Review of non-reactive and reactive wetting of liquids on surfaces.

A review of lead-free solders for electronics applications

After a brief presentation of thermodynamics and kinetics of non-reactive wetting, the recent results and theoretical developments concerning the reactive wetting of solids by liquid metals are reviewed. A section is devoted to illustrate and discuss the effect of interfacial reactions in removing the wetting barriers existing on many ceramic and metallic solids.

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Fundamental issues of reactive wetting by liquid metals

Preparation and characterization of nano-SiO2 reinforced gelatin-k-carrageenan biocomposites.

Surface and transport properties of Ag-Cu liquid alloys

Wetting in the Au–Sn System

Enhanced mechanical properties of polyurethane composite coatings through nanosilica addition

The application of a conformal coat has been considered as a mitigation strategy to prevent unintended shorting events induced by tin whisker formation in electronic products. While various conformal coatings have been shown to be effective at containing tin whiskers on treated coupons, the effectiveness of conformal coating on actual assembled hardware has not been adequately examined. In this study, the ability of six types of conformal coatings to contain tin whiskers was examined through their application to assembled gull-wing lead quad flat package test specimens. Nonuniform coverage of conformal coating on the gull-wing leads was found to be a primary concern. Quantitative image analysis using scanning electron microscopy in backscattered electron mode was developed to aid in quantifying coating coverage. The ability of applied coatings to contain tin whiskers was examined after specimens were subjected to sequential temperature cycling and elevated temperature/humidity conditions as well as exposure to corrosive gases. For all but one coating, tin whiskers were observed to escape areas of relatively thin coating. Parylene C coating was found to be the most effective coating in providing uniform coverage and thickness, and containing whiskers.

Evaluation of Effectiveness of Conformal Coatings as Tin Whisker Mitigation

Effects of curing conditions on structural evolution and mechanical properties of UV-curable polyurethane acrylate coatings

This paper describes the results of an intensive whisker formation study on Pb-free assemblies with different levels of cleanliness. Thirteen types of as-received surface-mount and pin-through-hole components were cleaned and intentionally contaminated with solutions containing chloride, sulfate, bromide, and nitrate. Then the parts were assembled on double-sided boards that were also cleaned or intentionally contaminated with three fluxes having different halide contents. The assemblies were subjected to high-temperature/highhumidity testing (85� C/85% RH). Periodic examination found that contamination triggered whisker formation on both exposed tin and solder fillets. Whisker occurrence and parameters depending on the type and level of contamination are discussed. Cross-sections were used to assess the metallurgical aspects of whisker formation and the microstructural changes occurring during corrosion.

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Stephan J. Meschter

Papers

Wetting in the Au–Sn System

Enhanced mechanical properties of polyurethane composite coatings through nanosilica addition

Evaluation of Effectiveness of Conformal Coatings as Tin Whisker Mitigation

Effects of curing conditions on structural evolution and mechanical properties of UV-curable polyurethane acrylate coatings

Whisker Formation Induced by Component and Assembly Ionic Contamination