Patent Description:
Generally, electronic parts generate a large amount of heat during operation thereof. Since heat generation of such electronic parts is likely to result in malfunctioning of or damage to the electronic parts, it is required to dissipate the heat generated from the electronic parts. A heat sink with multiple fins is widely used as a heat dissipation device for electronic parts.

Conventionally, a metal material such as aluminum or copper has been used as a material of a heat sink. Among them, aluminum is widely used in various industrial fields. For example, it is used in: airplanes, automobiles, ships, railways, etc. due to its low specific gravity (i.e., lightness); power transmission lines due to its good electric conductivity; industrial tableware and the like due to its strong corrosion resistance in the air and harmlessness to human body; and paint, aluminum foil packaging, building materials, reactor materials, and so on. Despite many advantages described above, aluminum has a problem in that it is relatively mechanically and physically weak.

Therefore, it is required to develop an aluminum-based heat sink made of a composite material including aluminum and other materials, the composite material having improved corrosion resistance, mechanical characteristics, and processability compared to pure aluminum or aluminum alloys.

A method of manufacturing a heat sink disclosed in <CIT> comprises extruding a billet composed of composite material of aluminum and carbon particles such as carbon nanotubes.

In addition, Non-Patent Document <NPL>discloses that carbon nanotubes reinforced aluminum matrix composites are fabricated by cold isostatic pressing (CIP) and hot extrusion techniques.

An objective of the present invention is to provide a method of manufacturing a light, high-strength, and high-conductivity aluminum-based clad heat sink having a competitive advantage in terms of price by using direct extrusion which is suitable for mass production due to its simplicity in process procedure and equipment.

Another objective of the present invention is to provide an aluminum-based clad heat sink produced by the method described above.

The present invention provides a method of manufacturing an aluminum-based clad heat sink as defined in claim <NUM>. The method includes: (A) preparing a composite powder by ball-milling (i) aluminum or aluminum-alloy powder and (ii) carbon nanotubes (CNT); (B) preparing a multilayered billet including the composite powder; and (C) directly extruding the multilayered billet using an extrusion die to produce a heat sink, in which the multilayered billet includes a core layer and two shell layers surrounding the core layer.

In the method of manufacturing an aluminum-based clad heat sink, the composite powder for the first shell layer contains <NUM> parts by volume of the aluminum or aluminum-alloy powder and <NUM> to <NUM> parts by volume of the carbon nanotubes.

In the method of manufacturing an aluminum-based clad heat sink, the ball-milling may be performed at a low speed of <NUM> to <NUM> rpm or at a high speed of <NUM> or more rpm for a duration of <NUM> to <NUM> hours, using a horizontal or planetary ball mill into which <NUM> to <NUM> parts by volume of milling balls and <NUM> to <NUM> parts by volume of an organic solvent with respect to <NUM> parts by volume of the composite powder are introduced.

In the method of manufacturing an aluminum-based clad heat sink, the organic solvent may be heptane.

In the method of manufacturing an aluminum-based clad heat sink, the multilayered billet includes a core layer, a first shell layer surrounding the core layer, and a second shell layer surrounding the first shell layer.

In the method of manufacturing an aluminum-based clad heat sink, the multilayered billet includes: a first billet that is can-shaped and serves as the second shell layer, a second billet disposed inside the first billet as the first shell layer, and a third billet disposed inside the second billet as the core layer.

In the method of manufacturing an aluminum-based clad heat sink, the second billet includes <NUM> to <NUM> parts by volume of the carbon nanotubes with respect to <NUM> parts by volume of the aluminum or aluminum-alloy powder, and the third billet includes <NUM> parts by volume of the carbon nanotubes with respect to <NUM> parts by volume of the aluminum or aluminum-alloy powder.

In the method of manufacturing an aluminum-based clad heat sink, in step (B), the preparing of the billet may include compressing the composite powder at a high pressure of <NUM> to <NUM> MPa.

