US20100006278A1

US20100006278A1 - Heat dissipation device and method for manufacturing the same

Info

Publication number: US20100006278A1
Application number: US12/499,947
Authority: US
Inventors: Shou-Shan Fan; Kai-Li Jiang; Chang-Hong Liu; Liang Liu
Original assignee: Tsinghua University; Hon Hai Precision Industry Co Ltd
Current assignee: Tsinghua University; Hon Hai Precision Industry Co Ltd
Priority date: 2008-07-11
Filing date: 2009-07-09
Publication date: 2010-01-14
Also published as: JP5795021B2; CN101626674A; JP2013168665A; JP2010021552A; CN101626674B; JP5485603B2

Abstract

A heat dissipation device for a heat generating element includes a fastening layer and a plurality of carbon nanotubes. The fastening layer is formed on the heat generating element. The carbon nanotubes are arranged in an array structure. The carbon nanotubes are arranged in a predetermined pattern. Ends of the carbon nanotubes are connected to the fastening layer.

Description

BACKGROUND

1. Technical Field
The disclosure relates to heat dissipation devices and methods for manufacturing the same, particularly, to a heat dissipation device based on carbon nanotubes and a method for manufacturing the same.
2. Description of Related Art
Currently, it is possible to combine multiple electronic elements into an efficient module to perform complex tasks. However, electronic devices with high efficiency, such as central processing units (CPUs), will generate a great amount of heat during operation. If the heat is not dissipated efficiently, the electronic devices may become unstable or damaged. Generally, a heat sink is attached to an outer surface of a CPU to dissipate heat from the CPU. Meanwhile, miniaturization is a continuing trend in the production of electronic devices. Consequently, there is a demand for developing a heat sink that meets miniaturization requirements.
A typical heat sink includes a substrate and a plurality of parallel fins extending up from the substrate. The heat sink abuts a heat source, such as a CPU. The heat sink transfers heat from the heat source to the surroundings, thus lowering the temperature of the heat source. Particularly, the heat sink is attached to the heat source via a thermal interface material. The thermal interface material is disposed between the heat sink and the heat source to provide a large contact surface area, and ensuring good heat transfer from the heat source to the heat sink. The thermal interface material is commonly a composite made of a polymer base and a plurality of electrically conductive particles dispersed in the polymer base. The electrically conductive particles are made of a material such as graphite, boron nitride, silicon dioxide, aluminum oxide, or silver.
As the efficiency of electronic devices improves, the demand for better heat dissipation increases. However, the thermal conductivity of material currently used cannot meet the increasing demand.
Furthermore, the thermal interface material between the heat sink and the heat source, causes additional difficulty in production of thin-type electronic devices.
What is needed, therefore, is a heat dissipation device having high heat dissipation efficiency and suitable to be employed in thin-type electronic devices.

BRIEF DESCRIPTION OF THE DRAWINGS

Many aspects of the present heat dissipation device and method for manufacturing the same can be better understood with reference to the following drawings. The components in the drawings are not necessarily to scale, the emphasis instead being placed upon clearly illustrating the principles of the present heat dissipation device.

FIG. 1 is a cross-sectional view of a first embodiment of a heat dissipation device on a heat generating element.

FIG. 2 is a vertical view of the heat dissipation device of FIG. 1.

FIG. 3 is a cross-sectional view of a second embodiment of a heat dissipation device on a heat generating element.

FIG. 4 is a cross-sectional view of a third embodiment of a heat dissipation device on a heat generating element.

FIG. 5 is a flow chart of an exemplary embodiment of a method for manufacturing the heat dissipation device.

FIG. 6 is a schematic view of the method for manufacturing a heat dissipation device on a heat generating element.

Corresponding reference characters indicate corresponding parts throughout the several views. The exemplifications set out herein illustrate at least one embodiment of the present heat dissipation device and method for manufacturing the heat dissipation device, in one form, and such exemplifications are not to be construed as limiting the scope of the disclosure in any manner.

