Effect of stacking chips and inlet positions on void formation in the encapsulation of 3D stacked flip-chip package

Abstract

The current study investigates the effects of increasing the number of stacking chips and applying three types of inlet positions to the void formation in three-dimensional (3D) stacked flip-chip packaging. A scaled-up single integrated circuit packaging was performed, and the mechanism of void formation was studied throughout the experiment. The entrapment of air was visualized clearly in the experiment because of the unstable flow front during encapsulation. In the 3D stacked flip-chip packaging, the Castro–Macosko model with curing effect was written into user-defined functions and incorporated into the FLUENT software to describe the behavior of the molding compound. The increase in the number of stacking flip-chips increased the void in the package, which tended to form at the stacking chips region. Moreover, the application of three different inlet positions, namely, typical, diagonal, and top center inlets, significantly influenced the flow mechanism and void concentration. Knit lines were identified at the interface between the flows that occurred in the encapsulation. The current modeling also predicted the conversion of the compound. The simulation and experimental results were validated, thus proving that the current virtual modeling could handle the problems during encapsulation excellently.