Viscoelastic Warpage Modeling of Fan-Out Wafer-Level Packaging During Wafer-Level Mold Cure Process

• Published in: IEEE transactions on components, packaging, and manufacturing technology (2011) packaging, and manufacturing technology (2011), 2020-07, Vol.10 (7), p.1240-1250
• Main Authors: Cheng, Hsien-Chie, Wu, Zong-Da, Liu, Yan-Cheng
• Format: Article
• Language: English
• Subjects: Computer simulation; Dynamic mechanical analysis; Electronic packaging; Fabrication; Fan-out wafer-level packaging (FOWLP); Fanout; Finite element method; Geometric nonlinearity; Gravitational effects; Material properties; Mathematical model; Mechanical properties; Modelling; Molding (process); Molding compounds; Molds; Packaging; Parametric analysis; process modeling; Silicon; Temperature; Temperature dependence; thermal annealing; viscoelastic constitutive modeling; Viscoelasticity; wafer thinning; Warpage
• ISSN: 2156-3950; 2156-3985
• DOI: 10.1109/TCPMT.2020.2992041

This article aims to characterize the warpage evolution of fan-out wafer-level packaging (FOWLP) during the wafer-level mold cure process. A finite-element analysis (FEA)-based process modeling framework, which includes the effects of geometric nonlinearity, gravity, and the cure-dependent chemical shrinkage of epoxy molding compound (MC), is presented to determine the warpage behavior of the molded wafer at different process steps. Focus is placed on the effect of the viscoelastic behavior of the epoxy MC on the process-induced warpage, where its linear viscoelastic properties are characterized using dynamic mechanical analysis in a frequency domain at different temperatures based on the thermorheological simplicity. In addition, its temperature-dependent thermal-mechanical properties and cure state are investigated through experiments. The simulation results are validated by the in-line warpage measurement data. The alternative emphasis is to explore the effects of thermal annealing and wafer thinning on the warpage. To fabricate thin molded wafer at better handing, an indirect two-step process is proposed. The process-induced warpage resulting from the two-step process is investigated and compared against that of the direct one-step process. Besides, the dependences of the process-induced warpage on the material properties of the epoxy MC and support carrier are examined through parametric analysis.