THERMAL-EXPANSION OF PARTICLE-FILLED PLASTIC ENCAPSULANT - A MICROMECHANICAL CHARACTERIZATION

The thermal expansion response of particle-filled polymer matrix compo sites is studied by micromechanical modeling. The model system used is the epoxy matrix filled with solid-sphere or hollow-sphere silica par ticles, with applications in microelectronics for encapsulating the se miconductor 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 s olid; 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 tha t rate-independent linear elasticity can give accurate predictions. Th e effects of particle spatial distribution on the average composite CT E are small. Local stresses generated from thermal mismatch between th e filler and the matrix, however, are strongly influenced by the matri x viscoelasticity and filler arrangement. Higher stresses in the epoxy are induced by higher thermal loading rates. The stresses are also hi gher 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 ma terials are discussed. (C) 1998 Acta Metallurgica Inc. Published by El sevier Science Ltd. All rights reserved.