Current stressing effects on interfacial reaction characteristics of fine-pitch microbump

The electrical reliability of Cu/Sn-3.5Ag microbumps under current stressing conditions were systematically evaluated. Intermetallic compound (IMC) growth was controlled by a diffusion-dominant mechanism and a chemical reaction-dominant mechanism with annealing and current-stressing time, respectively. Under current stressing condition, Intermetallic compound growth was significantly enhanced by current stressing where the growth rate follows a linear relationship with stressing time. The complete consumption time of Sn phase in electromigration condition was faster than that in annealing condition. Kirkendall voids, which would be detrimental to the reliability of Cu pillar bump, was observed at both Cu pillar/Cu₃Sn and Cu₃Sn/Cu under bump metallization interfaces.