Soldering and of and copper alloys Contents List of abbreviations

1. Introduction 4 5. Quality assurance 47 Abbreviations

2. Material engineering fundamentals 9 6. Case studies 48 Nd:YAG . Neodymium-doped yttrium laser SMD Surface-mounted device 2.1. Fundamentals of copper and copper alloys 9 6.1 Hot-air levelling of printed circuit boards 48 PVD Physical vapour deposition 2.2 Filler materials 10 6.2 Strip tinning 49 RoHS Restriction of (the use of certain) Hazardous Substances 2.2.1 Soft solder 11 6.3 Fabricating heat exchangers from copper 49 EG Europäische Gemeinschaft 2.2.2 Brazing filler 13 6.4 Manufacture of compact high-performance EC European Community 2.3 or brazing pure copper 16 from copper 49 MIG inert gas process 2.4 Soldering / brazing copper alloys 18 TIG inert gas process 2.4.1 Low-alloyed copper alloys 18 7. Terminology 50 DVGW German Technical and Scientific Association for Gas and Water 2.4.2. High-alloyed copper alloys 22 [Deutsche Vereinigung des Gas- und Wasserfaches] 8. Appendix 51 3. Design suitability for soldering/brazing 26 References 57 4. Soldering and brazing methods 29 Chemical elements and compounds Index of figures 58 4.1 The soldering/brazing principle 29 Ag 4.2 Surface preparation 30 Index of tables 59 Al Aluminium 4.3 Surface activation 32 Ar 4.3.1 Fluxes 33 Be 4.3.2 Protective atmosphere / Shielding gases 35 C

4.4 Applying the solder or brazing 36 CO2 Carbon dioxide 4.5. Soldering and brazing techniques 37 Cr 4.5.1 Soldering with 38 Cu Copper

4.5.2 Dip bath soldering or brazing 38 H2

4.5.3 Flame soldering or brazing 40 H2O Water 4.5.4 soldering or brazing 40 HF Hydrofluoric acid 4.5.5 Electric resistance soldering or brazing 43 Mn 4.5.6 Induction soldering or brazing 44 Ni

4.5.7 Electron beam brazing 45 O2 Oxygen 4.5.8 Arc brazing 45 P 4.5.9 Laser beam soldering or brazing 46 Pb S Sulphur Sb Antimony Si Sn Te Tellurium Zn Zr

2 | KUPFERINSTITUT.DE KUPFERINSTITUT.DE | 3 1. Introduction

Copper is a material that has been used by man for thousands of years because of its Chemical and metallurgical Physical special properties. As a native metal, i.e. one that is also found naturally in its pure me- properties properties Mechanical properties tallic form, copper was used early in human history because of its good malleability and · Chemical composition · Wettability · Strength and formability formability and because of its colour. Copper thus became man’s first working metal. · Oxidation behaviour · Solidus · Residual stresses · behaviour · · Diffusion and solubility characteristics · , · Ability to undergo precipitation heat treatment specific heat capacity · Microstructure 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 corrosion, and its generally materials to be joined. The factors that and development work in this field is Material suitability for high resistance to chemical attack. influence the or brazeability of continuing, enquiries should be directed to soldering/brazing 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 Solderability or wear, to be modified in a controlled way. soldering or brazing techniques can be brazeability of a 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/ workpiece 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 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 · 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/filler metal 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 oxide removal · Soldering or brazing cycle · Soldering/brazing rate · Post treatment · Joint clean-up · Joint testing

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

4 | KUPFERINSTITUT.DE KUPFERINSTITUT.DE | 5 Like , soldering and brazing are Soldering and brazing do not involve any The following points should, however, be Both physical and chemical processes are Heat is applied to melt the filler metal and σ important methods of thermally joining melting of the parent material, i.e. of the noted: the strength of a soldered or brazed involved in soldering/brazing. Soldering/ any being used. The method used to 1,2 1 materials, typically metals. As it is the surfaces to be joined. Instead, the joint is typically not as great as that of the brazing joints are created through surface heat the parts to be joined will depend on resulting joint – irrespective of the method workpieces are joined by introducing an parent material; the parent metal and the chemical reactions and diffusional processes the type of join to be created (see ϑ σ1,3 σ2,3 2 used to make it – that ultimately deter- additional molten metal, the ‘filler metal’, solder/braze metal have different chemical of the liquid filler metal and the solid parent Section 4.3). Fluxes serve to activate the mines the properties of the part being possibly in combination with a flux and/or potentials; there is a risk of chemical material. The soldering/brazing mechanism surfaces to be joined. The molten filler fabricated, the two methods are classified in a protective gas atmosphere [4]. corrosion due to the presence of flux comprises the following steps: [7] metal will only be able to wet the surfaces 3 (see e.g. [3]) in terms of the chemical residues; design restrictions may be 1. Heating of the parts to be joined to be joined if they are clean and free from nature of the joint, the chemical composi- Some of the advantages of soldering or relevant because of factors such as narrow oil, grease and other surface deposits. The 2. Surface activation, e.g. by a flux or a tion of the parent metal (or metals) and brazing compared to other joining soldering/brazing gaps and tight dimen- process is also influenced by 1 Surrounding vapour phase the type of filler material used, if any. Both methods are: [5] sional tolerances at the joint. Extensive capillary action of the molten filler, 2 Molten filler welding and soldering/brazing lead to the preparatory and after-treatment proce- 3. Flow of filler metal and wetting – the adhesion and diffusion processes between 3 Parent material · soldering/brazing enables dissimilar ϑ Contact angle molten filler metal flows into the gap formation of a metallic joint, however the materials to be joined; dures are often required, such as degreas- the liquid phase and the parent material. chemical composition of these joints differ. ing, etching, removal of flux residues, etc. [6]. between the mating surfaces or spreads figure 3 shows the wetting of the surface σ1,2 Surface tension between molten filler and the Whereas a welded joint has the same · as less heat is applied in the joining The related joining techniques of soldering across the surface by the molten filler metal. The contact surrounding atmosphere process, soldered or brazed parts tend σ1,3 Surface tension between the solid and chemical composition as that of the two and brazing are distinguished in the 4. Formation of the solder/braze metal angle ϑ is determined by the interaction to exhibit greater dimensional accuracy the surrounding atmosphere identical parent metals being joined, the DIN ISO 857-2 standard by the liquidus through (physical and chemical) inter- between the three surface tensions σ and less distortion; 2,3 Surface tension between molten filler and solid use of a filler alloy in a soldering or brazing temperature of the filler metal used. In action between the molten filler and involved in the wetting process: σ1,2 base metal procedure means that the soldered or · multiple soldered/brazed joints can soldering, the liquidus temperature of the the parent material (vapour-liquid surface tension), σ1,3 brazed joint has a different chemical be created on a single workpiece in a filler metal is below 450 °C; in brazing it is (vapour-solid surface tension) and σ2,3 Figure 3 - Wetting of a metallic surface with a 5. Solidification of the liquid solder/braze composition to that of the parent single operation; above 450 °C. Up until February 2007, (liquid-solid surface tension). liquid filler metal [7] metal. 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 Perfect wetting Adequate wetting Dewetting filler material. into the joint than welding, there is less residual stress and distortion in the component.

ϑ = 0° ϑ ≤ 30° ϑ > 90° Brazed joint

Table 1 – Relationship between contact angle and degree of wetting [7] Brazing seam Ag72Cu28 brazed metal Brazed metal zone 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 Cu Ag solution, a or an soldered/brazed joint, the filler metal After soldering or brazing, alloying intermetallic 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 Diffusion zone 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 Heat-affected zone 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 Figure 2 – Example of a brazed copper-silver joint. as diffusion. Although the parent material at the soldering/brazing temperature (Note that no filler metal was used; the alloy Ag72Cu28 is formed by diffusion during the brazing process.)

6 | KUPFERINSTITUT.DE KUPFERINSTITUT.DE | 7 2. Material engineering fundamentals

Figure 4 depicts the cross-section of a 2.1 Fundamentals of copper and Copper alloys may be classified in terms of Copper alloys are also classified as locally heated soldered/brazed joint. The copper alloys the treatment they have undergone: alloys, wrought alloys (e.g. strip, wire, parent material was heated only in the Copper is a non-ferrous metal with a · Precipitation hardening alloys tubing, ) and sintered alloys. Some 3 region of the joint, as would be the case in of 8.94 kg/dm . Copper has a (e.g. CuBe alloys) and of the best-known copper alloys are torch brazing or torch soldering. This face-centred cubic (fcc) crystal lattice (copper-zinc alloys) and localised heating can increase the level of structure and as such retains its excellent · Work-hardened alloys (=cold-worked (copper-tin alloys), but alloys of copper residual stress within the part. If the whole ductility and cold-working capacity down alloys), with nickel, manganese, aluminium, iron, assembly is heated, as in furnace brazing to low temperatures. Cold working copper or in terms of their chemical composition: beryllium, chromium and silicon are also or furnace soldering, the result is lower causes an increase in hardness (‘strain · Single-phase materials ((e.g. pure Cu) common. It should be noted that the terms residual stress and less distortion. In this hardening’, ‘work hardening’). or alloys that exist as a solid solution ‘’, ‘’, ‘Gunmetal’ and ‘nickel case, the entire assembly is heated and Copper also exhibits high electrical and of the elements (e.g. CuNi alloys, sing- silver’ are not standardised, though these cooled uniformly, which means that the thermal conductivity (the ratio of le-phase brass) and designations are still common commer- heat-affected zone covers the entire electrical to thermal conductivity is cially and elsewhere. structure (i.e. all of the parent material). constant) and shows good corrosion · Multiphase materials (e.g. two-phase An advantage of this approach is that resistance to a wide variety of chemical brass alloys) [11]. soldering/brazing can be carried out at media. the same time as heat treatment (e.g. precipitation hardening) of the workpiece.

1 2 3 A B 4

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. % t 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 j 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 1 Parent material Institute (www.kupferinstitut.de) 2 Parent material affected by the soldering/brazing process 3 Diffusion zone / Transition zone Table 2 - Comparison of the physical and mechanical properties of copper, important copper alloys and unalloyed steel 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 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: wires, 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 2.2.1. Soft crystals (diameter: approx. 1 µm; length: liquidus and the solidus curves. The microstructure with good mechanical The filler metals used for soldering melt at several millimetres) that can cause short liquidus curve separates the higher lying properties. This is the reason why eutectic temperatures below 450 °C. The low circuiting and thus damage to electronic region L, which represents the homogene- alloys, such as Ag72Cu28, are frequently strength of soft solder alloys and of the components. These crystals grow very ous liquid phase and the liquid-solid phase used in technical and engineering resulting soldered joint make these filler slowly so that they may take years to lying below. The solidus line represents the applications [13]. materials suitable for applications that are appear. Possible reasons for boundary between the solid phase and the subjected to low mechanical loads. They growth include residual stresses in liquid-solid phase. The phase diagram for find most frequent use in electrical and layers due to the presence of organic the copper-silver binary system also shows electronic applications. Soft solder alloys inclusions/contamination, and mechani- that there is a eutectic point at one specific can be selected using the cally induced stresses when tinned Figure 5 – Filler metal preforms [11] DIN EN ISO 9453 (2014) or the DIN 1707- materials are processed. Lead-free 100 (2011) standards. alternatives for soft include Composition (weight percentage) tin-copper, tin-silver and tin-copper-silver The filler metals are classified as soft In the past lead solders were often used to alloys. It should be noted that the price of solders or brazing filler metals depending 10 20 30 40 50 60 70 80 90 100 solder copper pipes and tubing. The the solder increases the more silver it on the liquidus temperature. There are a 1200 presence of lead improves the flow contains. In its technical application note number of criteria that can be used when 1084,87°C characteristics of the solder, produces GW 2, the German Technical and Scientific selecting a suitable filler metal: bright smooth surfaces and requires only Association for Gas and Water (DVGW) · Type and physical/mechanical 1000 961, 93°C L moderate soldering temperatures. stipulates the use of the solders Sn97Ag3 properties of the parent material However, lead is environmentally harmful and Sn97Cu3 for drinking water applica- and a recognised carcinogen. Since 1 July tions. Antimony-free solders are used for · Dimensions and manufacturing Ag Cu 800 780°C 2006, the inclusion of lead in solders has fine soldering applications, antimony-con- tolerances of the workpiece been prohibited by the RoHS Directive taining solders and low-antimony solders · Stresses at the soldered/brazed joint 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 Operating temperatures and pressures 600

Temperature [°C] Temperature use of certain hazardous substances in and cooling units, in the electrical industry · Ambient conditions at the soldered/ electrical and electronic equipment (later or for and installation work. brazed joint (e.g. aggressive media) superseded by Directive 2011/65/EU in Zinc-based and -based soft · Cost-efficiency 400 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 · Work safety certain sectors, such as medical, security cadmium, cadmium-containing solders are · Soldering/brazing method [6]. 200 and aerospace technologies. In the not prohibited. However, as cadmium is 0 10 20 30 40 50 60 70 80 90 100 electronics industry, lead-free tin solders regarded as harmful to health, the accident Ag Composition (atomic percentage) Cu 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’ Figure 6 - Silver-copper phase diagram (from [14]) formation of tin whiskers on the surface of liability insurance associations) must be the metal. Whiskers are filiform single observed [15].

10 | KUPFERINSTITUT.DE 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) 2.2.2. Brazing filler metals As an alloying element, phosphorous of the parent copper to yield copper Sn50Pb49Cu1 Electrical, The filler metals used to braze copper and shows low solubility in copper and is metaphosphate. By chemically reducing – 183/ 215 50 bal. 1,4 X (162) electronics 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. – S-Sn60Pb40Cu 183/190 60 bal. 0,15 X Electrical, are suitable for fabricating joints able to mechanical properties of copper-phospho- Silver alloy filler metals and copper-phos- Soft solders electronics, Sn60Pb39Cu1 withstand higher levels of mechanical rous filler metals are determined by size, phorus filler metals with the appropriate with copper – 183/190 60 bal. 1,4 X X PCBs (161) stress. Brazing temperatures are usually shape and arrangement of the Cu3P DVGW or RAL quality mark are used for Installation of copper within the approximate range 500– particles, whose precipitation is a function brazing gas and water pipes. Silver alloy Sn97Cu3 – 227/310 bal. 0,07 3 X X X X piping/tubing, metal 1000 °C. DIN EN ISO 17672 (2010) divides of the phosphorous content. If the filler metals have relatively low melting (402) goods brazing filler metals into classes. The filler phosphorous content of the filler metal is temperatures and exhibit good wettability Sn Pb Ag 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- – S-Sn50Pb46Ag4 178/210 50 bal. 3,5 X X Electrical, electronics, (copper-phosphorus), ‘Class Ag’ (silver about 300 °C and above, all copper-phos- rus filler metals are particularly well suited – S-Sn63Pb35Ag2 178 63 bal. 1,4 X X X PCBs 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, Sn96,3Ag3,7 – 221/228 bal. 0,07 3,7 X X X X recommended for brazing pure copper and wide melting range (e.g. CuP 179) can be cadmium was added to brazing filler (701) Installation of copper piping/tubing; high-melting copper alloys. As the amount used for brazing assemblies with large metals to further lower the melting Sn97Ag3 – 221/224 bal. 0,07 3 X X X X electrical of zinc in the brazing alloy rises to about joint clearances. As phosphorus has a temperature. Since December 2011, the (702) 40 %, the melting temperature decreases deoxidising effect, copper-phosphorus use of cadmium-containing filler metals Ag Cd Zn 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) – S-Cd82Zn16Ag2 270/280 2 bal. 16 X X Electrical, typically have a zinc content not exceeding to a certain extent bronze (CuSn6) 494/2011). They may only be used for Soft solders – S-Cd73Zn22Ag5 270/310 5 bal. 22 X X 40 %. Small amounts of silicon (0.1 % to surfaces without requiring the use of a safety reasons or for defence or aerospace with silver electric motors – S-Cd68Zn22Ag10 270/380 10 bal. 22 X X 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 Ag Pb Others vaporisation and hydrogen absorption. the oxygen in the air to form phosphorus Pb98Ag2 Sn Electrical, Torch brazing (also known as ‘flame pentoxide, which itself then reacts with – 304/305 2,5 bal. X X (181) 0,25 electric motors brazing’) is carried out using a slightly the Cu(I) and Cu(II) oxides on the surface Pb95Ag5 Sn for high operating oxidising flame of moderate intensity [16]. – 304/370 5,5 bal. X X (182) 0,25 temperaturesr Sn Electrical, – S-Pb95Sn3Ag2 304/310 1,75 bal. X X Figure 7 – Torch brazing a copper tube joint [12] 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 refrigeration (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 KUPFERINSTITUT.DE | 13 Average chemical Melting range in °C Average chemical Designation in acc. with composition Brazing Usage notes Designation in acc. with composition (mass Melting range in °C Usage notes (mass fractions in %) temperature in °C fractions in %)

