Thermal interface with silver-filled carbon nanotubes

An exemplary thermal interface (40) includes a silver colloid base (32), and an array of carbon nanotubes (22) disposed in the silver colloid base uniformly. The carbon nanotubes have nanometer-scale silver filled therein, are substantially parallel to each other, and extend from a first surface (42) to a second surface (44) of the thermal interface.

BACKGROUND OF THE INVENTION

1. Field of the Invention

The invention relates generally to thermal interfaces; and more particularly to a kind of thermal interface which conducts heat by using carbon nanotubes.

2. Description of Related Art

Electronic components such as semiconductor chips are becoming progressively smaller, while at the same time heat dissipation requirements thereof are increasing. Commonly, a thermal interface is utilized between the electronic component and a heat sink in order to efficiently dissipate heat generated by the electronic component.

A conventional thermal interface is made by diffusing particles with a high heat conduction coefficient in a base material. The particles can be made of graphite, boron nitride, silicon oxide, alumina, silver, or other metals. However, a heat conduction coefficient of the thermal interface is now considered to be too low for many contemporary applications, because it cannot adequately meet the heat dissipation requirements of modern electronic components.

A new kind of thermal interface has recently been developed. The thermal interface is obtained by fixing carbon fibers with a polymer. The carbon fibers are distributed directionally, and each carbon fiber can provide a heat conduction path. A heat conduction coefficient of this kind of thermal interface is relatively high. However, the heat conduction coefficient of the thermal interface is inversely proportional to a thickness thereof, and the thickness is required to be greater than 40 micrometers. In other words, the heat conduction coefficient is limited to a certain value corresponding to a thickness of 40 micrometers. The value of the heat conduction coefficient cannot be increased, because the thickness cannot be reduced,

U.S. Pat. No. 6,407,922 discloses another kind of thermal interface. The thermal interface is formed by injection molding, and has a plurality of carbon nanotubes incorporated in a matrix material. A first surface of the thermal interface engages with an electronic device, and a second surface of the thermal interface engages with a heat sink. The second surface has a larger area than the first surface, so that heat can be uniformly spread over the larger second surface.

However, the thermal interface formed by injection molding is relatively thick. This increases a bulk of the thermal interface and reduces its flexibility. Furthermore, the carbon nanotubes are disposed in the matrix material randomly and multidirectionally. This means that heat does not necessarily spread uniformly through the thermal interface. In addition, the heat does not necessarily spread directly from the first surface engaged with the electronic device to the second surface engaged with the heat sink.

A new thermal interface which overcomes the above-mentioned problems is desired.

BRIEF SUMMARY OF THE INVENTION

Accordingly, an object of the present invention is to provide a thermal interface having a reduced thickness, good flexibility and excellent heat conduction.

To achieve the above-mentioned object, the present invention provides a thermal interface comprising a silver colloid base and an array of carbon nanotubes embedded in the silver colloid base uniformly.

The silver colloid base comprises silver particles, boron nitride particles, and polysynthetic oils. The carbon nanotubes have nanometer-scale silver filled therein, are substantially parallel to each other, and extend from a first surface to a second surface of the thermal interface.

Unlike in a conventional thermal interface, the carbon nanotubes of the thermal interface of the present invention are disposed in the silver colloid base uniformly and directionally. Thus, each carbon nanotube of the thermal interface can provide a heat conduction path in a direction perpendicular to a main heat absorbing surface of the thermal interface. This ensures that the thermal interface has a high heat conduction coefficient.

Furthermore, the carbon nanotubes have nanometer-scale silver filled therein, and this further enhances the thermal conductivity and heat conduction stability.

DESCRIPTION OF THE PREFERRED EMBODIMENT

Referring toFIG. 1, an array of carbon nanotubes22having nanometer-scale silver24filled therein is shown. The carbon nanotubes22are substantially parallel to each other and directionally formed on a substrate11.

In a preferred method of the present invention, the carbon nanotubes22with the nanometer-scale silver24filled therein are manufactured as follows. Firstly, the substrate11is provided. The substrate11can be made of glass, quartz, silicon, or alumina. In the preferred method, the substrate11is made of porous silicon. A surface of the porous silicon is a porous layer. Diameters of apertures in the porous layer are extremely small, generally about 3 nanometers. Then a catalyst film (not shown) is uniformly deposited on the substrate11by thermal disposition, electron-beam disposition, or sputtering. The catalyst film12can be made of iron (Fe), cobalt (Co), nickel (Ni), or an alloy thereof. In the preferred method, the catalyst film12is made of iron.

Secondly, the catalyst film is oxidized to obtain catalyst particles. The substrate11with the catalyst particles disposed thereon is placed in a reaction furnace. A carbon source gas with nanometer-scale silver mixed therein is introduced into the reaction furnace at a temperature of 350–1000° C. to grow the array of carbon nanotubes22with the nanometer-scale silver24filled therein. The carbon source gas can be acetylene or ethene. A height of the array of carbon nanotubes22can be controlled by controlling the growth time thereof. The height of the array of carbon nanotubes22is generally in the range from 1 to 100 micrometers. In the preferred method of the present invention, the height of the array of carbon nanotubes22is about 100 micrometers. In the preferred method, the nanometer-scale silver24is nanometer-scale silver particles, and a purity thereof is about 99.9 percent. The nanometer-scale silver24is columnar, corresponding to the shapes of the carbon nanotubes22.

