Creep deformation of microstructurally stable Sn-3.5Ag-xBi solders

In the electronics industry worldwide, using lead-free solders is becoming increasingly mandatory. In that regard, a substantial amount of work related to lead free solders is under way, and Sn-3.5Ag based ternary alloys with Bi or Cu are strong candidate materials. In this work, Sn-3.5Ag-xBi alloys with five different levels of Bi (0, 2.5, 4.8, 7.5, 10 wt%) were prepared. For the Bi containing alloys, the brittle fracture mode appeared showing a small reduction in area, while the ductile fracture mode was found to hold for the Bi free alloy. Microstructural examination of ruptured specimens showed cavitations on grain boundaries normal to the load axis, and a significant of grain boundary sliding particularly for the 10 wt% Bi alloy. Using SEM, EDS, etc., the precipitates inside and on grain boundaries were identified and their roles in creep strength were explained