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

B-Cu60Zn narrow B-Ag56CuZ- 56Ag; 22Cu; 17Zn; narrow hand-fed or Cu 470a Cu 301 60Cu; 0,3Si; Rest Zn 875 895 Ag 156 AG102 620 655 Copper alloys (Si)-875/895 Copper and or wide nSn-620/655 5Sn inserted copper alloys hand-fed or B-Ag45CuZ- 45Ag; 27Cu; 2,5Sn; 1 2 with a solidus Ag 145 AG 104 640 680 B-Cu60Z- 58* Cu/ 60* Cu; inserted nSn-640/680 25,5Zn n(Sn)(Si) 0,175*1 Si/0,275*2 temperature narrow or Cu 471*1 Cu 304*2 870 900 above 950 °C B-Ag40CuZ- 40Ag; 30Cu; 2Sn; (Mn)- Si; 0,35Sn; 0,15Mn; wide Ag 140 AG 105 650 710 870/890 bal. Zn nSn-650/710 28Zn B-Cu36AgZ- 34Ag; 36Cu; 2,5Sn; Copper-phosphorus brazing filler metals CuP-alloys Ag134 AG 106 630 730 nSn-630/730 27,5Zn B-Cu92P- Preferentially CuP 182 CP 201 bal. Cu; 7,8 P 710 770 B-Cu36ZnAgSn- 30Ag; 36Cu; 2Sn; 710/770 copper, Ag 130 AG 107 665 755 665/755 32Zn Gunmetal, Copper and B-Cu93P- hand-fed or CuP 180 CP 202 bal. Cu; 7P 710 820 copper-zinc narrow B-Cu40ZnAgSn- 25Ag; 40Cu; 2Sn; copper alloys 710/820 inserted Ag 125 AG 108 680 760 alloys (brasses), 680/760 33Zn copper-tin alloys B-Cu94P- B-Ag44CuZn- CuP 179 CP 203 bal. Cu; 6,2P 710 890 (bronzes) Ag 244 AG 203 44Ag; 30Cu; 26Zn 675 735 710/890 675/735 Copper-phosphorus brazing filler metals Ag-CuP-alloys B-Cu38Z- Ag 230 AG 204 30Ag; 38Cu; 32Zn 680 765 B-Cu80AgP- nAg-680/765 CuP 284 CP 102 15Ag; 5P; bal. Cu 645 800 Copper, narrow 645/800 B-Cu40Z- Gunmetal, Ag 225 AG 205 25Ag; 40Cu; 35Zn 700 790 B-Cu89AgP- copper-zinc hand-fed or nAg-700/790 CuP 281 CP 104 5Ag; 6P; bal. Cu 645 815 645/815 alloys (brasses) narrow or inserted Ag-Cu-Zn-Ni-Mn-alloys and copper-tin B-Cu92AgP- wide CuP 279 CP 105 2Ag; 6,3P; bal. Cu 645 825 alloys (bronzes) B-Ag50CuZn- 645/825 Ni-660/705 hand-fed or Ag 450 660 750 Copper alloys narrow Silver alloy brazing filler metals Ag-Cu-Zn-alloys 50Ag; 20 Cu; inserted 28Zn B-Cu48ZnAg(Si) 12Ag; 48Cu; 40Zn; Ag 212 AG 207 800 830 narrow Zinkfreie Ag-Cu-Lalloys (without zinc) -800/830 0,15Si Copper and hand-fed or B-Cu55ZnAg(Si) 5Ag; 55Cu; 40Zn; copper alloys narrow or inserted B-Ag- Copper and Ag 205 AG 208 820 870 Ag 272 AG 401 72Ag; 28Cu 780 780 narrow inserted -820/870 0,15Si wide 72Cu-780 copper alloys

Table 5 - Selection of silver alloy filler metals containing more than 20 % silver for brazing copper and copper alloys Table 4 - Selection of copper-based filler metals for brazing copper and copper alloys

14 | KUPFERINSTITUT.DE KUPFERINSTITUT.DE | 15 2.3. Soldering or brazing pure copper Soldering Components of electric motors that are refrigeration applications. In some cases, Copper is very well suited to both Electronics is one of the main areas of subjected to high temperatures during the strength of a soldered lap joint between soldering and brazing. Care must be taken application of copper soldering. The solders operation should be preferentially soldered two tubular parts is greater than that of a to ensure that the oxide layers on the most commonly used for soldering using soft solders that have a higher solidus brazed joint, as the brazing process can surfaces to be joined have been properly electronic components are the tin-based temperature. Soldered joints made with reduce the strength of the copper parent removed by mechanical or chemical filler alloys as defined in DIN EN ISO 9453 these solders usually tend to show a higher metal. Soldered joints that will be subjected cleaning. The most commonly used (2014) and DIN 1707-100 (2011). The filler shear strength than those made with to higher temperatures should be made cleaning agents are: isopropanol, ethanol, alloys used for electrical and electronic tin-lead solders. The short-term shear with lead-free, thermally stable solders that , aqueous cleaner and nitric acid. soldering applications are usually unleaded. strengths of lap joints made with these can withstand permanent temperatures of The soldering/brazing (or tinning) process Lead-containing solders may only be used solders have been shown to be about 20 N/ up to 120 °C without damage. should take place immediately after the in exceptional cases, as listed in the Annex mm². Lead-free soft solders are also Like wrought copper, copper casting alloys surfaces have been prepared. Table 6 to ‘Directive 2011/65/EU of the European preferred when joining copper piping that as defined in DIN EN 1982 (2008) can be presents a selection of copper metals that Parliament and of the Council of 8 June carries drinking water (see DVGW technical soldered without difficulty. are particularly well suited to soldering or 2011 on the restriction of the use of certain application note GW 2) or when the brazing. hazardous substances in electrical and soldered joint will be exposed to low electronic equipment’ (RoHS). temperatures, e.g. in industrial

Suitability for soldering/ Designation Material number Composition [%] Area of use brazing Designation Specific examples Selected areas of use Flux Cu O P Pb88Sn12Sb Manufacturing of condensers 2.1.1 min. max. Antimony-containing solders Sn60Pb40Sb and cooling units 2.1.2 Oxygen-containing copper 2.1.3 Pb60Sn40 Tinning, plumbing, Soldering: v. good; Low-antimony solders 2.2.2 Sn60Pb40 galvanised thin sheet Cu-ETP CW004A 99,9 0,04 – Brazing: good (not for Electrical 2.2.3 torch brazing) 1.1.1 Electrical and Antimony-free solders Sn60Pb40E 1.1.2 Deoxidised copper (with phosphorus), oxygen-free Electronics 1.1.3 99,95 – 0,002- Soldering: v. good; Cu-HCP CW021A Electrical, cladding Sn99Cu1 0,007 Brazing: v. good 1.1.2 Lead-free solders for electronic Sn96Ag4 Electrical and electronics 1.1.3 99,90 – 0,015- Soldering: v. good; Construction, applications Sn96Ag3Cu1 Cu-DHP CW024A 1.2.3 0,040 Brazing: v. good piping/tubing Sn95Ag4Cu1 Oxygen-free copper, non-deoxidised Pb93Sn5Ag2 1.1.2 High-lead, RoHS-compatible For operating temperatures Soldering: v. good; technology, Pb98Sn2 1.1.3 Cu-OFE CW009A 99,99 – – soft solders up to 200 °C Brazing: v. good electronics Pb98Ag2 1.2.3 Drinking water piping 2.1.2 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) Lead-free solders for drinking Sn97Ag3 Other important applications in 3.1.1 water pipes Sn97Cu3 Table 6 - Selected types of copper 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

16 | KUPFERINSTITUT.DE KUPFERINSTITUT.DE | 17 Brazing content of the parent copper when to form water. As Cold-worked (work hardened) alloys brazing should be kept as small as possible Copper-lead Brazing is used if the joint will be selecting the brazing method. Brazing is more likely to occur in torch brazing or so that any reduction in material strength The CuPb1P (CW113C) alloy contains between subjected to high mechanical and thermal oxygen-containing copper can cause when brazing in a reducing atmosphere, Copper-silver is localised, though it is very important to 0.7 % and 1.5 % lead to improve its stresses. When brazing copper, the filler hydrogen embrittlement, i.e. the formation induction brazing or vacuum brazing are Copper-silver alloys such as CuAg0,10 make sure that the brazing temperature is machinability. A trace phosphorus content in metals of choice are brass brazing alloys, of cracks and voids after contact with preferred. If torch brazing has to be (CW013A) and CuAg0,10P (CW016A) are attained across the entire area to be the range 0.003 % to 0.012 % ensures a high copper-phosphorus and silver brazing hydrogen-containing gases. Types of performed, the parent metal should be an characterised by their high electrical and brazed. level of deoxidation in the material and alloys. Silver brazing filler metals have copper susceptible to this problem include oxygen-free and/or deoxidised copper in thermal conductivity values. These alloys safeguards against hydrogen embrittlement. lower brazing temperatures, which reduces those used in electrical and electronic order to avoid hydrogen embrittlement. are particularly well suited to applications Copper-iron CuPb1P has a very high electrical conductiv- the risk of coarse grains and applications. At high temperatures (above in which they are subject to continuous The copper-iron alloy CuFe2P (CW107C) ity. It is often used instead of pure copper enables faster brazing speeds 500 °C), hydrogen diffuses into the copper loads at high temperatures, as is the case contains between 2.1 % and 2.6 % of iron whenever both good machinability and good It is important to consider the oxygen and reacts with the oxygen in the copper 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 Specific examples as defined in 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 Brazing filler metal class Notes Example flux DIN EN ISO 17672 (2010) having a detrimental effect on electrical softening temperature. CuFe2P is therefore only limited . CuPb1P is also not conductivity. Copper-silver alloys are mainly used for electrical applications and well suited for brazing, but it can be soldered · suitable for drinking water pipes Ag 244 standardised in DIN CEN/TS 13388 (2013) large quantities are used in the fabrication of successfully. Silver alloy brazing filler metals · composed primarily of Ag, Cu, Zn Ag 134 FH10 and are very well suited to both soldering lead frames in chip packages (see figure 8). (Class Ag) · Brazing temperature: approx. Ag 145 and brazing. As is the case with pure copper, soldering 650–830 °C is carried out using tin-lead soft solders CuP 182 · no flux necessary due to Soldering is best carried out with containing between 40 % and 60 % tin. CuP 180 presence of phosphorus lead-free, tin-based solders (e.g. Sn99Cu1). Class 3.1.1 fluxes are recommended. For Copper-phosphorus brazing CuP 179 · recommended joint clearance for Suitable fluxes for electrical applications electrical applications, lead-free tin-based – filler metals (Class CuP CuP 284 P content of 5 %: 0.125 mm are those in the classes 3.1.1, 2.1.1 and 1.1.1 solders are used in combination with CuP 281 · Brazing temperature: approx. and 1.2.3. Because of the high softening non-corrosive fluxes (e.g. 1.1.2 or 1.1.3). CuP 279 650–730 °C temperature of the parent metal, soldering, if performed correctly, does not have a If brazing cannot be avoided, it is recom- Cu 470a · suitable for brazing solid structures detrimental effect on the high strength mended that a silver alloy brazing filler metal Brass brazing filler metals Cu 470 · composed primarily of Cu and Zn FH10 achieved through cold working. with a low brazing temperature (e.g. Ag 156) (Class Cu) Cu 680 · Brazing temperature: approx. 870–920 °C is used together with a flux of type FH10. Cu 681 Brazing, however, is carried out at higher Table 8 – Filler metals suitable for brazing copper 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 2.4. Soldering / brazing copper alloys to -200 °C. Copper alloys not included in can be improved not only by suitable heat to 0.007 % of phosphorus or another electrical conductivity. The phosphorus A copper alloy consists of copper and at this group are CuZn5, CuSn2, CuSn4, treatment (precipitation hardening), but deoxidising element, like , are the content of between 0.003 % and 0.012 % least one other metal. Alloying produces a CuSn5, CuAl5As and CuNi2, as these are also by cold working. In contrast, the most suitable parent metals for brazing Soldering can be carried out using tin-cop- makes the alloy resistant to hydrogen new material with new properties. Some of classified as belonging to the copper-zinc, strength of the non-heat-treatable applications. Generally speaking, brazing per solders that conform to DIN EN ISO embrittlement. the most well-known copper alloys include copper-tin, copper-aluminium and wrought copper alloys, such as CuAg0,10, can be carried out with most silver alloy 9453:2014, such as Sn99.3Cu0.7, and using brass, nickel silver, bronze and Gunmetal. copper-nickel alloy groups. The composi- CuSi1 and CuSn0,15, can only be achieved brazing filler metals using a flux such as fluxes in class 3.1.1. For information on solders, see section on tions of low-alloyed are specified by cold working [17]. Further information FH10. If the electrical conductivity of the copper-silver. 2.4.1. Low-alloyed copper alloys in DIN CEN/TS 13388 (2013). A distinction on low-alloyed copper alloys is available in brazed joint is particularly crucial, fluxless For brazing applications, silver alloy, Low-alloy coppers contain up to about is made between heat-treatable/hardena- the DKI monograph i8 (2012). brazing can also be carried out using the copper and phosphorus brazing filler Silver alloy filler metals in combination 5 % of alloying elements. One characteris- ble and non-heat-treatable/ hardenable filler metal Ag 272 (Ag72Cu28) under metals may be used in combination with with FH10 fluxes are recommended for tic feature of these alloys is their wrought copper alloys. In the case of vacuum or in a reducing atmosphere. No FH10 fluxes. brazing applications. Brazing reduces the behaviour at low temperatures, with no heat-treatable alloys, such as CuBe2, flux is required when brazing with a strength of the cold-worked copper-sul- embrittlement observed even down CuCr1Zr and CuNi1Si, material strength 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.

