Intermetallic compound and Kirkendall void growth in Cu pillar bump during annealing and current stressing

Cu pillar bump with eutectic SnPb was annealed and the micro structures were observed by scanning electron microscopy. Both of Cu₆Sn₅ and Cu₃Sn grew following parabolic rate law at 120 and 150degC. At 165degC, Cu₆Sn₅ growth was stagnated while Cu₃Sn growth rate was increased after 160 hour when all Sn was consumed. Kirkendall void was formed because of different diffusivities of Cu and Sn. The activation energies of Cu₆Sn₅, Cu₃Sn, and Kirkendall void growth were 1.77, 0.72, and 0.36 eV respectively. Intermetallic compound (IMC) growths during 150degC annealing and in current stressing condition were observed to investigate the effect of current stressing. In current stressing condition, the temperature was 150degC and the current density was 5 times10⁴ A/cm². IMC growth in current stressing condition was faster than that during annealing because of electron wind force.