Effects of electromigration on IMC evolution in Pb-free solder joints

In order to improve electronics reliability, it is essential to study electromigration (EM) in Pb-free solder joints. There are some phenomena of the EM in the solder, such as void formation and propagation, pileup or "hillocks" formation and intermetallic compounds (IMCs) morphology variation. In this paper, two groups of experiments are performed to investigate the effects of EM on IMC evolution in lead-free solder joints. One is a thermal aging experiment and the other is an EM experiment. In the thermal aging experiment, the IMC on the side of the substrate is thicker than that on the chip because the solder near the substrate suffers one more reflow cycle than that near the anode. In the EM experiment, under the influence of EM, IMC at the anode is thicker than it is at the cathode. In addition, IMC will dissolve and reform in the solder, and migrate from the cathode to the anode. Finally, IMCs at the anode and cathode are both thicker than those in the thermal aging experiment.