A Novel Equivalent Model for Underfill Molding Process On 2.2D Structure for High Performance Applications

Abstract

A novel methodology of 3D CAE modeling of capillary underfill of multi-chip packages with a large number of micro bumps is employed in this study. The capillary underfill flow is mainly driven by the surface-tension force based on the contact angle between bumps and substrate. On the other hand, the propagation of the melt front is mainly dominated by the dispensing design of underfill and the distribution of micro bumps. For the simulation of dispensing behavior, 3D modeling is unavoidable. However, the computing cost will become unaffordable due to the number of bumps. To ease the computing cost, an equivalent technique -The Equivalent Bump Group (EBG) model is proposed to the simulation. A simple package is studied to validate the proposed methodology. The case shows that the modeling solution of melt front by EBG model has a good agreement to the detailed model by according dispensing passes. Therefore, it is convinced that the proposed methodology provides a promising simulation solution for the microchip encapsulation for multi-chip packages with large number of micro bumps. A study for a multi-array package of different dispensing designs by EBG model is also conducted. The result shows that filling time can be predicted to get the best dispensing design with minimum filling time.