Electromigration induced failure in SnAg3.8Cu0.7 solder joints for flip chip technology

Abstract

Electromigration of SnAg3.8Cu0.7 Solder was investigated in flip chip solder bump. An under-bump metallization (UBM) of Cr/Cr-Cu/Cu tri-layer was deposited on the chip side and electroless Cu/Ni/Au pad was deposited on the BT board side. Electromigration damage was observed under the current density of 2 x 10(4) A/cm(2) at 100 degreesC. Voids were found at cathode side and crack was observed at solder/thin film UBM interface after current stressing, and the bump failed after 168-hour stressing. Copper atoms were found to move in the direction of electron flow. Intermetallic compounds of Cu-Sn an Ni-Cu-Sn were also observed to spread into the solder bump due to current stressing.