by Debra Vogler, senior technical editor, Solid State Technology

August 21, 2008 - This week Dow Corning unveiled a new thermally conductive compound, called "TC-5688," at the Intel Developer Forum (8/19-8/21, San Francisco, CA), touting it for use with Intel's newest mobile microprocessor, the Intel Core2 Extreme mobile processor QX9300.

The significance of the new non-curing thermal interface material (TIM) is its resistance to "pump out" -- i.e., thermal resistance does not increase under power cycling -- that has been seen with materials in the past. This makes it suitable for multi-chip packaging applications (see figure below). The company says the material exhibits "extremely low thermal resistance" at 0.05°C-cm²/W and high thermal conductivity at 5.67 W/mK

Andrew Lovell, industry marketing specialist at Dow Corning, explained to SST that during power cycling, microprocessor die can flex due to coefficient of thermal expansion (CTE) mismatch, placing thermo-mechanical stress on a TIM. "Multi-chip packages may enhance these stresses due to potential die height offset and other factors," he said. Dow Corning benchmarked its TC-5688 against two competing materials on a multi-chip tester that simulates a mobile processor. The power cycling consisted of the device being on for six minutes and then off for six minutes; the junction temperature reached ~85°C during the testing. The cycle was repeated ~2000 times.

"While the thermal grease and phase change material exhibit rapid and significant degradation of their thermal properties, TC-5688 shows almost no sign of change in performance," said Lovell. In particular, the phase-change material that was tested showed breakdown after ~500 power cycles. -- D.V.

Power cycling data on a multi-chip tester. (Source: Dow Corning)
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