Influence of Bi on microstructures evolution and mechanical properties in Sn-Ag-Cu lead-free solder

Sn-Ag-Cu-Bi solders, which have high quality and performance that can meet the requirement of electronic packaging, have been investigated in this paper. The research was focused on the influence of aging on the microstructural evolution and mechanical properties in Sn-3Ag-0.5Cu-xBi (x=0-3 wt.%) solders. The effect of Bi was discussed based on the experimental results. The experimental results indicated that the addition of Bi enhanced the tensile strength of the solders but decreased their elongation. After aging treatment, Sn-3Ag-0.5Cu solder showed significant change in strength and elongation which resulted from the obvious coarsening of Ag3Sn and Cu6Sn5 intermetallics. As for Bi-bearing solders, Bi precipitation in Sn matrix was only observed in Sn-3Ag-0.5Cu-3Bi solder after being aged at 120 deg. C for 100 h, while all the Bi-bearing solders exhibited relatively stable mechanical properties with aging time which can be attributed to the strengthening effect of Bi from solid solution strengthening to precipitating strengthening