper alloys can electric resistance brazing, installations; Cooling be brazed in air without a furnace brazing systems; Heat exchangers; flux using phosphorus- Automotive and aviation containing BFMs; construction; high-strength joints Power engineering; Electrical engineering / electronics

Table 40 - Examples of soldering and brazing applications

KUPFERINSTITUT.DE | 53 Parent Solder / Brazing filler metal (BFM) material

Silver- Copper- Tin-lead Silver-alloy copper- Copper-zinc Copper-nickel Copper alloy Lead solders phosphorus solders BFMs BFMs BFMs BFMs BFMs BFMs

Aluminium X X alloys

Beryllium X

Gold X

Cast iron – X X

Grey – X

Malleable – X X iron

Carbide X X

Copper X X X X X

Copper alloys X X X X X

Brass X X

Molybdenum X

Nickel X X X X X X

Nickel alloys X X X X

Unalloyed X X – X X X steel

Alloyed steel X X – X X X

High- X – X strength steel

Corrosion- X – X (–) resistant steel

Creep- – X resisting steel

Titanium X

Tungsten X

Zirconium X

x common combination; – unsuitable combination

Table 41 - Matrix for selecting commonly used combinations of parent metals and solders or brazing filler metals

54 | KUPFERINSTITUT.DE Solder or brazing Advantages Disadvantages filler metal

∙ low creep resistance ∙ allotropic transformation of tin at low ∙ good engineering properties temperatures (risk of ) Tin-lead solders ∙ good plasticity ∙ risk of low-temperature embrittlement ∙ enhanced corrosion under damp or tropical conditions

∙ high plasticity ∙ poor resistance to corrosion ∙ good processability Soft solders Lead solders ∙ toxicity concerns (harmful to health and ∙ better thermal stability than tin-lead solders the environment) ∙ good low-temperature stability

∙ longer soldering times ∙ slower surface-wetting rate Lead-free solders ∙ recyclable ∙ elevated operating temperatures ∙ risk of metal whiskering ∙ Tip corrosion on hot-iron soldering irons

∙ good thermal conductivity ∙ good electrical conductivity ∙ high plasticity ∙ high strength Silver alloy BFMs ∙ good corrosion resistance ∙ high purchase price ∙ good wettability ∙ oxides exhibit low strength/stability ∙ good buffer between materials with differing thermal expansion coefficients

∙ very low viscosity ∙ risk of liquation Copper- ∙ low brazing temperature ∙ Risk of increased porosity through phosphorus BFMs ∙ self-flowing phase separatio ∙ good plasticity

∙ elatively low melting temperature, which is Brazing ∙ Low strength at high temperatures compared Silver-copper-palla- useful for parent materials that are susceptible filler metals with other palladium-containing filler metals dium BFMs to grain coarsening at elevated temperatures ∙ high purchase price ∙ good wetting and flow properties

∙ plasticity decreases as zinc content rises ∙ good plasticity ∙ zinc vaporises at elevated brazing Copper-zinc BFMs ∙ high strength temperatures leading to porous joints ∙ high thermal stability ∙ not suitable for brazing in a protective gas atmosphere or in a vacuum

∙ good heat resistance Copper-nickel BFMs ∙ good creep-resistance

∙ Lowest vapour pressure of all brazing ∙ risk of gas entrapment and solidification filler metals Copper BFMs cracking with oxygen-containing coppers ∙ good viscosity and an oxidising atmosphere ∙ good flow behaviour

Table 42 – Summary of some advantages and disadvantages of selected solders/brazing filler metals

KUPFERINSTITUT.DE | 55 Regulation / Directive / Hazardous substance Notes Technical rules RoHS Directive 2011/65/EU – since 2006 Lead Frequently contained in solders (earlier Directive: 2002/95/EG)

since 2009 TRGS 528 Solder fumes

since 2006 TRGS 900 Workplace exposure limits

∙ Boric acid Regulation (EC) No. 1272/2008 ∙ Boron trioxide (‘CLP Regulation’); 67/548/EEC since 2012 ∙ Borax (sodium borate, anhydrate) Frequently contained in fluxes (30th/31st DVS technical leaflet ∙ Borax decahydrate 2617 ∙ Borax pentahydrate Brazing fillers that contain a Commission Regulation (EU) cadmium concentration since 2011 Cadmium 494/2011 greater than 0.01 % by weight are

