Effect of anisotropic mechanical properties of woven composite substrates on warpage orientation of printed circuit boards

Abstract

In this study, a mechanism of warpage orientation determination is investigated for thin package substrates. Understanding the mechanism is important because assembly process yield will significantly increase if the warpage orientation is controllable. We found that the copper clad laminate (CCL) itself already contains considerable residual stress from its thermo-compression fabrication, due to low coefficient of thermal expansion (CTE) of the woven glass/epoxy core substrate. It was interesting that most of the specimens bent in bias direction of the glass fabric. Concentrating on thermo-mechanical properties of the composite substrate, it was verified that the warpage orientation is sensitively determined by both anisotropic moduli and CTEs of the thin and compliant core substrate.