The growth behavior of interfacial intermetallic compound between Sn–3.5Ag–0.5Cu solder and Cu substrate under different thermal-aged conditions

Abstract

The interfacial reaction, morphology, activation energies and growth behavior of interfacial intermetallic compounds (IMCs) between the Sn–3Ag–0.5Cu (in wt%) solder and Cu substrate during reflow at 280 °C for 10 min and aging at different temperatures for up to 360 h were investigated, and the growth kinetics of the interfacial Cu–Sn binary IMC layers were monitored during the isothermal aging. The results showed that the thickness of IMCs increased linearly with square root of aging time, and the diffusion coefficient related to the Cu–Sn IMC layer increased with increasing aging temperature. During aging at medium temperature (180 °C), the scallop-like Cu6Sn5 IMC layer at the SAC305/Cu interface gradually transformed into planar type with prolonged aging time. Nevertheless, in the case of high temperature (200 °C) aging, the solder/Cu6Sn5 interface became uneven because the Cu atoms came from the bulk solder would accumulate on the Cu6Sn5 IMC surface to directly thicken the existed IMC layer. Beside, the Kirkendall voids within Cu3Sn layer and the neighborhood of the Cu3Sn/Cu interface almost aggregated into continuous regions to formed micro-voids. The activation energies of the total Cu–Sn, Cu6Sn5 and Cu3Sn IMCs were obtained by plotting the diffusion constants (D) as a function of the aging temperature (1/T), and were 115.2, 122 and 98 kJ/mol, respectively.