Year of Publication

2012

Degree Name

Master of Science (MS)

Document Type

Master's Thesis

College

Engineering

Department

Mechanical Engineering

First Advisor

Dr. Rodney Andrews

Abstract

High performance/small package electronics create difficult thermal issues for integrated circuits. Challenges exist at material interfaces due to interfacial contact resistances. Multiwall carbon nanotube (MWCNT) arrays are considered to be excellent candidates for use as thermal interface materials (TIMs) due to outstanding thermal/mechanical properties. In this work, MWCNT array TIMs are analyzed in aluminum and carbon fiber composites via flash diffusivity analysis. The effect of TIM thickness, areal/bulk density, surface cleanliness, and volumetric packing fraction; along with the effect of substrate finish and interfacial contact pressure on thermal performance are analyzed. Trends show the best TIMs possess low thickness, high bulk density and packing fraction, and clean surfaces. Pressure dramatically increases thermal performance after establishing contact, with diminishing returns from additional pressure. Diffusivities approaching 40 mm2/s and 0.65 mm2/s are recorded for aluminum and composite systems. Oxygen plasma etching and high temperature annealing (“Graphitizing”) are investigated as methods to remove amorphous carbon from array surfaces. Graphitized TIMs report diffusivity improvements up to 53.8%. Three methods of incorporating MWCNTs into composites are attempted for thermal/mechanical property enhancement. Conductance calculations show increasing diffusivity without increasing thickness enhances thermal performance in composites. MWCNTs for mechanical property enhancement produce no change, or detrimental effects.

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