Brazed Carbon Nanotube Thermal Interface Material
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Solution Overview
Problem
High thermomechanical stress at bonded interfaces between dissimilar materials under high temperature applications leads to mechanical failure and disrupted thermal transport, as existing methods for enhancing interfacial bonding for thermal or electronic transport are inadequate for high temperature conditions, especially in miniaturized devices like thermoelectric generators and solid oxide fuel cells.
Innovation Solution
A thermal interface material comprising vertically oriented carbon nanotubes (CNTs) with their distal ends brazed using a braze material like titanium, zirconium, or chromium, which is applied to both substrates to reduce contact resistance and enhance mechanical robustness, allowing for relative motion while maintaining thermal conductivity.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Loss of energy
If strongly bonded interfaces are used to enhance thermal transport, then interfacial thermal resistance is reduced, but thermomechanical stress increases leading to mechanical failure at high temperatures
Solution Approach 1:
The interface is segmented into multiple functional layers: a compliant bonding layer that accommodates thermomechanical stress, a reinforcement layer with high strength-to-density ratio, and a thermal management layer. This segmentation allows each layer to perform its specific function without compromising the others, reducing overall interfacial thermal resistance while maintaining reliability under stress
Solution Approach 2:
A composite interface structure is employed combining materials with different properties: a soft compliant bonding material (such as polymer or metal matrix composite) integrated with a rigid reinforcement layer (such as carbon fiber or ceramic reinforcement). This composite structure provides both mechanical compliance to reduce thermomechanical stress and adequate thermal conductivity to maintain low interfacial thermal resistance
2Strength
If conventional bonding methods are used to achieve mechanical robustness, then joint strength is improved, but thermal transport is disrupted
Solution Approach 1:
Different regions of the interface are assigned different material properties and functions: the bonding layer provides mechanical adhesion and stress compliance, while embedded high-conductivity pathways (such as metal traces, carbon fiber bundles, or ceramic particles) provide thermal transport channels. This local differentiation allows the interface to simultaneously achieve strong bonding and maintain thermal transport efficiency
Solution Approach 2:
An intermediary thermal pathway is introduced within the bonding layer, such as a metal matrix, carbon-based filler, or ceramic trace system that acts as a thermal bridge across the interface. This intermediary structure provides dedicated thermal conduction paths that are decoupled from the mechanical bonding function, allowing strong joints without thermal disruption
3Loss of energy
If vertically oriented CNT arrays are used to reduce contact resistance, then thermal conductivity is improved, but manufacturing complexity increases
Solution Approach 1:
The CNT array fabrication is merged with the substrate manufacturing process itself. CNTs are grown directly on the substrate using CVD or other vapor-phase techniques during the same processing cycle used to prepare the substrate surface, eliminating separate CNT deposition steps and reducing overall manufacturing complexity while achieving low contact resistance
Applied Scientific Principles
This section explains which scientific principles are used to turn an abstract innovation direction into a practical engineering solution.
Function Achieved in This Case
The solution achieves a greater than 10-fold reduction in thermal interface resistance and maintains low resistance even after thermal cycling and shock, demonstrating robust thermomechanical performance and exceptional heat transfer characteristics.
Implementation Method 1
brazing the distal ends of the plurality of carbon nanotubes with a braze material such that the braze material wets and binds a significant portion of the carbon nanotubes
Implementation Method 2
vertically oriented carbon nanotubes (CNTs) with their distal ends brazed using a braze material like titanium, zirconium, or chromium, which is applied to both substrates to reduce contact resistance and enhance mechanical robustness, allowing for relative motion while maintaining thermal conductivity
Data Source
AI summary
A thermal interface material and method of making the same includes growing a carbon nanotube array on a first substrate and brazing the distal ends of the carbon nanotube array to a second substrate using a braze material. In at least one embodiment, the braze material includes active elements. The method further includes performing the brazing process in an inert or vacuum atmosphere.