Special Aspects of the Metallographic Preparation of Electronic And

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Special aspects of the metallographic preparation of electronic and microelectronic devices Katja Reiter, Mario Reiter, Each individual step in the prepara- ten made to achieve a good prepa- Thomas Ahrens tion from cutting, through grinding ration result by, for example, polis- Fraunhofer Institut für to the final polishing stage is of sig- hing for longer times. However, Siliziumtechnologie, nificance. Mistakes made in the even if a scratch-free and appar- Modulintegration, first stages of preparation can only ently well-polished surface has been D-25524 Itzehoe, Germany be corrected during subsequent achieved, this is often at the ex- steps with considerable difficulty or pense of edge retention and sample Contents not at all. For each step, the rate of planeness. The objective is always 1. The problem material removal and the deforma- to prepare a flat sample exhibiting 2. Typical materials and their uses tion layer which remains are impor- a high degree of edge retention. 3. Preparation and microstructure tant factors. development The polishing parameters used 2. Typical materials and 4. Applications (grinding surface, type of abrasive, their uses 4.1 Ceramic composites grain size, lubricant) must be care- The materials most commonly used 4.2 Circuit boards fully selected on the basis of the in packaging and interconnection 4.3 Silicon and glass diodes physical properties. The general technology (electronic packaging) 4.4 Capacitors and resistors rules for the preparation of solid are listed in Table 1. 4.5 Gold wire bonds: preparation of materials are that soft and medium- Electronic components are most a transistor hard materials should be plane commonly constructed from combi- 5. Artefacts ground using SiC papers, whereas nations of the following materials: 6. References hard materials require resin-bonded alumina, fritted-glass-filled or metal-bonded diamond grinding duromers, tin-lead solder, circuit Preface discs. In the composite materials boards (epoxy-fibreglass sheet) and In Structure 32, we reported on the described here, one is dealing with copper. techniques used for the analysis of both extremely hard components, microstructures and materials in e.g. ceramics such as Al2O3, and Each of these materials has a differ- the electronics packaging industry. very soft materials, e.g. tin-lead sol- ent characteristic property. The

In this article, which can be re- der. In such cases, preparation must Al2O3 ceramic is extremely hard and garded as a continuation of our ear- seek a compromise. brittle, the tin-lead solder and the lier article, we are concerned with copper are very soft. The soft solder the metallographic preparation of If only grinding papers are used to microstructures are easily ‘washed individual samples and the possible grind hard materials, then edge out’ during polishing, and the cop- sources of erroneous results that rounding and relief formation set in per tends to “smear”. The epoxy one should be aware of. Recom- at an early stage. Plane grinding resin matrix from which the circuit mended processing techniques should be performed using the abra- board is made has a similar hard- which avoid preparation artefacts sive most suited to the sample ma- ness to that of copper. However, the will also be presented. terial. The finest grain size should 1. The problem be chosen which Material Common applications Universal Electronic and microelectronic de- will still allow the in mounting and hardness vices are complex material compos- sample to be connection technology [HU] ites. Imaging and analysis of the ground flat and Al2O3 ceramic carriers (hybrid technology), various material microstructures, smooth in an ac- body of components 17000 layered structures and interfaces ceptable time. Silicon semiconductors, transistors, ICs 9300 are necessary if the quality of prod- The removal rate NiP resist layer, metallization 4000 ucts is to be assessed. The dimen- when using SiC sions of the individual features wet grinding pap- Kovar (FeNiCo) lead frames, circuit board core 1900 range from fractions of a micron ers on soft mate- Invar (FeNi42) lead frames, lead wires, 1800 (micrometre) to several centimetres. rials is consider- housing covers Due to the close packing of the vari- able, but these Aluminium housing, heat sinks, capacitor foils 1300 ous materials within a small vol- grinding papers Copper-silver solder solder (brazing) 1100 ume, microstructure analysis is cause a high Gold surface finishing layers faced with the problem of simulta- degree of surface (connectors, solder, adhesive and neously imaging different materials deformation. In wire bond contacts) 500 which have very different proper- such cases, an Tin-silver solder soft solder 300 ties. Sample preparation for micro- attempt is still of- structure investigations therefore Copper metallization on circuit boards, 300 lead frames involves the simultaneous processing of hard, often brittle, materials Table 1: Epoxy-fibreglass sheet circuit board material 280 Materials used in and soft materials exhibiting plastic electronic mounting and Tin-lead solder soft solder 230 deformation. connection technology

