Computational simulation of underfill encapsulation of flip-chip ICs. I. Flow modeling and surface-tension effects

This paper presents a computational technique for time-accurate prediction of the filling pattern during underfill encapsulation of flip-chip ICs. In order to accurately track the propagation of the resin front while taking into account the geometry of the underfill cavity, including bumps and edges, as well as all the boundary conditions that are transmitted to the resin front through the air, a two-phase model of the combined flow of resin and air in the underfill cavity is used. The two-phase flowfield is modeled using a Volume-of-Fluid (VOF) methodology embedded in a general-purpose, three-dimensional, flow-solver. A new surface-tension model is developed for computing the capillary-action forces that are exerted on the resin front and which drive the flow in underfill encapsulation processes