18 | KUPFERINSTITUT.DE KUPFERINSTITUT.DE | 19 Copper-tellurium Heat-treatable/hardenable alloys Where possible, brazing should be carried Copper--beryllium are also being used increasingly for to avoid the time-dependent softening of The copper-tellurium alloy CuTeP (CW118C) If cold-worked wrought copper alloys are out between the solution treatmentstage The alloy CuCo2Be (CW104C) with between connector plugs in the automotive the parent metal at the elevated tempera- with 0.4–0.7 % tellurium and 0.003–0.012 % brazed, they tend to suffer some loss of and the precipitation hardening (heat 2.0 and 2.8 % cobalt and 0.4 to 0.7 % industry. tures used in brazing. phosphorus has the same properties as the material strength in the region that is treatment) stage. In most cases, low-melt- beryllium is a highly conductive cop- copper-sulphur alloy described above. heated. In the case of heat-treatable/ ing silver alloy filler metals with low per-beryllium alloy. Compared with the Here, too, soldering temperatures are Copper-zirconium hardenable alloys, in contrast, certain brazing temperatures in the range binary copper-beryllium alloys, CuCo2Be is below the precipitation hardening The copper-zirconium alloy CuZr For information on solders, see section on types of brazing can be used without 650–670 °C, such as Ag 156, are used in of slightly lower strength but exhibits temperature so that soldering does not (CW120C), which contains between 0.1 % copper-silver. having a negative impact on the material’s combination with low-melting fluxes that more than double the electrical conductiv- have any appreciable effect on the and 0.3 % zirconium, is insensitive to mechanical properties. In fact in furnace contain high-activity fluorides. In order ity while also having a significantly higher mechanical properties of the parent annealing in a hydrogen-containing By adding tellurium to the alloy composition, brazing, the brazing step and the heat not to compromise the later precipitation thermal stability. This alloy is used mainly material. Suitable solders are tin-lead atmosphere. The alloy exhibits a very high the temperature at which tempering causes treatment can be combined into a single hardening stage, the brazing joint must be to manufacture electrically conducting solders used in combination with fluxes electrical conductivity and stress a loss of strength in the material (stress operation. heated rapidly (it may even be necessary and thermally stressed springs, as well as in class 3.1.1. relaxation resistance as well as superior relaxation resistance) can be raised to about to cool the areas surrounding the joint) components for the plastic processing strength and creep rupture strength. At 300 °C. If soldering is performed correctly, it Copper-beryllium and the part quenched once the filler industry and resistance welding elec- It is recommended that brazing is carried high temperatures, however, there is a risk is possible to avoid any significant reduction The copper-beryllium alloys CuBe 1.7 metal has solidified. Rapid brazing is trodes. out using low-temperature silver brazing of oxidation due to the high affinity of in the strength of the cold-worked alloy. (CW100C) and CuBe2 (CW101C) with essential, as even a brazing time exceeding alloys together with fluxes of type FH10. zirconium for oxygen. 1.6–2.1 % beryllium exhibit average 30 seconds will impair the ability of the The information on soldering and brazing The strength of the parts being brazed Brazing is usually carried out using silver electrical conductivity, very high tensile parent material to respond to precipitation copper-beryllium alloys applies for the can be detrimentally affected at high No special aspects need to be taken into alloy filler metals and a type FH10 flux. strength in their hardened state and a high hardening. High-melting brazing alloys, most part also to copper-cobalt-beryllium. brazing temperatures or if brazing times account when soldering this alloy. As the However, brazing reduces the strength of the degree of thermal stability. Copper-- such as Ag 272 (Ag72Cu28) which melts at If it is important to retain the strength of are long. alloy has a high softening temperature, worked-hardened parent metal back to that lium is used in a wide variety of applica- 780 °C, are available for special cases. the precipitation hardened state, high-melting solders can be used. If fluxes of the material in its original untreated state. tions, such as in the manufacture of Though high, the melting temperature is low-melting silver alloy filler metals should Copper-chromium-zirconium of type 3.2.2 are not permitted because of membranes, wear-resistant components always within the solution annealing 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 Copper-zinc and non-sparking tools. Parts that are to be range. Because of the greater propensity short. 0.5–1.2 % chromium and 0.03–0.3 % should be used. The alloy CuZn0.5 (CW119C) contains soldered or brazed should be free of grease for oxidation at these temperatures, zirconium. In contrast to the binary 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 Copper-nickel-beryllium copper-chromium alloy, copper-chromi- If brazing is performed with a filler metal to 0.02 % phosphorus. CuZn0.5 exhibits high parent alloy has been prepared, soldering or recommended. In order to ensure that the Shortages in the supply of cobalt led to um-zirconium shows higher notch whose melting temperature is above the electrical conductivity, has excellent cold brazing should be carried out immediately material can undergo subsequent the development of the alloy CuNi2Be strength at elevated temperatures and is softening temperature of copper-zirconium, working properties, is resistant to hydrogen before the surfaces to joined become precipitation hardening, the brazed parts (CW110C), in which the cobalt in cop- often now preferred in applications in brazing times must be kept short to avoid 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 per-cobalt-beryllium alloy is replaced by which CuCr1 (CW105C) was formerly used. reducing the strength of the hardened welding and brazing. Its main area of braze the parent material immediately, the metal has solidified and are then quenched nickel. The mechanical and physical The alloy exhibits high strength at room parent metal. The softening temperature application is therefore semiconductor surfaces to be joined should be plated with in water. properties of this alloy are equivalent to temperature, has a high softening rises the more zirconium is present in the technology where the alloy is used for a thin protective coat of copper, silver or tin those of CuCo2Be. In terms of soldering temperature and improved creep rupture alloy; with 0.2 % zirconium, the softening manufacturing lead frames. As the alloy also that acts as a compound layer and improves Copper-beryllium-lead and brazing, the two alloys behave very strength, even at elevated temperatures. temperature is around 575 °C. exhibits good deep- capabilities it surface wettability. The alloy CuBe2Pb (CW102C) has similarly. The advantage of a CuNi2Be alloy also finds frequent use in the production of properties similar to those of CuBe2. The compared with a CuCo2Be alloy is that the As the heat-treated (i.e. precipitation hollow ware of all kinds and of heat Soldering is always carried out after the presence of lead does, however, improve former exhibits slightly higher electrical hardened) parts have a high stress exchanger elements. hardening stage using solders with a flow the machinability of the alloy. CuBe2Pb and thermal conductivity values. relaxation resistance, soldering can temperature below the typical softening can be soldered and brazed in a manner normally be carried out without any loss of For information on solders, see section on temperature of the copper-beryllium analogous to the copper-beryllium alloys. Copper-nickel-silicon material hardness. Suitable solders include copper-silver. parent metal. Soldering is typically carried Copper-nickel-silicon alloys, such as the tin-lead solders, but more common Rapid soldering does not lead to any out using the lead-free solder Sn60P- CuNi1Si (CW109C), CuNi2Si (CW111C), solders are the lead-free varieties, such as softening of the cold-worked parent b39Cu1. Copper-containing solders such CuNi3Si (CW112C) with between 1.0 and Sn95Ag5 , Sn97Ag3 or Sn95Sb5 in material. as Sn97Cu3 can also be used. Depending 4.5 % nickel and 0.4 to 1.3 % silicon, combination with a flux of type 3.1.1. on the nature of the surfaces to be joined, are materials that have average Brazing is usually carried out with silver alloy fluxes of type 3.2.2 or 3.1.1 can be used. electrical conductivity values but high For brazing applications, low-melting silver filler metals and a type FH10 flux. Pre-tinned parts can be soldered using tensile strengths. They are used brazing filler metals are used with type -based (colophony-based) fluxes of primarily for the production of , FH10 fluxes. The brazing heating cycle type 1.1.2 or 1.1.3. bolts and overhead line hardware. They should be kept as short as possible in order

20 | KUPFERINSTITUT.DE KUPFERINSTITUT.DE | 21 Copper-chromium Copper-zinc alloys (Brasses) brittle when the parts to be joined are Brazing Phosphorus-containing filler metals flow Copper-tin alloys (Bronzes) The copper-chromium alloy CuCr1 Of all the copper alloys, the copper-zinc wetted with liquid solder. The risk of Brazing is used to join brass workpieces freely on pure copper. When used to braze Copper-tin alloys (commonly known as (CW105C) contains between 0.5 % and alloys (commonly known as ‘brasses’) are soldering embrittlement is particularly large that are subjected to greater mechanical brass, however, these filler metals need to ‘bronzes’) are important materials in the 1.2 % chromium. It is a wrought copper the most common and the most widely when the parts to be soldered are worked and thermal stresses. The risk of liquid be combined with a flux. Leaded cop- electrical engineering (e.g. electrical springs) alloy that because of its reduced notch used. The ubiquity of these alloys is due to or reshaped while they are being wetted metal embrittlement can, however, be per-zinc alloys, particularly those with a and mechanical engineering (e.g. slide strength at elevated temperatures has now the appealing colour, the ease with which with the molten solder. The binary avoided by stress relief annealing, by using lead content above 3 %, are harder to bearings, bearing linings, membranes). They been largely replaced by the copper-chro- they can be processed and their favoura- copper-zinc alloys with a pure α phase low-melting brazing alloys and by braze than the binary alloys and may well are classified into wrought alloys and casting mium-zirconium alloy described above. The ble physical and strength properties. (alpha brasses), e.g. CuZn30 (CW505L), are minimising external stresses. The brass exhibit brittle joints. With certain alloys. soldering and brazing properties of the Copper-zinc alloys are classified into more susceptible to liquid metal embrittle- brazing filler metals Cu 470a and Cu 680 limitations, leaded brasses can be brazed two alloys are very similar. The copper ment (LME) than those with an α+β are suitable for brazing binary copper-zinc using low melting silver brazing alloys and Soldering · binary copper-zinc alloys (containing casting alloy CuCr1-C (CC140C) continues structure, e.g. CuZn37 (CW508L). If in alloys with low zinc content, as their a flux of type FH10. Copper-zinc alloys Like pure copper, copper-tin wrought alloys no other alloying elements), to be used, however, as it has proved very doubt, the stresses present in the parent brazing temperatures are below the solidus containing aluminium can be brazed can be soldered with little difficulty, difficult – if not impossible – to produce · copper-zinc-lead alloys that contain metal should be relieved by annealing the temperatures of the parent metals. without difficulty. If the alloy contains although surface wetting is not as rapid. In copper-chromium-zirconium casting added lead and cold-worked parts before soldering. Low-melting silver brazing alloys may also more than 1 % aluminium, fluxes of type some situations (e.g. ), it is alloys. The copper-chromium casting alloy · complex (multi-element) copper-zinc Experience shows that this effectively be used depending on the brazing FH11 must be used. Brazing can be carried proves expedient to tin the surfaces to be is rarely soldered or brazed, but its alloys that contain a number of additi- eliminates the risk of LME. temperature and the required ductility at out with low-melting filler metals. If the joined beforehand with the lead-free solder suitability for soldering and/or brazing is onal alloying elements. the joint. As a result of the heat generated parts are likely to be subjected to a Sn99Cu1. Soldering is normally carried out no different to that of the wrought alloy. Soldering is carried out using fluxes in during brazing, the strength of the brazed corrosive environment, silver brazing alloys using lead-free solders, such as Sn96Ag3Cu1 Copper-zinc alloys are available as both classes 3.1.1, 3.1.2, 2.1.2 and 2.2.2. joint is lower than that of the parent with a higher silver content should be or Sn99Cu1. The alloy can be soldered with lead-tin wrought and casting alloys. metal. If the amount of overlap between used. For parts exposed to a marine solders or with higher melting lead-free Copper-zinc wrought alloys containing the surfaces being brazed is large enough, environment, brazing filler metals with a For fine soldering applications, fluxes in the solders in combination with a flux without Soldering additional alloying elements (special brasses) 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. detrimentally affecting the strength of the Despite the fact that the elements zinc and can be soldered without difficulty. One joint but in the peripheral annealed area recommended. Suitable filler metals For general soldering applications, fluxes in parts being joined. tin are incompatible in solders, both binary exception to this rule is the aluminium-con- (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. Brazing is typically performed with and lead-bearing copper-zinc alloys (brass taining copper-zinc alloys where the higher installations, fittings made from cop- VG 81245-3 (1991) standard lists all Bronze casting alloys are hardly ever low-melting silver alloy filler metals. If the and leaded brass) can be soldered without oxygen affinity of the aluminium (propensity per-zinc alloy are typically brazed to non-ferrous heavy-metal filler metals for soldered, however, their solderability is very filler alloy Ag 156 is used and if brazing difficulty. If possible, copper-zinc alloys to form oxide films) can cause a number of copper pipes using the filler metals welding and brazing that are suitable for similar to that of wrought copper-tin alloys times are kept short, the loss of strength is should be soldered using low-antimony problems. However, fluxes can be used to CuP 279, CuP 179, Ag 145, Ag 134 or use in shipbuilding or in the construction of comparable composition. relatively small. solders (containing no more than 0.5 % remove these aluminium oxide films. Ag 244 in combination with a flux of type of other floating equipment [19]. The antimony). If solders with a higher amount Brass casting alloys are rarely soldered. FH10. US-AWS 5.8 specification recommends the Brazing 2.4.2. High-alloyed copper alloys of antimony are used, tensile stresses in the Their ability to be soldered is very similar to use of the nickel-bearing silver brazing Brazing copper-tin wrought alloys also tends Copper alloys that contain more than 5 % soldered structure may lead to the that of wrought copper-zinc alloys of alloy BAg-3 (50 % silver) for marine to cause softening in the joint. The filler of alloying elements are referred to as formation of brittle antimony-zinc crystals comparable composition. applications. However, BAg-3 contains metals of choice are low-melting silver high-alloyed coppers. They are standard- causing solder embrittlement in both the cadmium, which is prohibited in the brazing alloys, such as Ag 156. For capillary ised in DIN CEN/TS 13388 (2013). Examples joint and the parent material. Depending on European Union by EU Regulation brazing applications copper-phosphorus filler include the copper-zinc alloys (brasses), the particular application, tin-lead, lead-tin, 494/2011. A cadmium-free alternative is, metals such as CuP 179 or CuP 182 are used. copper-tin alloys (bronzes) and cop- tin-copper and tin-silver solders can be for instance, Ag 450. The brazing of If other filler metals are used, there is a risk per-nickel-zinc alloys (nickel silvers). used. The solders Sn97Ag3, Sn95Ag5 and copper-zinc casting alloys is carried out in of localised melting of the parent material Sn97Cu3 can be used for soldering the same way as brazing the correspond- and associated embrittlement through the applications in the food industry, e.g. brass ing wrought alloys. formation of coarse grains. For brazing fittings and taps for copper drinking water temperatures below 800 °C fluxes of type systems. In contrast to pure copper, Selected areas of use FH10 are appropriate; above 800 °C, fluxes of cold-worked brasses tend to exhibit Figure 9 – Metallographic longitudinal section through a Soldered/brazed components made from type FH20 are preferred. Castings from soldering embrittlement if extended brazed joint between a pipe and a pipe fitting copper-zinc alloys are fabricated in very copper-tin alloys that do not contain more soldering (or brazing) times are used or if (filler alloy: Ag-CuP) [18] large volumes for a very wide range of than 1.5 % of lead are well suited to brazing large amounts of solder (or brazing alloy) applications in the electrical and automo- with silver brazing filler metals. For parts are applied. If there is a non-uniform tive industries, communications and exposed to marine environments, the same distribution of stresses at the joint to be domestic appliance technologies, and for recommendations apply as for copper-zinc made, the parent material may become electrical and mechanical systems. alloys (see section on the brazing of copper-zinc alloys above).

