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CARBON NANOTUBES

Application of Carbon Nanotubes to Thermal Interface Materials

[+] Author and Article Information
Drazen Fabris1

Department of Mechanical Engineering, Santa Clara University, Santa Clara Center for Nanostructures,  Santa Clara University, Santa Clara, California 95053dfabris@scu.edu

Michael Rosshirt, Christopher Cardenas

Department of Mechanical Engineering, Santa Clara University, Santa Clara Center for Nanostructures,  Santa Clara University, Santa Clara, California 95053

Patrick Wilhite, Toshishige Yamada

Santa Clara Center for Nanostructures,  Santa Clara University, Santa Clara, California 95053

Cary Y. Yang

Department of Electrical Engineering, Santa Clara University, Santa Clara Center for Nanostructures,  Santa Clara University, Santa Clara, California 95053

1

Corresponding author.

J. Electron. Packag 133(2), 020902 (Jun 07, 2011) (6 pages) doi:10.1115/1.4003864 History: Received December 06, 2009; Revised February 18, 2011; Published June 07, 2011; Online June 07, 2011

Improvements in thermal interface materials (TIMs) can enhance heat transfer in electronics packages and reduce high temperatures. TIMs are generally composed of highly conductive particle fillers and a matrix that allows for good surface wetting and compliance of the material during application. Two types of TIMs are tested based on the addition of carbon nanotubes (CNTs): one mixed with a commercial TIM product and the other only CNTs and silicone oil. The materials are tested using an in-house apparatus that allows for the simultaneous measurement of temperature, pressure, heat flux, and TIM thickness. Results show that addition of large quantities of CNTs degrades the performance of the commercial TIM, while the CNT-silicone oil mixtures showed improved performance at high pressures. Thickness and pressure measurements indicate that the CNT-thermal grease mixtures are more compliant, with a small increase in bulk thermal conductivity over the range of tested pressures.

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Copyright © 2011 by American Society of Mechanical Engineers
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Figures

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Figure 1

(a) A cross-sectional view of the TIM apparatus revealing the meter bars shown centered in the lower half, the thermocouple holes along the center of the two meter bars, the heater holes above the upper meter bar, the insulation shroud (in black), the guard heater, and the heat sink beneath the lower meter bar, (b) TIM system assembly with micrometer for TIM thickness measurements

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Figure 2

The TIM apparatus measures Rtc″ using eight K-type thermocouples to extract the thermal gradient along an upper and lower meter bar. The temperature drop at the interface is extrapolated from the gradient.

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Figure 3

FLOWTHERM simulation of the temperature profile through the test section of the TIM apparatus including the insulation and guard heater. The test section in the center shows 1-D conduction while the insulation and guard heater protect the system from radiation and convection losses.

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Figure 4

Scanning electron microscope image of Artic Silver® 5 and CNTs. The mixture is composed of small (micron scale) silver particles and long submicron diameter CNTs visible as the curled tubes.

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Figure 5

Total thermal resistance per unit surface area, Rtc″, of Arctic Silver®5 and CNT TIM mixtures over the applied presure range. CNT inclusions changed the compliance of the TIM in all cases while the lowest percent weight fractions demonstrated the best thermal performance.

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Figure 6

Total thermal resistance per unit surface area relative to in situ sample thickness for CNT-AS mixtures. This quantity is inversely proportional to the mixture’s bulk thermal conductivity.

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Figure 7

Thermal contact resistance, Rtc″CNT, and silicone oil mixtures. No trend line is plotted for the Arctic Silver®5 data. CNT-oil mixtures show greater reduction in Rtc″ with increasing pressure.

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Figure 8

Total thermal resistance per unit surface area relative to in situ sample thickness for the silicone oil and CNT TIMs. A greater reduction in resistance with thickness occurs at higher pressures.

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