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April 8th, 2009

Diamond-copper combo improves heat sink

Published on April 8th, 2009 | By: pwray@ceramics.org
Diamond crystal with a carbide film (white), Credit: © Fraunhofer IFAM

Diamond crystal with a carbide film (white). Credit: © Fraunhofer IFAM

Researchers at one of Germany’s Fraunhofer Institute think they have come up with a better material to dissipate heat in electronics, using a material that combines traditional materials like copper with diamond power.

A novel material is needed because of the new challenges arising as more and more previously separated electronic units are being combined on single chips. More components mean more heat in a shrinking volume, yet components and connecting elements need to be kept in the safe zone – 90°C to 130°C.

Currently, copper or aluminum plates are attached to the chip’s components to act as heat sinks. But, the expansion and contraction of the metal plate (which can expand about three or four times as much as the silicon and other ceramic material in the rest of the chip) often leads to cracks and breaks at solder points.

Fraunhofer staffers at the Institute for Manufacturing Engineering and Applied Materials Research IFAM in Dresden have been looking for an alternative to the copper or aluminum plates. Their ideal material would be something that conducts heat better and has a small expansion coefficient, and these researchers think they have found it.

“We did this by adding diamond powder to the copper. Diamond conducts heat roughly five times better than copper,” says Thomas Schubert, project manager at IFAM. “The resulting material expands no more than ceramics when heated, but has a conductivity one-and-a-half times superior to copper. This is a unique combination of properties.”

The researchers faced one major hurdle: How to bond the diamond and copper? “One ingredient we can use to achieve this [bond] is chrome. Even small amounts form a carbide film on the diamond surface, and this film easily bonds to copper,” Schubert explains.

Fraunhofer is partnering on this project with Siemens and Plansee, among others, as part of the EU project “ExtreMat.” ExtreMat is an interesting effort to accelerate novel material development. Its website describes it as a project that “assembles this critical mass of experts from different materials-related industries, research centers, universities and science institutes in Europe in a multi-sectorial and cross-cutting approach. The ExtreMat project consortium currently comprises 37 institutions in 12 European countries. It forms the unique pool of expertise, competencies and facilities which is needed to fulfill the ambitious objectives of this Integrated Project.”

The Fraunhofer effort is part of a special ExtreMat subproject “to develop novel heat sink composites and to test their performance under extreme loading conditions. By extreme, they mean up to 1000°C. The route that’s been laid out is to use a copper matrix reinforced with ceramic and intermetallic (nano) particles or fibers. Besides something with a thermal conductivity similar to copper, they are looking for materials that also have a heat flux removal capability of up to 20 MW/m2.


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