Heat spreader with vapor chamber defined therein

A heat spreader includes a bottom wall (12) and a cover (14) hermetically connected to the bottom wall. Cooperatively the bottom wall and the cover define a space (11) therebetween for receiving a working fluid therein. A wick structure (15) is received in the space and thermally interconnects the bottom wall and the cover. The wick structure includes at least a carbon nanotube array, which can conduct heat from the bottom wall to the cover and draw condensed liquid of the working fluid from the cover toward the bottom wall.

BACKGROUND OF THE INVENTION

1. Field of the Invention

The present invention relates to an apparatus for transfer or dissipation of heat from heat-generating components, and more particularly to a heat spreader having a vapor chamber defined therein.

2. Description of Related Art

As electronic industry continues to advance, electronic components such as central processing units (CPUs), are made to provide faster operational speeds and greater functional capabilities. When a CPU operates at a high speed, its temperature frequently increases greatly. It is desirable to dissipate the heat generated by the CPU quickly.

To solve this problem of heat generated by the CPU, a heat sink is often used to be mounted on the top of the CPU to dissipate heat generated thereby. For enhancing the heat dissipation capability of the heat sink, a heat spreader is arranged between the heat sink and the CPU, which is made of a material having a heat conductivity higher than that of the heat sink, for enhancing the speed of heat transfer from the CPU to the heat sink. However, as the CPU operates faster and faster, and, therefore generates larger and larger amount of heat, the conventional heat spreader, which transfers heat via heat conduction means, cannot meet the increased heat dissipating requirement of the CPU.

For the foregoing reasons, therefore, there is a need in the art for a cooling device which overcomes the above-mentioned problems.

SUMMARY OF THE INVENTION

The present invention relates to a heat spreader including a bottom wall and a cover hermetically connected to the bottom wall. Cooperatively the bottom wall and the cover define a space therebetween for receiving a working fluid therein. A wick structure is received in the space and thermally interconnects the bottom wall and the cover. The wick structure includes at least a carbon nanotube array (CNT array).

DETAILED DESCRIPTION OF THE INVENTION

FIG. 1is a cross-sectional view of a cooling device incorporating a heat spreader10in accordance with a first embodiment of the present invention. The cooling device is arranged on a heat-generating component20, such as CPU (central process unit), VGA (Video Graphics Array), LED (light-emitting diode), NB (north bridge), and so on.

In this embodiment, the cooling device includes a heat spreader10and a fin-type heat sink30arranged on the heat spreader10. The heat sink30is made of material with highly thermal conductivity, such as copper, aluminum, or their alloys. The heat sink30as shown in this embodiment is an extruded aluminum heat sink, including a chassis31and a plurality of pin fins32extending upwardly from the chassis31. Apparently, the fins32are used for increasing the heat dissipation area of the heat sink30. Alternatively, the fins32can be plate-like shaped. The fins32and the chassis31can be formed separately, and then connected together by soldering.

Also referring toFIGS. 2-3, the heat spreader10includes a bottom wall12and a cover14hermetically connected to the bottom wall12to thereby form a sealed space11for containing working liquid therein. The cover14and the bottom wall12are made of copper. Alternatively, the cover14and the bottom wall12can be made of other materials with highly thermal conductivity, such as aluminum, or its alloys. The bottom wall12is a square-shaped plate. The bottom wall12includes a bottom surface122for contacting with and absorbing heat from the heat-generating component20, and a top surface124opposing the bottom surface122. The cover14includes a top wall144parallel to the bottom wall12and a side wall142. The top wall144is square-shaped with a size smaller than that of the bottom wall12. The side wall142extends perpendicularly and downwardly from four sides of the top wall144. A flange140extends transversely and outwardly from a free end of the side wall142. An outer periphery of the flange140has a size substantially the same as that of the bottom wall12. The flange140of the cover14and an outer periphery120of the top surface124of the bottom wall12connect together by a soldering process which is a method widely used to connect two discrete metallic components together. Thus, the discrete cover14and bottom wall12are soldered together to form the sealed space11therebetween. The space11is in a vacuumed condition. The working liquid, such as water or alcohol, which has a lower boiling point, is received in the space11.

A plurality of carbon nanotube arrays (CNT arrays)15which function as heat transfer enhancing structures and wick structures are arranged between and thermally interconnect the bottom wall12and the top wall144of the cover14. The carbon nanotube arrays (CNT arrays)15are fixed in the heat spreader10by interference fit: bottom and top ends of each carbon nanotube array15are interferentially pressed by the top surface124of the bottom wall12and a bottom surface148of the top wall144of the cover14. Alternatively, grooves can be defined in the top and bottom walls144,12to receive the top and bottom ends of the carbon nanotube arrays (CNT arrays)15therein. Thus, the carbon nanotube arrays (CNT arrays) can be firmly assembled in the space11. In this embodiment, the carbon nanotube arrays (CNT arrays)15include seven carbon nanotube arrays (CNT arrays) evenly spaced from each other along a horizontal direction, and thus eight longitudinal channels16are defined therebetween. Each carbon nanotube array15has a shape of elongated cube, in which a width W (as shown inFIG. 3) thereof is larger than a length L (as shown inFIG. 2) thereof. The width W of each carbon nanotube array15is a little smaller than that of the space11, and thus two traverse channels17are defined by opposite sides (i.e., front and back sides) of the space11. The traverse channels17communicate with the longitudinal channels16.

