IBM's cool discovery

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Not a great title, but it’s late in the day.

Reader Jason Blair has pointed us to an article over at Ars Technica about IBM’s discovery that how you pack the thermal paste on to a processor can make a big difference.

The Cliff’s notes (but the whole thing is interesting if you have the time to click over and read it):

A CPU’s heatspreader is normally attached directly to the core by use of a paste or glue that has been enriched with micrometer-sized ceramic or metal particles. These particles then form heat-evacuation bridges between the core and the cooler, and it’s these bridges that carry heat into the heatspreader.

In its current form, the process is quite inefficient: IBM’s says that up to 40% of a CPU’s total thermal budget (i.e., the cooling capacity available to draw heat away from the core) is consumed by these particles. This inefficiency is made worse because the particles aren’t truly spread evenly throughout the paste. Instead, particles clump together, forming what IBM refers to as the “Magic Cross”, as shown below at Figure 1. This thickened area is a non-homogeneous mixture of paste and particles that dramatically worsens total cooling efficiency across the core.

IBM’s solution was to design a series of micrometer-length trenches into the copper cap that sits above the CPU core, as shown in the top diagram (“hierarchical branched channels”). These larger and smaller trenches allow for paste to be evenly distributed at precisely the points where it would normally pile up and form a Magic Cross-like structure.

The results are quite impressive. Paste thickness could be reduced by a third, and the pressure required to properly fit a CPU cooler on top of a core was cut in half. All of this, and IBM says that cooling capabilities are effectively doubled.

That’s right, doubled. Hopefully Intel and AMD will adopt the technology and this stuff will start appearing in a supercomputer near you.