Warpage Prediction of PCB in Multi-Laminating Processes Considering Cure Shrinkage and Anisotropic Visco-Elastic Properties of Prepreg Core

초록

Warpage in ultra-thin printed circuit board (PCB) substrates remains a critical challenge in advanced semiconductor packaging, particularly under multi-step lamination processes. Conventional models often neglect woven-fabric (WF) anisotropy and the coupled effects of cure shrinkage, viscoelastic relaxation, and thermal–mechanical anisotropy, limiting predictive accuracy. This study develops a fully coupled experimental–numerical framework to capture process-dependent warpage evolution of WF-reinforced prepregs during sequential lamination and baking. In-situ fiber Bragg grating (FBG) and dielectric monitoring quantified effective cure shrinkage, with a representative value of 0.0475% during the first lamination. Pronounced anisotropy was measured in flexural moduli—10.06 GPa (0°) to 4.07 GPa (135°)— and the in-plane shear modulus (GLT = 1.31 GPa). Thermo-viscoelastic characterization showed relaxation moduli decreasing from ~10 GPa to 4 GPa, while directional CTEs ranged from 17.4 to 18.4 ppm °C⁻¹. A process-driven finite element model incorporating anisotropic thermo-viscoelasticity, directional CTEs, and measured cure shrinkage accurately reproduced experimental residual stress and warpage, including lamination-dominated deformation of 1.86 mm (first cycle) and 2.86 mm (second cycle). Baking-induced stress relaxation was also well captured. The results show that accurate warpage prediction requires explicit consideration of WF anisotropy, viscoelasticity, cure shrinkage, and full process history is essential for reliable warpage prediction and process optimization in next-generation PCB substrates.

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