In the method of manufacturing an aluminum-based clad heat sink, in step (B), the preparing of the billet may include subjecting the composite powder to spark plasma sintering performed at a temperature of <NUM> to <NUM> and a pressure of <NUM> to <NUM> MPa for a duration of <NUM> second to <NUM> minutes.

The aluminum-based clad heat sink may be of fin type heat or bar type.

In the aluminum-based clad heat sink, the fin type may be a straight fin (SF) type or a pin fin (PF) type.

The manufacturing method according to the present invention has an advantage of producing a light high-strength high-conductivity aluminum-based clad heat sink having a competitive advantage in terms of price because the manufacturing method is based on direct extrusion which is suitable for mass production due to its simplicity in process procedure and equipment required.

In describing the present invention, well-known functions or constructions will not be described in detail when it is determined that they may obscure the gist of the present invention.

Since embodiments in accordance with the concept of the present invention can undergo various changes and have various forms, only some specific embodiments are illustrated in the drawings and described in detail in the present specification. While specific embodiments of the present invention are described herein below, they are only for illustrative purposes and should not be construed as limiting to the present invention. Thus, the present invention should be construed to cover not only the specific embodiments but also cover all modifications, equivalents, and substitutions that fall within the concept and technical spirit of the present invention.

The terminology used herein is for the purpose of describing particular embodiments only and is not intended to limit the scope of the present invention. As used herein, the singular forms "a", "an", and "the" are intended to include the plural forms as well unless the context clearly indicates otherwise. It will be further understood that the terms "comprise" or "has" when used in the present specification specify the presence of stated features, regions, integers, steps, operations, elements and/or components, but do not preclude the presence or addition of one or more other features, regions, integers, steps, operations, elements, components and/or combinations thereof.

<FIG> is a process flowchart illustrating a method of manufacturing an aluminum-based clad heat sink according to one embodiment of the present invention.

Hereinafter, a method of manufacturing an aluminum-based clad heat sink will be described with reference to <FIG>.

Referring to <FIG>, the method of manufacturing an aluminum-based clad heat sink includes: a composite powder preparation step S10 of preparing a composite powder by ball-milling (a) an aluminum or aluminum-alloy powder and (b) carbon nanotubes (CNT); a billet preparation step S20 of preparing a multilayer billet using the composite powder; and a direct extrusion step S30 of directly extruding the multilayer billet using an extrusion die.

First, a mixture of aluminum or aluminum-alloy powder and carbon nanotubes (CNT) is ball-milled to produce a composite powder in step S10.

The aluminum-alloy powder is the powder of any one aluminum alloy selected from the group consisting of <NUM> series, <NUM> series, <NUM> series, <NUM> series, <NUM> series, <NUM> series, <NUM> series, and <NUM> series.

Since the composite powder contains the carbon nanotubes, the aluminum-based clad heat sink made of the composite powder is light and has high thermal conductivity and strength. Thus, this heat sink is very useful as a heat dissipation member for various electronic parts and lighting devices.

The composite powder may contain an additional metal powder in addition to the aluminum or aluminum-alloy powder. The additional metal powder is the powder of any one metal selected from the group consisting of copper, magnesium, titanium, stainless steel, tungsten, cobalt, nickel, tin, and alloys thereof.

When preparing the composite powder, there are problems: the aluminum or aluminum alloy particles are difficult to disperse due to a large difference in size between the nano-sized carbon nanotubes and the micro-sized aluminum or aluminum alloy particles; and the carbon nanotubes easily agglomerate due to a strong Van der Waals force. Therefore, a dispersion agent is added to uniformly blend the carbon nanotubes and the aluminum particles or aluminum alloy particles.

The dispersion agent is nano-sized ceramic particles selected from the group consisting of nano-SiC, nano-SiO<NUM>, nano-Al<NUM>O<NUM>, nano-TiO<NUM>, nano-Fe<NUM>O<NUM>, nano-MgO, nano-ZrO<NUM>, and mixtures thereof.

