Reliability and Failure Mechanism of Current-Stressed 99.3Sn-0.7Cu/96.5Sn-3Ag-0.5Cu Composite Flip-Chip Solder Joints with Cu or Au/Ni/Cu Substrate Pad Metallization

Electromigration and thermomigration in the flip chip package are apparent in the reliability test. The 99.3Sn-0.7Cu/96.5Sn-3Ag-0.5Cu composite flip-chip solder joints with Ti/Ni(V)/Cu under bump metallurgy and different surface finishes are investigated when applied current density of 10 kA/cm² and 15 kA/cm² at 150degC and 125degC, respectively. Experimental results show the solder migrates to the Al trace in the chip when the solder joint was subjected to a test condition of 15 kA/cm² at 125degC. This is because the combined effect from electromigration and thermomigration causes trace peeling in the flip chip package at a high current density over 15 kA/cm². It is also revealed that the mean time to failure of the solder joint with Au/Ni/Cu pad surface finish under 10 kA/cm² at 150degC is 1141 h longer than the one with Cu pad finish. The dendrite of Cu-Sn compound under 15 kA/cm² at 125degC is different from that under 10 kA/cm² at 150degC.