Effects of minor alloying additive on the shear strength of Sn-58Bi solder joint

Abstract

The use of Pb has been limited in the electronic industry because of the toxicity of lead. As the result, the research and development activities in developing lead-free solders have been accelerated and some lead-free solders were introduced as alternative. Sn-Bi-based alloys are an alternative 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 interface between Sn-58Bi solder and Cu substrate were investigated. Solid state IMC compound layer growth was also examined following the thermal aging of the solder joint. Results after aging show that minor added elements were effective in suppressing the intermetallics at the interface during solid state growth. The results also show that the added In was highly effective in limiting the Bi phase coarsening. Mechanical properties of solder joints, before and after heat treatment, were also investigated by shear and micro-vickers tests.