Investigation of the mechanical compliance of highly conductive and durable carbon nanotube-polymer composite thermal interface materials

摘要

In the past several decades, the increasing performance of integrated circuits has put increasing demands on thermal management solutions. The thermal interface resistance of a typical electronics package can often comprise the majority of the total thermal resistance. While much effort has been put into developing high conductivity materials for thermal interface material (TIM) applications, in practice the observed thermal resistances are dependent on many other factors beyond the conductance of the material. A particularly important but somewhat overlooked factor in TIM performance is the mechanical compliance of the material. CTE mismatch between the various materials in typical packages can result in TIMs that need to accommodate chip center-to-edge warpages greater than 50 um. In multichip applications TIMs may need to accommodate chip-to-chip offsets of 100 um or more. These challenges are exacerbated in burn in and device testing applications where temperatures are often higher and contact with the device is a dynamic process sometimes requiring multiple insertions per device tested. There are many different types of TIMs to help mitigate the problem including solders, greases, adhesives, phase change materials, gels, and pads. In this work, carbon nanotube-polymer composite TIMs are investigated as a potential highly compliant, low thermal resistance solution. Vertically aligned carbon nanotubes grown on metal foils can deliver low thermal resistances due to their high in plane conductivity, mechanical compliance and achievable contact area for heat transfer. As carbon nanotube height increases, the TIM becomes more mechanically compliant, but also has a higher thermal resistance. This work focuses on how to make the CNT-polymer composites mechanically compliant while keeping thermal resistance low. Carbon nanotube-polymer TIMs will be stacked to improve compliance while keeping thermal resistance low. A variable force thickness gauge is used to measure the deformation of different TIM composites at different pressures. In addition to initial deformation, compression set and TIM rebound will be evaluated to understand how the candidate TIMs will perform over time and under changing mechanical conditions.