Polymer matrix composites reinforced with expanded and unexpended graphite Particles for electronic packaging applications

Polymer composites with high thermal conductivity are used more frequently in thermal management of electronic packaging systems. In this study, conductive polymer composites were prepared by melt mixing of ethylene-vinyl acetate (EVA) copolymer with graphite at different volumetric concentrations up to 29.3%. Two kinds of graphite were used as reinforcement to prepare composites: untreated natural graphite (UG) having particle sizes ranging from 20 μm to 25 μm and expanded graphite (EG) having originally particle sizes ranging from 5 to 6 μm in length. Upon mixing at high shear forces EG exfoliates in thin sheets of a few nanometers in thickness. Due to this high aspect ratio of graphite sheets, nanocomposites filled with expanded graphite have a lower percolation threshold for electrical conductivity, about (5 to 6) vol.% compared to the composites filled with untreated graphite (UG) which have a percolation threshold of (15 to 17) vol.%. Thermal diffusivity of the samples was measured by photothermal radiometry. At similar concentrations, thermal diffusivity values for the nano-composites, EG-filled EVA, were significantly higher than those composites filled with UG.