| Objectives | Background | Approach |
To construct and evaluate compact, cost-effective
high performance thermosyphons using various synthetic
high thermal conductivity materials, with potential for
easy integration into packaging for high heat flux applications.
New concepts of high performance heat sinks for heat removal rates of 100 W/cm2 or higher have been proposed by some CALCE members. These involve liquid cooled heat sink configurations with potential for cost effective fabrication. Incorporated within the liquid heat sink system, a boiling enhancement structure made of high thermally conductive material, in conjunction with the high removal capability of liquids makes this an attractive option for certain high performance applications. Boiling enhancement structures can be attached directly to the chip, thereby eliminating many of the interface resistances. The availability of low thermal resistance bonding techniques is key to getting the maximum advantage of the high thermal conductivity of the boiling structure material for heat spreading.
This project will evaluate the performance of various high thermally conductive materials for use in fabricating heat exchange structures, employing two-phase flow. CALCE has extensive experience with thermosyphons for high performance passive heat removal. This project will extend our prior work by first optimizing the performance of existing liquid cooled thermosyphon technology, and then testing various materials for the fabrication of the boiling enhancement structures. The thermosyphon optimization portion of this project will be performed by testing such physical changes in the existing system as tubing position, tubing size, and structure-to-chip attachment techniques. Once the thermosyphon is thought to be at its highest performance level, heat exchanger structures of varying materials will be tested to find even higher performance over the presently used copper structures. Such high thermally conductive materials that are in consideration are sintered copper, graphite foam, and eventually diamond. Special attention will be paid to identifying the best bonding and assembly techniques. The heat removal capabilities of these structures will be experimentally evaluated by supplying known power inputs and measuring resulting temperatures of thermal test dies attached to them.