METALLURGY OF LOW-TEMPERATURE PB-FREE SOLDERS FOR ELECTRONIC ASSEMBLY

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 tha t 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 sold ers of interest for electronic assembly using organic substrates (sold er liquidus temperatures between 100 and 232 degrees C). This data (pr imarily on Sn-based binary eutectic alloys containing Ag, Bi, Cu, and In) provides a foundation for further study of both these alloys and m ore 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 corr osion behaviour.