Electromigration failures at Cu/Sn joint interface

Stressed by a high current density, several EM-induced reliability issues would likely occur at the flip-chip Cu/Sn joint interface. At the cathode interface, EM-induced Cu-pad consumption occurred at the current-entry point (maximum current-density) and voiding occurred at the other joint corner away from the current-entry point (minimum current-density). At the anode interface, EM-enhanced Kirkendall voids coalesced into a gap at the Cu₃Sn/Cu interface near the current-exit corner. We believe that the above various EM-induced failure modes were resulted from different current-stressing densities at the joint interfaces. Also, a rare EM failure at the anode interface was found and would be discussed in this study.