The nano-sized ceramic particles function to uniformly disperse the carbon nanotubes among the aluminum particles or aluminum alloy particles. Since nano-sized silicon carbide (SiC) particles have high tensile strength, sharpness, constant electrical conductivity, constant thermal conductivity, high hardness, and high resistance to chemicals, and thermal shock. Since the nano-sized SiC particles are highly stable at high temperatures and under chemicals, they are widely used as a material for an abrasive or a fireproofing member. In addition, the nano-sized SiC particles present on the surfaces of the aluminum particles or the surface of the aluminum alloy particles have a function of preventing direct contact between the carbon nanotubes and the aluminum particles or aluminum alloy particles to inhibit formation of undesirable aluminum carbide which is formed through a reaction between the carbon nanotubes and the aluminum particles or aluminum alloy particles.

The composite powder may include <NUM> parts by volume of the aluminum powder or aluminum-alloy powder and <NUM> part by volume of the carbon nanotubes.

When the content of the carbon nanotubes is less than <NUM> part by volume with respect to <NUM> parts by volume of the aluminum powder or aluminum-alloy powder, the strength of an aluminum-based clad heat sink made from the composite powder is similar to that of a pure aluminum sink or an aluminum alloy heat sink. In this case, the composite power cannot play a role as a reinforcing material. Conversely, when the content of the carbon nanotubes exceeds <NUM> parts by volume, an elongation decreases although the strength increases compared with pure aluminum or aluminum alloy. In addition, when the content of the carbon nanotubes is extremely large, the carbon nanotubes hinder dispersion of aluminum particles and degrade mechanical and physical properties of a product by serving as defect sites.

When the dispersion agent is included in the composite powder, the composite powder contains <NUM> to <NUM> parts by volume of the dispersion agent with respect to <NUM> parts by volume of the aluminum powder.

When the content of the dispersion agent is less than <NUM> part by volume with respect to <NUM> parts by volume of the aluminum powder, the effect of dispersing ingredients is insignificant. Conversely, when the content exceeds <NUM> parts by volume, the dispersion agent rather causes the carbon nanotubes to agglomerate, thereby hindering dispersion of the carbon nanotubes.

The ball milling is performed in an air or inert gas ambient condition (for example, nitrogen or argon ambient condition) at a low speed of <NUM> to <NUM> rpm or a high speed of <NUM> or more rpm for a duration of <NUM> to <NUM> hours, using a ball mill. For example, a horizontal or planetary ball mill is used for the ball milling.

The ball milling begins by charging <NUM> to <NUM> parts by volume of stainless steel balls (a <NUM>:<NUM> mixture of balls with a diameter of <NUM> and balls with a diameter of <NUM>) into a stainless steel container with respect to <NUM> parts by volume of the composite powder.

To reduce the coefficient of friction, any one organic solvent selected from the group consisting of heptane, hexane, and alcohol is used as a process control agent. In this case, the process control agent is added by <NUM> to <NUM> parts by volume with respect to <NUM> parts by volume of the composite powder. After the completion of the ball milling, the stainless steel container is opened so that the organic solvent volatilizes and the mixture of the aluminum powder and the carbon nanotubes remains.

The dispersion agent (herein, nano-sized ceramic particles) plays the same role as nano-sized milling balls due to the rotational force generated during the ball milling, thereby physically separating the agglomerated carbon nanotubes from each other and improving the fluidity of the carbon nanotubes. Thus, the carbon nanotubes can be uniformly dispersed on the surfaces of the aluminum particles.

Next, a multilayer billet is made from the obtained composite powder in step S20.

The multilayer billet produced in this step comprises a core layer and at least two shell layers surrounding the core layer. The shell layers except for the outermost shell layer are made of the composite powder. The outermost shell layer is made of (i) the aluminum or aluminum-alloy powder or (ii) the composite powder. The composite powders contained in the core and shell layers in the parts by volume of the carbon nanotubes with respect to the parts by volume of the aluminum or aluminum-alloy powder.