12 glass fibres break-out easily on orientation of the features to be problem with epoxy is its modest grinding. In the next section, two imaged and is often marked on the hardness (approx. 280 HU) com- preparation methods for developing assembly plan. If the defect site has pared to ceramics (17,000 HU) microstructure are introduced. This been located then this will deter- which means that long polishing is followed by a description of appli- mine the grinding plane. times will inevitably lead to edge cations of these techniques to vari- rounding in the ceramic parts of the ous combinations of materials. II Sampling and mounting sample. Another side effect is a This stage of the preparation was comparatively long curing time of 3. Preparation and micro- treated in detail in Part 1 (see about twelve hours. structure development Structure 32). It is worth noting Metallographic preparation can be once more that the sample must re- III Grinding and polishing divided into the following steps: main wholly undamaged after sec- The two grinding and polishing I Optical inspection tioning and that when mounting, no techniques particularly well suited II Sampling and mounting heat must be transferred to the to the preparation of composite ma- III Grinding and polishing sample as even small quantities of terials are listed in Table 2. IV Assessment of microstructure heat can cause changes in the by light microscopy microstructure. Components In preparation method 1, the sam- mounted on a circuit board are best ple is fine ground in several stages I Optical inspection sectioned with a simple fret saw, using graded SiC papers down to a The initial stage involves the mac- whereas ceramic composites will re- 1200 grit size and is then polished roscopic visual inspection of the quire using a diamond cutting using diamond suspension on silk structure of the assembly. This al- blade. If the test piece has aged, it cloths. In method 2, the sample is lows critical sites to be located and is advisable to impregnate the sam- ground plane using SiC paper with the locations of both obvious and ple before cutting. This should al- a 180 grit size, fine ground on a possible defects to be marked. Typi- ways be performed under vacuum to Struers MD-Largo disc with dia- cal sites include: poor solder joints, prevent cavities remaining below mond suspension as abrasive, and cracks in components, or defects in the component. finally polished using diamond sus- the circuit board material. These pension on silk cloths. In both faults are then investigated more Because of its low curing tempera- methods, final polishing with an closely using other techniques. Sub- ture and its low viscosity, epoxy OP-S suspension is performed. surface defects such as electrical resin is particularly suitable for discontinuities or short circuits can mounting electronic material com- Which method is applied depends often be analysed non-destructively posites. A further advantage is the upon the material combinations by ultrasound microscopy or x-ray transparency of the embedding me- present. Polycrystalline diamond radiography. The orientation of the dium which helps when performing suspensions are used. The rate of grinding plane will depend upon the the various preparation steps. One stock removal depends upon the following factors: the mixing ratio of diamond Preparation method 1 Grinding Polishing grains to solvent, the degree of wear of the grinding Step1-45678 paper or polishing cloth, and Grinding surface Grinding paper Plan-O-Grip DP-Dur DP- Dur OP-Chem the cleanliness of the cloths used. Abrasive SiC diamond diamond diamond OP-S The type of lubricant employed also Grit/grain size # 180-1200 6 µm 6 µm 1 µm 0.25 µm affects the quality of the prepara- Lubricant Water Blue Red Red tion. Alcohol-based lubricants in- Rotation speed [rpm] 300 250 250 150 150 crease the removal rate but also result in a greater deformation depth. Time [min] until plane 10-20 5-10 2 0.5 With oil-based lubricants, removal rates and deformation depths are Preparation method 2 Grinding Polishing both lower. Step 1 2 3 4 5 It is therefore advisable to use an Grinding surface Grinding paper MD-Largo DP-Dur DP- Dur OP-Chem alcohol-based lubricant for rough polishing and an oil-containing Abrasive SiC diamond diamond diamond OP-S lubricant for the final polishing Grit/grain size # 180 9 µm 6 µm 1 µm 0.25 µm stages. Lubricant Water Blue Red Red Grinding quality is also affected sig- nificantly by the amount of abrasive Rotation speed [rpm] 300 300 250 150 150

Time [min] Until plane approx. 5 approx. 1 approx. 0.5 0.5 Table 2: Preparation methods 1 and 2

13 used. The polishing cloths should be Figure 1: Cross-section through kept rigorously clean and should a power module not be made too wet by applying too much abrasive or lubricant.

