An analytical model for the underfill flow driven by capillary forces in chip packaging

Underfill process is an essential step in chip packaging due to its significant impact on the reliability of electronic devices. The investigations of its flow characteristics are important for optimizing the filling process. There exist several analytical models wildly used to predict the underfill flow driven by capillary forces in chip packaging but cannot match the experimental values well. In this paper, we develop a reasonable model by more realistically simplifying the effect of solder bumps on the flow pattern, and separately considering the contact angles on the different material surfaces in the process. The proposed model is demonstrated to be superior to the previous according to its better consistency with the numerical and experimental results.