Effects of antimony on the growth of intermetallic compounds in Sa-Ag-Cu Pb-free solder joints

The effects of antimony on the microstructural evolution and the intermetallic compound (IMC) growth of Sn-3.5Ag-O.7Cu lead-free solder joints were investigated in this work. To investigate the element diffusion and the growth kinetics of IMC formation in solder joint, isothermal aging test is performed at temperatures of 100°C, 150°C, and 190°C respectively. Optical and scanning electron microscope (OM and SEM) were used to measure the thickness of intermetallic layers and observe the microstructure evolution of solder joint. The IMC phases were identified by energy dispersive X-ray (EDX) and X-ray diffraction (XRD). Results show that the thickness of IMC layer reduces and the grain size decreases with the increase in antimony composition. The activation energy and growth rate of the IMC formation were determined. Results reveal that adding antimony in Sn-3.5Ag-0.7Cu solder system could increase the activation energy, and thus reduce the atomic diffusion rate so as to inhibit the excessive growth of IMC. It is also observed that the fme particles precipitated along the grain boundary of IMC increase with the increase of Sb composition. Based on the observation of the microstructural evolution of the solder joints, a grain boundary pinnimg mechanism for the inhibition of IMC growth due to Sb addition was proposed.