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|Thermal Resistance Characterization of a Nano-Graphite Composite Thermal Interface Material|
|Keywords: thermal interface material, thermal resistance, thermal testing|
|In high power microelectronics packaging, the thermal resistance can be divided into two dominant parts: the thermal resistance from the heat sink to air and the thermal resistance of the interface material, the latter of which counts for over 50% of the total package thermal resistance. It is not surprising that innovative thermal interface materials have been an active area of research. There are two main approaches: nano-structured materials, such as carbon nanotubes or nano-graphite composites; metallic materials. Accurately testing and benchmarking these innovative TIMs is challenging as their expected thermal resistance can be as low as 0.01 0C/W. Measuring such a low resistance is beyond the capability of commercially available testers. We investigated composites containing Graphite Nano-Platelets (GNPs), which share the same high thermal conductivity as carbon nanotubes but are easier to handle. Yu, et al reported a graphite nanoplatelet-epoxy composite with a thermal conductivity of 6.44 W/mK -- a thermal conductivity enhancement of more than 3000% over the epoxy. However, this number is still relatively low as compared with the natural graphite thermal conductivity ~400 W/mK, and graphene thermal conductivity up to 3000 W/mK. We proposed a new formula matrix (using alternative polymers instead of epoxy) and created a grease-based material using GNPs provided by U. C. Riverside. In this paper, we will present testing results of nano-graphite composite TIMs using a proprietary designed high precision thermal resistance testing system as illustrated in Fig.1. The validation measurements were done with Sil-Pad 2000 samples of different thickness (10mil, 15mil and 20mil). The results are illustrated in Fig.2. There is good agreement between our measurements and those taken using the conventional ASTM D5470 method. This paper will serve two purposes. The first is to specify the design challenges for a high-precision TIM tester and how we performed design optimization to meet these challenges. The second is to present the thermal resistance measurement results of these nano-graphite platelet composites and compare them with commercial TIMs. This study will demonstrate that graphene composites are a promising TIM for high power electronic cooling applications. Zhu, L., Wong, C., “Well-Aligned Carbon Nanotubes for Thermal Interface Material Applications,” Thermal Interface Materials Symposium, Georgia Institute of Technology, Atlanta, Georgia, Sept. 27, 2006 Xu, J; Fisher, TS, “Enhancement of thermal interface materials with carbon nanotube arrays”, International Journal of Heat and Mass Transfer, 49 (9-10): P1658 May 2006 Aiping Yu, Palanisamy Ramesh, Mikhail Itkis, Elena Bekyarova, and Robert Haddon, “Graphite Nanoplatelet-Expoxy Composite Thermal Interface Materials”, The J. of Phys. Chem. Letters, C, R. J. Linderman, T. Brunschwiler, U. Kloter, B. Michel, and H. Toy, “Hierarchical Nested Surface Channels for Reduced Particle Stacking and Low-Resistance Thermal Interfaces”, Proceedings of Semitherm, 2007. David L. Saums, “Developments with metallic thermal interface materials”, electronics cooling, May, 2007 Clemens Lasance, Cameron Murray, David Saums and Marta Rencz, “Challenges in Thermal Interface Material Testing”, Proceedings of Semitherm, 2006, P42|
|Yan Zhang, Senior R&D Engineer
San Jose, CA