Die Shift Assessment of Reconstituted Wafer for Fan-Out Wafer-Level Packaging

This study aims to conduct a thorough investigation of the die shift of the reconstituted molded wafer for fan-out wafer level packaging (FOWLP) during the fabrication process. Both the fluid flow and thermo-mechanical effects are accounted for, where the former is simulated through the coupled fluid-structure analysis for exploring the die shift caused by the flow-induced drag forces, and the latter through process modeling for determining the die shift caused by the process-induced thermal-mechanical deformations. The effects of the temperature/conversion-dependent viscosity and cure shrinkage of the molding compound (MC), and the high temperature mold tape adhesive behavior on the die shifts are explored. The study starts from experimental characterization of the material properties, namely the high temperature mechanical properties of the mold tape adhesive, and the temperature-dependent Young's modulus and coefficient of thermal expansion of the MC. In addition, the cure state of the MC during compression molding and the corresponding cure kinetics model are established using differential scanning calorimetry tests together with mathematical modeling. Moreover, the temperature/conversion-dependent viscosity mathematical model is constructed using the developed cure kinetics model along with the measured MC's viscosity data The modeled die shift and warpage are compared against the online measurement data. Finally, the effects of some process, geometry and material parameters on the die shifts are also examined.