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Research Papers

Development of Scalable Silicon Heat Spreader for High Power Electronic Devices

[+] Author and Article Information
Qingjun Cai

 Teledyne Scientific & Image Company, 1049 Camino Dos Rios, Thousand Oaks, CA 91360qcai@teledyne.com

Bing-Chung Chen, Chailun Tsai, Chung-lung Chen

 Teledyne Scientific & Image Company, 1049 Camino Dos Rios, Thousand Oaks, CA 91360

J. Thermal Sci. Eng. Appl 1(4), 041009 (Jun 24, 2010) (7 pages) doi:10.1115/1.4001689 History: Received November 12, 2009; Revised April 21, 2010; Published June 24, 2010; Online June 24, 2010

A silicon heat spreader, called hexcell, is presented to develop thin, strong, interconnected, and scalable heat transfer devices for high power electronics cooling. Several key technical aspects, reflected characteristics of fabrication, thermomechanical, hermetic sealing, and heat transfer on wick structures, have been performed to underlie the system integration. The hexcell prototypes are developed through microelectromechanical system photolithography and dry-etch processes, associated with eutectic bonding to form a sealed silicon chamber. Hexcells are structurally optimized to minimize the stress, expanding the maximum operating pressure and temperature ranges. As a result, the developed hexcells can survive 0.32 MPa pressure difference and are able to sustain an operating temperature over 135°C. Experimental results of both helium and vapor leakage tests indicate that eutectic bonding with limited bonding surface area may not provide hermetic sealing. Vacuum sealing is achieved by introducing epoxy to fill the leak pine-holes on the bonding interface. The developed hexcell wick exhibits good heat and mass transport performance, reaching a maximum 300W/cm2 cooling capacity with 35°C superheat as demonstrated with a prototype of a 2×2mm2 heating area.

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Copyright © 2009 by American Society of Mechanical Engineers
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Figures

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Figure 1

Schematic of the hexagon cellular structure

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Figure 3

Deformation and stress contour, subject to 1 MPa pressure load: (a) baseline vapor chamber with no internal support, maximum stress 826 MPa; (b) central bonded posts, diameter 0.88 mm, maximum stress 557 MPa

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Figure 4

Parameter study of optimal post set location. Maximum stress: (a) 191 MPa, (b) 131 MPa, and (c) 344 MPa.

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Figure 5

Eutectic bond interface

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Figure 6

Sidewall metalization

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Figure 7

MEMS fabrication of a silicon hexcell

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Figure 8

Bonded silicon samples: (a) thickness dimensions of the sample and (b) bond alignment of the top and bottom silicon wicks

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Figure 9

Hexcell sealing, charging, and sidewall bonding: (a) a charged for vacuum sealing tests and (b) two sidewall-bonded hexcells

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Figure 10

Test chamber for high heat flux experiments

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Figure 11

Failure modes of the hexcell: (a) thick edge bond and failed post bond, (b) thin edge bond and failed post bond, and (c) failure caused by mechanical impact

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Figure 12

Experimental results of vapor leakage

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Figure 13

Liquid splashes during intense boiling/evaporation phase change

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