Electromigration-induced Kirkendall voids at the Cu/Cu3Sn interface in flip-chip Cu/Sn/Cu joints

Polarity void formation has been observed at the Cu3Sn/Cu interfaces in current-stressed Cu/Sn/Cu flip-chip joints. Electromigration voids were observed at the Cu3Sn/Cu anode interface, but no voids were found at the Cu3Sn/Cu cathode interface. The backstress in the anode's Cu trace line caused a vacancy backflow toward the Cu3Sn/Cu anode interface, which led to serious void formation. In the opposite Cu3Sn/Cu cathode interface, Cu atoms in the cathode's Cu trace line electromigrated toward the Cu3Sn/Cu cathode interface, which alleviated or healed possible Kirkendall void formation due to the normal annealing process. (c) 2007 American Institute of Physics.