Electromigration with Alternating Current in Solder Joints in Power Modules

Solder electromigration (EM) is recognized as a potential reliability problem in power modules. This study investigates the fundamental EM phenomena under Alternating Current (AC) and Direct Current (DC). A Cu/Ni-P/Sn-0.7Cu/Ni-P/Cu joint was investigated at 175°C and 50 A/mm2. The direction of the Direct Current (DC) was reversed every 96 or 48 hours in order to understand the effect of a reverse current on the EM. In the DC-EM, the growth of a P-rich layer in the Ni-P layer caused an open failure due to internal voids. In the AC-EM, Ni was EM transferred from/to the Ni-P layer depending on the electron flow direction and the P-rich layer thickness increased/decreased accordingly, resulting in suppression of the P-rich layer growth. This effect became significant with the shorter cycle time. Copyright© The Japan Institute of Electronics Packaging.