Study on the cracking mechanism of Au Bump during temperature-humidity test

With the continuous development of integrated circuits (IC), the reliability of microelectronic packaging technology becomes a big challenge. Au bump is widely used in packaging like light-emitting diodes (LED), display driver IC and micro-electromechanical systems (HEMS), in which the bump and under bump metallization (UBM) layers have a great influence on the performance of the final devices. Therefore, it's vital to reveal the mechanism of cracking at the UBM/Au interface during the temperature-humidity test such as the pressure cook test (PCT) and temperature humidity test (THT). In this study, finite element modeling was used to analyze the cracking mechanism of Au bumps. It was found that the stress of the Au bump during PCT and THT was concentrated near the undercut termination location which contributes to the stress-corrosion cracking at the UBM/Au interface. In addition, larger undercut shapes would result higher stress concentration. Thus, optimizing the UBM etching process to decrease the undercut would help to slack the Au bump cracking. Those research results will take positive implications for how to avoid cracks caused by stress concentration in the follow-up.