Full details of the technique, which Bruno Michel, manager of the advanced thermal packaging group at the IBM Laboratories, says is one of the most promising that the group is researching, are due to be given at the ITherma conference next week in San Diego, California. The seminar on chip cooling is aligned to the IEEE organized Electronic Components and Technology Conference.

Michel said recent experiments with the immersed jet impingement technique have shown cooling power densities of up to 370W/cm² with a single phase water cooler.

The current limit of most air cooling technologies now in use is about 60 W/cm², and Michel says most chip makers will stick with air cooling techniques until other alternatives being researched can be shown to be more cost effective.

In the IBM Zurich set-up, the nozzle pitches are about 100 micron for typical microprocessor cooling applications. Using parallel inlet and outlet manifolds, the team has implemented a distributed return concept that Michel says can scale up to 50,000 nozzles on an area of just 4cm².

“We believe a large number of small and short channels will perform better than a single large channel, and that arrays of tiny nozzles perform better than a single large nozzle.” He adds the immersed jet impingement set-up, where the direct cooling of the chip backside eliminates a thermal interface between chip and coolant, is a very promising technique, but stresses that the work is still at an early stage.

He adds one of the main challenges of direct jet coolers is finding a way to overcome the need for a coolant-isolation scheme. Michel maintains one promising method being followed is to fix the jet nozzle plate to a chip back-side at the periphery using a low temperature bonding process that creates a hermetic seal.

As well as liquid jet impingement cooling, the team at Zurich is also looking into miniaturized convective cooling.

By: DocMemory
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