Abstract

This study presents a comprehensive assessment of the process-induced warpage of molded wafer for chip-first, face-down fan-out wafer-level packaging during the fan-out fabrication process. A process-dependent simulation methodology is introduced, which integrates nonlinear finite element analysis and element death-birth technique. The effects of the cure-dependent volumetric shrinkage, geometric nonlinearity and gravity loading on the process-induced warpage are examined. The study starts from experimental characterization of the temperature-dependent material properties of the applied liquid type epoxy molding compound (EMC) system through dynamic mechanical analysis and thermal mechanical analysis. Furthermore, its cure state (heat of reaction and degree of cure) during the compression molding process is measured by differential scanning calorimetry tests. Besides, the cure dependent-volume (chemical) shrinkages of the EMC system after the in-mold cure and post-mold cure are experimentally determined, by which the volumetric shrinkage at the gelation point is predicted through a linear extrapolation approach. To demonstrate the effectiveness of the proposed theoretical model, the prediction results are compared against the in-line warpage measurement data. One possible cause of the asymmetric/non-axisymmetric warpage is also addressed. Finally, the influences of some geometric dimensions on the warpage of the molded wafer are identified through parametric analysis.

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