IV Assessment of microstructure by optical microscopy If steps I-III have been completed Preparation method 1 Preparation method 2 successfully, the microstructure can then be examined by optical or scanning electron microscopy. The following aspects are assessed: Inter-material bonding at interfaces Metallurgical reaction at interfaces or in the bulk (growth of inter-metallic phases) Size and distribution of defects such as voids, inclusions and flaws 2a: Surface ground using a series of 180, 500, 800 3a: Surface ground using a 180 grit SiC paper Geometrical shape and dimen- and 1200 grit SiC papers. The figure shows the sur- sions of the elements in the face after grinding with the 1200 grit SiC paper assembly (layer thicknesses, solder meniscus, curvature of wire bond loops, etc.)

The light-optical microscopy techniques used in these investigations include bright-field and dark-field illumination, differential interference contrast and polarisation inter- ferometry, the latter also being known as ‘optical contrasting’. The scanning electron microscopy meth- 2b: After polishing for approx. 5 min. on 3b: After fine grinding for approx. 5 min on a ods applied are secondary electron Plan-O-Grip with a 6µm diamond suspension MD-Largo disc with a 9µm diamond suspension and backscattered electron imaging and topographic contrast imaging. Each of these methods was treated in detail in Part 1 (see Structure 32).

4. Applications 4.1 Ceramic composites Results obtained from applying the two preparation methods 1 and 2 (see Table 2) to ceramic composites are compared. The specimen in this 2c: After polishing for approx. 5 min. on a 3c: After polishing for approx. 1 min. on a case was a power module assembly. DP-Dur cloth with a 6µm diamond suspension DP-Dur cloth with a 6µm diamond suspension The module comprises a silicon chip soldered onto a DCB substrate (di- rect copper bonding: copper/Al2O3 ceramic/copper) with an eutectic tin-silver solder (melting point: 221°C). To improve heat dissipation, the entire assembly (DCB + silicon

Figures 2a-2d, 3a-3d: Comparison of the results obtained after the different grinding and polishing procedures of the two preparation methods 2d: After polishing for approx. 5 min. on a 3d: After polishing for approx. 0.5 min. on a applied to a power module assembly DP-Dur cloth with a 1µm diamond suspension DP-Dur cloth with a 1µm diamond suspension

14 chip) is soldered onto a solid copper ple is ground in four stages and polycrystalline diamond suspension. heat sink. For this second solder then subsequently polished on silk Polishing follows the same steps as joint, a conventional tin-lead solder cloths using a polycrystalline dia- in method 1, though with much (melting at 183°C) is used. We are mond suspension of grain sizes shorter polishing times. Figures therefore dealing here with a so- 6 µm and 1 µm. A final OP-S polish 2a-d show the sample after the indi- called step solder technique. The is carried out on an OP-Chem cloth. vidual grinding or polishing steps of first solder joint has a higher melt- The OP-S suspension is suitable for method 1; Figures 3a-d refer to ing point and does therefore not relief polishing and visualization of preparation method 2. melt when the second joint is the inter-metallic phases of the soft formed. solder microstructure and it also re- Once the final polished state has In the following section, the indi- moves the smeared layers. been achieved (see Figures 2d and vidual steps in the preparation In preparation method 2, the sam- 3d), the materials and the solder methods mentioned above are de- ple is initially ground with a coarse microstructures are examined in described and optical microscopic im- grinding paper and then fine tail. Figures 4a-c and 5a-c present ages from each step are presented. ground on the new Struers MD- detailed images of the following in- In preparation method 1, the sam- Largo preparation disc using 9 µm terfaces: (a) Solder joint (SnAg) between the silicon chip and the copper Preparation method 1 Preparation method 2 metallization on the DCB Soldered joint (SnAg) between the silicon chip and the copper metallization on the DCB substrate substrate (b) Interface between the copper

and the Al2O3 ceramic of the DCB substrate (c) Soldered joint (SnPb) between the copper of the DCB substrate and the copper carrier.

The detailed images of the polished surfaces have a magnification of x500. The comparison of the two prepara- 4a: Solder microstructure rather blurred, 5a: Inter-metallic phases and solder Micro- tion methods shows clearly that a inter-metallic phases in different focal planes structure clearly distinguishable in one plane surface of better planeness is achieved by using method 2. At the Interface between the copper and the Al2O3 ceramic of the DCB substrate same level of magnification, both the copper/SnAg solder/silicon interface and the copper/SnPb solder boundary can be imaged equally well. This is not possible after preparation using method 1. In this case, the formation of steps and edge rounding on the ceramic are clearly discernible. By using the MD-Largo fine grinding disc, sample preparation is per- 4b: Ceramic and copper cannot be imaged in 5b: Interface between the ceramic and the copper formed more effectively and with the same plane metallization on the DCB substrate is clearly visible better results. Solder joint (SnPb) between the copper of the DCB substrate and the copper carrier The extreme differences in hardness between the various layers place very special demands upon any preparation method. To illus- trate this, Figure 6 depicts the universal hardness of the various layers which lie adjacent to one another in the prepared section. The figure shows that particular diffi- culties are to be expected when attempting to image the interface

