Electromigration at the high-Pb–eutectic SnPb solder interface

Abstract

The electromigration behavior of the composite solder composed of eutectic and high-lead SnPb was investigated with 5.7 × 104 A/cm2 current stressing. Voids and hillocks were found only within the eutectic solder, and the high-lead solder remained intact. Electromigration was accelerated dramatically at 150 °C, and Pb became the major migration species of eutectic SnPb for the microstructure change at the anode. The polarity of the opposite current direction was also studied. When electrons drift from the eutectic side to the high-lead side, voids occurred at the eutectic–Cu interface whereas hillocks accumulated at the eutectic–high-lead interface. When the current was reversed, voids occurred at the eutectic–high-lead interface whereas hillocks accumulated at the eutectic–Cu interface. The anchoring effect, which results from the attaching of the lead-rich grains in the eutectic solder to the high-lead solder, was considered to retard the electromigration damage only in this current direction.