Thermomigration of Ti in flip-chip solder joints

Titanium has a very large heat of transport value of −768 kJ mol–1. However, thermomigration of Ti in solder joints has not been examined. In this study, void formation was observed in non-current-stressed Al traces during electromigration and thermomigration tests of SnAg solder joints. Voids formed inside the traces located above the solder bumps with no current flow. We found that Ti thermomigration occurred in the joint, resulting in the reaction of Al and Cu, leaving voids behind in the Al trace.