DETAILED DESCRIPTION OF THE EMBODIMENTS

Referring to FIG. 1 and FIG. 2, a first embodiment of a heat dissipation device 20 for a heat generating element 30, includes a fastening layer 201 and a plurality of carbon nanotubes 203. The fastening layer 201 is formed on the heat generating element 30. Ends of the carbon nanotubes 203 are connected to the fastening layer 201. The fastening layer 201 is configured to fix the carbon nanotubes 203 in a predetermined arrangement. In the present embodiment, the heat dissipation device 20 dissipates heat from the heat generating element 30 For example, the heat generating element 30 can be a central processing unit (CPU), but can be deployed for use with a variety of heat generating elements, whether they be micro-scale devices or large-scale devices..
The fastening layer 201 is made of thermal conductive material. The thermal conductive material can be a composite with electrically conductive properties, such as a polymer composite or a ceramic composite. For example, the thermal conductive material can be a composite of plastic and carbon nanotubes. Alternatively, the thermal conductive material can include a metal with a low melting point, such as tin (Sn), indium (In), lead (Pb), antimony (Sb), silver (Ag), bismuth (Bi), or alloys thereof. The alloy can be an alloy of tin and lead, an alloy of indium and tin, or an alloy of tin and silver.
In the present embodiment, the fastening layer 201 should be designed to have suitable thicknesses allowing the heat dissipation device 20 to achieve a required performance. If the fastening layer 201 is too thick, the heat dissipation will have low heat dissipation efficiency. On the contrary, if the fastening layer 201 is too thin, the carbon nanotubes 203 cannot be firmly fastened on the heat generating element 30. In the present embodiment, a thickness of the fastening layer 201 ranges from 0.1 mm to 1 mm.
The carbon nanotubes 203 are arranged in an array structure (as shown in FIG. 2). The array is formed by arranging the carbon nanotubes 203 substantially parallel to each other. Any two adjacent carbon nanotubes are spaced by a distance in a range of about 0.1 nanometers (nm) to about 5.0 nm. The carbon nanotubes 203 extend from the fastening layer 201, with embedded ends 203 a of the carbon nanotubes 203 embedded in the fastening layer 201 and exposed portions 203 b of the carbon nanotubes 203 exposed from the fastening layer 201, as shown in FIG. 1. The parallel carbon nanotubes 203 may be substantially perpendicular to a surface of the fastening layer 201. The fastening layer 201 holds the carbon nanotubes 203 upright. The exposed portions 203 b of the carbon nanotubes 203 absorb and dissipate heat from the heat generating element 30 to the surrounding environment, thereby cooling the heat generating element 30.
Referring to FIG. 1 to FIG. 3, the carbon nanotubes 203 exposed from the fastening layer 201 may be made into a predetermined pattern. That is, the array of carbon nanotubes 203 may be patterned into a specific configuration. Particularly, some portions of the carbon nanotubes 203 exposed from the fastening layer 201 may be removed to form a crisscross pattern (as shown in FIG. 1 and FIG. 3), a circular pattern, or an annular pattern. Moreover, the exposed portions 203 b of the carbon nanotubes 203 remaining on the fastening layer 201 can be further treated to have substantially equal lengths (as shown in FIG. 1) or unequal lengths (as shown in FIG. 3). In the present embodiment, a space P is defined by the carbon nanotubes 203 with the predetermined pattern, e.g. the channels defined by the crisscross pattern. The space P is provided to allow convection, causing heat to be transferred to the surrounding environment rapidly. Alternatively, referring to FIG. 4, the array of carbon nanotubes 203 on the fastening layer 201 can be made to present a wavy pattern.
In the present embodiment, each of the carbon nanotubes 203 has a length in a range from about 0.5 mm to about 5.0 mm. For example, lengths of the carbon nanotubes 203 are about 1 mm. It is understood that the carbon nanotubes 203 are longer than the thickness of the fastening layer 201. Thus, the carbon nanotubes 203 aid in conducting heat to the surrounding environment because of the exposed portions 203 b. In the present embodiment, the carbon nanotubes 203 can be selected from the group of consisting of single-walled carbon nanotubes (SWCNTs), double-walled carbon nanotubes, multi-walled carbon nanotubes (MWCNTs), and combinations thereof. In such case, a diameter of each of the SWCNT is in a range from about 0.5 nm to about 100 nm. A diameter of each the double-walled carbon nanotube is in a range from about 1.0 nm to about 100.0 nm. A diameter of each the MWCNT is in a range from about 1.5 nm to about 100.0 nm. Moreover, any two adjacent carbon nanotubes are spaced apart from each other by a distance in a range from about 0.1 nm to about 5.0 nm.
The heat dissipation device 20 of the present embodiment can be deployed for use in a variety of heat generating elements with almost any shape, because the carbon nanotubes 203 are flexible. That is, regardless of the configuration of a heat generating element, the heat dissipation device 20 of the present embodiment is suitable to be attached to a non-planar surface.
Referring to FIG. 5 and FIG. 6, an embodiment of a method for manufacturing a heat dissipation device 20 is shown. Step S1 includes providing a fastening layer 201 in a molten state on a surface of a heat generating element 30. In step S2, a carbon nanotube array having a plurality of carbon nanotubes 203 is formed on a substrate 204. In step S3, ends of the carbon nanotubes 203 are inserted into the fastening layer 201 while it is in the molten state. In step S4, the fastening layer 201 is cooled. In step S5, the substrate 204 is removed. In step S6, the carbon nanotubes array is made into a predetermined pattern.
The method is described in more detail as follows.