One kind of such a carbon nanotube array15can be obtained by a method of chemical vapor deposition (CVD). Firstly aligned carbon nanotube arrays are synthesized in a hot filament plasma enhanced chemical vapor deposition (HF-PECVD) system. A substrate (metal, glass, silicon, etc.) is coated with nickel nano-particles and then introduced to the CVD chamber. Then the aligned carbon nanotube arrays are mixed with distilled water by firstly vacuuming the aligned carbon nanotube arrays to remove air therein, and then filling the distilled water in the aligned carbon nanotube arrays. The aligned carbon nanotube arrays filled with distilled water are then cooled to form a composite material of carbon nanotube arrays combined with water. Finally incises the carbon nanotube arrays from the substrate in a manner that the carbon nanotube arrays have a predetermined length; thus the carbon nanotube arrays15are obtained.

When assembled, the bottom surface122of the bottom wall12is thermally attached to the heat-generating component20, and a top surface146of the top wall144is thermally attached to the chassis31of the heat sink30. As the heat generated by the heat-generating component20, which is attached to the bottom surface122of the bottom wall12, is transferred to the heat spreader10, the working fluid contained therein absorbs the heat and evaporates into vapor. Since the vapor spreads quickly, it quickly fills an interior of the heat spreader10, and whenever the vapor comes into contact with cooler wall of the heat spreader10(i.e., the top wall144of the heat spreader10) which thermally contact with the heat sink30, it releases the heat to the heat sink30. After the heat is released, the vapor condenses into liquid, which is then brought back by the carbon nanotube arrays (CNT arrays)15to the bottom wall12of the heat spreader10. Since the heat spreader10transfers the heat by using phase change mechanism involving the working fluid, the heat transferred to the heat spreader10from the heat-generating device is thus rapidly and evenly distributed over the entire heat spreader10and is then conveyed to the heat sink30through which the heat is dissipated into ambient air.

Furthermore, the carbon nanotube arrays (CNT arrays)15are capable of transferring heat from the bottom wall12to the top wall144directly. Due to the carbon nanotube arrays15in the heat spreader10, a heat transfer efficiency of the heat spreader10is highly enhanced. As nano-material have a very small size with a diameter ranging from 1˜100 nm, a surface area of the nano-material is much larger than that of the same material which has the same volume. Thus a heat transfer area of the heat spreader10is much enlarged by having the carbon nanotube arrays (CNT arrays)15, which, in result, improves heat transfer efficiency of the heat spreader10. For example, the carbon nanotubes has a heat transfer coefficient about 3000-6600 W/(m·k), which is ten times more than that of copper which has a heat transfer coefficient of 375 W/(m·K). The heat spreader10which adopts the carbon nanotube arrays (CNT arrays)15thus can have a much larger heat transfer efficiency. Thus, the heat of the heat-generating component20can be rapidly and efficiently transferred from the bottom wall12to the top wall144of the heat spreader10through the carbon nanotube arrays (CNT arrays)15, thereby can enhance heat transfer efficiency of the heat spreader10from the bottom wall12to the top wall144. Thus, during operation, the heat generated by the heat-generating component20can be transferred to the heat sink30by the heat spreader10through either phase change mechanism or heat conduction which adopts nano-material with high heat transfer efficiency. In addition, heat transfer threshold by the liquid if the liquid is not able to timely contact with the top surface148of the top wall144during the initial phase of heat transfer from the bottom wall12to the top wall144can be overcome by the carbon nanotube arrays (CNT arrays) which thermally connects the bottom wall12and the top wall144. Accordingly, the heat spreader10is still workable to transfer the heat from the heat-generating component20to the heat sink30even when the heat spreader10is put in an inclined position.

FIG. 4shows a second embodiment of the heat spreader10a. Also the heat spreader10ahas a bottom wall12and a cover14hermetically connected to the bottom wall12to thereby form the sealed space11. The carbon nanotube arrays15are arranged in the space11and thermally interconnect the bottom wall12and the top wall144of the cover14. The difference between the second embodiment and the first embodiment is that the heat spreader10afurther has a second wick structure17aarranged on the top surface124of the bottom wall12and the bottom surface148of the top wall144. The second wick structure17ahas one of the following four configurations: sintered powder, grooves, fibers and screen meshes. In this embodiment, the second wick structure17ais configured of screen mesh. The condensed vapor thus can be brought back by the carbon nanotube arrays15and the second wick structure17atogether.

FIG. 5shows a third embodiment of the heat spreader10b. Similar to the second embodiment, the heat spreader10bhas a cover14, a bottom wall12, the carbon nanotube arrays15arranged between the bottom wall12and the cover14, and a second wick structure17barranged on the top surface124of the bottom wall12and the bottom surface148of the top wall144of the cover14. In this embodiment, the second wick structure17bis made of a material like that forming the carbon nanotube arrays15, i.e., carbon nanotubes (CNTs). The second wick structure17bcan also be formed as the carbon nanotube arrays15, i.e., by firstly forming the carbon nanotubes on a silicon substrate and then fixing the carbon nanotubes to the top and bottom walls144,12of the heat spreader10by for example gluing. Alternatively, the second wick structure17bcan be formed on the top and bottom walls144,12of the heat spreader10directly. In this case, the top and bottom walls144,12are adopted as the substrate to form the carbon nanotubes (CNTs) of the wick structure17bthereon. Thus the heat spreader10and the second wick structure17bare integral, and assembly of the second wick structure17bto the heat spreader10by gluing can be avoided.