Computer processors could be cooled more effectively simply by improving the way different bits are glued together, researchers say.
Keeping chips cool is a major challenge in the constant drive to increase processor performance, says Bruno Michel, who led the research at IBM鈥檚 Zurich Research Laboratory in Switzerland.
Currently, this involves attaching a piece of metal called a heat sink to the surface of a chip. This conducts heat away from the circuit and is often finned to increase its surface area. These heat sinks are usually air-cooled by a fan.
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However, Michel and colleagues found that the paste used to attach heat sinks to chips suffers from unusual fluid dynamics during attachment, with more of it accumulating along an X-shape between corners.
The problem occurs when the heat sink is being applied to the chip. 鈥淲hen you are squeezing paste out of the gap it always moves to a path of least resistance, moving towards the edges,鈥� says Michel. At the diagonals the force pushing it towards both edges is equal, causing it to build up along these lines, he explains.
Irrigation system
This interferes with the heat transfer process because it creates hotspots, with thicker regions of paste failing to conduct the heat properly, preventing parts of the chip from cooling effectively.
IBM鈥檚 solution to this problem is a pattern of micrometre-sized channels in the under-surface of the heat sink. Working with a company called Momentive Performance Materials, they created a patterned network of channels consisting of different sizes.
Collectively these channels act like an irrigation system for the paste. The pattern is designed to draw it away from areas where it would normally build up, providing a much more even distribution.
Reliability issue
Tests have shown that this approach reduces the thermal resistance of the paste layer by more than three times, meaning it retains significantly less heat. As a result, more heat is transferred to the sink and removed by the fan.
Bashir Al-Hashimi of the electronic systems design group at Southampton University in the UK says heat is 鈥渧ery much a reliability issue鈥�, since components on a chip exposed to more heat are more likely to fail. Al-Hashimi sees IBM鈥檚 approach as a simple yet sensible solution to the problem.
Often space is wasted on a chip to keep the power down and prevent overheating, Michel says. Using micro-channels could allow space to be used more efficiently and so help increase the speed of processors, he suggests.
The micro-channels could start to appear in chips in 2008. The research was presented at the IEEE Semi-Therm Symposium in San Jose, California in the US.
