Electromigration and thermomigration characteristics in flip chip Sn-3.5Ag solder bump

Electromigration test of flip chip solder bump is performed at 140 degrees C and 4.6 x 10(4) A/cm(2) conditions in order to compare electromigration with thermomigration behaviors by using electroplated Sn-3.5Ag solder bump with Cu under-bump-metallurgy. As a result of measuring resistance with stressing time, failure mechanism of solder bump was evaluated to have four steps by the fail time. Discrete steps of resistance change during electromigration test are directly compared with microstructural evolution of cross-sectioned solder bump at each step. Thermal gradient in solder bump is very high and the contribution of thermomigration to atomic flux is comparable with pure electromigration effect.