Numerical simulation of the flip-chip underfilling process

Flip chip technology is being positioned as the ultimate solution to the requirements of the electronics industry for faster, smaller, and cheaper packages. As long as the substrate in a flip chip assembly is made of some organic material, underfilling can significantly increase the fatigue life of a flip chip. This paper numerically investigates the capillary-driven flow during the underfilling process. A computer code which combines the newly proposed MAB (marker and boundary) method with the FEM (finite element method) is developed for this purpose. The computational results have shown that the underfill time is proportional to the surface tension and inversely proportional to the viscosity of the fluid. About 50% of the time is spent in filling only the final <10% of the cavity volume. The nondimensional underfilling time was found to have a fixed relationship with the nondimensional location of the flow front for different kinds of underfill materials