Coarsening of Bi phase and intermetallic layer thickness in Sn-58Bi-X (X=In and Ni) solder joint

The use of Pb has been limited in the electronic industry because of the toxicity of lead. Sn-Bi-based alloys are alternatives to replace Pb-based solders in the low temperature ranges. However, Sn-Bi-based solders show brittle behavior in both the bulk and the interface. Generally, the addition of impurity elements to the solders can improve the ductility of the solder joint in both the bulk and the interface by refining the solder microstructure and suppressing the intermetallics at the interface, respectively. In this study, the effect of third elements, i.e., Ni and In (1 and 0.5wt.%) on the microstructure of the Sn-58Bi solder and thickness of the intermetallic compound (IMC) at the interface between Sn-58Bi solder and Cu substrate after the reflow and 1, 3 and 6 weeks of aging at 80 °C were investigated. The joint strength of the new solder alloys were also investigated.