Advanced Thermal Interface Materials:

Thermal Performance and Reliability of Thermal Interface Materials
Michael Osterman –  PI
Avram Bar-Cohen – Co-PI
Michael Pecht – Co-PI
Vinh Khuu – Graduate Research Assistant

Objective:

• Assess the feasibility of using the laser flash method to characterize the thermal performance of select TIMs.
• Study the thermal performance of select TIMs when subjected to temperature cycling.

Background:
Thermal interface materials (TIMs) are used to reduce the interfacial thermal resistance between contacting surfaces inside electronic packages, such as at the die-heat sink or heat spreader-heat sink interfaces. Interface thermal resistance minimization has been identified as a critical issue for the thermal management of electronic systems by the NEMI technology roadmap.  In current high-performance air-cooled microelectronic applications, the component-to-heat sink interfacial contact thermal resistance can be comparable to that of the heat sink.  The characterization methods currently employed by TIM vendors to characterize TIM thermal performance do not always permit nominal measurement data to translate to application environments since the characterization environment are often poorly representative of the mechanical and thermal applications.  In addition, characterization methods typically differ between vendors, preventing direct comparison of TIM performance, resulting in a need for improvement in thermal characterization methods. 

Current Effort:
In this study, the change in thermal performance was measured for elastomeric gap pads, gap fillers, and an adhesive throughout reliability tests. Three-layer composite structures were used to simulate loading conditions encountered by thermal interface materials in actual applications. The thermal resistance of the thermal interface material, including contact and bulk resistance, was calculated using the Lee algorithm, an iterative method that uses properties of the single layers and the 3-layer composite structures, measured using the laser flash method. Test samples were subjected to thermal cycling tests, which induced thermomechanical stresses due to the mismatch in the coefficients of thermal expansion of the dissimilar coupon materials. Scanning acoustic microscopy was used to examine the TIM-coupon interfaces.

This work is supported by CALCE consortium project C07-29.

Recent Publications:
Khuu, V., Osterman, M., Bar-Cohen, A., and Pecht, M., “Thermal Performance Measurements of Thermal Interface Materials Using the Laser Flash Method,” Interpack 2007 Conference, July 8-11, 2007, Vancouver, British Columbia, Canada.

Abstract: Thermal interface materials are used to reduce the interfacial thermal resistance between contacting surfaces inside electronic packages, such as at the die-heat sink or heat spreader-heat sink interfaces. In this study, the change in thermal performance was measured for elastomeric gap pads, gap fillers, and an adhesive throughout reliability tests. Three-layer composite structures were used to simulate loading conditions encountered by thermal interface materials in actual applications. The thermal resistance of the thermal interface material, including contact and bulk resistance, was calculated using the Lee algorithm, an iterative method that uses properties of the single layers and the 3-layer composite structures, measured using the laser flash method. Test samples were subjected to thermal cycling tests, which induced thermo-mechanical stresses due to the mismatch in the coefficients of thermal expansion of the dissimilar coupon materials. The thermal resistance measurements from the laser flash showed little change or slight improvement in the thermal performance over the course of temperature cycling. Scanning acoustic microscope images revealed delamination in one group of gap pad samples and cracking in the putty samples.