Numerical simulation of conventional capillary flow and no-flow underfill in flip-chip packaging

We developed a numerical method for simulating the underfill flow of conventional capillary flow and no-flow types in flip-chip packaging. The analytical models for the two types of underfill encapsulation processes are proposed. In the capillary flow type, the underfill material is driven into the cavity with solder bump by the surface tension with an effect of contact angle as the capillary action. In the no-flow type, the movement of IC chip during the reflow attachment is controlled by an appropriate loading to get the proper interconnect between IC chip and substrate. In both types, the flow behavior and filling time of underfill material in underfilling encapsulation process are investigated, taking the fluid dynamic force acting on the solder bump into account. It is found that the proposed analytical models have a considerable potential for predicting the underfill flow.