Experimental and numerical verification of water ingress into a void of plastic packages by quick diffusion

Moisture that penetrates into the electronic package causes catastrophic crack propagation during reflow process, known as ldquopop-corningrdquo. The void at interface between encapsulant and other non-polymeric components such as metal lead frame plays an important role in crack initiation and propagation. As packages experience high temperature over 240degC during reflow process, the pressure inside the void rises significantly. Kitano et al. found the pressure to be close to the saturated vapor pressure. This pressure on void walls make the initial crack to grow rapidly during reflow process. It was conjectured that there is some amount of water inside voids and vaporizes during reflow process. The entrapment of water within the package interface void has been a persistent research theme. Several known possible mechanisms of moisture ingress into and outgassing from the void were investigated and summarized by Jang et al. . In his paper, he proposed that quick moisture diffusion at high reflow temperature can result in high vapor pressure inside voids and the vapor pressure could rise up to its maximum within tens of seconds, which is short enough to be within the reflow profile. In this paper, a special experiment fixture was designed and used to support his conclusions In addition to experiments, 3D finite element models were used to analyze the experimental results.