Effects of Current Stressing on Formation and Evolution of Kirkendall Voids at Sn-3.5Ag/Cu Interface

摘要

Kirkendall voids (KVs) are known to be formed at the Cu/Cu_(3)Sn interface, which can remarkably weaken solder joints. In this paper, the formation and evolution processes of KVs at Sn-3.5Ag/Cu joints were systematically investigated under isothermal aging and current stressing. It was found that the processes develop faster when joints are subjected to current stressing as opposed to thermal aging. This can be illuminated by the high KV densities caused by current stressing at both cathode and anode Cu/Cu_(3)Sn interfaces. Moreover, KVs formed under current stressing showed some polarity characteristics, namely that higher KV density was observed on the anode side compared with the cathode side. The interfacial reaction generated at the Cu_(3)Sn/Cu_(6)Sn_(5) interface, which was partly affected by current stressing, contributed to this polarity effect. As the holding time was prolonged, microvoids coalesced into larger porosities and microcracks. These defects will greatly threaten the reliability of the interface.