Two-Medium Model for the Bond Line Thickness of Particle Filled Thermal Interface Materials

Abstract

Thermal interface materials (TIMs) are widely used in electronics packaging. Increasing heat generation rates require lower values of the TIM thermal resistance, which depends on the material thermal conductivity and the TIM thickness, or the bond line thickness (BLT). The variation of the TIM thickness is not well understood. The major difficulty comes from the complexity of TIMs as condensed particle systems, especially when the TIM thickness is squeezed to several multiples of the filler particle diameter. This confined heterogeneous structure makes the behavior of TIMs different from that of homogeneous fluids. In this study, we propose a two-medium model for the BLT. The variation of BLT with attachment pressure is modeled using two parameters: the viscidity of the fluids and the interactions of particles. The predictions are compared with the measurements for TIMs made of aluminum oxide particles (sizes: 0.6–6 microns, volume fractions: 30%–50%) and silicon oil (kinematic viscosity: 100 cst and 1000 cst). Reasonable agreement is obtained for different applied pressures. Results indicate that the impact of the particle interactions is an important factor governing the variation of the TIM BLT, especially when the BLT is small.