22 | KUPFERINSTITUT.DE KUPFERINSTITUT.DE | 23 Copper-nickel-zinc alloys (Nickel silvers) Copper-nickel alloys (Cupronickels) copper as the filler metal. Generally, Copper-aluminium alloys Copper-tin-zinc casting alloys Brazing and soldering of copper and Copper-nickel-zinc wrought alloys (also Copper-nickel alloys (also known as however, copper-based filler metals, such (Aluminium bronzes) (Gunmetal) copper alloys to themselves and to known as ‘nickel silvers’) are used in ‘cupronickels’) are some of the most as Cu 470a to Cu 680 or Cu 681, are used Copper-aluminium alloys (also referred to The copper-tin-zinc casting alloys other materials electrical engineering applications (for corrosion-resistant copper materials in combination with fluxes of type FH21, as ‘aluminium bronzes’) exhibit an (‘Gunmetal’) exhibit low friction and good There are many practical applications in springs), in the construction industry, in known. The wrought alloys are important or silver brazing alloys are used with fluxes exceptionally high resistance to cavitation anti-seizure properties, as well as high which copper and copper alloys are joined precision engineering e.g. as spectacle materials in marine construction (particu- of type FH10 that prevent oxidation at the erosion and are some of the most resistance to cavitation, wear and to other metals. One of the most common temples and hinges, in the arts and crafts larly for condensers and undersea piping), brazing surfaces. The filler metals should corrosion-resistant copper alloys known. salt-water corrosion. Typical uses include procedures involves brazing copper-based sector, and for . The casting alloys in the plant construction sector and in the be phosphorus-free in order to avoid Both the wrought and casting alloys are water taps, valve and pump housings, materials to steel. As and nickel are used, for instance, for marine electrical engineering sector (e.g. as embrittlement. For iron-bearing cupronick- therefore indispensable materials in the fittings and sliding bearings. Depending on alloys can both form brittle phases, they hardware, fixtures and fittings, and cast resistance wire). In addition to marine els, brazing is usually carried out with the chemical and mechanical engineering the particular application, Gunmetal can be cannot be joined together by brazing with ornamental ware. The solderability of the applications, casting alloys are filler metals Cu 773 and Ag 244. industries. Brazing and soldering of soldered with selected tin-lead solders a CuP filler metal. The choice of brazing copper-nickel-zinc casting alloys is very used in the mechanical engineering and CuNi13Sn8 is a CuNiSn alloy with higher copper-aluminium alloys always requires containing at least 60 % tin. Fluxes from filler metal is determined by the parent similar to that of the corresponding chemical industries. nickel and tin content that is used for the use of fluxes to remove the highly the flux classes 3.1.1 and 3.1.2 are material of lower brazeability. When wrought alloys. manufacturing high-quality, thin chemically resistant oxide films. Cop- appropriate. In the plumbing sector, fittings designing the joint and the soldering/ Soldering lightweight spectacle frames with per-aluminium casting alloys are rarely and tap components used in drinking water brazing method to be used, the different Soldering The solderability of these alloys is similar excellent flexibility and is brazed using soldered or brazed, however, their piping systems are soldered using lead-free properties of the materials to be joined Soldering is best carried out either with to that of pure copper. The somewhat silver alloy filler metals. For marine solderability or brazeability is very similar and antimony-free solders. Castings that (e.g. thermal conductivity, thermal lead-tin solders or with lead-free Sn97Ag3 sluggish wetting of these alloys with soft applications, the brazing filler metal to that of wrought copper-aluminium contain less than 1.5 % lead can be brazed expansion, specific heat capacity) must be or Sn95Ag5 solders, as they have better solders can be improved by the addition of should have a silver content of about 40 % alloys of comparable composition. effectively using silver alloy brazing filler taken into account. bonding and wetting characteristics. The a flux. In particularly difficult cases, the to 56 %. The VG 81245 Part 3 (1991) metals containing at least 30 % silver and The increasing significance of metal/ temperatures reached during soldering are surfaces to be joined should be pre-tinned. standard ‘Filler metals for welding and Soldering fluxes of type FH10. Brazing of copper composites in industrial applica- not high enough to cause any softening of Suitable solders are the lead-free tin-silver brazing applications in shipbuilding and Copper-aluminium alloys are rarely tubing with flanges made of Gunmetal is tions has led to the study of these material the work-hardened parent material. For and tin-copper solders, such as Sn95Ag5, the construction of other floating soldered, as the wettability of the parent common in the equipment manufacturing combinations and has driven the develop- wetting to be successful, the joint to be Sn97Ag3 or Sn97Cu3. Compared to the equipment’ [19], specifies the use of the metal deteriorates as the amount of sector. Undersea piping is subject to the ment of appropriate soldering and brazing soldered must be free of grease and leaded tin solders used previously, the silver brazing alloys Ag 140, Ag 155 and aluminium in the alloy increases, making regulations of the classification societies, solutions. Copper and alumina (Al2O3) can oxides. To facilitate optimum wetting, the lead-free solders exhibit improved Ag 244 as defined in the ISO 17672 (2010) bonding difficult and necessitating the use which stipulate, for instance, that the now be brazed using active filler metals or surfaces to be soldered should be prepared hardness, higher corrosion resistance and standard. For marine applications, the of special fluxes. If soldering is performed, brazing filler metals used must have a soldered with tin-lead solders. Active filler by very careful acid pickling (e.g. with a greater temperature stability. Fluxes of US-AWS 5.8 specification recommends the it can be carried out using the solders silver content of around 50 %. If Gunmetal metals generally contain the metal 10 % sulphuric acid solution) and type 3.2.2 or 3.1.1 are appropriate. In use of the nickel-bearing silver brazing Sn97Cu3 or Sn97Ag3; for applications in fittings are used in the copper piping for , which reacts at the interface degreased. Strongly activating fluxes of electrical applications, copper-nickel alloys alloy BAg-3 (50 % silver). BAg-3 is a which the parts will be subjected to higher drinking water supply systems, the filler between the filler metal and the ceramic, type 3.2.2 or 3.1.1 should be used.. are frequently pre-tinned or pre-silvered, cadmium-containing brazing filler metal; temperatures, CdAg5 can be used. metals CuP 279 or CuP 179 in combination making the surface more amenable to then soldered with rosin-based (colopho- the cadmium-free alternative is the filler Cadmium-containing solders are, however, with a flux of type FH10 are recommended. wetting [9]. Brazing ny-based) fluxes of type 1.1.2 or 1.1.3. The metal Ag 450 as defined in DIN ISO 17672 no longer readily available as they are Copper-nickel-zinc alloys can be brazed alloy CuNi9Sn2 (CW351H), which is used (2011). A brazing flux of type FH11 is regarded as a health risk. Special fluxes for Copper-lead-tin casting alloys with silver-bearing brazing filler metals. particularly for the fabrication of spring recommended. The brazeability of the aluminium alloys belonging to flux classes (High-leaded tin bronzes) The most commonly used brass filler metal components, exhibits excellent tarnish cupronickel casting alloys is similar to that 2.1.2 or 2.1.3 can be used. The leaded tin bronzes are important Cu 681 has the same silver-grey colour as resistance and therefore very good of the copper-nickel wrought alloys of engineering and bearing materials that are the copper-nickel-zinc parent metal. solderability even after storage for a long comparable composition. Brazing rarely joined by brazing or soldering. Suitable fluxes are those of type FH10. If period. Higher-melting solders are used for Brazing can be carried out without Soldering can be performed using tin-lead the parts are brazed in a furnace, there soldering electrical resistors that are difficulty provided that appropriate fluxes solders with 50–60 % tin and a flux of may be some deterioration in the hardness exposed to elevated temperatures. The are used. Suitable brazing filler metals are class 3.1.1 or 3.1.2. Brazing is possible using characteristics achieved through prior cold cupronickel casting alloys are rarely the silver brazing alloys with low to low-melting silver brazing alloys (e.g. working of the material. Leaded nickel soldered. medium brazing temperatures, such as Ag 156) and a flux of type FH10, though silvers have a tendency to crack when Ag 156. For parts exposed to marine the brazeability of leaded tin bronzes is annealed, particularly if they have been Brazing environments, the same recommendations limited. If alloys with a higher lead content significantly cold worked prior to brazing. The solidus temperature of the cop- given for copper-zinc alloys apply (see are brazed, very significant diffusion These alloys should therefore be brazed per-nickel alloys is higher than that of section on brazing copper-zinc alloys should be expected. using low-melting silver alloy filler metals copper. This is the reason why cop- above). and heating should be carried out per-nickel alloys, particularly those with a gradually. high nickel content, can be brazed with

24 | KUPFERINSTITUT.DE 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, 200 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: The gap widths should be designed to be of parent material to be joined and the as narrow as possible in order to fully brazing technique to be used. A distinction (Narrow-gap) brazing, gap < 0.5 mm Braze welding, gap > 0.5 mm exploit the capillary effect when brazing 150 is made between the brazing techniques Manual braze (see figure 11). The capillary effect is a used to join materials and those used for welding surface tension phenomenon. It produces surface cladding work (also known as (flux-assisted) a force that draws the flux and the molten ). Brazing joining techniques are Manual filler metal into the gap between the 100 further classified into normal brazing (flux-assisted) components to be joined. (i.e. ‘narrow-gap’) brazing and braze welding. Machine brazing (flux-assisted)

Capillary pressure [mbar] 50 Brazing in a protective gas atmosphere

Vacuum brazing 0 0,05 0,1 0,2 0,3 0,4 0,5 Gap width [mm] 0 0,1 0,2 0,3 0,4 0,5 Gap width [mm] (Narrow-gap) brazing Figure 11 - Capillary pressure as a function of gap width [12] 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 500 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. The gap width for normal brazing should be by 20–50 °C [9]. 400 between 0.05 mm and 0.5 mm. In addition to bM bN b 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 fillet has a capillary pressure 4.5 times greater than in a parallel flat gap [9]. Braze welding 200 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 100 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]. Capillary pressure [mbar]

Table 9 - Difference between standard (narrow-gap) Table 10 - Distinction between the terms ‘assembly gap’, ‘brazing gap’ and ‘brazing seam’ brazing and braze welding Figure 12 - Capillary pressure as a function of gap geometry [12]

26 | KUPFERINSTITUT.DE KUPFERINSTITUT.DE | 27 4. Soldering and brazing methods

When designing the assembly to be be configured so that the flux can flow Other factors that need to be taken into 4.1. The soldering/brazing principle figure 13 illustrates the characteristic The reflow temperature of the solder/braze joined, the direction of flow of the filler out again and any air can escape. In account when designing a soldered or Melting the solder or brazing filler metal temperatures and times during soldering/ metal corresponds roughly to the melting metal should be considered. There should general, the solders and filler metals used brazed joint are the detailed shape of the requires the uniform application of brazing and the terminology as defined in temperature of the solder/filler metal be no discontinuities in the gap that and the solder/braze metal in the finished gap and the condition of the mating surfa- thermal energy to the entire soldering/ DIN ISO 857-2 is explained in Section 6. applied. If the soldered/brazed assembly would prevent the filler metal from joint are not as strong as the parent ces. Score marks and grooves on the brazing zone. A specific temperature-time The thermal profile shown below is typical will be subjected to high service stresses, a flowing and filling the joint area. The material. The joining surface should surfaces to be joined are generally profile is followed that consists fo the of that observed during furnace soldering higher reflow temperature is desirable in region around the joint should be therefore be as large as possible in order undesirable. If there is scoring on the following sequence of steps: [6] or furnace brazing. order to optimise the quality of the designed so as to minimise stress concen- to achieve a strong, secure join. This is surface, it is important that the score 1. Melting the flux soldered/brazed joint. This can be achieved tration factors, bending loads and frequently achieved by designing a lap or marks are aligned with the direction of For reasons of cost, the holding time at by significantly extending the holding geometric notch sensitivity factors. Shear insertion joint. Other geometrical variants flow of the molten filler metal. Any 2. Activating the surface the soldering/brazing temperature is temperature, which to a diffusi- stressing of soldered/brazed joints is of soldered/brazed joints are listed in component after-treatment procedures 3. Melting the solder or filler metal usually restricted to the time needed to on-driven change in the chemical beneficial. If a flux is used, the gap must table 11. should also be taken into account when 4. Wetting of mating surfaces by the achieve a uniform temperature in the composition of the solder/braze metal and designing the brazing joint and/or molten solder or filler metal assembly. After a relatively short holding thus to a shift in the solidus and liquidus assembly. Any residual flux, binder or time, the assembly is allowed to cool in temperatures of the solder/braze metal. 5. Flowing of solder or filler metal into the solder mask should be readily removable. still air at room temperature or under The soldered/brazed joint can then be soldering/brazing gap α = 0° / 180° 0° < α < 90° α = 90° 90° < α < 180° As with welded joints, the fatigue strength defined cooling conditions. During this subjected to diffusion annealing at the of a brazed or soldered joint is enhanced 6. Filling of soldering/brazing gap by the period the soldered/brazed metal solidifies. soldering/brazing temperature [1]. Square butt joint Inclined joint T-joint Inclined joint when there are no sharp changes in the solder or filler metal. 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/brazing temperature 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 Dwell temperature 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 [°C] Temperature joining surfaces joining surfaces joining surfaces

Lap joint Insertion joint

Parallel or fully overlapping joint

Dwell time · Suitable for Preferred Holding soldering/ · Large soldering/brazing surfaces soldered/brazed Heating time time Cooling time brazing and ensure a strong joint joints braze welding Soldering/brazing time · Large joining surfaces can Total time be achieved · Preferred joint Time type for sheet Figure 13 - Characteristic temperatures and times during soldering/brazing [20] metals and tubing

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

28 | KUPFERINSTITUT.DE KUPFERINSTITUT.DE | 29 Parent material Notes Formulation

4.2. Surface preparation and other auxiliary materials; the structure Table 13 contains recommendations for With hot sulphuric acid (H2SO4); sequential In order to achieve a high quality soldered/ and condition of the mating surfaces; and pickling the surfaces of copper and dipping in two solutions: brazed joint between metallic materials, heat transfer during the soldering/brazing copper alloys. The surfaces must always I. 65 ml 96 % sulphuric acid ( H2SO4) diluted the mating surfaces need to carefully process. Soldering/brazing should be be degreased prior to pickling and rinsed Copper-chromium alloys with water to give 100 ml of solution; prepared. Surface preparation can involve carried out as soon as possible after the thoroughly afterwards. Further recom- solution used while hot chemical, mechanical or thermal cleaning surfaces have been prepared. Once mendations regarding surface prepara- II. 3 ml 96 % sulphuric acid (H2SO4) diluted procedures or a combination thereof (see cleaned, the parts should be protected tion techniques are described in the DVS with water to give 100 ml of solution 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- a) 5 ml 96 % sulphuric acid (H SO ) diluted Prior mechanical removal of oxides may be 2 4 might inhibit wetting, such as oxides, oil, phere. The following procedures can be with water to give 100 ml of solution Copper and copper alloys required (copper or brass wire brush, grease, dirt, rust, paint, cutting fluids, etc. used to prepare the surfaces of copper and b) 50 ml 65 % nitric acid (HNO ) diluted with emery cloth) 3 (see figure 14). Furthermore, the wetting copper alloys. Which procedure(s) to adopt water to give 100 ml of solution 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 Sequential dipping in two solutions: factors: the properties of the parent and the geometry of the surfaces to be I. 2 ml 40 % hydrofluoric acid (HF) with 3 ml 96 % material, the solder or brazing filler metal cleaned [21]. 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

Cleaning procedure Example With hot sulphuric acid (H2SO4); sequential dipping in two solutions: Eintauchen in zwei Lösungen Prior mechanical removal of oxides may be Degreasing with commercially available solvents (e.g. isopropanol, acetone); Steam degreasing I. 65 ml 96 % sulphuric acid (H2SO4) diluted with Copper-nickel alloys required (copper or brass wire brush, emery with hydrocarbons and chlorinated hydrocarbons; water to give 100 ml of solution; solution used cloth) Chemical cleaning Cleaning with aqueous alkaline solutions; emulsion cleaning using mixtures of hydrocarbons, fatty while hot acids, wetting agents and surface activators; II. 3 ml 96 % sulphuric acid (H2SO4) diluted with Pickling treatments using acids, acid mixtures or salts (see table 13) water to give 100 ml of solution

