IBM to Chips: Chill Out
By Suzanne Deffree -- 10/26/2006
Electronic News
Using a technique based on the human circulatory system, IBM researchers today presented an approach for improving the cooling of computer chips.
Delivered at the BroadGroup Power and Cooling Summit in London, IBM researchers discussed the technique, called “high thermal conductivity interface technology,” that they claim allows a twofold improvement in heat removal over current methods.
The technique is one of several being explored by scientists from the IBM Zurich Research Laboratory to address the problem of excessive heat brought on as performance continues to progress according to Moore’s Law.
“Electronic products are capable of amazing things, largely because of the more powerful chips at their heart,” said Bruno Michel, manager of the Advanced Thermal Packaging research group at IBM’s Zurich lab, in a statement this morning. “We want to help electronics makers keep the innovations coming. Our chip-cooling technology is just one tool at our disposal to help them do that.”
The approach used by IBM addresses the connection point between the hot chip and the various cooling components used to draw the heat away, including heat sinks. Currently, special particle-filled viscous pastes are typically applied to this interface to guarantee that chips can expand and contract with the thermal cycling. This paste is kept as thin as possible in order to transport heat from chip to the cooling components efficiently. However, IBM warned, squeezing these pastes too thin between the cooling components and chip would damage or even crack the chip if the conventional technologies are used.
To alter that, IBM researchers developed a chip cap with a network of tree-like branched channels on its surface. The pattern is designed such that when pressure is applied, the paste spreads much more evenly and the pressure remains uniform across the chip, allowing the right uniformity to be obtained with nearly two-times less pressure, and a 10-times better heat transport through the interface, according to IBM. IBM credited the design’s idea to biology, where systems of hierarchical channels can be found manifold in nature or the human circulatory system.
Looking Ahead to Water Cooling
The prototype demonstrated at today’s summit is part of a large effort within IBM’s Research and Development organizations to improve cooling performance of next and future generations of computer systems. Noted IBM, the cooling bottleneck results from the demand for more powerful computer chips, a severe constraint on overall chip performance, and added that today’s high-performance chips already generate a power density of 100 watts per square centimeter. Tomorrow’s chips may attain even higher power densities, IBM said, projecting surface temperatures close to that of the sun when not cooled (approx. 6000 °C).
Current cooling technologies, mainly based on forced air convection, or fans, blowing across heat sinks with densely spaced fins, have essentially reached their limits with the current generation of electronic products, according to IBM, which also pointed out that the energy needed to cool computer systems is rapidly approaching the power used for calculations, thus almost doubling the overall power budget.
“Cooling is a holistic challenge from the individual transistor to the datacenter. Powerful techniques, brought as close as possible to the chip right where the cooling is needed, will be crucial for tackling the power and cooling issues,” Michel said.
Beyond air-cooling systems, IBM’s Zurich researchers are taking their branched channel design and are developing an approach for water-cooling. Called direct jet impingement, it squirts water onto the back of the chip and sucks it off again in a closed system using an array of up to 50,000 tiny nozzles and a complicated tree-like branched return architecture, the company described.
Lab results of the water technique have demonstrated cooling power densities of up to 370 watts per square centimeter, more than six-times beyond the current limits of air-cooling techniques on less energy for pumping than other cooling systems do, IBM said.
