MODELING AND EXPERIMENTS OF UNDERFILL FLOW IN LARGE DIES WITH NON-UNIFORM BUMP PATTERNS

摘要

This paper presents numerical modeling and experimental results for the problem of underfill flow in a large die with a non-uniform bump pattern in a flip-chip packaging configuration. Two different 2-D flow models coupled with the volume-of-fluid (VOF) method are applied to track the underfill flow front during the simulation of flip-chip encapsulation. The first model employs the modified Washburn model and uses a time-dependent inlet velocity to account for the flow resistance across the gap direction in the presence of bump interconnects. The second model introduces a momentum source term in the Stokes equation to represent the gapwise resistance. Rheological properties, surface tension, and dynamic contact angles for an underfill material are experimentally determined. Simulation results based on the two models are compared with in-situ flow visualization conducted using bumped quartz dies. The comparison demonstrates the applicability of each model for simulating the underfill encapsulation process.