Numerical analysis on the effects of different inlet gates and gap heights in TQFP encapsulation process

Finite volume method (FVM) based simulation of encapsulation process in thin quad flat pack (TQFP) packages is presented in this paper. The 3D model of TQFP package is built and meshed with tetrahedral elements using GAMBIT, and simulated by FLUENT software. Castro-Macosko viscosity model and volume of fluid (VOF) technique are applied for flow front tracking of the encapsulant. Curing kinetics is taken into consideration in the simulation using Kamal's equation. To solve the Castro-Macosko and Kamal models, suitable user defined functions (UDFs) are developed using MS VISUAL STUDIO.NET software and incorporated into the FLUENT. The parameters such as mold filling time, flow front profiles, pressure distribution in the package and void formation, for three different inlet gate arrangements and gap heights, are analyzed. The degree of conversion of the molding compound during the encapsulation process is also studied for different number of inlet gates. It is found that the filling time and void occurrence could be reduced by increasing the number of inlet gates, and the variation of gap height within the cavity is crucial in controlling the peak pressure. Moreover, the combined effect to two competing events, such as, reduction of viscosity with shear rate due to non-Newtonian behavior of the polymer fluid and increase in viscosity during the curing reaction, are effectively demonstrated. The simulation results are compared with previous experimental results and found in good conformity.