Efficient Cooling of Multiple Components in a Shielded Circuit Pack

[+] Author and Article Information
Marc Hodes

Bell Laboratories, Lucent Technologies, Murray Hill, NJ 07974hodes@alcatel-lucent.com

Cristian Bolle, Paul Kolodner

Bell Laboratories, Lucent Technologies, Murray Hill, NJ 07974

J. Electron. Packag 129(2), 216-218 (Sep 05, 2006) (3 pages) doi:10.1115/1.2721095 History: Received December 12, 2005; Revised September 05, 2006

We describe a technology in which multiple components inside a circuit pack shielded from electromagnetic interference (EMI) are efficiently cooled by individual heat sinks that protrude into an external airflow through openings in the lid of the shield. Compliant, electrically conductive gaskets are used to form perimeter seals between the bases of the heat sinks and the lid of the enclosure. The gaskets accommodate variations in the heights of the components and allow solid-to-solid contact in the thermal-grease-filled interface between the components and their heat sinks without compromising EMI shielding. This technology provides efficient cooling because the heat sinks can be tailored to the thermal loads of the individual components. Moreover, a set of small heat sinks presents a lower flow resistance to the cooling airflow than the conventional configuration of fins covering the entire lid of an EMI shield. We have examined the implementation of this solution by numerical modeling and by experiment. It leads to acceptable thermal performance, and lower flow resistance relative to the conventional approach. It may reduce cost and weight and it eases rework.

Copyright © 2007 by American Society of Mechanical Engineers
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Grahic Jump Location
Figure 4

Picture showing a circuit pack and how the current technology would be implemented on it. Heat sinks are shown in red and EMI gaskets in light blue

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Figure 3

Oblique view of the computational model of the original circuit-pack design

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Figure 2

A proposed solution: each device is cooled by its own heat sink, which is sealed against a flat lid using a compliant, electrically conductive gasket to compensate for variations in chip height. (Optimally thin layers of thermal interface material between the tops of the components and the bottoms of their respective heat sinks are not shown)

Grahic Jump Location
Figure 1

The basic problem: in a shielded enclosure with many heat sources, because allowances must be made for variations in chip height, there is inevitably a grease-filled gap between the top of each device and the bottom of its heat-transfer block




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