Two-Phase Flow Simulation of Capillary Underfilling as a Design Tool for Heterogenous Integration

Encapsulation is gaining relevance for the miniaturization of power modules to enhance dielectric, mechanical, and thermomechanical reliability. Capillary underfill is a flexible method for encapsulating vertical integration concepts in power electronics. To ensure defect-free application, a robust and accurate two-phase flow model is presented that can predict both shape and velocity of the moving interface. The study discusses three general concepts for targeted flow control and void prevention: Local flow speed adaption, gap compartmentation, and arcuate shapes to force a chip near confluence of multiple flow fronts. The beneficial effect of these design features is verified with experimental test setups. Simulated and experimentally captured flow fronts are quantitatively evaluated using the normalized difference in filled gap area as a benchmark for experimental validation. A very good agreement is found with 2.8-3.4% relative deviation. For void-critical applications, this study demonstrates the ability to use a VOF based two-phase flow model to derive individually tailored flow manipulation measures, highlighting the potential of a simulation-based design tool for capillary underfilling.