Effects of antioxidants and the solid component on the thermal stability of polyol-ester-based thermal pastes

2008

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.

Section: Introductionmentioning

confidence: 99%

Nanoclay Paste as a Thermal Interface Material for Smooth Surfaces

2008

“…16,[18][19][20]22 The polyol esters in the vehicle are Corp., at 1.000 wt.% of the vehicle) dissolved in the vehicle is used to promote the thermal stability of the pastes. Detailed information on the selected antioxidants is given in prior work.…”

Section: Methodsmentioning

confidence: 99%

“…Prior work 16,18,20,22 on the rheology of thermal pastes has emphasized viscosity measurement, with relatively little attention being paid to the yield stress, storage modulus, loss modulus, loss tangent, and critical strain. This limitation stems from the fact that the rheological study in much of the prior work was measured by using a viscometer rather than a rheometer, which is powerful for dynamic rheological behavior study.…”

Section: Introductionmentioning

confidence: 99%

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Rheological Behavior of Thermal Interface Pastes

2009

Self Cite

Polyol-ester-based thermal pastes containing carbon black, fumed alumina or nanoclay exhibit Bingham plastic behavior with shear thinning. Carbon black gives double yielding, but fumed alumina and nanoclay give single yielding. The plastic viscosity increases with the solid content. Antioxidants increase the plastic viscosity and yield stresses. Nanoclay (1.0 vol.%) gives low shear moduli, high critical shear strain, and high loss tangent, thus resulting in low bond-line thickness and high thermal contact conductance for smooth (0.009 lm) proximate surfaces. Carbon black (Tokai, 8.0 vol.%) gives high moduli, low critical strain, and low loss tangent, thus resulting in high bondline thickness, though the high thermal conductivity due to the high solid content results in high thermal contact conductance for rough (15 lm) proximate surfaces. Antioxidants enhance the solid-like character, increase the yield stress, plastic viscosity, and bond-line thickness, and decrease the thermal contact conductance.

“…All levels of thermal stability shown in Table I are low compared to levels attained by commercial thermal pastes that are similarly tested. 32 However, they can be significantly improved by the use of antioxidants. Commercial thermal pastes tend to contain antioxidants.…”

Section: Viscositymentioning

confidence: 99%

Electrically Nonconductive Thermal Pastes with Carbon as the Thermally Conductive Component

Howe

2007

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.