Why Liquid Cooling?

Abstract

We have reached the technology pivot from air to industrial scale board-level liquid cooling of high-heat flux electronics. This has been on the horizon for a decade or more, and we have watched it getting closer as die-level heat fluxes and package densities relentlessly rose.

Forcing more air does not help since convective heat transfer coefficients have already flat-lined and fan speed, pressure, power and noise levels have hit thresholds.

The only option available to keep hanging on to board-level air-cooling is to engineer increasingly larger fin structures with bigger/more fans.

Larger air-cooled heat sinks require sophisticated integrated heat spreaders, such as heat pipes and vapour chambers, as the metal fins get progressively further away from the source.

This ballooning of the heat sink has managed to keep air-cooling on the table. However, the idea of cooling highly integrated, highly miniaturised, highly compact, highly cost-optimised boards with proportionately massive, heavy and expensive heat sinks is contrary to the entire notion of miniaturising electronics. From an electronics packaging perspective, the board and the air-cooling technologies are moving in opposite directions.

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A.J.Robinson