The number of the shell layers included in the multilayer billet is not particularly limited, but it is preferably <NUM> or less in terms of cost efficiency.

<FIG> is a diagram schematically illustrating a multilayer billet preparation process. Referring to <FIG>, the billet is prepared by charging the composite powder <NUM> into a metal can <NUM> through a guider G in step S20-<NUM>. The composite powder <NUM> is sealed and compressed with a cap C so that the composite power cannot flow out of the metal can <NUM> in step S20-<NUM>.

The metal can <NUM> may be made of any metal being thermally and electrically conductive. Preferably, the metal can <NUM> is made of aluminum, copper, or magnesium. The thickness of the metal can <NUM> ranges from <NUM> to <NUM> when a <NUM>-inch billet is used, but it varies depending on the size of the billet used.

<FIG> is a diagram illustrating an exemplary multilayer billet produced in the present step. The exemplary multilayer billet includes a core layer and two shell layers surrounding the core layer. Specifically, the multilayer billet includes a core layer, a first shell layer surrounding the core layer, and a second shell layer surrounding the first shell layer.

Referring to <FIG>, a second billet <NUM> serving as the first shell layer and having a different composition from a first billet <NUM> is disposed inside the first billet <NUM> serving as the second shell layer and having a hollow cylinder shape. In addition, a third billet <NUM> having a different composition from the second billet <NUM> and serving as the core layer is disposed inside the second billet <NUM> to form the multilayer billet.

The first billet <NUM> has a hollow cylindrical shape. That is, the first billet <NUM> is in the form of a can with one end closed or in the form of a hollow cylinder with both ends being open. The first billet <NUM> is made of aluminum, copper, magnesium, or the like. The first billet <NUM> having a hollow cylinder shape is manufactured by melting a base metal and injecting molten metal into a mold. Alternatively, it can be manufactured by machining a metal block.

The second billet <NUM> includes the prepared composite powder. The second billet <NUM> is in the form of a lump or powder of the composite powder.

When the second billet <NUM> is in the form of a lump of metal, the second billet <NUM> specifically has a cylinder shape. The multilayer billet is prepared by inserting the cylindrical second billet <NUM> into the first billet <NUM>. The insertion of the second billet <NUM> into the first billet <NUM> may be performed by the steps of: melting and pouring the composite powder for the second billet <NUM> into a mold to form a cylindrical shape; and press-fitting the cylindrical shape into the first billet <NUM>. Alternatively, the insertion may be performed by directly charging the composite powder into the cavity of the first billet <NUM>.

The third billet <NUM> may be a lump of metal or a metal powder.

When the second billet <NUM>, the third billet <NUM>, or both are in the form of a lump of the composite powder, the lump of the composite powder is produced by compressing the composite powder at a high pressure or by sintering the composite powder.

In this case, the composite powder of the second billet <NUM> and the composite powder of the third billet <NUM> differ in the parts by volume of the carbon nanotubes with respect to <NUM> parts by volume of the aluminum power or the aluminum-alloy powder. That is, in <FIG>, the second billet <NUM> and the third billet <NUM> differ in the parts by volume of the carbon nanotubes with respect to <NUM> parts by volume of the aluminum or aluminum alloy.

The composite powder of the second billet <NUM> contains <NUM> to <NUM> parts by volume of the carbon nanotubes with respect to <NUM> parts by volume of the aluminum or aluminum-alloy powder, and the composite powder of the third billet <NUM> contains <NUM> part by volume of the carbon nanotubes with respect to <NUM> parts by volume of the aluminum or aluminum-alloy powder.

Alternatively, the second billet <NUM> is made of the composite powder, and the third billet <NUM> is a mass or powder of a metal selected from the group consisting of aluminum, copper, magnesium, titanium, stainless steel, tungsten, cobalt, nickel, tin, and alloys thereof.

Of the total volume of the composite billet, the second billet accounts for <NUM> to <NUM> vol%, the third billet accounts for <NUM> to <NUM> vol%, and the first billet <NUM> accounts for the rest.

