Effects of stacking sequence of electrodeposited Sn and Bi layers on reflowed Sn-Bi solder alloys

Eutectic Sn-Bi alloy is gaining considerable attention in the electronic packaging applications. This alloy exhibits favorable properties such as low melting temperature, good wettability, high yield strength and fracture strength at room temperature. Miniaturization of electronic devices limited the choices of deposition technique where electrodeposition is identified as one of the most suitable ones. This work focuses on the formation of eutectic Sn-Bi solder alloys by reflowing a metal stack containing sequentially electrodeposited Sn and Bi layers. Three layer sequential deposition of Sn-Bi alloys is a new attempt in the electroplating field. The effects of layer sequence on the composition and microstructure of the resulting alloy is investigated. Irrespective of the layering sequence, a homogeneous microstructure is achieved after reflow. Near-eutectic alloy of composition Sn- 54.6 wt.% Bi is obtained from this sequential plating method.