Table 43 – Hazardous substances prohibited

Conversion tables

DIN EN 29454-1 DIN 8511 Sn50Pb49Cu1 L-Sn50PbCu (162) 1.1.1 F-SW31 Sn50Pb32Cd18 1.1.2 F-SW26 SnPb32Cd18 (151) 1.1.3 F-SW27 Sn96Ag4 L-SnAg5 F-SW32 (701) 1.2.2 F-SW28 Sn97Ag3 L-SnAg5 (702) 1.2.3 F-SW33 Sn95Sb5 2.1.1 F-SW24 L-Sn95 (201) 2.1.3 Sn97Cu3 L-SnCu3 2.2.3 (402) 2.1.2 F-SW25 Pb98Ag2 L-PbAg3 (181) 2.2.2 2.1.3 F-SW23 Table 44 - Soft solders 2.2.1 2.2.3 2.2.3 F-SW34 3.1.1 F-SW12 F-SW21 3.1.2 F-SW22 3.2.1 F-SW13 3.2.2 F-SW11

Table 45 – Flux designations

56 | KUPFERINSTITUT.DE References [15] H. Bell, Reflowlöten, Bad Saulgau: [29] Merkblatt DVS 2602 - Hartlöten mit der [1] D. e. R. Muhs, Maschinenelemente. Eugen G. Leuze Verlag, 2005. Flamme, 2011. Normung, Berechnung, Gestaltung, Wiesbaden: Vieweg+Teubner GWV [16] W. Müller und J.-U. Müller, Löttechnik. [30] Günther-Köhler-Institut für Fügetechnik Fachverlag, 2009. Leitfaden für die Praxis. Band 127., und Werkstoffprüfung GmbH, Jena, 2012. Düsseldorf: DVS-Verlag GmbH, 1995. [2] DIN 8514 - Lötbarkeit, 2006. [31] H. Bell; Rehm Thermal Systems GmbH, [17] Deutsches Kupferinstitut Berufsverband „Reflowlöten,“ Blaubeuren, 2012. [3] K. Wittke und U. Füssel, Kombinierte e. V., „Niedriglegierte Kupferwerkstoffe - Fügeverbindungen, Berlin: Eigenschaften, Verarbeitung, [32] „Lötverfahren,“ AG & Co. KG, Springer-Verlag, 1996. Verwendung,“ 2012. [Online]. Available: http://www.technicalma- terials.umicore.com/de/bt/brazingCenter/ [4] H. J. Fahrenwaldt, Praxiswissen Schweiß- [18] Wieland-Werke AG, show_de_V_03_Loetverfahren.pdf. [Zugriff technik. Werkstoffe, Prozesse, Fertigung. Schliffbild Rohr-Fittings, 2012. am 25 09 2012]. 4. Auflage, Wiesbaden: Vieweg+Teubner GWV Fachverlag, 2011. [19] VG 81245-3 - Nichteisen-Schwermetalle; [33] Berkenhoff GmbH, 2013. Schweißzusätze und Hartlote; Auswahl, 1991. [5] H. J. Fahrenwaldt, Praxiswissen Schweiß- [34] Merkblatt DVS 0938-1 - Lichtbogenlöten technik. Werkstoffe, Prozesse, Fertigung, [20] DVS Merkblatt 2607 - Prozesskontrolle - Grundlagen, Verfahren, Anforderungen an Wiesbaden: Vieweg+Teubner GWV beim Hochtemperaturlöten, 2007. die Anlagentechnik, 2012. Fachverlag, 2009. [21] DVS Merkblatt 2606 - [35] Merblatt DVS 0938-2 - Lichtbogenlöten [6] K.-J. Matthes, Fügetechnik. Überblick, Hinweise auf mögliche Oberflächen- Anwendungshinweise, 2005. Löten, Kleben, Fügen durch Umformen, vorbereitungen für das flußmittelfreie Leipzig: Carl-Hanser-Verlag, 2003. Hart- und Hochtemperaturlöten, 2000. [36] U. Berger und R. Mainhardt, „Welding Journal,“ 2009. [7] M. Türpe, Löttechnik. Vorlesung Löten, TU [22] H. Kleinert, Klebtechnik, Lehrmaterialien Dresden, 2008. der Fakultät Machinenwesen, Professur [37] E. Schmid, „Proceedings 9. Int. Fügetechnik und Montage, 2010 Aachender Schweißtechnik Kolloquium [8] DVS Fachgruppe 3.3, Fügetechnik „Fügen im Fahrzeugbau“,“ 2004. Schweißtechnik, Düsseldorf: DVS Media [23] DIN EN 29454-1 - Flussmittel zum GmbH, 2012. Weichlöten, 1994. [38] Petrunin, Handbuch Löttechnik, Moskau: Verlag Technik GmbH Berlin, 1984. [9] D. Schnee, Umicore AG & Co. KG, [24] A. Ament; Lötmittel Techno Service Businessline BrazTec, Grundlagen des Lötens, GmbH & Co.KG, 2012. [39] VDE/VDI Schulungsblätter für die 2010. Leiterplattenfertiung, 1999. [25] DIN EN 1045 - Flussmittel zum [10] DIN ISO 857-2 - Schweißen und Hartlöten, 1997. [40] L. Tikana und A. Klassert, „Kupfer-Kühler verwandte Prozesse - Teil 2: Weichlöten, für Leistungsstarke Motoren,“ Metall, Bd. 62. Hartlöten und verwandte Begriffe, 2007. [26] DVS Merkblatt 2617 - Neueinstufung Jahrgang, 10/2008. und Etikettierungsvorschriften für Flussmit- [11] G. Schulze, Die Metallurgie des tel zum Hartlöten, die Borsäure, Boraxpen- [41] „www..com,“ 2013. [Online]. Schweißens, Berlin: Springer-Verlag, 2004. tahydrat oder di-Bortrioxid enthalten, 2012. [Zugriff am 07 05 2013].