In the case of making a heat sink from the multilayer billet structured as described above using a direct extrusion process, it is possible to locally enhance the strength of a portion having a relatively small thickness.

On the other hand, since the multilayer billet includes the second or third billet <NUM> or <NUM> made of the composite powder, the multilayer billet may be compressed at a high pressure of <NUM> to <NUM> MPa before being enclosed (step S20-<NUM>).

Since the multilayer billet is compressed, the multilayer billet can be directly extruded using an extrusion die in the next step. When the pressure for compressing the composite powder is less than <NUM> MPa, there is a possibility that pores occur in an aluminum-based clad heat sink thus manufactured or the composite powder flows down. When the pressure exceeds <NUM> MPa, the second billet (meaning second and subsequent billets) is likely to expand in volume.

Further, since the multilayer billet includes the second billet containing the composite powder and/or the third billet containing the composite powder, a process of sintering the multilayer billet may be additionally performed (step S23-<NUM>) to directly extrude the multilayer billet using an extrusion dies.

A spark plasma sintering apparatus or a hot press sintering apparatus may be used for the sintering. However, any sintering apparatus can be used if the same objective can be achieved. However, when it is necessary to precisely sinter the multilayer billet in a short time, it is preferable to use discharge plasma sintering. In this case, the discharge plasma sintering is performed at a temperature in a range of <NUM> to <NUM> and a pressure in a range of <NUM> to <NUM> MPa for a duration of <NUM> second to <NUM> minutes.

Next, the multilayer billet is directly extruded using an extrusion die to produce an aluminum-based clad heat sink (step S30).

The extrusion dies may be solid dies, hollow dies, or semi-hollow dies.

The direct extrusion may be performed at a die angle of <NUM> to <NUM>, an extrusion ratio of <NUM> to <NUM>, an extrusion rate of <NUM> to <NUM>/s, an extrusion pressure of <NUM> to <NUM>/cm<NUM>, and a billet temperature of <NUM> to <NUM>. The extrusion ratio is a ratio of the cross-sectional area of the billet to the cross-sectional area of the aluminum-based clad heat sink.

On the other hand, when the multilayer billet includes the second billet containing the composite powder and/or the third billet (meaning second and onward billets) containing the composite powder, it is necessary to compress or sinter the multilayer billet at a high pressure as described above to directly extrude the multilayer billet using the extrusion dies.

The method of manufacturing an aluminum-based clad heat sink may further include a post-treatment process in which the aluminum-based clad heat sink is selectively thermally treated. In the case where the aluminum-based clad heat sink is manufactured by the method described above, a better heat treatment effect can be obtained even when the heat treatment is performed under general heat treatment conditions.

An aluminum-based clad heat sink according to another embodiment of the present invention can be manufactured by the above-described manufacturing method.

<FIG> are photographs and diagrams illustrating a heat sink manufactured by the manufacturing method of the present invention.

The shape of the heat sink manufactured by the manufacturing method of the present invention is not particularly limited. For example, the heat sink manufactured by the manufacturing method of the present invention may be a fin-type heat sink (see <FIG>) or a bar-type heat sink (see <FIG>).

The heat sink illustrated in <FIG> is a straight fin-type (SF-type) heat sink including a main body and a plurality of fins extending from the main body. The heat sink illustrated in <FIG> is a bar-type heat sink. The main body of the bar-type heat sink includes three layers-an outer layer, an inner layer, and an intermediate layer positioned between the outer layer and the inner layer.

For example, the outer layer is made of aluminum <NUM> (AI6063), the inner layer is made of aluminum <NUM> (AI3003), and the intermediate layer is made of the AI-CNT composite powder (Al-CNT) described above. In addition, the multiple pins of the heat sink are made of aluminum <NUM> (AI6063).

Each of the heat sinks is manufactured by: preparing a multilayer billet including a first billet having a hollow cylindrical shape and made of aluminum <NUM>, a third billet having a solid cylinder shape, made of aluminum <NUM>, and disposed in the first billet, and a second billet containing the composite powder and infilled between the first billet and the third billet; compressing or sintering the multilayer billet; and directly extruding the multilayer billet.

