The Woodruff School

SUMMARY

A significant portion of the thermal resistance of an electronic package is due to the thermal interface material (TIM) used to join different materials. With continued demands of device's performance and size, improvements of TIM selection and characterization are of increased importance. Due to the reported high axial thermal conductivity and robust mechanical properties, CNTs have attracted much attention as future TIMs. Due to their high processing temperatures (over 700 oC), transfer of the CNT array to a separate processed substrate has been of interest. The thesis focuses on the characterization and analysis of novel TIMs based on vertically aligned multiwall carbon nanotubes. The first part of the thesis describes the development of a microscopic infrared (IR) steady-state measurement of the total TIM thermal resistance. The technique is demonstrated to be effective in evaluation of commercial TIMs and is extended to the measurement of CNT-based TIM. Measurements are compared to measurements made through a laser flash technique. The performance of these materials after additional thermal reliability is also examined. The second part of the thesis theoretically analyzes the role of different interface structures for CNT based TIM, with particular emphasis on a metal based thermal conductive adhesive used to anchor a CNT array to an active die. A control volume approach which includes intrinsic thermal conductivity of the components and boundary thermal resistances expected in anchoring of the array is used to estimate the lowest potential thermal resistance through a parametric study. The results are then compared to the VACNT TIM measurements made through the steady-state IR measurement. Finally, a novel transient IR imaging technique is demonstrated for experimentally evaluating the thermophysical properties of a multilayer sample. This transient technique can provide additional insight into the individual thermal resistances which contribute to the total resistance, as measured through the steady-state IR technique and thus can be used as an effective tool in the characterization of TIMs. Future studies regarding further development and improvement of this method are outlined for its potential application in measuring next generation TIMs.

SUBJECT:	Ph.D. Dissertation Defense

BY:	Andrew McNamara

TIME:	Friday, November 8, 2013, 9:00 a.m.

PLACE:	MRDC Building, 2405

TITLE:	Characterization and Measurements of Next Generation Vertically Aligned Carbon Nanotube Based Thermal Interface Materials

COMMITTEE:	Dr. Yogendra Joshi, Co-Chair (ME) Dr. Zhuomin Zhang, Co-Chair (ME) Dr. Baratunde Cola (ME) Dr. Satish Kumar (MSE) Dr. Zhiqun Lin (MSE) Dr. Matthew Yao (GE Energy)

SUMMARY A significant portion of the thermal resistance of an electronic package is due to the thermal interface material (TIM) used to join different materials. With continued demands of device's performance and size, improvements of TIM selection and characterization are of increased importance. Due to the reported high axial thermal conductivity and robust mechanical properties, CNTs have attracted much attention as future TIMs. Due to their high processing temperatures (over 700 oC), transfer of the CNT array to a separate processed substrate has been of interest. The thesis focuses on the characterization and analysis of novel TIMs based on vertically aligned multiwall carbon nanotubes. The first part of the thesis describes the development of a microscopic infrared (IR) steady-state measurement of the total TIM thermal resistance. The technique is demonstrated to be effective in evaluation of commercial TIMs and is extended to the measurement of CNT-based TIM. Measurements are compared to measurements made through a laser flash technique. The performance of these materials after additional thermal reliability is also examined. The second part of the thesis theoretically analyzes the role of different interface structures for CNT based TIM, with particular emphasis on a metal based thermal conductive adhesive used to anchor a CNT array to an active die. A control volume approach which includes intrinsic thermal conductivity of the components and boundary thermal resistances expected in anchoring of the array is used to estimate the lowest potential thermal resistance through a parametric study. The results are then compared to the VACNT TIM measurements made through the steady-state IR measurement. Finally, a novel transient IR imaging technique is demonstrated for experimentally evaluating the thermophysical properties of a multilayer sample. This transient technique can provide additional insight into the individual thermal resistances which contribute to the total resistance, as measured through the steady-state IR technique and thus can be used as an effective tool in the characterization of TIMs. Future studies regarding further development and improvement of this method are outlined for its potential application in measuring next generation TIMs.