Thermo-mechanical and Mold Flow Analyses of Die Shift in Wafer Reconstitution Process for Advanced Packaging Technology

Abstract

In advanced wafer level packaging, a process called wafer reconstitution was developed as a strategy for decoupling IC/MEMS fabrication and packaging. However, several concern such as die-shift and warpage are found during reconstitution and they induce problems for subsequent wafer process. In this paper, it is desired to examine the key factor of die-shift on wafer. The investigation procedures including fluidic and thermomechanical effects are introduced. Preliminarily, the die-shift problem is deduced as interaction of fluid load, thermal expansion, shrinkage of molding compound and viscoelastic effect. To gain a deeper insight, simplified fluid model and finite element analyses have been constructed to mimic the entire process. As current results shown, defects of molding is not the dominating factor in reconstitution process as those usually reported previously. Meanwhile, simulation of thermal model has a consistent tendency with actual situation and is close to the observed defects. In summary, the presented model in this work is able to provide the basis failure phenomena for the wafer reconstitution. However, the situations are actually sensitive to processing parameters and a more sophisticated finite element model to include those detail processing should be further developed for further optimizing the reconstitution process for a better yield models in the near future.