Cathodic peeling damage of Cu6Sn5 phase in Cu/SnAg3.0Cu0.5/Cu bridge interconnections under current stressing

Abstract

The cathodic interfacial damage behavior that has been attributed to electromigration is serious but has often been confused with thermomigration damage in solder interconnections. In this paper, after the effects of the non-uniform temperature distribution of Cu/SnAg3.0Cu0.5/Cu bridge joints are decoupled from the effects of the current stress, the microstructural evolution of the cathodic Cu6Sn5 phase is investigated under an average current density of 7.12 × 107 A·m−2 for 0–350 h. The results show that the interfacial Cu6Sn5 peels rather than dissolving completely at the cathode, because of both adhesion degradation at the Cu6Sn5/Cu interface and sustained cathodic stresses. This unrecorded peeling behavior will contribute to the rapid formation of interfacial voids and will thus dramatically increase the risk of interfacial failure. Fortunately, by restricting the intergranular diffusion and enhancing the bond strengths between adjacent Cu6Sn5 grains, an aging pre-treatment of the solder joints is found to be an effective way to slow down the Cu6Sn5 peeling process and achieve robust solder interconnections.