Three-dimensional simulation of underfill process in flip-chip encapsulation

Underfill is an important process in flip-chip encapsulation because of its great impact on the reliability of the electronic packagings. This paper focuses on the study of the fluid flow in capillary-driven underfill encapsulation, and a three-dimensional simulation approach of the underfill process is proposed. Firstly, the driven mechanism of the capillary action is analyzed by first presenting an inter-motivation model, according to which the capillary action is modeled as two different forces, the adhesive tension force close to the wall and the surface tension force on the free surface. Those two forces motivate each other during the fluid flow process. Then, based on this, the fluid flow simulation of the underfill process is established. During the solution, two common Petrov–Galerkin (PG) methods are employed to solve the governing equations. Finally, the piecewise linear interface calculation (PLIC)-flow analysis network (FAN) method is proposed to track and reconstruct the melt-front for each time step. Compared with the experimental data and the predictions of the other numerical methods, the proposed approach shows a good performance in predicting the fluid flow in the capillary-driven underfill process.