Evaluation of interface reaction and reliability of solder joints by thermal aging in power semiconductor devices

Abstract

Power semiconductors supply and control the electric power required by electronic components, In particular, it has recently attracted great attention as a key component of electric vehicles and hybrid electric vehicles (HEV). In the case of Si-based power semiconductor modules, it is important to maintain the junction temperature below the appropriate level, since the operating temperature of automobile driving elements is about 150℃ on average, and the temperature is applied up to 200℃ in special cases. This study analyzed the composition and physical change of solder (Pb-free) over time at high temperatures of 200℃ and 250℃ to evaluate the thermal reliability of the power semiconductor device of the finished product after packaging. In order to confirm, the change in the thickness and composition of the interface was checked using an electron microscope after measuring the electrical characteristic by curve tracer. Firstly, it was confirmed that the IMC layer had grown at 200°C with time. In particular, after more than 100 hours, cracks in the layer and layers were found at the Ni/Cu-Sn interface, and after 200 hours, cracks were observed at the Cu/Cu-Sn interface. Secondly, the physical change of the solder was noticeable at the temperature of 250℃. After 1 hour, voids occurred in the bulk solder area as well as in the joint. After 2 hours, more than 80% of the voids in the bulk solder area progressed. As this problem occurred, the current characteristics showed an open waveform on the IV curve. After all, it can lead to an increase in resistance, which can significantly affect the durability of the device.