Further details of the method for growing the array of carbon nanotubes22can be found in pages 512–514, Vol. 283, Science 1999, and in pages 11502–11503, Vol. 123, J. Am. Chem. Soc. 2001. Moreover, U.S. Pat. No. 6,350,488 discloses a method for mass synthesis of arrays of carbon nanotubes. These three publications are incorporated herein by reference.

In an alternative method, the carbon nanotubes22with the nanometer-scale silver24filled therein are manufactured by an arc discharge method. Firstly, a catalyst film (not shown) is uniformly deposited on the substrate11, with a shape of the catalyst film being circular. Graphite poles with silver filled therein are provided as cathode electrodes and anode electrodes. Secondly, voltages are applied to the cathode electrodes and anode electrodes, thereby generating arc discharging. The anode electrodes are consumed, and the carbon nanotubes22with the nanometer-scale silver24filled therein are formed on the substrate11.

In a further alternative method, the carbon nanotubes22with the nanometer-scale silver24filled therein are manufactured by a deposition method. Firstly, the array of carbon nanotubes22are directionally formed on the substrate11by thermal chemical vapor deposition or plasma enhanced chemical vapor deposition. Secondly, an opening is formed in a free end of each carbon nanotube22by a physical method or a chemical method, as known in the art. Thirdly, the nanometer-scale silver24is filled in the carbon nanotubes22via the openings, thereby providing the carbon nanotubes22with the nanometer-scale silver24filled therein formed on the substrate11.

In the following description, the formed carbon nanotubes22with the nanometer-scale silver24filled therein will simply be referred to as “the carbon nanotubes22.”

FIG. 2shows the carbon nanotubes22substantially submerged in a silver colloid base32. The silver colloid base32comprises nanometer-scale silver particles, nanometer-scale boron nitride particles and polysynthetic oils, and has a high heat conduction coefficient and a low volatility. Diameters of the nanometer-scale silver particles are in the range from 1 to 900 nanometers. A purity of the nanometer-scale silver particles is about 99.9%. Diameters of the nanometer-scale boron nitride particles are in the range from 1 to 900 nanometers. The nanometer-scale boron nitride particles can ensure stable heat conduction. A viscosity of the silver colloid base32is required to be below 100 cps (centipoise).

Referring toFIG. 3, the silver colloid base32is cooled and solidified, and the solidified silver colloid base32with the carbon nanotubes22secured therein is peeled off from the substrate11to obtain a thermal interface40. A thickness of the thermal interface40is preferably about 100 micrometers, being equal to the height of the carbon nanotubes22. That is, the thickness of the thermal interface40is determined by the height of the carbon nanotubes22. Thus, the thickness of the thermal interface40can be varied by controlling the height of the carbon nanotubes22.

FIG. 4shows the thermal interface40of the present invention in isolation. The thermal interface40comprises the silver colloid base32, and the array of carbon nanotubes22embedded in the silver colloid base32uniformly. The thermal interface40has a first surface42to contact a thermally conductive body, and a second surface44opposite to the first surface42to contact a thermal source. Alternatively, the first surface42can contact a thermal source, and the second surface44can contact a thermally conductive body. The carbon nanotubes22are substantially parallel to each other, and extend from the first surface42to the second surface44. In the preferred embodiment, the carbon nanotubes22are perpendicular to the first surface42and the second surface44. Thus, each carbon nanotube22can provide a heat conduction path in a direction perpendicular to a selected main heat absorbing surface of the thermal interface40. Therefore, the thermal interface40has a high heat conduction coefficient and can conduct heat uniformly. Furthermore, because the carbon nanotubes22have the nanometer-scale silver24filled therein, the thermal conductivity and heat conduction stability of the thermal interface40is further enhanced.

FIG. 5shows an application of the thermal interface40of the present invention. The thermal interface40is sandwiched between a heat sink60and an electronic device80to provide good heat contact between the heat sink60and the electronic device80. The first surface42of the thermal interface40engages with a surface (not labeled) of the heat sink60, and the second surface44of the thermal interface40engages with a surface (not labeled) of the electronic device80. Because the thickness of the thermal interface40is on a micron scale, the thermal interface40has good flexibility. Thus, even if the surface of the electronic device80is uneven, the thermal interface40can provide good heat contact between the heat sink60and the electronic device80.

It is understood that the above-described embodiments and methods are intended to illustrate rather than limit the invention. Variations may be made to the embodiments and methods without departing from the spirit of the invention. Accordingly, it is appropriate that the appended claims be construed broadly and in a manner consistent with the scope of the invention.