Metal Bonded Nanotube Array Thermal Interface
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Solution Overview
Problem
Current thermal interface materials, such as polymers and greases, have low thermal conductivity and can be ineffective due to microscopic gaps between heat sources and sinks, and high thermal conductivity materials like solder require similar coefficients of thermal expansion, leading to potential damage.
Innovation Solution
A metal bonded nanotube array using a eutectic bond between carbon nanotubes and a substrate, allowing for low-pressure attachment and efficient heat transfer by aligning nanotubes perpendicularly to accommodate thermal expansion differences.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Area of stationary object
If polymer or thermal grease is used as thermal interface material, then contact area between heat source and heat sink is increased, but thermal conductivity is reduced creating a thermal bottleneck
Solution Approach 1:
The patent uses carbon nanotubes as a composite material that combines the flexibility and conformability of polymer materials with extremely high thermal conductivity. The nanotubes form a bridge between the heat source and heat sink, providing both large contact area and high thermal conductivity simultaneously, eliminating the thermal bottleneck created by traditional polymer-based TIMs.
Solution Approach 2:
The patent changes the thermal conductivity parameter of the thermal interface material from low (polymer/grease) to extremely high (carbon nanotubes). This parameter change allows the interface material to efficiently conduct heat while maintaining the ability to conform to surface roughness, resolving the contradiction between contact area and thermal conductivity.
2Reliability
If solder is used as thermal interface material to achieve high thermal conductivity, then thermal bottleneck is reduced, but coefficients of thermal expansion must be very similar to avoid cracking
Solution Approach 1:
The patent employs carbon nanotubes that act as flexible structures capable of bending and deforming to accommodate differences in thermal expansion between the heat source and heat sink. Unlike rigid solder joints that crack under thermal stress, the flexible nanotube structure absorbs expansion differences through elastic deformation, eliminating the need for matched thermal expansion coefficients.
Solution Approach 2:
The patent introduces dynamic flexibility into the thermal interface through carbon nanotubes that can bend and adjust their shape in response to thermal expansion differences. This dynamic adaptation allows the interface to maintain integrity under varying thermal conditions, unlike static solder joints that require precise thermal expansion matching.
3Reliability
If carbon nanotubes are grown directly on heat source or heat sink, then thermal interface is achieved, but high growth temperatures destroy integrated circuits or damage heat sinks
Solution Approach 1:
The patent introduces a temporary growth substrate as an intermediary that allows carbon nanotubes to be grown at high temperatures in a controlled environment. The nanotubes are then transferred to the heat source or heat sink at low temperatures. This intermediary approach decouples the high-temperature growth process from the temperature-sensitive final application, protecting integrated circuits and heat sinks from thermal damage.
Solution Approach 2:
The patent performs the carbon nanotube growth operation preliminarily on a dedicated substrate before final assembly. By completing the high-temperature nanotube synthesis in advance on a temperature-resistant substrate, the heat source and heat sink are never exposed to damaging temperatures, yet still receive the benefits of directly-grown nanotube thermal interfaces.
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 eutectic bonding process enables efficient heat transfer with minimal pressure and temperature requirements, preventing damage to sensitive components and improving thermal interface efficiency.
Implementation Method 1
Carbon nanotubes (CNTs) have extremely high thermal conductivities and can act as a thermal interface material that transports heat between a heat sink and a heat source
Implementation Method 2
elevating the temperature of the nano-elements, the metal layers, and the substrate such that the metal layers form at least one of a eutectic bond, a metal solid solution, and an alloy bond between the nano-elements and the substrate
Implementation Method 3
when the CNTs are aligned substantially adjacent one another, similar to the strands of a hairbrush, the CNTs are aligned perpendicularly to the substrate and therefore can accommodate differences in thermal expansion by bending perpendicular to the direction along the tubes
Data Source
AI summary
A method for bonding nano-elements to a surface is described. The method includes applying a layer of a first metal to a first end of a plurality of substantially aligned nano-elements, positioning a layer of a second metal adjacent to the layer of the first metal, placing a compressive force across the nano-elements, the metal layers, and the substrate, and elevating the temperature of the nano-elements, the metal layers, and a substrate adjacent the layer of the second metal such that the metal layers form at least one of a eutectic bond, a metal solid solution, and an alloy bond between the nano-elements and the substrate.