Technology Review: Thermal Interface Materials

(This article was featured in an issue of Qpedia Thermal e-Magazine, an online publication dedicated to the thermal management of electronics. To get the current issue or to look through the archives, visit http://www.qats.com/Qpedia-Thermal-eMagazine.)

Qpedia continues its review of technologies developed for electronics cooling applications. We are presenting selected patents that were awarded to developers around the world to address cooling challenges. After reading the series, you will be more aware of both the historic developments and the latest breakthroughs in both product design and applications.

Thermal Interface Materials
This Technology Review will focus on recent developments in Thermal Interface Materials. (Wiklmedia Commons)

We are specifically focusing on patented technologies to show the breadth of development in thermal management product sectors. Please note that there are many patents within these areas. Limited by article space, we are presenting a small number to offer a representation of the entire field. You are encouraged to do your own patent investigation.

Further, if you have been awarded a patent and would like to have it included in these reviews, please send us your patent number or patent application.

In this issue our spotlight is on thermal interface materials.

There are many U.S. patents in this area of technology, and those presented here are some recent. These patents show some of the salient features that are the focus of different inventors.

Thermal Interface Material with Carbon Nanotubes
US 7253442 B2 – Hua Huang, Chang-Hong Liu and Shou-Shan Fan


A thermal interface material includes a macromolecular material, and a plurality of carbon nanotubes embedded in the macromolecular material uniformly. The thermal interface material includes a first surface and an opposite second surface. Each carbon nanotube is open at both ends thereof, and extends from the first surface to the second surface of the thermal interface material. A method for manufacturing the thermal interface material includes the steps of: (a) forming an array of carbon nanotubes on a substrate; (b) submerging the carbon nanotubes in a liquid macromolecular material; (c) solidifying the liquid macromolecular material; and (d) cutting the solidified liquid macromolecular material to obtain the thermal interface material with the carbon nanotubes secured therein.

An object of the present invention is to provide a thermal interface material having a reduced thickness, small thermal interface resistance, good flexibility and excellent heat conduction. To achieve the above-mentioned object, the present invention provides a thermal interface material comprising macromolecular material and a plurality of carbon nanotubes embedded in the macromolecular material uniformly. The thermal interface material also comprises a first surface and an opposite second surface. Each carbon nanotube is open at two ends thereof, and extends from the first surface to the second surface of the thermal interface material.

Unlike in a conventional thermal interface material, the carbon nanotubes of the thermal interface material of the present invention are disposed in the macromolecular material uniformly and directionally. Thus, each carbon nanotube of the thermal interface material can provide a heat conduction path in a direction perpendicular to a main heat absorbing surface of the thermal interface material. This ensures that the thermal interface material has a high heat conduction coefficient. Furthermore, the thickness of the thermal interface material of the present invention can be controlled by cutting the macromolecular material. This further enhances the heat conducting efficiency of the thermal interface material and reduces the volume and weight of the thermal interface material.

Moreover, each carbon nanotube is open at two ends thereof, and extends from the first surface to the second surface of the thermal interface material. This ensures the carbon nanotubes can contact an electronic device and a heat sink directly. Thus, the thermal interface resistance between the carbon nanotubes and the electronic device is reduced, and the thermal interface resistance between the carbon nanotubes and the heat sink is reduced. Therefore, the heat conducting efficiency of the thermal interface material is further enhanced.

Transferrable Compliant Fibrous Thermal Interface
US 6676796 – Michael Pinter, Nancy Dean, William Willet, Amy Gettings and Charles Smith

In one aspect of the invention there is provided a fibrous interface material sandwiched between two layers of a removable paper or release liner. The interface comprises flocked, e.g. electroflocked, mechanically flocked, pneumatically flocked, etc., thermally conductive fibers embedded in an adhesive or tacky substance in substantially vertical orientation with portions of the fibers extending out of the adhesive. An encapsulant is disposed to fill spaces between portions of the fibers that extend out of the adhesive, leaving a free fiber structure at the fiber tips.

