A critical review of carbon-based thermal interface materials

This review of carbon-based thermal interface materials (TIMs) covers carbon pastes, carbon nanotube (CNT)-based TIMs, graphene-based TIMs, 3D-structured TIMs and other hybrid TIMs. The TIM material design is related to the TIM performance, which is described by the thermal contact conductance of the sandwich consisting of two surfaces sandwiching the TIM. The thermal conductivity alone is a misleading and inadequate description of TIM performance, although it is considered as the sole criterion that governs TIM performance in much of the TIM literature. TIMs comprising vertically aligned carbons (CNTs, graphene sheets and carbon fibers) have received much recent attention. However, due to the cost and performance, the practical hurdles to implementation are significant. The combined use of an array and a metal cap (involving a low-melting metal) alleviates the inadequacy of the interface between the top of the array and the surface that the TIM should touch. The carbon black paste (inexpensive and effective) excels due to the solid-state conformability of the carbon black. The liquid vehicle of the pastes is commonly an oil. The solid content needs to be optimized, as the conformability decreases with increasing solid content, whereas the thermal conductivity increases with increasing solid content. The pastes are effective at small TIM thicknesses, whereas the vertically aligned carbons and 3D-structured carbons tend to be effective at large TIM thicknesses.