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A paste in the form of a polyol ester vehicle (liquid) containing 0.6 vol.% nanoclay is an effective thermal interface material. Nanoclay with a high conformability and hence a small bond line thickness is preferred, namely montmorillonite containing a quarternary ammonium salt organic modifier (dimethyl dehydrogenated tallow) at 125 meq/100 g clay, after exfoliation by using the vehicle. When it is used between smooth (0.009 lm) copper surfaces at a pressure of 0.69 MPa, the thermal contact conductance reaches 40 9 10 4 W/m 2 K, in contrast to the corresponding values of 28 9 10 4 W/m 2 K, 28 9 10 4 W/m 2 K, 25 9 10 4 W/m 2 K, and 24 9 10 4 W/m 2 K previously reported for carbon black, fumed alumina, fumed zinc oxide, and graphite nanoplatelet pastes. Between rough copper surfaces (12 lm), the conductance provided by the nanoclay paste is slightly below those of the other pastes. The superiority of the nanoclay paste for smooth surfaces is attributed to the submicron bond line thickness; the inferiority for rough surfaces is due to the low thermal conductivity. The conductance provided by the nanoclay paste increases from 31 9 10 4 W/m 2 K to 40 9 10 4 W/m 2 K when the pressure is increased from 0.46 MPa to 0.92 MPa. This pressure dependence is stronger than that of any of the other pastes studied.

Electrically nonconductive thermal pastes have been attained using carbon (carbon black or graphite) as the conductive component and ceramic (fumed alumina or exfoliated clay) as the nonconductive component. For graphite particles (5 lm), both clay and alumina are effective in breaking up the electrical connectivity, resulting in pastes with electrical resistivity up to 10 13 WÁcm and thermal contact conductance (between copper surfaces of roughness 15 lm) up to 9 · 10 4 W/m 2 Á°C. For carbon black (30 nm), clay is more effective than alumina, providing a paste with resistivity 10 11 WÁcm and thermal contact conductance 7 · 10 4 W/m 2 Á°C. Carbon black increases the thermal stability, whereas either graphite or alumina decreases the thermal stability. The antioxidation effect of carbon black is further increased by the presence of clay up to 1.5 vol.%. The addition of clay (up to 0.6 vol.%) or alumina (up to 2.5 vol.%) to graphite paste enhances the thermal stability.