3-D Numerical Simulation and Validation of Underfill Flow of Flip-Chips

Abstract

A 3-D flow model, combined with the volume of fluid method, was developed to track capillary driven epoxy flow front, during the underfill process. Die edge effects and fillet spread based on the effect of process parameters were included in this model. Numerical results were validated against flow visualization data. Full field imaging experiments with quartz die were performed to observe flow front as a function of flow time. Development of this new modeling methodology focuses on predicting the capillary underfill flow behavior both in the first level interconnect area between a die and a substrate, and the area surrounding the die. This paper revealed that the edge flow effect contributes to pulling the overall flow front in the bump field area and formation of the fillet spread, which affects the risk associated with underfill delamination in flip chips. A comparative study, which included modeling results and experimental data, clearly indicated that the die edge effect cannot be neglected in order to capture the right trends of flow front shape evolution and an accurate fill time prediction. These comparisons also showed that the model developed in this paper is adequate to approximately simulate the fillet configuration all around the die after encapsulation of flip chips. The modeling methodology developed in this paper provides a fundamental understanding of underfill flow as a function of dispense process parameters, material properties, and package design parameters.