Capillary Underfill Flow Simulation and Experimental Study for Solder Mask Opening and Trace Distribution in Bump Layout Design

The capillary underfill (CUF) was used as the interconnection protection material in flip-chip packaging since it offers significant improvement of the solder joint reliability. However, good UF flowability should be guaranteed to prevent void trapping and weak UF interfacial adhesion. In this work, a three-dimensional finite volume model was constructed for computational fluid dynamics (CFD) simulation. And underfill behavior was analyzed, which considers not only process parameters affecting the capillary flow action, but also difference of bump gap in bump layout design. In simulation analysis, completing melt front analysis can be seen, and visualization experimental data by using scanning acoustic tomography (SAT) will be compared. Good simulation accuracy is observed, and UF void or weak UF adhesion point can be predicted at final bond line position.