Observation of void formation patterns in SnAg films undergoing electromigration and simulation using random walk methods.

With the ever-reducing sizes of electronic devices, the problem of electromigration (EM) has become relevant and requires attention. However, only the EM behavior of Sn-Ag solders within the solder joint structure has been focused on thus far. Therefore, in this study, a thin metallic film composed of Sn-3.5Ag (wt.%) was subjected to a current density of 7.77 × 10 A/cm at a temperature of 15 °C to test the ability of existing EM models to predict the nucleation and evolution of voids generated by the resulting atomic migration. A computer simulation was then used to compute the coupled current distribution, thermal distribution, and atomic migration problems. It relied on an original random walk (RW) method, not previously applied to this problem, that is particularly well suited for modelling domains that undergo changes owing to the formation of voids. A comparison of the experimental results and computer simulations proves that the RW method can be applied successfully to this class of problems, but it also shows that imperfections in the film can lead to deviations from predicted patterns.