Grinding, filing, abrasive blasting, Sequential treatment using the following two Mechanical cleaning solutions: Caution: Steel wire brushes must not be used to clean the surfaces of copper or copper alloys! I. 5 ml 65 % nitric acid (HNO3) diluted with water Cleaning in a reducing atmosphere, e.g. of hydrogen and hydrogen fluoride at to give 100 ml of solution Thermal cleaning temperatures above 800 °C 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 Table 12 - Cleaning procedures for copper and copper alloys [21] 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]

30 | KUPFERINSTITUT.DE KUPFERINSTITUT.DE | 31 4.3. Surface activation take place. This process is known as 4.3.1. Fluxes about 50 °C below that of the solder or Solder fluxes (classified according to Proper contact between the solder or surface activation. Some of the most According to DIN ISO 857-2 (2007), a flux brazing filler metal as this ensures that DIN EN 29454-1 (1994) brazing alloy and the surface of the common methods of surface activation is defined as a ‘non-metallic material the surface has been activated before it is A flux is normally required for soldering parent metal is an essential requirement are the use of fluxes, soldering/brazing in which, when molten, promotes wetting by wetted and before the solder or filler operations. Solder fluxes are classified in in any high-quality soldered or brazed a reducing atmosphere or soldering/ removing existing oxide or other metal starts to flow. As there is no terms of their chemical composition [4]. joint. However, sufficient contact brazing in a vacuum. Other techniques detrimental films from the surfaces to be universal flux, the composition of the flux between the molten solder or filler metal include soldering/brazing under an inert joined and prevents their re-formation must be carefully selected for the In practice, solder fluxes area also and the surface is not always established shielding gas, arc brazing, and soldering during the joining operation’ [10]. Fluxes proposed joining operation [1]. A categorised according to their chemical in all cases. Figure 14 represents a methods involving mechanical activation are available as powders, pastes, liquids distinction is made between fluxes for function. realistic cross-sectional view through the of the faying surface, as in ultrasonic or as solder-flux mixtures. soldering DIN EN 29454-1 (2004) and surface of an engineering metal. The dirt, soldering or abrasion soldering. Surface The melting range of the flux should be fluxes for brazing DIN EN 1045 (1997). 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 Flux type Base Activator Form Areas of use

[1] With rosin Electrical, [1] Resin [1] Without activator Electronics [2] Without rosin [2] Halide activator Particulate contamination approx. 104–105 nm (other activating agents (dust, abraded metal particles) [1] Water-soluble are available) Electrical, Electronics, [2] Organic [3] Non-halide activator [A] Liquid Contamination approx. 3 nm Metal goods [2] Not water-soluble (grease, oil) [B] Solid [1] With ammonium Plumbing applications Adsorbed layers approx. 0.3–0.5 nm chloride Cu and Cu alloys N [1] Salts O O H (HCs, CO2, H2O) [3] Inorganic [2] Without ammonium Ni and Ni-alloys Me [C] Paste Me Me Me chloride Precious metals Reaction layers approx. 1–10 nm [1] Phosphoric acid Cr, Cr-Ni-alloys [2] Acids (MexO, MexOH, MexN) [2] Other acids Stainless steels [1] Amines and/or [3] Alkaline Parent material with up to approx. 5000 nm modified microstructure

Table 14 - Solder fluxes (classified according to DIN EN 29454-1 (1994) (1994) [23] Parent material with undisturbed microstructure Functional class Key chemical constituent Mode of action

Figure 14 - Schematic cross-section of the surface of an engineering metal [22] Flux residues cause corrosion in copper and copper alloys (pitting); workpieces must be Corrosive fluxes washed after soldering with 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]

32 | KUPFERINSTITUT.DE KUPFERINSTITUT.DE | 33 Brazing fluxes (classified according to and tungsten. Fluxes in Table 17 lists substances that are contained covered by the legislation, will be cation and labelling rules for brazing fluxes DIN EN 1045 (1997) class FL are used when brazing light in a number of fluxes and which, since generated in the brazing torch flame and containing boric acid, pentahydrate The DIN EN 1045 (1997) standard metals, such as aluminium and aluminium 1 December 2010, are classified as will deposit on the workpiece and in the or trioxide is available (in German) in classifies brazing fluxes into two classes: alloys. Only class FH fluxes should be Category 1B reproductive toxins if present workplace. Boric acid deposits are toxic. For the DVS technical leaflet 2617 [26]. Table 17 FH and FL. Class FH fluxes are used in the used for brazing copper and copper in the amounts given in the table. Products this reason, brazing operations involving a also specifies the concentrations above brazing of heavy metals, such as steels, alloys. affected must be marked with the symbol product containing trimethyl borate are which the product is classified as hazardous. stainless steels, copper and copper alloys, ‘T’ and the R phrases R60 and R61. subject to the same regulations that apply nickel and nickel alloys, precious metals, 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 Effective Type Brazing temperature Description / Areas of use After-treatment temperature range 233-139-2 Boric acid ≥ 5,5 % 234-343-4 contains boron compoundsand Residues are corrosive; FH10 approx. 550 – 800 °C > 600 °C simple and complex fluorides; remove by washing or pickling Boron trioxide 215-125-8 ≥ 3,1 % multi-purpose flux 215-540-4 contains boron compounds and Borax anhydrate 235-541-3 ≥ 4,5 % simple and complex fluorides Residues are corrosive; FH11 approx. 550 – 800 °C > 600 °C 237-560-2 and chlorides; mostly used for remove by washing or pickling copper-aluminium Borax decahydrate 215-540-4 ≥ 8,5 %

contains boron compounds, Borax pentahydrate 215-540-4 ≥ 6,5 % elemental boron and simple and Residues are corrosive; Table 17 - Concentration levels for hazard classification purposes [26] FH12 approx. 550 – 850 °C > 600 °C complex fluorides; mostly used for remove by washing or pickling stainless steels, high-alloy steels and 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 contains boron compounds and Residues are corrosive; According to DIN ISO 857-2 (2007), a previously been cleaned ’ [10]. A protective flux residues removed. Using a protective FH20 approx. 700 – 1000 °C > 750 °C simple and complex fluorides; remove by washing or pickling protective atmosphere for soldering or atmosphere of shielding gas(es) improves atmosphere is, however, associated with multi-purpose flux brazing is the ‘gas atmosphere or vacuum the quality of the soldered/brazed joint, higher process and equipment costs. contains boron compounds; Residues are not corrosive; round a component, either to remove oxide enables precise control of soldering/brazing Table 18 contains examples and definitions FH21 approx. 750 – 1100 °C > 800 °C multi-purpose flux remove mechanically or by pickling or other detrimental films on the surfaces temperatures and soldering/brazing times, of the various protective atmospheres used in soldering and brazing operations. contains boron compounds, phos- phates and silicates; Residues are not corrosive; FH30 > 1000 °C Atmosphere Shielding gas Vacuum mostly used together with copper remove mechanically or by pickling and nickel filler metals reducing inert

contains chlorides and fluorides; ‘Pressure sufficiently below atmospheric so that the Residues are corrosive; ‘Gas which prevents the FH40 approx. 600 – 1000 °C boron-free; used when presence of formation of oxides will be prevented to a degree remove by washing or pickling Definition from DIN formation of oxides boron is not permitted ‘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] Table 16 - Brazing fluxes (classified according to DIN EN 1045 (1997) [25] 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

34 | KUPFERINSTITUT.DE KUPFERINSTITUT.DE | 35 4.4. Applying the solder or brazing by dipping the parts into the molten filler 4.5. Soldering and brazing techniques · method of application of the filler filler metal material, or by positioning filler metal Soldering and brazing techniques can be metal (e.g. dip soldering/brazing, In addition to selecting the correct method preforms where the joint is to be made. classified in different ways, such as by the soldering/brazing with filler metal of surface cleaning and surface activation, Filler metals are available in a variety of heating method (energy source) used (see applied to the joint) choosing the most suitable way to forms (e.g. wire, rod, strip, film, paste) and table 20). Other classification schemes are · method of fabricating the joint (e.g. introduce the filler metal into the joint is sizes to suit the design and dimensions of based on the: manual, partially automated or fully also an important aspect of the soldering the soldering or brazing gap. · nature of the soldering/brazing joint automated soldering/brazing) or brazing process. In most cases, the (cladding, (narrow-gap) soldering/braz- application of the filler metal is dictated by Table 19 shows a number of different ways ing, braze welding) the design of the assembly. The solder or of introducing the filler metal to the joint. · method of oxide removal brazing alloy can be introduced manually, (e.g. soldering/brazing in a protective gas atmosphere, vacuum soldering/ brazing, flux-assisted soldering/brazing)

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, Process Energy source Name of technique and the filler metal is brought to its mainly by contact with the components to be soldered or brazed. Soldering using a solid heat source ∙ Soldering with soldring iron gebracht. ∙ Dip soldering Soldering using a liquid heat source ∙ Wave soldering ∙ Drag solderingn Soldering or brazing with filler metal deposited or Soldering inserted in the joint Soldering with a gaseous heat source ∙ Flame soldering Process during which the filler metal is placed in the area of Soldering using an electric current ∙ Induction soldering in air the joint before heating, and is then heated to the soldering or brazing temperature together with the components to be Furnace soldering ∙ Furnace soldering soldered or brazed. 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 Dip soldering or brazing ∙ MIG, TIG, Plasma Process during which the components to be soldered or ∙ Laser beam brazing Brazing using radiation brazed are dipped in a bath of molten filler metal. ∙ Electron beam brazing Brazing ∙ Induction brazing ∙ Induction brazing in a protective gas atmosphere ∙ Indirect resistance brazing Soldering using electrical heating Soldering or brazing with components coated ∙ Direct resistance brazing with filler metal ∙ Furnace brazing in a reducing atmosphere Process during which the filler metal is applied ∙ Furnace brazing in an inert gas atmosphere before soldering/brazing by coating (e.g. roll cladding, ∙ Furnace brazing in a vacuum , vapour deposition or tinning).

Table 19 - Different ways of introducing the filler metal to the soldering or brazing joint (based on [10] Table 20 - Classification of soldering/brazing processes (based on [10])

36 | KUPFERINSTITUT.DE KUPFERINSTITUT.DE | 37 4.5.1. Soldering with soldring iron tion of the parts and greater erosion of Wave soldering source, the high reflectivity (up to 96 %) Hot-iron soldering is a soldering technique 4 the parent material. The workpiece is Wave soldering is chiefly used to solder of the shiny metallic components is not in which the thermal energy is supplied by 3 typically immersed for between 20 and electronic components onto printed conducive to heating and needs to be a solid medium. 2 60 seconds. Dipping speed needs to be circuit boards. taken into account when designing the The joint is heated and the solder is melted 1 carefully controlled. It should be selected process. The actual soldering stage by applying heat from a hot iron that is so that the workpiece reaches the The process comprises four stages with a occurs when the PCB assembly is controlled either manually or by a soldering or brazing temperature during conveyor transporting the printed circuit transported through the solder wave machine. Hot-iron soldering is not suitable all stages of the dipping process. A visible board (PCB) to the different zones. The zone. The final stage involves cooling the for fabricating narrow-gap joints with sign that the correct dipping speed has process begins with flux being applied to PCB assembly in the cooling zone, either large overlap zones. been chosen is the presence of a concave the PCB assembly. In the second stage, naturally under ambient conditions or by 1. Conductor 2. Printed-circuit board meniscus at the interface of the molten the PCB assembly is pre-heated using a forced cooling. [27]. Experience has Most soldering irons are equipped with a 3. Tip of soldering iron 4. Flux-cored solder solder of filler metal and the workpiece. convection heater or an lamp to shown that the PCB assembly is best built-in electrical heating element or with Large parts should be preheated prior to compensate for the different heat drawn across the surface of the solder 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 capacities and thermal expansion inclined at an angle of 7° [10]. such as natural gas, or propane. bath temperature when the workpiece is coefficients of the materials on and in The heat capacity and the shape of the immersed. Dip brazing is typically used in the PCB. PCBs contain epoxides, which as Drag soldering is a variant of wave soldering iron and its tip (also known as the manufacture of condensers, cooling poor conductors of heat make it difficult soldering. In drag soldering, the solder is Advantages the ‘bit’) must be suitable for the assembly units and metal vessels [16]. to raise the temperature of the assembly. applied not by contact with the solder · Low cost to be soldered. The more pointed the tip is, The PCB laminate therefore acts to cool wave, but by immersion in a static solder · Reproducible the easier it is to access the joint, though the surrounding metal components bath. The angle at which the assembly · Suitable for hard-to-access heat losses are also higher. Soldering iron 1 making it impossible to heat the assembly enters and exits the bath is typically joints tips have masses ranging from about 20 g 3 uniformly up to the soldering tempera- between 8° and 10°, and the immersion · Suitable for temperature- 2 to 1 kg and used to be almost exclusively ture. In addition, hot flux vapour causes a depth is usually about half the thickness sensitive components made of copper due to its excellent rise in temperature of the tempera- of the PCB. A rigid strip is used to remove · Good for single soldered joints thermal conductivity and good wettability. ture-sensitive electronic components. If the oxides (‘dross’) from the surface of In high-volume soldering work, these infrared radiation is used as the heat the solder bath [10]. 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 1 reason, copper-containing solders and tips degree of skill and manual dexterity plated with other materials were devel- =7° 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 2 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 3 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 1. Printed-circuit board 2. Dryer soldering application to be performed, liquidus temperature of the solder or filler of workpiece 4 between 15 W and 2000 W of thermal metal. Higher temperatures will lead to 3. Solder bath with solder wave · High maintenance 4. Wave fluxer or foam fluxer energy needs to be applied. The tip of the increased oxide formation on the surface 7° Conveyor angle 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- For the advantages and disadvantages of wave soldering, Table 22 - Advantages and disadvantages of dip Figure 17 – Wave soldering (based on [10]) see the section on dip soldering or brazing. soldering or dip brazing

