Molded underfill for flip chip package

Abstract

Air trap (Void) in a molded underfill package always exists. It is an annoying problem and needs further investigation. In this research, the mold filing phenomenon of molded underfill (MUF) was investigated through numerical method. The carrier was a flip chip (FC) package. Moldex3D software was used as the tool. The resin was modeled as a reaction fluid. Cure kinetics and viscosity was measured and modeled. Kamal's model was used for the cure kinetics. Castro Macosko's model was used for the viscosity model. The simulation results were compared with the experiment results and were found the short shot simulation results agreed well with the experiments. The simulation results also showed that the locations of the air trap (void) for each package could be accurately predicted if the simulation was well setup. The size of trapped air voids could also be well predicted if Boyle's Law was used as the constitutive model for the compressed air and considered air vent effect. The simulation results could serve as a good reference for engineers to solve the MUF problems.