| Popis: |
Cu pillar bumps with eutectic SnPb solder were annealed and their microstructures were investigated. Linear relationship was observed between thickness of intermetallic compounds (IMCs: Cu6Sn5, Cu3Sn) and square root of time at 120 and 150degC. Kirkendall voids, formed by the diffusivity differences between Cu and Sn, were observed near the interface between Cu and Cu3Sn. There was a change in slope of the linear relationship between IMCs thickness and square root of time at 165degC when all Sn was consumed. Cu6Sn5 growth rate was retarded, while Cu3Sn growth rate was accelerated. The activation energies for Cu6Sn5, Cu3Sn, and Kirkendall voids growth were estimated to be 1.77, 0.72, and 0.36 eV, respectively. The microstructures of Cu pillar bumps with pure Sn were investigated by in-situ scanning electron microscopy under annealing and high current-stressing conditions. It was found that IMC growth rate under annealing condition obeyed parabolic rate law, while that under high current-stressing condition IMC growth rate did not obeyed linear rate law. IMC growth rate under high-current stressing condition was faster than that under annealing condition which is presumed to be caused by the atomic migration enhancement due to the electron wind force. |
