Effect of Electromigration on Intermetallic Compound Formation in Sn-9Zn Solder Interconnect

Interfacial reactions from high-density electric currents were investigated in a eutectic SnZn solder/Cu interconnect. An abnormal "polarity effect" was found where the intermetallic compound layer at the cathode was thicker than that at the anode. A kinetic model, based on the Zn mass transport in the sample, was presented to explain the growth of the intermetallic compound at the anode and cathode. The back stress induced by electromigration of Sn in the solder interconnect is considered to drive Zn atoms drift to cathode.