Effects of Electromigration(EM) on the Kirkendall Void Formation in Sn-3.5Ag/Cu Solder Joints Open Access

Kirkendall voids and the micro voids induced by electromigration result in the serious failure in the solder interconnect. Interfacial reactions between Sn-3.5Ag solder and the electroplated Cu using SPS additive in the bath were investigated under high current condition. During subsequent isothermal aging at 150°C, the formation of Kirkendall voids was accelerated by S segregation at the void surface and Cu/Cu₃Sn interface, and then the voids were preferentially localized at the interface. And under high current flow (1X10⁴A/cm²) at the cathode side, electromigration caused the micro voids at the Cu₆Sn₅/Sn interface. The growth of Kirkendall voids and the micro voids were both affected by aging time and current density. Effects of current flow on the growth of Kirkendall voids and the micro voids were examined by applying high electric current during isothermal aging at 150°C. From the measurements of the fraction of voids at the Cu/Cu₃Sn and Cu₆Sn₅/Sn interfaces on SEM micrographs and analysis of the kinetics of void growth, which voids are more dominant was examined according to the time and the current density. Furthermore, under current flow the intermetallic compounds (IMC) thickening as well as voids growth was affected by polarity. Even though Cu was consumed remarkably, the growth of both Cu₃Sn and Cu₆Sn₅ IMCs was suppressed at the cathode side. On the other hands, the thickness of Cu₆Sn₅ at the anode side was increased by reaction with Cu flux atoms which migrate towards the anode from the cathode Cu line.