Thermal contact resistance of various carbon nanomaterial-based epoxy composites developed for thermal interface applications

Thermal interface materials (TIMs) are a vital component of electronic packaging as they facilitate heat removal from microchips by improving thermal contacts between the mating surfaces of chip and heat-sink. Filler-based polymer composite TIMs are utilized either as adhesives or pastes in electronic packaging. Carbon nanomaterials such as carbon nanotubes, graphite nanoplatelets (GNPs), few layered-graphene nanosheets (FLG) and carbon nanofibers have been extensively studied as fillers for the development of thermal interface adhesives or pastes due their high thermal conductivity. This work compares the thermal contact resistance (TCR) of epoxy composites incorporating FLG, GNPs or multiwalled carbon nanotubes (MWCNTs) under comparable conditions. GNPs and FLGs were produced by treating graphite flakes and graphite powder, respectively, via the Hummers' process followed by thermal reduction. Commercial MWCNTs and GNPs as well as in house-synthesized FLG and GNPs were dispersed into rubbery epoxy at 4 wt% (2.1 vol%) by a combined sonication and solvent mixing technique. The morphology of the fillers and resulting composites was studied by electron microscopy. The TCR of these composite TIMs, as adhesive coatings, was studied according to the ASTM D5470 method. The results showed that the TCR of MWCNT-epoxy composites increased with increase of MWCNT loading from 1 to 8 wt%. The TCR of 1 wt% MWCNT/rubbery epoxy composite was found to be 1.05x10(-4) m(2) K/W at a bond line thickness of 15 mu m, which was significantly higher than the value for corresponding FLG and GNP-based composites. The lowest TCR of 1.9x10(-5) m(2) K/W at bond line thickness of 18 mu m was obtained from the in-house GNP-based composite, half that of the corresponding FLG-based composite, and this was attributed to the less defective structure of the in-house GNP compared to FLG. Thus, epoxy composites developed with in-house synthesized GNPs offer higher heat dissipating capability than commercial GNP-, MWCNT- or FLG-based epoxy composites.