Electromigration effects on intermetallic growth at wire-bond interfaces

At a bimetallic interface, excessive intermetallic growth can cause device failure. For each intermetallic phase, a direct current flowing normal to the interface can change its thickening rate, increasing the rate for current in one direction and decreasing it for the reverse direction. In this paper, we present electrical resistance measurements on single wire-bond/bond-pad interfaces under the influence of current. Resistance increases are correlated with the growth of intermetallics observed in cross section of the wire bonds, providing a sensitive probe of microstructural evolution. The form of resistance change is clearly altered under applied current and depends on polarity. The resistance changes demonstrate key aspects of the effects of electromigration on intermetallic growth, but a fully quantitative interpretation of the changes is hampered by the appearance of more than one intermetallic phase and by the development of voids.