4c: Unclear phase boundary and an indistinct 5c: Sharp image of the SnPb microstructure and Figures 4a-4c, 5a-5c: solder microstructure a clear image of the individual phases Detailed images of the polished surfaces

15 Figure 6: The hardness profile of the prepared section Universal hardness [HU] Universal hardness

Travel in mm Figures 7,8: Height profile of the two differently Preparation method 1 Preparation method 2 prepared power modules Height in mm Heigh in mm

Travel in mm Travel in mm 7: Height profile after preparation using method 1: 8: Height profile after preparation using method 2: max. height difference: 30µm max. height difference: 10µm between copper and ceramic and In preparation method 1, a four enced metallographer ends up with from the silicon semiconductor to stage grinding procedure utilising something resembling a pyramid the tin-silver solder. SiC papers is performed. Grinding rather than a plane specimen. But the ceramic causes severe wear on even with sufficient skill, it is not The height profile measured on the the papers. The larger the amount possible to produce a surface whose sample prepared by method 1 (Fig- of material that has to be removed, planeness matches that achievable ure 7) exhibits a shape similar to the harder it is to generate a plane with method 2. Even after grinding that of the hardness profile in Fig- surface. The extreme differences in with the finest grade SiC paper, ure 6. The maximum difference in hardness make it difficult to achieve some relief is still discernible. The height is 30 µm. Figure 8 shows the a uniform rate of removal. polishing times with the 6µm and distinct advantage of using method It is therefore not unusual that, 1µm diamond suspensions are ex- 2; the maximum difference in when attempting to grind these tended depending on the extent of height in this case is only 10 µm. composite materials, an inexperi- relief. The longer the polishing

16 9a: Electrically cycled Peltier element prepared with method 1. 9b: Detail from 9a). Fused region on the central column. Imaging method: polarisation contrast Imaging method: polarisation contrast Figures 10a-d provide additional examples. Here we are dealing with the metallographic preparation of a memory module with a ceramic body. Figure 10a shows the solder joint of a so-called J–lead (J-shaped component joining pin) on an FR4 circuit board.

4.2 Polymer/glass fibre composites (circuit boards) 10b: Solder joint between the body of the component and the casing lid (hermetic seal - area A) Sample preparation of circuit board materials is performed to help lo- cate defects in the substrate material that carries an electronic assembly. Circuit boards are manufac- tured from an epoxy resin / fibreglass composite sheet. The glass fibres are very brittle in contrast to the epoxy matrix. When the material is ground, the fibres very often break out. The objective of any grinding procedure is, therefore, to minimize the extent of fibre break- 10a: View of the soldered component 10c: Hard soldered joint between the body of the out and to remove any of the result- component and the connection lead (area B) Figures 10a-10d: Cross-section through a J-lead ing flaws during the polishing of a memory module with a ceramic casing, stage. Both preparation methods prepared using method 2 can be used in this case. When applying method 2, it is ad- times, the greater the degree to visable to grind the sample on SiC which the edges become rounded paper with a 500 grit size. After fine and ‘wash-out’ occurs in the soft sol- grinding on the MD-Largo disc, all der joints since the softer materials evidence of break-out should have are removed more rapidly than the been removed. All that is needed hard. subsequently is a short polish using MD-Largo is a fine grinding disc 6µm and 1µm diamond suspension. that has been developed by Struers If the break-out flaws are not com- pletely eliminated, it can prove dif- for the preparation of composite 10d: Soft soldered joint between the component materials with a soft matrix. The connection lead and the circuit board (area C) ficult to unambiguously identify cir- disc has a steel foil base with hexa- cuit board defects such as gon segments of a composite mate- delamination, resin shrinkage, etc. rial distributed over its surface. The Two further examples of the prepa- The copper layers on the circuit removal rate at negligible surface ration of ceramic composites are il- boards consist of the copper base deformation using a 9µm diamond lustrated in Figures 9a and 9b. The layer (copper laminate on the base suspension is so high that the pictures show an electrically cycled material) and the electrolytically grinding marks from the 180 grit Peltier element with a column that deposited copper (sometimes con- SiC paper can be removed in a mat- has fused as a result of thermal sisting of several layers). ter of minutes. stress. The Peltier element com-

