Metallurgy of low temperature Pb-free solders for electronic assembly

Abstract

Recent interest in Pb-free solders was stimulated by the introduction of (US) legislation that proposed the banning of Pb from a wide variety of uses, including electronic solders. Although there are solders that do not contain Pb, there is no obvious replacement for the eutectic and near eutectic Sn-Pb alloys that are in common industrial use today. This review surveys the literature on the metallurgy of Pb-free solders of interest for electronic assembly using organic substrates (solder liquidus temperatures between 100 and 232°C). This data (primarily on Sn-based binary eutectic alloys containing Ag, Bi, Cu, and In) provides a foundation for further study of both these alloys and more complex systems. The review is divided into three major sections: physical metallurgy (including physical properties and microstructure); mechanical properties (including tensile and shear behaviour, creep, and isothermal and thermal fatigue behaviour); and oxidation and corrosion behaviour.