38 | KUPFERINSTITUT.DE KUPFERINSTITUT.DE | 39 4.5.3. Flame soldering or brazing work is available in the technical application reducing thermal stresses and distortion in vacuum conditions (10-3...10-7 mbar). In Medium Vacuum Reducing gas Inert gas Flux Flame soldering or brazing (or Torch notes GW 2 and GW 7 issued by the the workpiece. The temperature-time the majority of cases, the heating power of soldering/brazing’) can be performed by German Technical and Scientific Association profile is relatively easy to control. a vacuum furnace lies between 50 kW and hand or by machine. The heat is applied by a for Gas and Water (DVGW). For example, Workpieces with complex shapes and large 500 kW. Before any soldering or brazing Flux X X X flame of combustible gas (e.g. acetylene). drinking water installations are subject to numbers of joints can be soldered or can take place, the heating chamber needs The gas is fed to the torch head through a special requirements: copper piping larger brazed without difficulty. Additionally, to be cleaned and the components Reducing gas X pressure regulator. The choice of torch than 28 x 1.5 mm must only be joined by heat treatment and soldering/brazing can carefully positioned within it. The depends on the workpiece, material and gas brazing [28] [29]. be carried out in a single operation. The temperature of the furnace is then Inert gas O X being used. The first stage involves applying solder or brazing filler metals should have increased rapidly to about 50 °C below the 2 solidus temperature. The furnace is then flux to the surfaces to be joined. The joint 1 a narrow melting range in order to prevent Vacuum X gap must be dimensioned accordingly. The and erosion [6]. held at this temperature for a short time to parts to be soldered or brazed must be fixed facilitate temperature equilibration. This is in position to prevent them from slipping. Furnace soldering or brazing carried out in followed by rapid heating to approximately X – can be used simultaneously The workpiece should be pre-heated at the a controlled atmosphere (using inert gases 20–30 °C above the soldering or brazing O – can be used sequentially location of the joint and its immediate such as argon, helium or , or temperature of the solder or brazing filler Table 24 - Surface activation in furnace soldering or brazing vicinity so that the solder or filler metal can reducing gases like hydrogen or carbon metal. Depending on the work being flow easily. If the area to be soldered/brazed monoxide) is well suited to high-volume carried out, the soldering or brazing is not hot enough, the solder or filler metal 3 soldering or brazing jobs in which multiple temperature must be held for a period of will contract when it comes into contact joints need to be made, such as the 5–20 minutes. Process times can be with the cold surface and no wetting will 1. Components to be joined fabrication of condensers, cooling units, shortened by heating and cooling under a 3 4 5 6 7 8 occur. Pre-heating is done with a neutral or 2. Flux and solder 3. Flame heat exchangers and in automotive protective gas atmosphere. In such cases, 2 with a reducing or slightly reducing flame. Figure 18 – Torch soldering (based on [10]) construction [6]. the vacuum in the furnace chamber is 9 generated at higher temperatures [6]. 1 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 thoroughly cleaned prior to furnace place with a jig 10 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 1. Infeed 2. Extractor hood 3. Exit port for protective gas 4. Pre-heating zone 5. tube port be removed once the soldering or brazing workpiece possible if a flux is used [6]. 6. Soldering/brazing zone 7. Cooling water 8. Cooling zone 9. Exit 10. Entry port for protective gas process is finished. Copper-copper joints Figure 19 – Vacuum soldering/brazing furnace [30] Figure 20 - Schematic diagram of a continuous-feed furnace with an inert gas atmosphere (based on [6]) 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- Another means of classifying furnace required. Appropriate solders can be found nents that need to meet exacting quality soldering or brazing processes is in terms in the following standards: DIN EN ISO 4.5.4. Furnace soldering or brazing specifications. It is commonly used in the of the process consumables used, such as: Advantages Disadvantages 17672 (2010) for brazing filler metals; DIN Furnace soldering or brazing is nearly aviation, aerospace, electronics, automo- · Uniform heating and cooling ensures · All areas of the workpiece are 1707-100 (2011) and DIN EN ISO 9453 always carried out either in a protective tive, machine tool, plant equipment · Flux low-stress and undistorted components subjected to heat treatment (2014) for soft solder alloys. Torch soldering gas atmosphere or in a vacuum; it is rarely construction, and power engineering · Flux and protective gas · Soldering/brazing of complex assemblies · Long soldering/brazing times and brazing are used in numerous industrial done in an air atmosphere. industries. Vacuum furnaces also come in · Soldering/brazing and heat-treatment · High equipment costs · Reducing protective gas (e.g. hydrogen) sectors, including refrigeration and a variety of types. Examples include can be performed in a single step air-conditioning, mechanical construction It offers a number of advantages over radiation-heated glass vessels, resist- · Inert protective gas (e.g. argon, helium) [6]. · Process can be readily controlled of small-scale and large-scale equipment, other soldering or brazing processes. If ance-heated and induction heated · Multiple joints can be made in a plumbing and heating installations, and gas due consideration is given to the materials furnaces. Soldering or brazing is usually single step 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 Table 25 - Advantages and disadvantages of furnace soldering or brazing

40 | KUPFERINSTITUT.DE KUPFERINSTITUT.DE | 41 of solder pastes containing, for example, Convection reflow soldering in a nitrogen controlled externally by fans, blowers and soldering can also be done under vacuum. Reflow soldering is an important SnAgCu or SnAg alloys. In a reflow , atmosphere has gained in importance in injector nozzles. As can be seen in figure 22, Nevertheless, soldering faults can still technique in the electronics industry. It is the solder in the solder/flux paste melts recent years. The nitrogen partially a convection reflow oven has multiple arise, such as solder skips, tombstoning a common method of attaching surfa- creating a material bond between the displaces the air from the reflow oven thus process zones that can be controlled (unbalanced solder melting and wetting ce-mounted components to printed electronic components and the circuit reducing the oxygen content in the individually [31]. behaviour at the mounting pads on circuit boards. The technique makes use board (see figure 21). 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 Figure 21 - Surface-mounted component shown before the solder in the melts [31] 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 Condensation Radiation Convection Conduction (vapour phase) Pre-heating Peak Cooling Infrared Laser Air Nitrogen

Simultaneous X X X process Simultaneous X X batch process

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

Heat transfer to Partially PCB assembly Large energy Very large energy inhomogeneous if Homogeneous Homogeneous Homogeneous (inter- density density no planar contact 4.5.5. brazing: direct resistance soldering/brazing, comparison) to component 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 Maximum unalloyed steel and aluminium, but all other soldering/brazing, in which the current is region of the joint, neighbouring T can be T can be control- achievable T can be control- P T is limited by the P metallic materials can be soldered or brazed introduced to the part to be joined via an areas remain unaffected P controlled P led precisely temperature Temperature can Temperature can led very precisely choice of medium by this technique. without flowing through the · Short soldering/brazing times very precisely (max. hot-plate relative to the slightly exceed T slightly exceed T (max. gas temp. (max. temp. joint [6]. · Suitable for temperature- P P (max. gas temp. temperature temperature T on ≤ 350 °C) ≤ 260 °C) The solder of filler metal is applied to or sensitive parts P ≤ 350 °C) ≤ 350 °C) F the PCB assembly placed in the assembly gap before soldering or brazing begins. The (made, for Disadvantages Flexibility in example, from tungsten) are used to press · Geometry of assembly must be controlling the the mating surfaces together. The electric taken into account High Low Very high Very high Medium Medium to low 2 temperature current flowing in the secondary circuit of the transformer generates intense heat at profile 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. Component Solder paste and Requires a flat, Depending on the particular application, a 1 Special specifications No substrate must No No bare contact flux or a controlled atmosphere can be 3 requirements must be taken be suitable surface used. Soldering or brazing times range from into account a few milliseconds to a few seconds. There are two types of resistance soldering/ F The following heat sources may be used: light/radiation (e.g. infrared), convection (e.g. hot Table 26 - Comparison of the different reflow soldering heating modes [31] 1. Workpiece 2. Joint to be soldered nitrogen), vapour-phase condensation (latent heat) and conduction. Table 26 lists some of 3. Electrodes the characteristic properties of the various heat sources. Figure 23 – Direct resistance soldering (based on [10])

42 | KUPFERINSTITUT.DE KUPFERINSTITUT.DE | 43 4.5.6. Induction soldering or brazing Table 29 shows how the heat penetration 4.5.7. Electron beam brazing 4.5.8. Arc brazing Induction soldering or brazing can be depth (or ‘skin depth’) in copper and brass Electron beam brazing is carried out in a Advantages Electric arc brazing can be performed as used to join all types of metal and varies with frequency. It is readily apparent medium or high vacuum environment. It is · Highly localised heating of a MIG or TIG process. The arc is created typically uses a flux in an air or that lower frequencies are more suited to characterised by high power and parent material between a wire electrode and the parts controlled atmosphere. The technique is heat generation at greater depths, while a small beam diameter. The electrons are · Good reproducibility to be brazed, transforming electrical primarily used, however, for copper, higher frequencies are better for processing thermally emitted from the cathode and · Minimal distortion of components energy into heat at the brazing joint. The brass, steel and aluminium. The solder or at the workpiece surface. accelerated by the strong electric field that · No complex preparation or filler metal is typically a copper-based brazing filler alloy selected should have results from the high voltage (15–75 kV) after-treatment required alloy wire or rod whose melting range is a narrow melting range or a fixed Material Temperature [°C] Skin depth [mm] at the following frequencies: applied between the cathode and anode. below that of the parent metal. The melting point and good flow properties. The electron beam exits the beam Disadvantages solidus temperature of common filler 50 Hz 500 Hz 10 kHz 1 MHz The cleaned joint is surrounded by a generator through a in the anode. · Process carried out in a vacuum metals of this type is in the range 830 °C single-turn or multi-turn water-cooled Copper 600 17 5,5 1,2 0,12 When the tightly bundled electron beam · Potential x-ray hazard to 1060 °C. Electric arc brazing is induction coil. The induction coil must impacts the target material, the kinetic · Requires use of filler metal generally used for braze welding be shaped appropriately to fit the form Brass 600 26 8,5 1,8 0,18 energy of the fast-moving electrons is preforms or pre-coated parts applications. The most important filler of the workpiece. The technique is Table 29 - Skin depth as a function of operating frequency [32] converted into thermal energy, generating metals are listed in table 32. therefore particularly well suited for heat in the material. In electron beam rotationally symmetric parts. An AC Induction soldering/brazing offers a number temperature-sensitive parts. Drawbacks brazing, the parts to be joined must be Table 31 - Advantages and disadvantages of electron current flows in the coil, generating an of advantages over other soldering/brazing include the creation of an electromagnetic pre-coated with filler-metal or filler metal beam brazing alternating magnetic field that induces techniques. There is no exposure to high field during the soldering/brazing process preforms must be inserted at the location electric currents and therefore heat in levels of light, heat or noise at the workplace, and the high initial cost of the equipment, of the joint. Electron beam brazing is used DIN EN ISO 17672 Filler metal alloy DIN ISO 24373 (2009) the part being soldered or brazed [6]. systems can be readily which makes the technique more suited to for applications in which the joints have (2013) mechanised or automated, the process is the mass production of assemblies [6]. tight dimensional tolerances, where The technique requires a medium- energy efficient, heating is fast and localised, high-power, highly localised heating is Designation Material number Material number 4 frequency or high-frequency generator. which is beneficial when dealing with required, or where heating has to be 3 Silicon bronze CuSi2Mn1 Cu 6511 Cu 521 achieved extremely rapidly [6]. Silicon bronze CuSi3Mn1 Cu 6560 Cu 541 2 Medium frequency High frequency 1 1 Tin bronze CuSn6P Cu 5180A Cu 922 Frequency 1000 – 10.000 Hz 0.1 – 5 MHz Tin bronze CuSn12P Cu 5410 Cu 925 2 4 Size of copper parts Aluminium bronze CuAl7 Cu 6100 Cu 561 t = 4 – 12 mm t = 0.3 – 3 mm 3 6 [thickness t] 1. Components to be joined 2. Brazing joint 3. Induction coil 4. Generator 5 Aluminium bronze CuAl10Fe Cu 6180 Cu 565 8 Figure 24 – Induction brazing [10] (above) 7 9 Manganese bronze CuMn13Al8Fe3Ni2 Cu 6338 Cu 571 Output power 20 – 300 kW 2 – 30 kW Table 30 - Advantages and disadvantages of induction soldering or brazing (below) Table 32 - Overview of important filler metals used in laser and electric arc brazing Soldering or brazing time 0,5 – 4 min 5 – 60 sec Advantages · Contactless process In recent years MIG brazing with consuma- Precision engineering, · Short soldering/brazing times ble wire electrodes and plasma brazing have Appliance manufacturing, electrical engineering, tool grown in importance, particularly when Areas of application · High-quality soldered/brazed joints automotive engineering fabrication, aerospace · Uniform heating of the joining zinc galvanised sheet steel engineering components 10 11 (thickness: less than 3 mm) in the automo- tive industry. Figure 26 shows a continuous Coupling gap between Disadvantages 1.Vacuum chamber 2. Cathode 3. Anode peripheral MIG brazing seam on a motor 4. Power source connector terminals bike fuel tank [33]. the coil and the part to be 2 – 4 mm for Cu: 1–2 mm · High investment cost 5. Beam deflection system soldered or brazed · Joint must be accessible to 6 . Focusing lens 7. Hartlötkammer induction coil 8. Electron beam 9. Brazing joint 10. Device for moving/ positioning workpiece 11. Components to be joined 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 Figure 25 – Electron beam brazing [10] Figure 26 - Fuel tank from a Honda VT 1300CX with CuAl8 · Electromagnetic field brazing filler metal [33] Table 28 - Characteristic features of induction soldering or brazing [6]

44 | KUPFERINSTITUT.DE KUPFERINSTITUT.DE | 45 5. Quality assurance

Studies have shown that when electric 1 Quality assurance is one of the main contains all of the relevant standards and data are, however, essential when the arc brazing is carried out under a Advantages elements of a quality management system DVS technical leaflets relating to soldering soldering or brazing process is mechanised shielding gas, the commonly used · High productivity 2 and is concerned with verification. The aim and brazing. or fully automated, such as in a completely 3 7 copper-based (bronze) filler metals cause · Little preparation or after-treatment 5 of quality assurance is to prevent the encased continuous-feed furnace. diffusion and partial dissolution to occur required (no flux involved) 4 production or supply of defective products. In addition to the standards, the German at the interface of the parent metal and · Minimal distortion of components As in welding, the quality of a brazing or Welding Society DVS (Deutscher Verband Another important aspect when assessing the coating and filler metals. The metal · Can be readily mechanised soldering process depends on the skill and für Schweißen und verwandte Verfahren the quality of a soldered or brazed surfaces that come into contact with the · High brazing speed experience of the operator. Soldering and e.V.) also issues technical leaflets and connection concerns of the geometry and brazing filler alloy should be clean and · Low investment costs brazing are physicochemical processes in guidelines. There are fewer rules and metallurgical structure of the joint. bare so as to facilitate metallurgical · Optically well-finished joints 6 which a material bond is created through accepted methods of quality assurance for Dimensional and visual inspections are interaction between the parent metal and 1. Power source 2. Laser beam 3. Focusing lens interactions between the solid parent soldering and brazing than for welding. The obligatory. The presence of cracks and the wetting filler metal. Fluxes are not Disadvantages 4. Shielding gas 5. Brazing joint material and the molten solder or filler primary criteria are: appropriate qualifica- pinholes (pores) are typically demon- required as the surfaces are activated by · Precision electrode feeding required 6. Components to be joined 7. Filler wire metal. Phenomena such as capillary action tion and training of operating personnel; strated using dye penetration and the burning arc. The DVS technical leaflet · Arc blow may need to be taken Figure 28 – Laser beam brazing (based on [6]) and surface wetting are exploited in production monitoring; checking on magnetic particle inspection techniques. If 0938-1 (2012) contains further informa- into account soldering and brazing processes. If the assessing the quality of the joints made. soldering or brazing defects are to be tion on the principles and details of the Laser brazing is commonly used in the parent material and solder or filler alloy are assessed and the wetted joint area process as well as the equipment automotive industry to join zinc galvanised properly matched, and if the joint is The objective is to fabricate a high-quality determined, x-ray and ultrasonic testing requirements. Application notes on arc Table 33 - Advantages and disadvantages of electron body panels, as it enables high brazing properly designed and made, a soldered or soldered or brazed joint in a reproducible are used. The different materials and the arc brazing brazing are available in DVS technical speeds to be achieved while the small heat brazed joint can provide a more reliable join fashion while taking cost efficiency factors thicknesses of the parts must be taken leaflet 0938-2 (2005). One of the 4.5.9. Laser beam soldering or brazing affected zone minimises panel distortion than that achievable by welding [38]. This into consideration. The need for well- into account if these non-destructive advantages of electric arc brazing While both laser beam soldering and issues [36]. The images in table 34 show a section aims to provide an overview of trained and skilled personnel is important testing methods are deployed. Metallo- compared with laser beam brazing is brazing techniques are used, most of the roof seam fabricated using laser brazing quality assurance issues but does not claim not only for producing well-executed graphic sections are prepared in order the lower capital investment costs applications in the automotive industry and a CuSi3Mn1 silicon bronze filler. Filler to be complete. soldered or brazed joints, but also for fixing check the condition of the microstructure, [6] [34] [35]. involve laser beam brazing. The technique metals that are suitable for use in electron The following faults and defects can arise in or jigging the components of the soldered the transition zone, the seam width and enables high temperatures to be reached beam brazing (see table 32) can also be a soldering or brazing process: or brazed assembly. The following any erosion. If brazing is used in the so that high-melting copper-based filler used for laser beam brazing [37]. · flux burning when the temperatures guidelines and standards govern the construction of tanks, containers and metals can be processed without difficulty. used are too high, procedures to be followed in training piping, pressure and leak testing is A highly focused laser beam generates courses: DVS Guideline 1183 (2004), DIN required [6]. Destructive testing methods · inadequate wetting by the solder or 1 high power densities but only a small ISO 11745 (2011) and DIN EN ISO 13585 suitable for evaluating soldered joints are heat-affected zone. A particularly suitable filler metal alloy, (2012). set out in the standard DIN 8526 (1977); radiation source for copper-based filler · wrong choice of solder/filler or flux, those used to assess brazed joints are metals is a Nd:YAG solid-state laser as it · no preparation or improper preparation By identifying and, where necessary, described in DIN EN 12797 (2000). generates laser radiation at a wavelength of the mating surfaces, correcting workflow irregularities early, Non-destructive testing methods must of 1.06 µm by the filler alloy. It is Laser-brazed roof seam Laser-brazed roof seam monitoring procedures play an important conform with DIN EN 12799 (2000). on a Volkswagen Passat on an AUDI Q5 (2008) · de-wetting caused by oxidation at the important that the parts to be joined are role in ensuring that the soldering or CC (2008) joint because soldering/brazing times 2 5 pre-coated with filler metal or that the brazing process meets the required quality Other defects that can occur include Table 34 - Examples of a laser brazed seam [33] (above) were too long. 3 filler metal is precisely positioned. Laser Table 35 - Advantages and disadvantages of laser beam specifications while remaining cost-effec- cracking, lack of fusion, and voids.The DIN 4 beam soldering and brazing techniques are brazing (below) It is therefore important to produce and tive. Monitoring involves capturing key EN ISO 18279 (2004) standard provides a used primarily in the electrical, automotive maintain quality assurance documentation. process parameters (e.g. temperature time comprehensive classification system for and precision engineering sectors. Very The documentation should provide profile is) and observing the state of listing imperfections in brazed joints. short soldering or brazing times are Advantages safeguards against potential claims and soldering is, the filler alloys and other Permissible defects and imperfections are · Very high productivity 1. Wire electrode (filler metal) 2. Shielding gas possible. For example, single soldering provide the necessary proof that a fault or auxiliary materials and consumables. detailed in DIN 65170 (2009). This standard · Minimal preparation or after-treatment 3. Arc 4. Brazing joint 5. Power source times in the millisecond range are possible defect could not have occurred during the Manual processes, such as hot iron also specifies permissible wetted joint for surface mounted electronic compo- required (no flux involved) fabrication or production process. soldering, demand highly trained operators areas, which are an important criterion for Figure 27 - Electric arc brazing (MIG) (based on [6]) · nents [6]. Can be readily mechanised Important recommendations are contained with good manual dexterity as, in most assessing the quality of a brazed joint [6]. · Minimal distortion of components in the standards governing quality cases, devices measuring and displaying the · High brazing speed management systems: DIN EN ISO 9001 temperature at the workpiece are not used. Disadvantages (2008) and ISO/TS 16949 (2009). The Measuring instruments that can monitor · High capital investment costs DIN-DVS Manual 196 (Parts 1 and 2) also process parameters and record process · Positioning and feeding of filler wire has to be done very precisely

