Enhancement of melt-spun process Bi-Ag lead-free solder for high temperature applications

The enhancement of lead free solders has emerged as one of the most important issues in the electronics assembling industries. Bi-Ag hypo and eutectic alloys have been considerd as one of the lead free solders that can replace the Pb-Sn solder for high temperature applications. This study investigates the effect of various compositions of silver on the mechanical, thermal and electrical properties of the melt-spun process Bi-Ag hypo and eutectic alloys was directionally solidified using copper wheel technology.The microhardness (Hv), creep resistance were measured from solidified ribbons.The results showed that presence of -Bi phase, Ag99.5Bi0.5 (with a cubic structure Fm-3m) and Ag0.97Bi0.03 (with a cubic structure Fm-3m) embedded in Bi matrix. Furthermore, the eutectic composition Bi2.5wt% Ag shows the more regular microstructure than hypo eutectic composition. It is also concluded that the solderability of solder is significantly imported due to the surface tension of molten Bi-Ag lead-free solder decreases with the Ag content. The obtained results show a surprising desirable decrease in melting temperature with increasing Ag from 269 to 261 degrees C. Also, it was found that the eutectic composition Bi2.5 Ag exhibit good mechanical properties superior to hypo-eutectic composition.