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The effects of Bi on physical and microstructural characteristics of Sn-Ag-Cu lead-free solders

Lead-free solders were prepared by adding small amount of Bi element into the near eutectic Sn-Ag-Cu alloy solder. Melting point tests were carried out by DTA (Differential Thermal Analysis). Wettability tests were conducted on a wetting balance instrument. Test results of the experimental solders were compared with that of Sn-3.5Ag-0.5Cu to explore the effects of the addition of Bi on the microstructure, melting point, conductivity and wettability of the lead-free solders. It shows that Bi addition has positive effects on depressing the melting temperature but broadening the melting range. And with proper addition, Bi has a slight positive effect on wettability and conductivity. With the proper addition of Bi, grain refining effect can be achieved for the eutectic phases and thus it may improve the microstructure stability of the solders.