Failure mechanisms of dummy IGBT assembles constructed using liquid in-Sn/Nb system

Liquid solder joints have previously been proposed in order to improve the reliability of solder joints in general, and especially for those that are operated at elevated temperatures. The solder is designed to melt during high temperature operation, releasing the stresses on the joint. The component will remain mechanically attached to the substrate by use of a polymer underfill or glob-top. Assemblies of dummy insulated gate bipolar transistor (IGBT) devices were constructed using the In-Sn as a low melting point solder and Nb as a barrier layer, on both device bond pads and connecting wires. Silicone and epoxy based adhesives were used as glob top materials, and alumina was used as the substrate. Thermal cycling carried out between -20 and +125 °C lead to rapid joint failure, and analysis of the joints showed that the wires had moved under mechanical tests. Further testing is underway.