Flexible graphite modified by carbon black paste for use as a thermal interface material

Polyol-ester-based carbon black pastes are used to either coat or penetrate flexible graphite, thereby increasing the thermal contact conductance of flexible graphite between copper surfaces. Paste penetration by up to an effective paste thickness (the volume of the penetrated paste divided by the geometric area of the flexible graphite) of 5 μm increases the conductance by up to 350%, 98% and 36% for thicknesses of 50, 130 and 300 μm, respectively. Paste coating up to 10 μm increases the conductance by up to 200%, 120% and 65% for thicknesses of 50, 130 and 300 μm, respectively. The paste penetration is more effective than the paste coating in enhancing the conductance, when the thickness is below 130 μm. At thickness ⩾130 μm, paste penetration and paste coating are similarly effective. These results stem from the relatively low interfacial thermal resistivity provided by paste penetration and the relatively high through-thickness thermal conductivity provided by paste coating. Paste penetration decreases the thermal conductivity of flexible graphite, but paste coating does not affect the conductivity. Both penetration and coating decrease the interfacial resistivity. The highest thermal contact conductance is 1.4 × 105 W/m2 K, as provided by paste-penetrated flexible graphite of thickness 26 μm.