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Effect of Bi Addition on Microstructures, Properties and Interfacial Intermetallic Compound Growth of Low-Ag Sn-Cu Lead-Free Solder

The research on a new low-Ag lead-free solder has become a hot spot in the field of electronic packaging. In this work, the effects of Bi addition on microstructure, melting temperature, wettability of low-Ag solder, shear strength of solder joint and the growth of interfacial intermetallic compound (IMC) before and after thermal cycling were investigated. A moderate amount of Bi element resulted in the microstructural refinement and melting temperature reduction of Sn-0.2Ag-0.7Cu solder. Wetting test results showed that a small amount of Bi produced the significant effect on improving the wettability. In addition, it is shown that the thickness of interfacial IMC during thermal cycling decreased first and then increased; the shear strength of solder joint increased with the increase of Bi.