Graphite Foam

Minhua Lu

Larry Mok

IBM T.J. Watson Research Center,

1101 Kitchawan Road,

Yorktown Heights, NY 10598

R. J. Bezama

IBM Microelectronics Division,

Route 52,

Hopewell Junction, NY 12533

A Graphite Foams Based Vapor

Chamber for Chip Heat Spreading

A vapor chamber using high thermal conductivity and permeability graphite foam as a

wick has been designed, built, and tested. With ethanol as the working fluid, the vapor

chamber has been demonstrated at a heat flux of 80 W / cm2. The effects of the capillary

limit, the boiling limit, and the thermal resistance in restricting the overall performance

of a vapor chamber have been analyzed. Because of the high thermal conductivity of the

graphite foams, the modeling results show that the performance of a vapor chamber

using a graphite foam is about twice that of one using a copper wick structure. Furthermore, if water is used as the working fluid instead of ethanol, the performance of the

vapor chamber will be increased further. Graphite foam vapor chambers with water as

the working fluid can be made by treating the graphite foam with an oxygen plasma to

improve the wetting of the graphite by the water. DOI: 10.1115/1.2351908

Keywords: vapor chamber, graphite foam, heat spreader, chip cooling

Introduction

As a result of CMOS scaling, the circuit density and power

density of semiconductor chips are increasing. According to the

2004 update of The International Technology Roadmap for Semiconductors ITRS , the average power density of a chip may soar

to nearly 140 W / cm2 in a few years 1 and the average power

density of high-performance chips, especially at the hot spots,

could be even higher. Because of this high heat flux, it seems

inevitable that the use of liquid cooling will increase. However,

the engineering complexity as well as the costs associated with

liquid cooling makes it difficult to implement in products 2 .

Extensive efforts to extend the limits of air cooling are underway,

where...