It was recalled that recent observations had shown that a void could sometimes collapse so as to form a slit which ran almost perpendicular to the electric current. Such a slit often lay within a grain, rather than along a grain boundary. Earlier calculations had shown that diffusion at the void surface, driven by the electric current, could cause a circular void to translate in an infinite isotropic interconnect. It had recently been suggested that this solution might be unstable, and that 2 forces competed in determining void stability. Thus, surface tension favored a rounded void form while the electric current favored a slit form. A linear perturbation analysis revealed that the translating circular void was surprisingly stable against infinitesimal shape perturbations. Consequently, slit instability had to result from finite imperfections. The experimental and theoretical findings were reviewed here, and a numerical simulation of finite-void shape changes was described. The electric field was determined by using a complex variable conformal mapping technique, and the void shape after a time-step was updated by using a variational method. The simulation showed that a finite void-shape imperfection or surface-tension anisotropy could cause a void to collapse into a slit.

W.Wang, Z.Suo, T.H.Hao: Journal of Applied Physics, 1996, 79[5], 2394-403