46 | KUPFERINSTITUT.DE KUPFERINSTITUT.DE | 47 6. Case studies

Quality requirements in soldering and/or brazing 6.2. Strip tinning Tinned strips of copper or copper alloys The adapter tube on a CuproBraze® process joints are created Operational and Fabrication / Testing / Personnel are the raw materials for -in can be fabricated by brazing a flexible by brazing with the filler alloy CuNiSnP. administrative aspects Production Assessment 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 Quality management system Qualification testing Soldering and brazing Non-destructive tors for vehicle wiring looms, for electric arc brazing (TIG). Appropriate to them. Once brazed, the elements are DIN EN ISO 9001 (2008) of operators processes DIN EN 12799 (2000) computers and other electronic devices. filler materials are the high-tin bronze then assembled to make the heat ISO/TS 16949 (2009) DIN ISO 11745 (2011) DIN ISO 857-2 (2007) Component miniaturisation has placed rods, such as CuSn12P. In TIG brazing, exchanger and held in position by a jig. Destructive DIN EN 13585 (2012) increasingly tough demands on the the arc burns above a sharp-tipped Brazing paste is then applied again and DIN 8526 (1977)DIN EN 12797 DVS-Richtlinie 1183 (2004) quality of the strip tinning process. tungsten rod and the filler metal is fed the assembly is brazed in a conti- (2000) Meeting these quality specifications to the joint by hand. Well-executed nuous-feed furnace. There is no need for Defects / Imperfections requires the strip to be hot-dip tinned brazes have a visually appealing fluxes and subsequent rinsing proce- DIN EN ISO 18279 (2004) with non-corrosive, no-clean fluxes (see appearance [33]. dures [40] [41]. DIN 65170 (2009) table 15), which have to be carefully selected for the particular strip tinning

Table 36 - Summary of a number of important quality requirements 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]. 6.1. Hot-air solder levelling of ensure uniform reproducible results, solder printed circuit boards analyses should be conducted at regular 6.3. Fabricating heat exchangers Hot-air solder levelling (also: hot-air intervals. These analyses are generally from copper Figure 29 – Heat exchange tube [33] levelling – HAL) is used to coat exposed carried out free-of-charge by the solder Thanks to their good thermal conductiv- copper surfaces on a PCB with solder. To supplier [39]. ity and their high mechanical stability, make sure that the copper is wettable, it is heat exchangers made from copper/ Figure 30 – Compact high-performance [12] crucial that all dirt or tarnish is removed brass are commonly used for air-condi- from the PCB before HAL is performed. HAL process tioning systems in utility vehicles, for 6.4. Manufacture of compact After pre-cleaning, the flux is applied at radiators in construction machinery, or high-performance radiators the fluxing station. To restrict flux ∙ Fluxed PCB is dipped into a bath of hot solder for industrial cooling equipment. They from copper contamination in the HAL system, the ∙ Board withdrawn after a short period are manufactured in four steps. The The CuproBraze® process is used to amount of flux applied should kept to the vertical ∙ Excess solder is blown off by jets of hot air (‘hot-air knives’) initial stage involves machine-tinning manufacture compact high-performance minimum needed. In semi- and fully ∙ Result: some plated-through holes missed and non-uniform solder brass strip by hot-dipping in a tinning heat exchangers from copper and automated systems, the solder application thickness on the PCB, horizontal HAL method is therefore preferred bath and then drawing into tubes. The non-ferrous metals. The compact highly process can be carried out with the PCB tubes are then brazed with copper fins efficient design of these heat exchan- oriented vertically or horizontally (see Wave tinning Roller tinning in a furnace. Dip brazing is then used to gers makes them particularly well suited table 37). The horizontal process can be join the tubes to the tube sheet. Finally, for applications in the automotive and further classified into wave tinning ∙ PCB travels at constant speed ∙ PCB is accelerated after the water tank is manually brazed to the aviation industries, but also for coolers, systems, in which the solder is applied over the entire length of the passing through the fluxing zone tube sheet. Non-corrosive or no-clean condensers or evaporators in the when the PCB passes through a solder HAL machine ∙ PCB guided through up to fluxes are preferred for all steps of the refrigeration and electrical engineering wave bath, and roller tinning systems, in PCB is pulled though a solder three pairs of rollers production process. To achieve the best sectors. One of the advantages of horizontal ∙ which the PCB passes through a set of wave bath ∙ Excess solder blown off possible brazing results, the fluxes are radiators made from copper or copper pinch rollers [39]. ∙ Excess solder removed by selected for the particular brazing alloys over those made from aluminium hot-air knives operation. Corrosive fluxes are only used is that they prevent biofouling and thus If lead solders are used in the HAL process, ∙ Contact time with molten in exceptional circumstances as they eliminate the bad odours that would the choice of solder is critical, as solders solder longer than in roller require additional rinsing operations that otherwise be generated by fungus and with a copper content of more than 0.3 % tinning drive up process costs [24]. bacteria in the cooling channels. In the will result in uneven soldered surfaces. To

Table 37 - Process steps in vertical and horizontal HAL systems

48 | KUPFERINSTITUT.DE KUPFERINSTITUT.DE | 49 7. Terminology 8. Appendix The tables below present a selection of standards and guidelines relating to soldering and brazing

Standard Title / (Year of publication)

Cooling time Holding time Design suitability for soldering/brazing DIN 8514 Brazeability, solderability (DIN 8514:2006-05) 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 General Welding and allied processes – Vocabulary – Part 2: Soldering and brazing processes DIN ISO 857-2 ambient temperature [10]. manufacturing process [2]. and related terms (ISO 857-2:2005) Capillary attraction Graphical Representation of Welded, Soldered and Brazed Joints – Concepts and Terms for Heating time Force, caused by surface tension, which Closed joint DIN 1912-4 Time during which the soldering/brazing draws the molten filler metal into the gap Joint in which the gap is filled principally Soldered and Brazed Joints and Seams (DIN 1912:1981) temperature is reached. It includes the between the components being joined, even by capillary action with filler metal, i.e. Welding and allied processes - Symbolic representation on drawings - Welded joints Engineering desig DIN EN ISO 2553 equalising (preheating) time and can also against the force of gravity [10]. either a butt joint or a lap joint between (ISO 2553:2013); German version EN ISO 2553:2013 include other times, e.g. the degassing parallel faces of the components to be time [10]. Liquidus temperature soldered or brazed [10]. Aerospace – Brazed and high-temperature brazed components – DIN 65169 Temperature above which a material is Directions for design (DIN 65169:1986) Wetting completely liquid. Soldering or brazing temperature Processes / Spreading and adhesion of a thin continuous Temperature at the joint where the filler DIN EN 14324 Brazing – Guidance on the application of brazed joints (German version EN 14324:2004) Manufacturing 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 Copper and copper alloys – Compendium of compositions and products DIN CEN/TS 13388 produced by soldering or brazing so as to there is sufficient material flow [10]. (DIN CEN/TS 13388:2013 Diffusion zone / Transition zone meet the requirements of its intended use [2]. Filler metals for soft soldering, brazing and brazewelding– Designation Layers formed during soldering or brazing Soldering or brazing time DIN EN ISO 3677 with a chemical composition that is different Material suitability for soldering/brazing Time period for the soldering or brazing (ISO 3677:1992; German version EN ISO 3677:1995 from that of the parent material(s) and that Property of a material that is influenced by cycle [10]. DIN EN ISO 17672 Brazing – Filler metals (ISO 17672:2010; German version EN ISO 17672:2010 of the solder or braze metal [10]. the manufacturing process and, to a lesser extent, by its design [2]. Filler material DIN 1707-100 Soft solder alloys – Chemical composition and forms (DIN 1707-100:2011-09) Equalising temperature Added metal required for soldered or brazed Parent materials / Soft solder alloys – Chemical compositions and forms (ISO 9453:2014; Temperature at which the components being Solder metal or braze metal joints, which can be in the form of wire, Solders and filler DIN EN ISO 9453 joined are held so that they are uniformly Metal formed by the soldering or brazing inserts, powder, pastes, etc [10]. metals / Fluxes German version EN ISO 9453:2014) heated through [10]. process [10]. Brazing – Fluxes for brazing – Classification and technical delivery conditions Soldering or brazing paste DIN EN 1045 (German version EN 1045:1997) 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 Soft soldering fluxes – Classification and requirements – Part 1: Classification, DIN EN 29454-1 soldered or brazed are held at the equalising/ material is used that has a lower liquidus used, for example, in reflow soldering; labelling and packaging (ISO 9454-1:1990; German version EN 29454-1:1993) preheating temperature [10]. temperature than the solidus temperature brazing pastes are used, for example, in the Soft soldering fluxes – Classification and requirements – of the parent material(s), which wets the brazing of pipes made of copper or DIN EN ISO 9454-2 De-wetting surfaces of the heated parent material(s) galvanised steel. Part 2: Performance requirements (ISO 9454-2:1998; German version EN ISO 9454-2:2000) Separation of solid filler material which, and which, during or after heating, is drawn Brazing – Qualification test of brazers and brazing operators (ISO 13585:2012; although it had spread over the surfaces of into (or, if pre-placed, is retained in) the Solidus temperature DIN EN ISO 13585 German version EN ISO 13585:2012) 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 DIN EN 13134 Brazing – Procedure approval (German version EN 13134:2000) cleaning or fluxing [10]. Brazing for aerospace applications – Qualification test for brazers and brazing operators – Manufacturing suitability for Parent material affected by the soldering/ DIN ISO 11745 Soldered or brazed assembly soldering/brazing brazing process Brazing of metallic components (ISO 11745:2010; DIN ISO 11745:2011-01) Assembly formed by soldering or brazing Property of the manufacturing process that Material with properties different from those DIN EN 12797 Brazing – Destructive tests of brazed joints (German version EN 12797:2000) 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]. DIN 8526 Testing of soldering joints – Gap soldered joints, shear test, creep shear test (1977) Total time Test procedures Period which includes the heating time, the Soldering or brazing seam Heat-affected zone DIN EN 12799 Brazing – Non-destructive examination of brazed joints (German version EN 12799:2000) holding time and the cooling time [10]. Region of the joint comprising the solder/ Zone of parent materials affected by the Brazing – Imperfections in brazed joints (ISO 18279:2003; DIN EN ISO 18279 braze material and the diffusion/transition soldering/brazing process [10]. German version EN ISO 18279:2003) (2004) Parent material zones [10]. Material being brazed/soldered [10]. Effective temperature range Aerospace series – Brazed and high-temperature brazed metallic components – DIN 65170 Temperature range within which a flux or a Technical specifications; Text in German and English (2009) protective atmosphere is effective [10]. 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

50 | KUPFERINSTITUT.DE 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’ Temperature in acc. Liability Insurance Association] (04/2001) with DIN Process Filler materials Soldering / brazing method Example applications Löten in der Hausinstallation – Kupfer – Anforderungen an Betrieb und Personal ISO 857-2 (2007) Richtlinie [Technical guidelines: Soldering/ brazing in domestic installation work – Copper – Requirements to be met DVS 1903-1 by companies and their employees] (10/2002) Manufacture of condensers, Soft solders mostly Hot-iron soldering, cooling units and metal tin-based; commonly used in Löten in der Hausinstallation – Kupfer – Rohre und Fittings – Lötverfahren – Befund von Lötnähten ≤ 450 °C Soldering wave soldering, vessels; Electronics; Richtlinie combination with a flux: [Technical guidelines: Soldering/brazing in domestic installation work – Copper – Pipes and fittings – Soldering/brazing dip soldering Fabrication of PCBs; DVS 1903-2 joint strength is relatively low procedures – Inspecting soldered/brazed joints] (10/2002) Tinning Merkblatt Lichtbogenlöten – Grundlagen, Verfahren, Anforderungen an Anlagentechnik DVS 0938-1 [Technical leaflet: Electric arc brazing – Principles, methods and technical requirements] (08/2012) Refrigeration and air-conditioning; Merkblatt Lichtbogenlöten – Anwendungshinweise Typically used with a flux; DVS 0938-2 [Technical leaflet: Electric arc brazing – Application notes] (05/2005) Gas and water installations; suitable brazing filler Mechanical construction Merkblatt Hartlöten mit der Flamme metals (BFMs) are: of small-scale and DVS 2602 [Technical leaflet: Torch brazing] (04/2011) silver-based BFMs, brass Torch brazing, large-scale equipment; BFMs, copper alloy BFMs; induction brazing, > 450 °C Brazing Plumbing and heating Merkblatt Öfen für das Hart- und Hochtemperaturlöten unter Vakuum copper and copper alloys can electric resistance brazing, installations; Cooling DVS 2604 [Technical leaflet: Furnaces for brazing and high-temperature brazing under vacuum] (02/2008) be brazed in air without a furnace brazing systems; Heat exchangers; flux using phosphorus- Automotive and aviation Merkblatt Hinweise auf mögliche Oberflächenvorbereitungen für das flussmittelfreie Hart- und Hochtemperaturlöten containing BFMs; DVS 2606 [Technical leaflet: Information on surface preparation methods for flux-free brazing and high-temperature brazing] (12/2000) construction; high-strength joints Power engineering; Electrical Merkblatt Prozesskontrolle beim Hochtemperaturlöten engineering / electronics DVS 2607 [Technical leaflet: Process control during high-temperature brazing] (02/2008)