Another aspect of the invention is a method of making a fibrous interface. In the method, thermally conductive fibers of desired length are provided and, if necessary, cleaned. A release liner is coated with an adhesive or tacky substance, and the fibers are flocked to that release liner so as to embed the fibers into the adhesive or tacky substance with a portion of the fibers extending out of the adhesive.

The adhesive is cured and the space between fibers if filled with a curable encapsulant. A second piece of release liner is placed over the fiber ends. Then the fibers in the adhesive with the release liner over the fibers in the adhesive with the encapsulant in the spaces between the fibers is compressed to a height less than the normal fibers’ length and clamped at the compressed height.

Thereafter the encapsulant is cured while under compression to yield a free fiber tip structure with the fiber tips extending out of the encapsulant.

Liquid Metal Thermal Interface for an Integrated Circuit Device
US 7348665 B2 – Ioan Sauciuc and Gregory Chrysler


One possible solution to meet the heat dissipation needs of microprocessors and other processing devices is to employ an active cooling system—e.g., a liquid based cooling system that relies, at least in part, on convective heat transfer initiated by the movement of a working fluid—rather than (or in combination with) heat sinks and other passive heat removal components. Disclosed herein are embodiments of a cooling system for an integrated circuit (IC) device—as well as embodiments of a method of cooling an IC device—wherein the cooling system includes a liquid metal thermal interface that is disposed between a die and a heat transfer element, such as a heat spreader or a heat sink. Embodiments of a method of making a liquid metal thermal interface are also disclosed.

This patent is for a liquid metal thermal interface for an integrated circuit die. The liquid metal thermal interface may be disposed between the die and another heat transfer element, such as a heat spreader or heat sink. The liquid metal thermal interface includes a liquid metal in fluid communication with a surface of the die, and liquid metal moving over the die surface transfers heat from the die to the heat transfer element. A surface of the heat transfer element may also be in fluid communication with the liquid metal.

Per Figure 2, the cooling system 200 is coupled with an IC die 10. During operation of the IC die 10, the die may generate heat, and the cooling system 200 is capable of dissipating at least some of this heat, such as may be accomplished by transferring heat away from the IC die 10 and to the ambient environment. The IC die 10 may comprise any type of integrated circuit device, such as a microprocessor, network processor, application specific integrated circuit (ASIC), or other processing device.

Heterogeneous Thermal Interface for Cooling
US 7219713 B2 – Jeffrey Gelorme, Supratik Guha, Nancy LaBianca, Yves Martin and Theodore Van Kessel

The present invention is a thermal interface for coupling a heat source to a heat sink. One embodiment of the invention comprises a mesh and a liquid, e.g., a thermally conductive liquid, disposed in the mesh. The mesh and the thermally conductive liquid are adapted to contact both the heat source and the heat sink when disposed there between. In one embodiment, the mesh may comprise a metal or organic material compatible with the liquid. In one embodiment, the liquid may comprise liquid metal. For example, the liquid may comprise a gallium indium tin alloy. A gasket may optionally be used to seal the mesh and the liquid between the heat source and the heat sink. In one embodiment, the heat source is an integrated circuit chip.

In another aspect of the invention, a method for cooling a heat source with a heat sink is provided. In one embodiment, the method includes providing a thermal interface having a mesh and a liquid disposed in the mesh. The thermal interface is interposed between the heat source and the heat sink, such that the mesh and the liquid are in contact with the heat source on a first side of the thermal interface and in contact with the heat sink on a second side of the thermal interface.

In another aspect of the invention, a method of fabricating a thermal interface for assisting the thermal transfer of heat from a heat source to a heat sink is provided. In one embodiment, the method includes providing a mesh. A liquid is disposed in the mesh in sufficient quantity to substantially fill the mesh. The liquid comprises liquid metal. Optionally, the liquid metal may subsequently be frozen in place.

For more information about Advanced Thermal Solutions, Inc. (ATS) thermal management consulting and design services, visit https://www.qats.com/consulting or contact ATS at 781.769.2800 or ats-hq@qats.com. To register for Qpedia and to get access to its archives, visit https://www.qats.com/Qpedia-Thermal-eMagazine.

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