Geometrical size effect on interfacial reaction of Cu/SAC305/Cu during high-temperature storage aging

The growth of interfacial intermetallic compounds (IMC) and consumption of metal substrate during aging affect interconnection reliability. The interfacial interaction has been significantly influenced by geometric size of solder joints with the solder size shrink from macro-scale to meso-scale. In this paper, the growth behavior of IMC and consumption trend of Cu layer in Cu/Sn-3.0Ag-0.5Cu(SAC305)/Cu sandwich structures of different solder thickness (δ=15~50μm) during high-temperature storage (HTS) aging at 160°C was investigated. The constituents´ concentration in solder layer was analyzed after HTS aging. Results showed that solid state diffusion of interfacial elements is greatly dependent upon solder thickness during HTS aging. The thinner the solder layer was, the thinner the Cu₆Sn₅ layer and Cu₃Sn layer grew after HTS aging. The growth rate of IMC layer (Cu₆Sn₅ layer+Cu₃Sn layer) decreased with the decrease of solder thickness during HTS aging. Furthermore, the faster consumption rate of Cu layer tended to appear in the sandwich samples with greater thickness of solder layer. The concentration of Sn in solder layer revealed a decrease trend whereas that of Cu tended to increase with decreasing the solder thickness during HTS aging.