LOSTCIRCUITS

Acknowlegements:

Carbon Black was provided by Deborah D.L. Chung, Ph.D., Niagara Mohawk Endowed Chair Professor of Materials Research, Composite Materials Research Laboratory, University at Buffalo, State University of New York, who we also wish to thank for helpful discussions and comments.

Further Readings:

• Chia-Ken Leong and D.D.L. Chung, "Carbon Black Dispersions as Thermal Pastes that Surpass Solder in Providing High Thermal Contact Conductance", Carbon 41(13), 2459-2469 (2003).
• Yunsheng Xu, Xiangcheng Luo and D.D.L. Chung, "Lithium Doped Polyethylene-Glycol-Based Thermal Interface Pastes for High Thermal Contact Conductance", J. Electronic Packaging 124(3), 188-191 (2002).
• D.D.L. Chung, "Thermal Interface Materials", J. Materials Engineering and Performance 10(1), 56-59 (2001).

Summary

The development of thermal interface materials (TIM) has focused for several years on high thermal conductance. However, recent research has targeted increased spreadability and elasticity of the filler materials rather than high conductance that is necessary to overcome thicker interface layers. Carbon Black is one of the new "wonder substances" even though the theory behind its action strictly abides by the laws of physics.

Lab and theory are one thing, daily life and the inadequacies of commercially available products are another issue altogether. We have brought the pioneer in TIM, that is Arctic Silver out of retirement and compared it with the new kid on the block as well as with the latest offering from Arctic Silver, that is Céramique and have the results all at one glance using dynamic temperature monitoring during one run of 3DMark2001SE.

The cooling industry is thriving on new designs that have very little in common with the solutions that we saw only some 5 years ago and which would, in most cases, only suffice to delay the thermal death of today's processors. All copper or aluminum-copper hybrid designs are standard today, huge surface areas help to increase dissipation of the thermal energy into the environment and solid cores are mandatory to buffer the transients in heat output as generated in a typical home user environment.

Carbon Black

"Carbon Black" as it arrived from the Composite Materials Research Laboratory at SUNY Buffalo. Carbon Black thermal paste invention is the subject of a filed patent and the technology is available for licensing from State University of New York by contacting Dr. Chung.

One of the critical questions is still, how to transfer the heat from the CPU to the heatsink. Thermal compounds amongst which are the pink interface pads, silicon-based zinc emulgates or else some carefully balanced copper, silver or ceramique-based mineral oil suspensions are have promised miracles in the past and yet failed to deliver the "cooler's paradise". Admittedly, there are differences between the pink or grey pads and any cooling paste, however, the differences appear to not so much in the thermal conductivity but rather in the mechanical consistency of the compound.

In the past, we have argued that there is very little difference between cod liver oil and arctic silver, aside from the naturally occurring degradation of the first and the rather odor-less nature of AS. Combined, these features make a decision rather simple. We have further raised the issue that, no matter what thermal conductance any medium might have, it won't make any difference if the compound was not applied properly. Moreover, we have repeatedly criticized claims that a thicker, richer compound would do any good, on the contrary, the opposite is true which is the reason why standard mineral oil works quite well. Our recommended compound for the past few years, therefore, has been Arctic Silver, diluted with the RadioShack Thermal Pen compound that turns the highly viscous AS into a silvery oil film covering the die / processor surface.

In lieu of any boring repetitions of numbers, suffice it to say that at an average thickness of 25 µm for any compound, its thermal conductance would have to be increased by a factor of about 100 to result in a drop of CPU temperature by a single centigrade. On the other hand, variation in the thickness or the consistency of the interface compound will have a huge impact on the overall cooling efficacy of the entire setup, especially with respect to local hot spots that can easily evade any detection by standard measuring techniques.

We have had numerous discussions with who we believe are the top people in the cooling field, namely Gabe Rouchon (Swiftech), Nevin House (Arctic Silver) and a few others from Thermacore, Arkua, Zalman (in no particular order). The main argument that has been made against a low-viscosity transfer medium is the lack of endurance, that is, even if the solutions we brew up in our own labs worked during the average testing period, there was no guarantee that the consistency would remain unaltered during a prolonged period of use, something to keep in mind especially for OEM applications. A case in point is the so-called creeping of silicon-based compounds that, after a few weeks of use can result in gaps in the thermal interface media (TIM) which then block thermal transfer.

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