Spreading in the heat sink base: phase change systems or solid metals??

Presently, the microelectronics industry needs thermal solutions that are able to dissipate high heat fluxes at low thermal resistance. The majority of original equipment manufacturers (OEMs) within the microelectronics industry would like to achieve this by extending the application of air-cooling technologies since it implies minimal impact to the design of computer systems and is known to be a cost effective solution space. Spreading resistance through the base of the heat sink is one major component of the total thermal resistance from the silicon junction to the local ambient, especially if larger volume heat sinks are to be used. Until now, most of the research has focused on using phase change systems (i.e., vapor chambers) for reducing the spreading resistance of the heat sink base. Since no significant improvements have been achieved, there is a need to determine the envelope of the limitations for phase change-heat spreaders used in processor cooling, and to compare their performance against high thermal conductivity solid metals. Two simple models are presented to address the heat transfer limitations in phase change systems. Using these models, the ratio of phase change spreading resistance over solid metal spreading can be estimated.