Just last week, Intel Corporation (Santa Clara, CA) earned U.S. Patent 7,704,791 for packaging of integrated circuits with carbon nanotube arrays to enhance heat dissipation through a thermal interface.
On the surface of it, this sounds like an exciting development in thermal management and heat sink invention, as noted in the article written by Alton Parrish on the news site “Before It’s News“:
According to inventors Valery M. Dubin and Thomas S. Dory a layer of metal is formed on a backside of a semiconductor wafer. Then, a porous layer is formed on the metal layer. A barrier layer of the porous layer at the bottom of the pores is thinned down. Then, a catalyst is deposited at the bottom of the pores. Carbon nanotubes are then grown in the pores. Another layer of metal is then formed over the porous layer and the carbon nanotubes. The semiconductor wafer is then separated into microelectronic dies. The dies are bonded to a semiconductor substrate, a heat spreader is placed on top of the die, and a semiconductor package resulting from such assembly is sealed. A thermal interface is formed on the top of the heat spreader. Then a heat sink is placed on top of the thermal interface.
Nano-carbon tube based materials have promised a revolution in thermal interface material technology but have never really delivered. In fact, many of us in thermal engineering have been anxiously awaiting a breakthrough development using nano-technology.
Nano-carbon tube technology has a lot of promise to solve the age old problem of contact resistance. The promise of nano-technology includes a few approaches from growing it on the semiconductor chip and eliminating TIM1 to growing it on the backside of the heat sink and minimizing or eliminating TIM2.
Unfortunately, many of these venture funded companies are no longer in business as the technologies maturation and commercialization simply hasn’t been there. From our vantage point as thermal scientists and engineers at ATS, nano-materials are an attractive proposition in certain university or corporate laboratories; with funding you can experiment and see if these technologies lead someplace. However, the real world issues of production in volume, sustaining production quality, cost, application and the biggest of all â€“ the environmental hazard (nano-carbon tube has similar characteristics as asbestos) continue to create barriers to the real world utility of nano-carbon tube materials. While being a fascinating material to work with, the widespread, real world applications are limited at this juncture of technology life cycle and perhaps for the foreseeable future.
Perhaps most useful to the thermal management industry and to real world thermal engineering problems would be a comparison between nano-material based heat sinks and Aluminum or Copper; especially on a cost performance basis. ATS did a comparison between three geometrically identical heat sinks made of Copper, Aluminum and High-performance Graphite (though not nano-tube) and we did not see any difference. Surprisingly, the only advantage that high-performance Graphite offered was its light-weight, but, thermally and mechanically it was the worst (readers may download a copy of our study at ECNMag.com at this link: “Comparing the Impact of Different Heat Sink Materials on Cooling Performance“).
If we extrapolate our concerns and findings in our study to a heat sink made of nano-carbon tube material, (laying aside environmental factors and poor performance as nano-carbon tubes are isotropic â€“ heat goes only in one direction), cost is a concern. Today’s electronics’ market is highly cost sensitive to their thermal development budget on a given project. Also, RoHS compliance is mandatory and studies are continuing on the health impact of nano-technology materials. Such work may not yield products for another five to 10 years. For the latest in the U.S. National Initiative in nano-scale technology, please visit the NNI’s 2011 Budget Supplement and Annual Report.
ATS applauds Intel for thinking out of the box and trying to create new ways of approaching the issue of thermal management. Semiconductor companies such as Intel who see themselves as part of the solution to thermal management are welcomed as fellow travellers to cooler and more reliable electronics.