Thermal expansion of particle-filled plastic encapsulant: A micromechanical characterization

The thermal expansion response of particle-filled polymer matrix composites is studied by micromechanical modeling. The model system used is the epoxy matrix filled with solid-sphere or hollow-sphere silica particles, with applications in microelectronics for encapsulating the semiconductor devices. Finite element analyses based on the axisymmetric unit-cell model, with two types of filer arrangement, are performed. The epoxy phase is characterized as an isotropic linear viscoelastic solid; the silica phase is characterized as an isotropic linear elastic solid. The coefficient of thermal expansion (CTE) of the composite is found to be insensitive to the viscous behavior of the matrix, so that rate-independent linear elasticity can give accurate predictions. The effects of particle spatial distribution on the average composite CTE are small. Local stresses generated from thermal mismatch between the filler and the matrix, however, are strongly influenced by the matrix viscoelasticity and filler arrangement. Higher stresses in the epoxy are induced by higher thermal loading rates. The stresses are also higher with an aligned particle arrangement than a staggered arrangement. Issues regarding the thermal expansion modeling, and implications of the present findings to damage initiation in plastic encapsulation materials are discussed. (C) 1998 Acta Metallurgica Inc. Published by Elsevier Science Ltd. All rights reserved.