Microstructure changes and compound growth dynamic at lead-free/Cu interface under different conditions

The atom diffusion and growth behavior of intermetallic compound (IMC) at Sn3.5Ag0.5Cu/Cu interfaces under isothermal aging and thermal-shearing cycling conditions were investigated. The results show that the morphology of Cu6Sn5 IMCs formed at Sn3.5Ag0.5Cu/Cu interface changed gradually from scallop-like to chunk-like, and IMCs thickness developed with the isothermal aging and thermal-shearing cycling times increasing. Furthermore, Cu₆Sn₅ IMC growth rate under the thermal-shearing cycling condition was higher than that of under isothermal aging. Compared to isothermal aging condition, only one Cu₆Sn₅ layer was formed and developed at the interface between SnAgCu solder and Cu substrate after 720 cycles. IMC growth dynamic equation is Y = K_epsivradic(D^epsiv _Cut) + K_etaradic(D^eta _Cut) with K_eta is about 10^-5mum²/s under isothermal aging, and that is Y = y₀ + K_etaradic(D^eta _Cut) under the thermal-shearing cycling condition with dynamic parameter K_eta = radic(2)(C^eta/epsiv _eta - C^eta/beta _eta)^frac12/(C^eta/beta _eta - C^beta/eta _beta)^frac12 is about 10^-5 to 10^-4mum²/s.