Effects of electromigration on interfacial reactions in cast Sn/Cu joints

The Sn/Cu/Sn/Cu/Sn sandwich-type couples prepared by the casting method are used for examining the effects of electromigration on Sn/Cu interfacial reactions. The samples are reacted at 170 and 180 °C for 24–240 h by passing an electric current with a density of 5000 A/cm². At the interfaces where electrons flow from the Sn side to the Cu side, uniform layers of Cu₆Sn₅ and Cu₃Sn are formed. The results are similar to those without passage of an electric current. The relatively thicker Cu₆Sn₅ layer is attributed to the extra Cu source from the dissolved Cu during the sample preparation. At the interfaces where electrons flow from the Cu side to the Sn side, large and nonplanar Cu₆Sn₅ phase regions are formed. Formation of large Cu₆Sn₅ regions is the result of electromigration-enhanced Cu diffusion through the grain boundaries and surfaces.