Formation of Sn-Bi solder alloys by sequential electrodeposition and reflow

摘要

Eutectic Sn-Bi alloy is gaining considerable attention in the electronic packaging industry because of its favorable properties such as low melting temperature, good wettability, and good mechanical properties. Miniaturization of electronic devices requires small solder bumps, a few tens of micrometers in diameter. Electrodeposition is a reliable technique for the deposition of small volume of solder. This work focuses on the formation of eutectic Sn-Bi solder by reflowing a metal stack containing sequentially electrodeposited Sn and Bi layers. The effects of layering sequence on the composition and microstruc-ture of the resulting alloy is investigated. Irrespective of the layering sequence, a homogeneous microstructure is achieved after reflow. The microstructure of the reflowed samples is the same as that of a metal lurgically processed Sn-Bi alloy. Near-eutectic alloy with the composition Sn-54.6 wt% Bi is obtained by the sequential electrodeposition method.