Effects of joint size and isothermal aging on interfacial IMC growth in Sn-3.0Ag-0.5Cu-0.1TiO2 solder joints

The influence of the joint size on the growth of intermetallic compound (IMC) between Sn-3.0Ag-0.5Cu-0.1TiO2 composite solder and Cu pad during isothermal aging at temperatures of 100 °C, 120 °C, and 150 °C has been investigated in this study. Scanning electron microscopy was used to observe the microstructural evolution of the solder joints and to measure the thickness of IMC layer. Results for micro-joints show that the size of the solder joints has a significant effect on the interfacial reaction. The IMC thickness and the growth rate increase, whereas the activation energy decreases with the increase in joint size for all aging temperatures. The size effect might be due to the difference in Cu concentration near the IMC interface. Finite-element model was applied to examine the thermo-mechanical stresses at the interface of the solder joint as thermo-mechanical stress can cause the formation of crystal defects in solder matrix and interfacial IMC layer. We assume that these crystal defects serve as fast diffusion paths for atomic diffusion and affect Cu distribution.