On the advantages of Bi addition into Sn-Cu-S lead-free solder

Incorporation of Bi into Sn-0.7Cu-0.08S lead-free solder alloy was applied to investigate its advantages on the melting temperature, wettability, microstructure, mechanical properties and corrosion behaviour. The results indicate that the addition of Bi lowers the melting temperature of the Sn-0.7Cu-0.08S, but enlarges its pasty range. The wettability of Sn-0.7Cu-0.08S on Cu substrate is considerably enhanced with the increase of Bi, as well as the ultimate tensile strength and vickers hardness. The improvement of the mechanical properties can be attributed to the refined microstructure by Bi addition. The corrosion resistance of Sn-0.7Cu-0.08S is obviously increased with the increase of Bi content. Analyses by SEM and XRD indicate that the corrosion product on the solder alloy surface is SnO 2 .