All that is subsequently required in prises two copper-coated Al2O3 ce- The copper-plated through-holes are order to achieve an optimal surface ramic sheets (DCB substrate) and themselves made up of a nucleation quality is a short polish using 6µm P- and N-doped bismuth-telluride layer with electrolytically deposited and 1µm diamond suspension on columns which are soldered on to the copper on top. In order to examine silk cloths. DCB copper using bismuth solder. the structure of the copper layers, it

17 11: Defects within a multilayered structure

Figures 11, 12: Examples of the metallographic preparation of multilayer circuit boards

13: Glass diode soldered onto a multilayer circuit board and showing a crack in the glass body

Figures 11 and 12 show etched sections of circuit boards. In Figure 11 one can see the defec- tive internal structure of a multilayer board. A number of features are visible: Bud formation in the copper metallization layer (1) Two-point attachment of an internal annular ring from a laminate onto the through-hole metallization (2) Resin recession at the copper lined through-hole (3)

Figure 12 depicts an alternative internal wiring scheme. Instead of nu- merous structured laminates, lac- 12: Circuit board with lacquered copper wire as 14: Silicon chip with an aluminium wire bond. internal wiring. quered copper wires are used. fine grinding paper. The sample is is necessary to etch the copper. A 4.3 Silicon and glass diodes subsequently polished until any suitable etching solution consists of Silicon and glass are brittle materi- break out at the edges or any prepa- 6 parts of distilled water to 6 parts als. Thus, in order to be able to dis- ration cracks have been eliminated. of 25 % ammonia solution and 0.1 tinguish between ‘real’ cracks (i.e. The polishing procedure used is part of hydrogen peroxide. The sam- those present in the component in that described for preparation ples should be etched immediately its as-supplied state) and those ar- method 1. after polishing with OP-S. It is im- tefacts resulting from the prepara- Figure 13 shows a prepared SMD portant that the etching agent is tion procedures, very careful prepa- diode that is free from artefacts. made up freshly just before use. ration is necessary. These materials The glass body was cracked after should only be ground using very soldering. In Figure 14, a well-pol

Figures 15a-b, 16a-b, 17a-b: Close-ups of electronic components with images of the prepared sample 15a: Close-up of a capacitor 16a: Close-up of a resistor 17a: Close-up of a melf resistor

15b: SnPb solder microstructure of a capacitor. 16b: SnPb solder microstructure of a resistor. 17b: Melf resistor, laser soldered using a Imaging method: polarisation contrast Imaging method: polarisation contrast high-temperature soft solder. Imaging method: polarisation contrast

18 18c: Cross-section through the Au bond wire. Imaging method: light microscopy

Figures 18a-d: 18a: View of the transistor 18b: Radiographic image of the Preparation of a transistor transistor ished semiconductor silicon crystal Once both the defect and the posi- with an aluminium wire bond is de- tion of the bond wire have been lo- picted. calised, the epoxy-mounted sample can be prepared. As the bond wire is 18d: Cross-section through the 4.4 Capacitors and resistors exceptionally thin, one must grind Au bond wire. Imaging method: A typical capacitor dielectric mate- towards the bond very carefully us- scanning electron microscopy rial is barium titanate. Cracks can ing 1200 grit SiC paper. Subsequent appear during soldering or as a re- polishing utilises 6µm and 1µm dia- number of pictures of artefacts sult of mechanical stress. For this mond suspensions. The force ex- which can arise during sample reason, these materials require erted during polishing must not be preparation. Artefacts can occur as careful metallographic preparation. too high in order to prevent the gold a result of unequal rates of removal The capacitors should not be ground from smearing. After the 1µm when grinding a sample, or from ap- with a grinding paper whose grit polish, it is recommended that a plying too great a pressure during size is coarser than 800. Further final polish using an OP-A suspen- polishing, or from the use of incor- polishing can be carried out in the sion on an OP-Chem cloth is per- rect amounts of abrasives and lubri- manner described for either prepa- formed. cants. In the case of soldered joints ration method 1 or 2. Under a light microscope, cracks in which have been prepared for Resistor bodies are generally made the gold wire can only be suspected analysis some time previously, ap- from alumina ceramic and method 2 even at a magnification of x800. As parent cracks can arise along the is used for sample preparation the bond wire is bonded to the cop- grain boundaries in the solder after (alumina has a higher hardness per substrate chemical etching can some storage time. This is espe- than barium titanate). only be carried out with some diffi- cially true when the soldered joint culty and SEM imaging is the is subject to stress as a result of e.g. 4.5 Gold wire bond connections, method of choice. The electron mi- preparation of a transistor croscope image (18d) clearly shows Figures 19-24: Images of various artefacts The metallographic preparation of a crack at the foot of the bond. gold wire bonds is illustrated here 20: Circuit board ground with 500 grit SiC paper. Material removal is non-uniform.Grinding a with reference to a transistor with 5. Preparation artefacts as ceramic causes the SiC paper to wear rapidly. eight leads. One such transistor “bad examples” The surface becomes uneven which causes (18a) showed an electronic defect In this final section, we present a problems when polishing and preparation of a cross-sectional sample was used to determine the Figures 19a,b: Images of two differently cause of failure. prepared samples of SnPb solder 19a: Cleanly polished lead and tin-lead solder of a flip chip The connection between the bond pad on the silicon and the lead frame is realised using gold wire bond connectors. The wire bonds are only 25µm thick and their exact position is uncertain. The transistor is encapsulated within a fritted- glass-filled duromer using an injec- tion moulding technique. Defects associated with the bond wires can only be detected and localised initially with the aid of electrical measurements. Even after successfully locating the defect, the position of the bond wire or the connections remains unknown. Radiogra- phy is useful in this regard (see Figure 18b).

