Microstructure comparative analysis of the solder joints based on SAC/SN100 soldering alloy type depending on the cooling rate

Microstructural analysis in the section of solder joints show a multilayer structure composed of IMC layers caused by the interface phenomena specific to soldering processes and a typical volume, unaffected by these phenomena, but depending of soldering process thermal profile, especially by the cooling zone parameters. In the paper were theoretically studied and experimentally evidenced genesis of the multilayer structure depending on the type of alloy and the specific cooling rate of the soldering process. Experiments were designed in order to obtain similar volumes of solder joints unaffected by the interface phenomena, taking into consideration Vapour Phase Soldering (VPS) processes characterized by different cooling rates and 6 types of Lead-Free solder pastes. The results highlight the microstructural differences in the unaffected by dissolution and diffusion volume of solder joints, between and for each type of solder pastes depending on the cooling rate. Based on these practical results could be improved the thermal profile of the soldering processes in VPS technology in order to increase the solder joints reliability.