Stress relaxation behavior of Cu/Sn/Cu micro-connect after electrical current

The effect of electromigration on stress relaxation behavior of pure tin solder joints was investigated. It was found that the stress relaxation rate was accelerated significantly after the sample was subjected to current stressing. The accelerating effect increased with the current stressing time. Measurements of the activation energy and stress exponent suggested that the dominant mechanism of the stress relaxation of pure tin solder joint went from dislocation climb to grain boundary diffusion after electromigration. As a result of grain boundary diffusion and sliding, grain boundary grooves were observed on the surface of the tin solder joints after electromigration. The groove was associated with the divergence of vacancy concentration at the grain boundaries. The vacancy concentration at the grain boundaries, which increased with the current stressing time, promoted the atomic diffusion along the grain boundaries, resulting in a higher stress relaxation rate.