Phase Diagrams and Their Applications in Pb‐Free Soldering

Abstract

Pb-free soldering is one of the most important technologies in the electronics industry. A phase diagram is a comprehensive representation of thermodynamic properties of a multicomponent material system. Basic knowledge and information of phase diagrams of Pb-free solder systems are reviewed. In this chapter, several examples of applications of phase diagrams in Pb-free soldering are presented, including general applications of melting, solidification and intermetallic compounds (IMC) formation caused by interfacial reactions. With the aid of phase diagrams, interpretations of some abnormal phenomena in Pb-free soldering such as effective undercooling reduction by Co doping, unexpected IMC growth rate in Sn-Bi/Fe couples, unexpected solder melting in Sn-Sb/Ag joints, special up-hill diffusion in the Cu/Sn-Cu/Ni sandwich structure, and the influence of limited Sn supply upon the interfacial reactions in the Au/Sn/Cu sandwich specimens, and so on, will be given.