In step S1, the fastening layer 201 in the molten state is applied on the surface of the heat generating element 30. In the present embodiment, the fastening layer 201 is disposed on the heat generating element 30 by a coating process or a printing process. Since the fastening layer 201 is applied while in a molten state, the fastening layer 201 can conform to the surface of the heat generating element 30. Furthermore, in order to avoid the heat generating element 30 from being damaged while the molten fastening layer 201 is applied, the fastening layer 201 is chosen to have a melting point lower than that of the heat generating element 30. The fastening layer 201 is made of thermal conductive material including a metal with a low melting point, such as Sn, In, Pb, Sb, Ag, Bi or alloys thereof. The alloy can be an alloy of tin and lead, an alloy of indium and tin or an alloy of tin and silver. In the present embodiment, the fastening layer 201 is made of silver.
In step S2, the carbon nanotube array is formed on the substrate 204 by, for example, chemical vapor deposition (CVD), arc-discharge deposition, or laser vaporization deposition. In the present embodiment, the carbon nanotube array is formed by chemical vapor deposition. Particularly, the carbon nanotube array is obtained by the following steps: firstly, the substrate 204, which is substantially flat and smooth, is provided. In the present embodiment, the substrate 204 can be made of glass, silicon, silicon dioxide, metal, or metal oxide. Preferably, the substrate 204 is made of silicon dioxide. Then, a catalyst layer is uniformly formed on the substrate 204. The catalyst layer can be made of a material selected from the group consisting of iron (Fe), cobalt (Co), nickel (Ni) and alloys thereof. Secondly, the substrate 204 with the catalyst layer is annealed in air at about 700° C. to about 900° C. for about 30 minutes to about 90 minutes. The treated substrate 204 is put into a furnace. The furnace is then heated to about 500° C. to about 740° C. with a protecting gas flowing therein. Next, a carbon source gas is introduced into the furnace for about 5 minutes to about 30 minutes to grow a plurality of parallel carbon nanotubes 203 on the substrate 204. Thus, the carbon nanotube array is obtained and the carbon nanotubes 203 are substantially perpendicular to the substrate 204.
In the present embodiment, the carbon source gas can be acetylene, ethylene or methane. The protecting gas can be inert gas or nitrogen. Particularly, acetylene is chosen as the carbon source gas while argon gas is chosen as the protecting gas.
In step S3, the substrate 204 on which the carbon nanotube array is formed is flipped over to allow the carbon nanotubes 203 to approach the fastening layer 201 in a molten state. Then, ends of the carbon nanotubes 203, which are far away from the substrate 204, are slowly inserted into the fastening layer 201. In this step, it is noted that the fastening layer 201 should be maintained in the molten state to facilitate insertion of the carbon nanotubes 203. The ends of the carbon nanotubes 203 can be inserted to various depths in the fastening layer 201 according to practical needs. In the present embodiment, the carbon nanotubes 203 are inserted deeply until the carbon nanotubes 203 are contacting the heat generating element 30.
In step S4, the fastening layer 201 in which the ends of the carbon nanotubes 203 are inserted is cooled at room temperature to allow the fastening layer 201 to change from the molten state to a solid state. Thus, the ends of the carbon nanotubes 203 are fixed and standing upright in the fastening layer 201.
In step S5, the substrate 204 on which the carbon nanotube array is formed is removed by, for example, mechanical polishing or chemical etching. In the present embodiment, the substrate 204 is removed by chemical etching. In use, an etchant having a capacity of dissolving the substrate 204 is provided. In the present embodiment, hydrochloric acid is chosen as the etchant for removing the substrate 204 made of silicon dioxide. The substrate 204 carrying the carbon nanotubes is immersed into the etchant for about 30 minutes to 1 hour. Then, the substrate 204 and the catalyst layer formed on the substrate 204 will be removed completely. The opposite ends of the carbon nanotubes 203, which are far away from the fastening layer 201, are exposed to the surrounding environment (as shown in FIG. 6).
In step S6, the carbon nanotubes array fastened by the fastening layer 201 and disposed on the heat generating element 30 is made into a predetermined pattern, thereby obtaining the final heat dissipation device 20. In the present embodiment, the carbon nanotubes array is patterned by a laser beam, using for example, a carbon dioxide laser. In addition, the track of the laser beam emitted from the carbon dioxide laser can be controlled by the computer. Particularly, the predetermined pattern can be designed in advance and inputted into the computer program. That is, the emitted laser beam can be controlled by the computer program to trace the predetermined pattern, thereby forming the predetermined pattern on the carbon nanotubes array. In the present embodiment, a laser beam with a power density in a range from about 70000 watts/mm²to about 80000 watts/mm²is employed. The laser is driven to move with a velocity in a range of about 1000 to about 1200 mm/second.
In conclusion, the heat dissipation device of the present embodiment is formed directly on a heat generating element. In principle, the heat energy from the heat generating element travels to the fastening layer and then to the carbon nanotube array, where it is dissipated, thereby lowering the temperature of the heat generating element. The heat dissipation efficiency is improved by virtue of having good thermal transfer capacity along the axial directions of the carbon nanotubes because the carbon nanotubes are substantially perpendicular to the surface of the heat generating element. Furthermore, due to a large ratio of length to diameter of the carbon nanotube, the heat dissipation efficiency on the heat dissipation device is increased by way of an increase of heat dissipation surface.
Finally, it is to be understood that the above-described embodiments are intended to illustrate rather than limit the disclosure. Variations may be made to the embodiments without departing from the spirit of the disclosure as claimed. The above-described embodiments illustrate the scope of the disclosure but do not restrict the scope of the disclosure.
It is also to be understood that above description and the claims drawn to a method may include some indication in reference to certain steps. However, the indication used is only to be viewed for identification purposes and not as a suggestion as to an order for the steps.

