Rheological Behavior of Thermal Interface Pastes

Polyol-ester-based thermal pastes containing carbon black, fumed alumina or nanoclay exhibit Bingham plastic behavior with shear thinning. Carbon black gives double yielding, but fumed alumina and nanoclay give single yielding. The plastic viscosity increases with the solid content. Antioxidants increase the plastic viscosity and yield stresses. Nanoclay (1.0 vol.%) gives low shear moduli, high critical shear strain, and high loss tangent, thus resulting in low bond-line thickness and high thermal contact conductance for smooth (0.009 μ m) proximate surfaces. Carbon black (Tokai, 8.0 vol.%) gives high moduli, low critical strain, and low loss tangent, thus resulting in high bond-line thickness, though the high thermal conductivity due to the high solid content results in high thermal contact conductance for rough (15 μ m) proximate surfaces. Antioxidants enhance the solid-like character, increase the yield stress, plastic viscosity, and bond-line thickness, and decrease the thermal contact conductance.