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

摘要

To meet the requirement of environment protection, Pb-free solders will replace traditional Sn-Pb solders in electronics manufacturing. Meanwhile, the trend of electronic components packaging toward miniaturization and high density makes the issue of electromigration (EM) more serious. In order to improve electronics reliability, it is essential to study EM in Pb-free solder joints. There are some phenomena of the EM in the solder, such as voids 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 thermal aging experiment and the other is EM experiment. In the thermal aging experiment, the IMC on the side of the substrate is thicker than it on the of the chip because the solder near the substrate suffers once more reflow cycle than it near the anode. In the EM experiment, under the influence of EM, IMC at the anode is thicker than it at the cathode. In addition, IMC will dissolute 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.