[12] Umicore AG & Co.KG, Businessline [27] A. Rahn, Bleifrei löten. Lötprofile für Bilder Deckblatt: BrazeTec, 2013. bleifreie Lote, Legierungen, Parameter, www.iew.eu Prozesse. Band 2., Bad Saulgau: Eugen G. [13] W. Schatt und H. Worch, Werkstoffwis- Leuze Verlag, 2005. senschaft, Weinheim: Wiley-VCH Verlag GmbH & Co. KGaA, 2003. [28] „Flammlöten mit der Acetylenflamme,“ Linde AG, [Online]. Available: http://www. [14] ASM International, linde-gas.de/international//lg/de/ „Binary Alloy Phase Diagrams“. like35lgde.nsf/repositorybyalias/praktiker- tipps_flamml%F6ten/$file/flammloeten.pdf. [Zugriff am 20 09 2012].

KUPFERINSTITUT.DE | 57 Index of figures

Figure 1 Definition of solderability/brazeability (see [2]) 5 Figure 2 Example of a brazed copper-silver joint 6 Figure 3 Wetting of a metallic surface with a liquid filler metal [7] 7 Figure 4 Schematic diagram of a soldered/brazed joint [10] 8 Figure 5 Filler metal preforms [11] 10 Figure 6 Silver-copper phase diagram (from [14]) 10 Figure 7 Torch brazing a copper tube joint [12] 13 Figure 8 Lead frames [17] 19 Figure 9 Metallographic longitudinal section through a brazed joint between a pipe and a pipe fitting (filler alloy: Ag-CuP) [18] 23 Figure 10 Difference between ‘narrow-gap’ soldering/brazing and weld brazing 26 Figure 11 Capillary pressure as a function of gap width [12] 27 Figure 12 Capillary pressure as a function of gap geometry [12] 27 Figure 13 Characteristic temperatures and times during soldering/brazing [20] 29 Figure 14 Schematic cross-section of the surface of an engineering metal [22] 32 Figure 15 Example of hot-iron soldering on a printed-circuit board (based on [10]) 38 Figure 16 Dip soldering/brazing (based on [10]) 38 Figure 17 Wave soldering (based on [10]) 39 Figure 18 Torch soldering (based on [10]) 40 Figure 19 Vacuum soldering/brazing furnace [30] 41 Figure 20 Schematic diagram of a continuous-feed furnace with an inert gas atmosphere (based on [6]) 41 Figure 21 Surface-mounted component shown before the solder in the solder paste melts [31] 42 Figure 22 Schematic diagram of a convection reflow oven [31] 43 Figure 23 Direct resistance soldering (based on [10]) 43 Figure 24 Induction brazing [10] 44 Figure 25 Electron beam brazing [10] 45 Figure 26 Fuel tank from a Honda VT 1300CX with CuAl8 brazing filler metal [33] 45 Figure 27 Electric arc brazing (MIG) (based on [6]) 46 Figure 28 Laser beam brazing (based on [6]) 46 Figure 29 Heat exchange tube [33] 49 Figure 30 Compact high-performance radiator [12] 49

