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Carbon Nanotube Sheet Metal Matrix Composites as Die Attach Thermal Interface Materials
Keywords: Carbon Nanotube, Thermal Interface Materials, Metal Matrix Composites
Carbon nanotube (CNT) sheets have outstanding thermal and mechanical properties in the in-plane direction yet they typically have high thermal resistance across their thickness because heat transfer in this direction is orthogonal to the direction of CNT alignment. Metalizing the CNT sheets provides a means to increase the cross plane thermal conductivity of CNT sheets by lowering contact resistance between individual tubes in the sheet and reducing the thermal resistance at contacts to the CNT sheet when the metal is diffusion bonded to the interface surfaces. Two techniques were implemented to metalize CNT sheets: sputter deposition of gold nanoparticles in high vacuum, and deposition of palladium nanoparticles using palladium thiolate solution. The metalized surfaces were then annealed to grow and connect the nanoparticles into a matrix. Scanning electron microscopy was used to study the nanoparticle morphology and growth dynamics. Annealing the samples increased nanoparticle size and heating of the samples during deposition initiated alignment of the nanoparticles along CNT sidewalls. These CNT sheet were then diffusion bonded between a silicon substrate and a silver foil to act as a die attachment material. Photoacoustic (PA) measurement was employed to determine the total thermal resistance of the CNT sheet interfaces with and without metallization at a contact pressure of 20 psi. The thermal resistance of CNT sheet interfaces without metal bonding was 84.0 mm2K/W ±10mm2K/W. Metallization and bonding produced a substantial decrease in the total thermal resistance of the interface. These results and the mechanism that govern the improved performance will be discussed to conclude this talk.
Cristal J. Vasquez, Graduate Research Assistant
Georgia Institute of Technology
Atlanta, Georgia

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