Finite element analysis of compliant coating

Abstract
Finite-element analysis (FEA) was used to explore the effect of key materials and process parameters relating to die-coat chemistry and thickness on the die surface and internal-package stress. Lower stresses are achieved with silicone gel compared to silicone RTV, modified polyimide, and polyimide coatings, as predicted by internal-stress calculations based on the integral of Young's modulus and thermal coefficient of expansion (TCE). The stress reduction mechanism is related to the decoupling of the die-surface/molding-compound interface. It is verified that thin-film cracking can be eliminated by using a thin film of silicone gel as shown by improved thermal cycle performance of a 68-lead plastic-leaded chip-carrier (PLCC) package.

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