Hygrothermal Effect on Deformations and Stresses in QFN Packages

摘要

The hygrothermo-mechanical behaviors of a quad flat non-lead (QFN) package without a chip inside are investigated experimentally and numerically. The present study is focused on understanding the effect of the inherent hygrothermal behaviors of epoxy molding compound (EMC) on the deformations of QFN package. The full-field moire interferometry is used for measuring the real-time deformations of the specimen induced by thermal and moisture loading. In addition, the finite element method is adopted for validating the experimental observations and further understanding the hygrothermal mechanics of the specimen. The experimental results of the full-field deformations of the specimen, due to the temperature, and a combination of the temperature and moisture, are presented. The experimental observations have been validated by the finite element analysis. It was observed that the maximum moisture-induced deformation (strain) can be up to as large as 50% of the thermal deformation (strain) caused by ΔT=50℃ for the specimen. As a result, neglecting moisture-induced deformations (strains) would cause the significant amount of error in thermal deformation (strain) measurement of plastic packages. Furthermore, the present study has laid down the fundamental mechanics and approaches for the QFN packaging structural design and analysis in terms of hygrothermal effects.