Claims

1. A heat dissipation device for a heat generating element, comprising:

a fastening layer formed on the heat generating element; and

a plurality of carbon nanotubes arranged in an array structure, the plurality of carbon nanotubes arranged in a predetermined pattern and having ends of the carbon nanotubes connected to the fastening layer.

2. The heat dissipation device as claimed in claim 1, wherein the fastening layer is made of thermal conductive material including a metal with a melting point lower than that of the heat generating element.

3. The heat dissipation device as claimed in claim 1, wherein the fastening layer comprises a metal selected from the group consisting of tin, indium, lead, antimony, silver, bismuth, and alloy thereof.

4. The heat dissipation device as claimed in claim 1, wherein the fastening layer comprises a composite selected from the group consisting of polymer composite and the ceramic composite.

5. The heat dissipation device as claimed in claim 1, wherein a thickness of the fastening layer ranges from about 0.1 mm to 1 mm.

6. The heat dissipation device as claimed in claim 1, wherein the carbon nanotubes are substantially parallel to each other and extend from the fastening layer.

7. The heat dissipation device as claimed in claim 1, wherein portions of the carbon nanotubes exposed from the fastening layer have substantially unequal lengths.

8. The heat dissipation device as claimed in claim 1, wherein the ends of carbon nanotubes are embedded in the fastening layer.

9. The heat dissipation device as claimed in claim 8, wherein the ends of the carbon nanotubes are contacting the surface of the heat generating element.

10. The heat dissipation device as claimed in claim 1, wherein the carbon nanotubes are arranged to be substantially perpendicular to a surface of the heat generating element.

11. The heat dissipation device as claimed in claim 10, wherein the surface of the heat generating element is a non-planar surface.

12. The heat dissipation device as claimed in claim 1, wherein the carbon nanotubes have lengths ranging from about 0.5 mm to about 5.0 mm.

13. The heat dissipation device as claimed in claim 1, wherein any two adjacent carbon nanotubes are spaced by a distance in a range of about 0.1 nm to 5.0 nm.

14. The heat dissipation device as claimed in claim 1, wherein a plurality of channels are defined by the carbon nanotubes within the predetermined pattern; the plurality of channels allow air convection.

15. The heat dissipation device as claimed in claim 1, wherein the predetermined pattern is selected from the group consisting of crisscross pattern, circular pattern, annular pattern and wavy pattern.

16. A method for manufacturing a heat dissipation device, the method comprising:

providing a fastening layer in a molten state on a surface of a heat generating element;

forming a carbon nanotube array on a substrate, the carbon nanotube array comprising a plurality of carbon nanotubes;

bringing the carbon nanotubes to the fastening layer in the molten state and inserting ends of the carbon nanotubes, which are far away from the substrate, into the fastening layer in the molten state;

cooling the fastening layer to change from the molten state to a solid state;

removing the substrate on which the carbon nanotube array was formed; and

making the carbon nanotubes connected to the fastening layer into a predetermined pattern.

17. The method as claimed in claim 16, wherein the fastening layer, while in the molten state, is coated or printed on the surface of the heat generating element.

18. The method as claimed in claim 16, wherein the fastening layer is cooled at room temperature.

19. The method as claimed in claim 16, wherein the substrate is removed by mechanical polishing or chemical etching.

20. The method as claimed in claim 16, wherein the carbon nanotubes are made into the predetermined pattern by a laser beam.