Nanoclay Paste as a Thermal Interface Material for Smooth Surfaces

Abstract

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.

Rheological Behavior of Thermal Interface Pastes

“…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.…”

“…Detailed information on the selected antioxidants is given in prior work. 22 Both the cases with and without antioxidants are included in the present study.The solid components used in the thermal pastes are carbon black (CB, including two types that differ in the aggregate size, as indicated by the DBP values 16 ; the type of larger aggregate size being Vulcan XC72R GP-3820, Cabot Corp., Billerica, MA, and the type with smaller aggregate size being Tokaiblack #3800, a graphitized carbon black supplied by Tokai Carbon Co., Ltd., Tokyo, Japan), trimethoxyoctylsilane-treated fumed alumina (Aeroxide ALU C 805, Degussa AG, Hanau, Germany 19 ), and nanoclay (Cloisite 15A, Southern Clay Products, Inc., Gonzales, TX; a natural montmorillonite phyllosilicate intercalated with an organic modifier, namely dimethyl dehydrogenated tallow, a quaternary ammonium salt at 125 meq/ 100 g clay 20 ). The compositions of the various pastes and the particle sizes of the fillers are listed in Table I.…”

“…Nanoscale solid components that have been found to be effective to various degrees include carbon black (CB), [12][13][14][15][16] graphite nanoplatelet (GNP), 17,18 fumed metal oxides (e.g., fumed alumina), 19 and nanoclay. 20,21 The rheological behavior refers to the flow behavior, which is basic to the behavior of any type of paste. This behavior pertains to the stress and strain associated with shear deformation of the paste at various strain rates and relates to the viscosity, yield stress, storage modulus, loss modulus, loss tangent, critical shear strain (strain at the limit of the linear regime in which stress and strain are linearly related), and their dependence on temperature and the formulation.…”

“…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.…”

Solder–Graphite Network Composite Sheets as High-Performance Thermal Interface Materials

“…The comparison involves a large variety of TIMs, due to the extensive prior work of one of the authors (D.D.L.C.). [1][2][3][4][5][6][7]10,11,20,21 EXPERIMENTAL PROCEDURES…”