58 | KUPFERINSTITUT.DE Index of tables

Table 1 Relationship between contact angle and Table 31 Advantages and disadvantages of electron degree of wetting [7] 7 beam brazing 45 Table 2 Comparison of the physical and mechanical Table 32 Overview of important filler metals used properties of copper, important copper alloys in laser and electric arc brazing 45 and unalloyed steel 9 Table 33 Advantages and disadvantages of electron Table 3 Soft solders for copper and copper alloys as arc brazing 46 classified in the DIN EN ISO 9453 (2014) Table 34 Examples of a laser brazed seam [33] 46 and DIN 1707-100 (2011) standards 12 Table 35 Advantages and disadvantages of laser Table 4 Selection of copper-based filler metals for beam brazing 46 brazing copper and copper alloys 14 Table 36 Summary of a number of important Table 5 Selection of silver alloy filler metals containing more quality requirements 48 than 20 % silver for brazing copper and copper alloys 15 Table 37 Process steps in vertical and horizontal Table 6 Selected types of copper 16 HAL systems 48 Table 7 Soft solders suitable for soldering copper 17 Table 38 Selected standards covering soldering and Table 8 Filler metals suitable for brazing copper 18 brazing processes 51 Table 9 Difference between standard (narrow-gap) Table 39 Regulations, technical guidelines and leaflets soldering/brazing and braze welding 26 covering soldering and brazing processes 52 Table10 Distinction between the terms ‘assembly gap’, Table 40 Examples of soldering and brazing applications 53 ‘soldering/brazing gap’ and ‘soldering/brazing seam ’ 26 Table 41 Matrix for selecting commonly used Table 11 Geometric configurations of common combinations of parent metals and solders or soldered/brazed joints [6] 28 brazing filler metals 54 Table 12 Cleaning procedures for copper and copper alloys [21] 30 Table 42 Summary of some advantages and Table 13 Recommended pickling solutions for copper and disadvantages of selected solders/brazing copper alloys that will undergo fluxless brazing [21] 31 filler metals 55 Table 14 Solder fluxes (classified according to Table 43 Hazardous substances 56 DIN EN 29454-1 (1994) (1994) [23] 33 Table 44 Soft solders 56 Table 15 Chemical function of solder fluxes [24] 33 Table 45 Flux designations 56 Table16 Brazing fluxes (classified according to DIN EN 1045 (1997) [25] 34 Table 17 Concentration levels for hazard classification purposes [26] 35 Table 18 Protective atmospheres used in soldering/ brazing operations 35 Table 19 Different ways of introducing the filler metal to the soldering or brazing joint (based on [10]) 36 Table 20 Classification of soldering/brazing processes (based on [10]) 37 Table 21 Advantages and disadvantages of hot-iron soldering 38 Table 22 Advantages and disadvantages of dip soldering or dip brazing 38 Table 23 Advantages and disadvantages of torch soldering or torch brazing 40 Table 24 Surface activation in furnace soldering or brazing 41 Table 25 Advantages and disadvantages of furnace soldering or brazing 41 Table 26 Comparison of the different reflow soldering heating modes [31] 42 Table 27 Advantages and disadvantages of electric resistance soldering or brazing 43 Table 28 Characteristic features of induction soldering or brazing [6] 44 Table 29 Skin depth as a function of operating frequency [32] 44 Table 30 Advantages and disadvantages of induction soldering or brazing 44

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