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New Class of Thermal Interface Materials Delivers Ultralow Thermal Resistance for Compact Electronics

July 5, 2017

NREL has characterized the thermal performance of new, high-performance thermal interface materials (TIMs) capable of thermal resistance one-third lower than any other state-of-the-art TIM. Ever-growing demand for high-performance electric-drive vehicles (EDVs) and smaller, yet more powerful, consumer electronics necessitates better thermal management systems to keep these technologies operating optimally and to minimize the risk of overheating. TIMs play a major role in thermal management of electronics components.

NREL collaborated with Texas A&M University (TAMU) on a Defense Advanced Research Projects Agency (DARPA)-funded project to characterize the thermal conductivity and resistance of new, high-performance TIMs. This new class of TIMs utilizes the chemical integration of boron nitride nanosheets (BNNS), soft organic linkers, and a copper matrix. Research results, which were published in the journal ACS Applied Materials & Interfaces, demonstrate dramatically decreased thermal resistance, which could significantly enable compact, high-power-density power electronics packaging for EDVs and other applications.

When electronics get smaller and more powerful, the heat dissipated per unit area of the electronics devices increases, and moving components of machinery operate at higher speeds, creating additional heat. TIMs facilitate the removal of heat generated from the operation of electronic, electro-chemical, and mechanical devices. Conventional TIMs include thermal greases, polymer composites, and solders. These TIMs fill the gaps between thermal transfer surfaces—such as microprocessors and power electronics devices—and the heat sinks to increase thermal transfer efficiency.

Thermal grease and polymer composite TIMs are compliant and reusable, but their low thermal conductivity and poor thermal transport across the boundaries pose a significant thermal barrier to high power-density operations. In addition, these TIMs also suffer from pump-out and dry-out issues when subjected to thermal cycling and elevated temperatures, which degrades their performance.

Solder TIMs, which are fusible metal alloys with low melting temperatures, are prone to thermally induced high-stress failure. Another type of TIM is made with highly oriented pyrolytic graphite, but delamination and flake-off are known challenges associated with nanosheets made from this material.

Two ways to resolve the issues with these TIMs are to further improve the thermal properties of a compliant matrix, or further improve the mechanical properties of a high-thermal-conductivity matrix.

TAMU and NREL's collaborative efforts on this new class of nanocomposite TIMs enhances the mechanical properties of the metal matrix by covalently integrating BNNS functionalized with soft organic linkers and a copper matrix. Researchers selected BNNS as a filler due to its extremely high in-plane thermal conductivity, low coefficient of thermal expansion, and superior thermal and chemical stability. Copper was selected for its very high thermal conductivity.

These chemically integrated metal/organic/inorganic hybrid nanocomposites provide a promising start to a thermal management solution that can significantly reduce thermal resistance in applications with high heat dissipation and can help achieve the broader goals of compact, high-power-density components for EDVs, and other renewable energy and energy-efficiency applications.