Merkblatt Reparatur von Hochtemperaturlötverbindungen Table 40 - Examples of soldering and brazing applications 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 KUPFERINSTITUT.DE | 53 Solder or brazing Advantages Disadvantages filler metal Parent Solder / Brazing filler metal (BFM) material ∙ low creep resistance ∙ allotropic transformation of tin at low Silver- Copper- ∙ good engineering properties temperatures (risk of tin pest) Tin-lead Silver-alloy copper- Copper-zinc Copper-nickel Copper alloy Tin-lead solders Lead solders phosphorus ∙ good plasticity ∙ risk of low-temperature embrittlement solders BFMs BFMs BFMs BFMs BFMs ∙ enhanced corrosion under damp or BFMs tropical conditions Aluminium X X ∙ high plasticity alloys ∙ poor resistance to corrosion ∙ good processability Soft solders Lead solders ∙ toxicity concerns (harmful to health and ∙ better thermal stability than tin-lead solders Beryllium X the environment) ∙ good low-temperature stability Gold X ∙ longer soldering times – X X ∙ slower surface-wetting rate Lead-free solders ∙ recyclable ∙ elevated operating temperatures Grey cast iron – X ∙ risk of metal whiskering Malleable ∙ Tip corrosion on hot-iron soldering irons – X X iron ∙ good thermal conductivity X X ∙ good electrical conductivity ∙ high plasticity Copper X X X X X ∙ high strength Copper alloys X X X X X Silver alloy BFMs ∙ good corrosion resistance ∙ high purchase price ∙ good wettability Brass X X ∙ oxides exhibit low strength/stability ∙ good buffer between materials with Molybdenum X differing thermal expansion coefficients Nickel X X X X X X ∙ very low viscosity ∙ risk of liquation Copper- ∙ low brazing temperature Nickel alloys X X X X ∙ Risk of increased porosity through phosphorus BFMs ∙ self-flowing Unalloyed phase separatio X X – X X X ∙ good plasticity steel ∙ elatively low melting temperature, which is Brazing ∙ Low strength at high temperatures compared Alloyed steel X X – X X X Silver-copper-palla- useful for parent materials that are susceptible filler metals with other palladium-containing filler metals High- dium BFMs to grain coarsening at elevated temperatures X – X ∙ high purchase price strength steel ∙ good wetting and flow properties

Corrosion- ∙ plasticity decreases as zinc content rises X – X (–) resistant steel ∙ good plasticity ∙ zinc vaporises at elevated brazing Copper-zinc BFMs ∙ high strength temperatures leading to porous joints Creep- – X ∙ high thermal stability ∙ not suitable for brazing in a protective resisting steel gas atmosphere or in a vacuum Titanium X ∙ good heat resistance Copper-nickel BFMs Tungsten X ∙ good creep-resistance

Zirconium X ∙ Lowest vapour pressure of all brazing ∙ risk of gas entrapment and solidification filler metals Copper BFMs cracking with oxygen-containing coppers ∙ good viscosity x common combination; – unsuitable combination and an oxidising atmosphere ∙ good flow behaviour Table 41 - Matrix for selecting commonly used combinations of parent metals and solders or brazing filler metals

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

54 | KUPFERINSTITUT.DE KUPFERINSTITUT.DE | 55 Regulation / Directive / Hazardous substance Notes References [15] H. Bell, Reflowlöten, Bad Saulgau: [29] Merkblatt DVS 2602 - Hartlöten mit der Technical rules [1] D. e. R. Muhs, Maschinenelemente. Eugen G. Leuze Verlag, 2005. Flamme, 2011. Normung, Berechnung, Gestaltung, RoHS Directive 2011/65/EU – since 2006 Lead Frequently contained in solders Wiesbaden: Vieweg+Teubner GWV [16] W. Müller und J.-U. Müller, Löttechnik. [30] Günther-Köhler-Institut für Fügetechnik (earlier Directive: 2002/95/EG) Fachverlag, 2009. Leitfaden für die Praxis. Band 127., und Werkstoffprüfung GmbH, Jena, 2012. since 2009 TRGS 528 Solder fumes Düsseldorf: DVS-Verlag GmbH, 1995. [2] DIN 8514 - Lötbarkeit, 2006. [31] H. Bell; Rehm Thermal Systems GmbH, since 2006 TRGS 900 Workplace exposure limits [17] Deutsches Kupferinstitut Berufsverband „Reflowlöten,“ Blaubeuren, 2012. [3] K. Wittke und U. Füssel, Kombinierte e. V., „Niedriglegierte Kupferwerkstoffe - ∙ Boric acid Regulation (EC) No. 1272/2008 Fügeverbindungen, Berlin: Eigenschaften, Verarbeitung, [32] „Lötverfahren,“ AG & Co. KG, ∙ Boron trioxide (‘CLP Regulation’); 67/548/EEC Springer-Verlag, 1996. Verwendung,“ 2012. [Online]. Available: http://www.technicalma- since 2012 ∙ Borax (sodium borate, anhydrate) Frequently contained in fluxes (30th/31st DVS technical leaflet terials.umicore.com/de/bt/brazingCenter/ ∙ Borax decahydrate 2617 [4] H. J. Fahrenwaldt, Praxiswissen Schweiß- [18] Wieland-Werke AG, show_de_V_03_Loetverfahren.pdf. [Zugriff ∙ Borax pentahydrate technik. Werkstoffe, Prozesse, Fertigung. Schliffbild Rohr-Fittings, 2012. am 25 09 2012]. Brazing fillers that contain a 4. Auflage, Wiesbaden: Vieweg+Teubner Commission Regulation (EU) cadmium concentration GWV Fachverlag, 2011. [19] VG 81245-3 - Nichteisen-Schwermetalle; [33] Berkenhoff GmbH, 2013. since 2011 Cadmium 494/2011 greater than 0.01 % by weight are Schweißzusätze und Hartlote; Auswahl, 1991. [5] H. J. Fahrenwaldt, Praxiswissen Schweiß- [34] Merkblatt DVS 0938-1 - Lichtbogenlöten Table 43 – Hazardous substances prohibited 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 Conversion tables [6] K.-J. Matthes, Fügetechnik. Überblick, Hinweise auf mögliche Oberflächen- Anwendungshinweise, 2005. Löten, Kleben, Fügen durch Umformen, vorbereitungen für das flußmittelfreie DIN EN 29454-1 DIN 8511 Leipzig: Carl-Hanser-Verlag, 2003. Hart- und Hochtemperaturlöten, 2000. [36] U. Berger und R. Mainhardt, Sn50Pb49Cu1 L-Sn50PbCu „Welding Journal,“ 2009. (162) 1.1.1 F-SW31 [7] M. Türpe, Löttechnik. Vorlesung Löten, TU [22] H. Kleinert, Klebtechnik, Lehrmaterialien Sn50Pb32Cd18 1.1.2 F-SW26 Dresden, 2008. der Fakultät Machinenwesen, Professur [37] E. Schmid, „Proceedings 9. Int. SnPb32Cd18 (151) Fügetechnik und Montage, 2010 Aachender Schweißtechnik Kolloquium 1.1.3 F-SW27 [8] DVS Fachgruppe 3.3, Fügetechnik „Fügen im Fahrzeugbau“,“ 2004. Sn96Ag4 L-SnAg5 F-SW32 Schweißtechnik, Düsseldorf: DVS Media [23] DIN EN 29454-1 - Flussmittel zum (701) 1.2.2 F-SW28 GmbH, 2012. Weichlöten, 1994. [38] Petrunin, Handbuch Löttechnik, Moskau: Sn97Ag3 Verlag Technik GmbH Berlin, 1984. L-SnAg5 (702) 1.2.3 F-SW33 [9] D. Schnee, Umicore AG & Co. KG, [24] A. Ament; Lötmittel Techno Service Sn95Sb5 2.1.1 F-SW24 Businessline BrazTec, Grundlagen des Lötens, GmbH & Co.KG, 2012. [39] VDE/VDI Schulungsblätter für die L-Sn95 2010. Leiterplattenfertiung, 1999. (201) 2.1.3 [25] DIN EN 1045 - Flussmittel zum Sn97Cu3 L-SnCu3 2.2.3 [10] DIN ISO 857-2 - Schweißen und Hartlöten, 1997. [40] L. Tikana und A. Klassert, „Kupfer-Kühler (402) 2.1.2 F-SW25 verwandte Prozesse - Teil 2: Weichlöten, für Leistungsstarke Motoren,“ Metall, Bd. 62. Pb98Ag2 Hartlöten und verwandte Begriffe, 2007. [26] DVS Merkblatt 2617 - Neueinstufung Jahrgang, 10/2008. L-PbAg3 (181) 2.2.2 und Etikettierungsvorschriften für Flussmit- 2.1.3 F-SW23 [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]. Table 44 - Soft solders 2.2.1 2.2.3 [12] Umicore AG & Co.KG, Businessline [27] A. Rahn, Bleifrei löten. Lötprofile für Bilder Deckblatt: 2.2.3 F-SW34 BrazeTec, 2013. bleifreie Lote, Legierungen, Parameter, www.iew.eu Prozesse. Band 2., Bad Saulgau: Eugen G. 3.1.1 F-SW12 [13] W. Schatt und H. Worch, Werkstoffwis- Leuze Verlag, 2005. F-SW21 senschaft, Weinheim: Wiley-VCH Verlag GmbH & Co. KGaA, 2003. [28] „Flammlöten mit der Acetylenflamme,“ 3.1.2 F-SW22 Linde AG, [Online]. Available: http://www. 3.2.1 F-SW13 [14] ASM International, linde-gas.de/international//lg/de/ 3.2.2 F-SW11 „Binary Alloy Phase Diagrams“. like35lgde.nsf/repositorybyalias/praktiker- tipps_flamml%F6ten/$file/flammloeten.pdf. Table 45 – Flux designations [Zugriff am 20 09 2012].

56 | KUPFERINSTITUT.DE KUPFERINSTITUT.DE | 57 Index of figures Index of tables

Figure 1 Definition of solderability/brazeability (see [2]) 5 Table 1 Relationship between contact angle and Table 31 Advantages and disadvantages of electron Figure 2 Example of a brazed copper-silver joint 6 degree of wetting [7] 7 beam brazing 45 Figure 3 Wetting of a metallic surface with a Table 2 Comparison of the physical and mechanical Table 32 Overview of important filler metals used liquid filler metal [7] 7 properties of copper, important copper alloys in laser and electric arc brazing 45 Figure 4 Schematic diagram of a soldered/brazed joint [10] 8 and unalloyed steel 9 Table 33 Advantages and disadvantages of electron Figure 5 Filler metal preforms [11] 10 Table 3 Soft solders for copper and copper alloys as arc brazing 46 Figure 6 Silver-copper phase diagram (from [14]) 10 classified in the DIN EN ISO 9453 (2014) Table 34 Examples of a laser brazed seam [33] 46 Figure 7 Torch brazing a copper tube joint [12] 13 and DIN 1707-100 (2011) standards 12 Table 35 Advantages and disadvantages of laser Figure 8 Lead frames [17] 19 Table 4 Selection of copper-based filler metals for beam brazing 46 Figure 9 Metallographic longitudinal section through a brazing copper and copper alloys 14 Table 36 Summary of a number of important brazed joint between a pipe and a pipe fitting Table 5 Selection of silver alloy filler metals containing more quality requirements 48 (filler alloy: Ag-CuP) [18] 23 than 20 % silver for brazing copper and copper alloys 15 Table 37 Process steps in vertical and horizontal Figure 10 Difference between ‘narrow-gap’ Table 6 Selected types of copper 16 HAL systems 48 soldering/brazing and weld brazing 26 Table 7 Soft solders suitable for soldering copper 17 Table 38 Selected standards covering soldering and Figure 11 Capillary pressure as a function of gap width [12] 27 Table 8 Filler metals suitable for brazing copper 18 brazing processes 51 Figure 12 Capillary pressure as a function of Table 9 Difference between standard (narrow-gap) Table 39 Regulations, technical guidelines and leaflets gap geometry [12] 27 soldering/brazing and braze welding 26 covering soldering and brazing processes 52 Figure 13 Characteristic temperatures and times during Table10 Distinction between the terms ‘assembly gap’, Table 40 Examples of soldering and brazing applications 53 soldering/brazing [20] 29 ‘soldering/brazing gap’ and ‘soldering/brazing seam ’ 26 Table 41 Matrix for selecting commonly used Figure 14 Schematic cross-section of the surface of an Table 11 Geometric configurations of common combinations of parent metals and solders or engineering metal [22] 32 soldered/brazed joints [6] 28 brazing filler metals 54 Figure 15 Example of hot-iron soldering on a Table 12 Cleaning procedures for copper and copper alloys [21] 30 Table 42 Summary of some advantages and printed-circuit board (based on [10]) 38 Table 13 Recommended pickling solutions for copper and disadvantages of selected solders/brazing Figure 16 Dip soldering/brazing (based on [10]) 38 copper alloys that will undergo fluxless brazing [21] 31 filler metals 55 Figure 17 Wave soldering (based on [10]) 39 Table 14 Solder fluxes (classified according to Table 43 Hazardous substances 56 Figure 18 Torch soldering (based on [10]) 40 DIN EN 29454-1 (1994) (1994) [23] 33 Table 44 Soft solders 56 Figure 19 Vacuum soldering/brazing furnace [30] 41 Table 15 Chemical function of solder fluxes [24] 33 Table 45 Flux designations 56 Figure 20 Schematic diagram of a continuous-feed furnace Table16 Brazing fluxes (classified according to with an inert gas atmosphere (based on [6]) 41 DIN EN 1045 (1997) [25] 34 Figure 21 Surface-mounted component shown before the Table 17 Concentration levels for hazard solder in the solder paste melts [31] 42 classification purposes [26] 35 Figure 22 Schematic diagram of a convection reflow oven [31] 43 Table 18 Protective atmospheres used in soldering/ Figure 23 Direct resistance soldering (based on [10]) 43 brazing operations 35 Figure 24 Induction brazing [10] 44 Table 19 Different ways of introducing the filler metal Figure 25 Electron beam brazing [10] 45 to the soldering or brazing joint (based on [10]) 36 Figure 26 Fuel tank from a Honda VT 1300CX with Table 20 Classification of soldering/brazing processes CuAl8 brazing filler metal [33] 45 (based on [10]) 37 Figure 27 Electric arc brazing (MIG) (based on [6]) 46 Table 21 Advantages and disadvantages of Figure 28 Laser beam brazing (based on [6]) 46 hot-iron soldering 38 Figure 29 Heat exchange tube [33] 49 Table 22 Advantages and disadvantages of dip Figure 30 Compact high-performance radiator [12] 49 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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