Microstructural Transformation on SnAgCu/Cu Interface Induced by Thermal-shearing Cycling

The changes of morphology and growth tropism of inter-metallic compound (IMC) and IMC growth rate at lead-free solders/Cu interface of solder joints often limit the reliability of the entire package during service. Furthermore, during thermal-shearing cycling process, the thickness of IMC at the interface grows significantly and growth tropism of IMC changes, resulting in in-service evolution of the fatigue behavior. In this paper, the growth mechanism and tropism Of Cu₆Sn₅ at Sn3.5Ag0.5Cu/Cu interface are studied. It can be found that the results are correlated with shear stress-strain from the solder subjected to thermal-shearing cycling conditions. The average diffusion coefficient of IMC is from 10^-5 ¿m²/s to 10^-4 ¿m²/s. The IMC growth follows parabola growth kinetics, implying that the IMC growth is controlled by atomic diffusion.