Experimental Damage Mechanics of Micro/Power Electronics Solder Joints under Electric Current Stresses

Abstract

Experimental damage mechanics of flip chip solder joints under current stressing is studied using 20 test vehicle flip chip modules. Three different failure modes are observed. The dominant damage mechanism is caused by the combined effect of electromigration and thermomigration, where void nucleation and growth lead to the ultimate failure of the module. It is observed that thermomigration driving forces are stronger than electromigration; as a result thermomigration, not electromigration, determines the site of void nucleation. The void nucleation and growth modes and their preferred sites are also observed and discussed in detail. The interface between the Ni barrier layer and the solder joint is found to be the favorite site of void nucleation and growth. The effect of pre-existing voids on the failure process of a solder joint is also studied. It is observed that Black’s time to failure law for thin films is unreliable for solder joints.