19b: Poorly polished lead and tin-lead solder, 21: Poorly polished the black specks are embedded grains of the circuit board showing polishing abrasive break-out of glass fibres

19 thermal cycling. For this reason, samples should be analysed and documented immediately after preparation. 22a: Well prepared sample. Detection of a crack in 22b: Crack and evidence of break-out in a glass a diode diode caused by grinding with too coarse a paper 6. References ‘Erfahrungen mit einer neuen Präparationsmethode bei Werk- stoffverbunden.’ Vortrag auf der 10. Internationalen Metallographie- tagung in Leoben und wird veröffentlicht im Sonderband 30 der Praktischen Metallographie., ‘[Expe- rience with a new method of prepar- ing composite materials’. Oral presentation at the 10th Interna- tional Metallography Meeting in Leoben. To be published in a special 23: Embedded diamond grains from the 24: Apparent cracking along the grain boundary edition of Praktische Metallographie diamond polish and copper sliver detached in a polished sample that was left for a long time (Vol. 30).], K. Reiter, T. Ahrens, during grinding before examination. Imaging method: differential FHG ISiT, Itzehoe, Germany. interference contrast microscopy.

‘Ein neues Konzept für metallo- Preparation Discs in the MD-Sys- structure and materials analysis in graphische Probenpräparation’, [‘A tem’, H-H.Cloeren, Struers GmbH, electronic mounting and connection new concept in metallographic sam- Willich, Germany and Michael technology], F. W. Wulff, American ple preparation’], James A. Nelson, Rückert, Struers A/S, Copenhagen, Fine Wire Ltd, Singapore, T. Ahrens, Buehler Ltd. Lake Bluff, Il, USA, in Denmark, in Structure 32. Fraunhofer ISIT, Itzehoe, Germany, Praktische Metallographie. ‘Gefüge- und Werkstoffanalyse für in Structure 32. ‘MD-Piano and MD-Largo, New die Aufbau- und Verbindungs- technik in der Elektronik’ [Micro-

Article Contest on Ceramics

The editorial board has selected the prize winning articles for the contest presented in Structure 31. Contributions were invited in the field of ceramics; the articles which the board found suitable have been printed in Structure 32, 33, 34 and the last one will be printed in Structure 35. We would like to thank all participants for their interesting contributions.

1st prize has been awarded to 2nd prize goes to and 3rd prize goes to

Ulrike Täffner and Richard E. Chinn, F. Jorge Lino, Veronika Carle, 2535 Del Rio CtSE, Albany, DEMEGI/SMPT, Faculdade de Max Planck Institut für Oregon, USA Engenharia da Universidade do Metallforschung, Stuttgart, Ger- for his article: Porto, Porto, Portugal many for their article: Preparation of Microstructures of for the article: Ceramography - an exciting area in Alumina Ceramics. Pull-out During Grinding of Ceram- materialography. ics Containing an Amorphous Phase. with the sub titles: Insight into ceramographic preparation Interpretation of microstructure in ceramic components.

Many congratulations to the winners!