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This paper addresses thermal interface materials for thermal conduction of excess heat for microelectronic applications. Carbon black (30 nm) thixotropic paste based on polyol ethers is comparable to carbon black fluidic paste based on polyethylene glycol (PEG) in its effectiveness as a thermal paste, and in its dependence on pressure history. Prior pressure (up to 0.69 MPa) application is helpful. The optimum carbon black content is 2.4 vol.% for the thixotropic paste. The thermal contact conductance across copper surfaces is 30 ϫ 10 4 and 11 ϫ 10 4 W/m 2 -°C for surface roughness of 0.05 µm and 15 µm, respectively. The volume electrical resistivity is 3 ϫ 10 3 Ω-cm. Boron nitride (BN) (5-11 µm) and graphite (5 µm) thixotropic pastes are less effective than carbon black thixotropic paste by up to 70% and 25%, respectively, in thermal contact conductance, due to low conformability.

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This work provides phase-change thermal interface materials (TIMs) with high thermal stability and high heat of fusion. They are based on antioxidants mainly in the form of hydrocarbons with linear segments. The thermal stability is superior to paraffin wax and four commercial phase-change materials (PCMs). The use of 98.0 wt.% thiopropionate antioxidant (SUMILIZER TP-D) with 2.0 wt.% sterically half-hindered phenolic antioxidant (GA80) as the matrix and the use of 16 vol.% boron nitride particles as the solid component give a PCM with a 100°C lifetime indicator of 5.3 years, in contrast to 0.95 year or less for the commercial PCMs. The heat of fusion is much higher than those of commercial PCMs; the values for antioxidants with nonbranched molecular structures exceed that of wax; the value for one with a branched structure is slightly below that of wax. The phase-change properties are degraded by heating at 150°C much less than those of the commercial PCMs. The stability of the heat of fusion upon phase-change cycling is also superior. The viscosity is essentially unaffected by heating at 150°C. Commercial PCMs give slightly lower values of the thermal contact conductance for the case of rough (12 lm) mating surfaces, in spite of the lower values of the bond-line thickness.

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