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Peltier Enhanced Heat Spreading for Localized Hot Spot Thermal Management

[+] Author Affiliations
Gary L. Solbrekken

University of Missouri at Columbia, Columbia, MO

Paper No. IPACK2005-73471, pp. 2199-2205; 7 pages
doi:10.1115/IPACK2005-73471
From:
  • ASME 2005 Pacific Rim Technical Conference and Exhibition on Integration and Packaging of MEMS, NEMS, and Electronic Systems collocated with the ASME 2005 Heat Transfer Summer Conference
  • Advances in Electronic Packaging, Parts A, B, and C
  • San Francisco, California, USA, July 17–22, 2005
  • Conference Sponsors: Heat Transfer Division and Electronic and Photonic Packaging Division
  • ISBN: 0-7918-4200-2 | eISBN: 0-7918-3762-9
  • Copyright © 2005 by ASME

abstract

Localized areas of high heat flux on microprocessors are currently being identified as a dominant challenge for the thermal management community. Heat flux values up to 1 kW/cm2 prevailing over a fraction of the overall CPU surface area create local hot spots that need to be cooled. However, thermal solutions designed for the maximum heat flux overcool the rest of the CPU, wasting resources and creating large on-die temperature gradients. Wasting resources obviously has a negative economic and thermodynamic impact. However, it has been argued that large on-die temperature gradients reduce chip reliability and increase the difficulty in laying out the electric circuits. The current study proposes a strategy to reduce local hot spots by enhancing heat spreading through the use of the Peltier effect. The Peltier effect is most commonly associated with the operation of thermoelectric modules. In thermoelectric modules, heat is transported across the module by electrons. Ideally, the material used for the thermoelectric module would have a very low thermal conductivity to reduce the amount of back heat conduction through the thermoelectric elements, and the electric resistivity would be very low to minimize the Joule heating. Using today’s best commercially available thermoelectric materials, the thermal conductivity, electric resistivity, and Seebeck coefficient are such that the COP for the thermoelectric module is on the order of 1. This implies that in order to cool a processor dissipating 100W, an additional 100W of electric power must be supplied to the thermoelectric module. A total of 200W must then be rejected by the heat sink and any building HVAC system. A more pragmatic approach is to use the Peltier effect to not cool the entire CPU, but rather only the high heat flux region. This is accomplished by placing the thermoelectric elements laterally on the backside of the CPU. The cooling junction is placed in the proximity of the high flux region, while the heating junction is placed in contact with the CPU in low heat flux area that can tolerate the additional heat, effectively creating an active heat spreader. The Peltier enhanced heat spreading proposed here is shown to provide a reduction in the temperature of a localized hot spot relative to passive heat spreading. The amount of reduction in temperature depends on the thickness of the material as well as the thermal conductivity, but values up to 50% are illustrated.

Copyright © 2005 by ASME

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