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Anisotropic viscoelastic properties of prepreg and their influence on warpage of thin PCB substrates
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DOI：10.1016/j.compositesa.2026.110151.png)
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Abstract
En 中文
Warpage in ultra-thin printed circuit board (PCB) substrates is a critical thermo-mechanical reliability issue in advanced semiconductor packaging. Despite orthotropic nature of woven-fabric (WF) reinforced prepregs (PPGs), most studies assume isotropic behavior, neglecting the coupled effects of cure shrinkage (CS), directional stiffness, viscoelastic relaxation, and anisotropic thermal expansion. In this study, anisotropic thermo-viscoelastic behavior of three industrial WF prepregs—fine fiber–high resin (FF-HR), thick fiber–high resin (TF-HR), and thick fiber–low resin (TF-LR)—with varying fiber diameter, weave density, and resin content (66–76%) was systematically investigated and incorporated into a finite element analysis (FEA) for accurate warpage prediction. In situ fiber Bragg grating (FBG) sensing quantified effective post-gel CS ranging from 0.0373% to 0.0475%. Directional flexural tests confirmed pronounced in-plane orthotropy. Time–temperature superposition (TTSP) was used to construct viscoelastic master curves, which were transformed into time-domain data for FEA. Full-field 3D digital image correlation (3D-DIC) measured anisotropic coefficients of thermal expansion (12.45–18.4 ppm/°C) and identified subtle ± 45° asymmetry. Warpage measurements of asymmetrically etched Cu/PPG/Cu laminates revealed strong dependence on Cu-pattern orientation and prepreg anisotropy. The anisotropic thermo-viscoelastic model accurately predicted warpage, whereas isotropic homogenization consistently underestimated deformation. Among the laminates, TF-LR exhibited lowest warpage, demonstrating improved dimensional stability for advanced semiconductor packaging substrates.
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