Formation and growth of intermetallics evolution at the SAC305 and SAC0307 solder joints after wave soldering

The experimental results show that the formation of inter-metallic layers is controlled by diffusion and that the inter-metallic layers grow in a parabolic manner by the thermal activation. The results indicate three symptoms. The first one is that the thickness of IMC increases as the aging time extends. The second one is that Cu is partially molten, which the IMC interface between solder pastes and plating Cu of OSP PCB moves to the plating Cu side. The last one is that high Ag contents can induce rapid interface growth rate at the beginning of the formation. Starting from 100°C of the aging temperature, Diffusion coefficient D of SAC0307 at 150°C is greater than that of SAC305. As the temperature reaches 200°C or beyond, Diffusion coefficient D of SAC0307 is smaller than that of SAC305. The quantity of copper dissolution extremely goes up and it benefits the growth of SAC305 IMC, because the operation temperature, 200°C, is higher than the melting point, 217°C, of SAC305. Based on the whole trend, the greater the Activation Energy of SAC305 grows, the slower the sensibility to temperature is.