Voids in thermal interface material layers and their effect on thermal performance

One of the key challenges in the thermal management of microelectronic devices is interfaces such as those between the chip and heat spreader and between the heat spreader and heat sink or cold plate. Typically, thermal interfaces are filled with materials such as thermal adhesives and greases. Interface materials reduce the contact resistance between the mating heat generating and heat sinking units by filling voids and grooves created by the nonsmooth surface topography of the mating surfaces, thus improving surface contact and the conduction of heat across the interface. With shrinking thermal budgets, the role of these layers in the cooling of microelectronic devices has become more critical. Voids in thermal interface material (TIM) layers may be trapped during the flow of the TIM during assembly, due to outgassing during the curing process, or due to insufficient volume. The negative effect of such voids on the thermal resistance of a TIM layer can be devastating. In applications where the TIM performs the function of a structural adhesive, voids may negatively affect the adhesion strength and reliability of the TIM layer. In this work, the effect of voids and their characteristics on the thermal performance of thermal interface adhesive layers is reported.