Hereinafter, the method will be described in detail with reference to examples.

Examples can be modified into various other forms. Examples are provided to more fully describe the method to the ordinarily skilled in the art.

Carbon nanotubes (manufactured by OCSiAl headquartered in Luxembourg) having a purity of <NUM>%, a diameter of <NUM> or less, and a length of <NUM> or less were used. Aluminum powder (manufactured by MetalPlayer headquartered in Korea) having an average particle size of <NUM> and a purity of <NUM>% was used.

A multilayer billet was manufactured such that a third billet having a columnar shape was positioned at the center of a metal can serving as a first billet and a second billet (composite powder) was positioned between the first billet and the third billet.

The second billet includes aluminum-CNT composite powder containing <NUM> part by volume of carbon nanotubes with respect to <NUM> parts by volume of aluminum powder. The first billet was made of aluminum <NUM>, and the third billet was made of aluminum <NUM>.

The second billet was manufactured in manner described below. <NUM> parts by volume of the aluminum powder and <NUM> parts by volume of the carbon nanotubes were introduced into a stainless steel container to fill <NUM>% of the total volume of the stainless steel container. Stainless steel milling balls (a mixture of balls having a diameter of <NUM> and balls having a diameter of <NUM>) were introduced into the container by <NUM>% of the total volume of the container, and <NUM> of heptane was added to the mixture in the stainless steel container. The mixture was ball-milled at a low speed of <NUM> rpm for <NUM> hours using a horizontal ball mill. After the completion of the ball milling, the container was opened to allow the heptane to be completely volatilized, and the remaining aluminum-CNT composite powder was collected.

The aluminum-CNT composite powder thus prepared was charged into a gap <NUM>. 5t between the first billet and the third billet and was compressed at a pressure of <NUM> MPa to prepare a multilayer billet.

The multilayer billet was extruded using a direct extruder under the conditions of an extrusion ratio of <NUM>, an extrusion rate of <NUM>/s, an extrusion pressure of <NUM>/cm<NUM>, and a billet temperature of <NUM> to obtain a straight fin-type aluminum clad heat sink.

In the same manner as in Example <NUM>, an aluminum-CNT composite powder containing the carbon nanotubes in an amount of <NUM> part by volume was prepared, and a multilayer billet was prepared from the composite powder.

The prepared multilayer billet was directly extruded under the same conditions as in Example <NUM> to produce an aluminum-based clad heat sink of a straight fin type.

In the same manner as in Example <NUM>, an aluminum-CNT composite powder containing the carbon nanotubes in an amount of <NUM> parts by volume was prepared, and a multilayer billet was prepared from the composite powder.

An aluminum-CNT mixture composed of <NUM> wt% of CNT and <NUM> wt% of aluminum powder was mixed with a dispersion agent (a <NUM>:<NUM> mixture of a solvent and a natural rubber solution) in a ratio of <NUM>:<NUM> and then exposed to ultrasonic waves for <NUM> minutes to produce a dispersion mixture. The dispersion mixture was heat-treated in an inert gas ambient condition at a temperature of <NUM> in a tubular furnace for <NUM> hours to completely remove the dispersion agent to prepare an aluminum-CNT composite powder.

The aluminum-CNT composite powder thus prepared was charged into an aluminum can having a diameter of <NUM> and a thickness of <NUM> to fill the aluminum can. The composite powder was extruded using a hot extruder (UH-500kN manufactured by Shimadzu Corporation in Japan) at an extrusion temperature of <NUM> and an extrusion ratio of <NUM> to produce of an aluminum-based clad heat sink of a straight fin type. That is, the aluminum-based clad heat sink was manufactured through hot powder extrusion.

The tensile strength, elongation, and Vickers hardness of the aluminum-based clad heat sinks prepared in Examples <NUM> to <NUM> and Comparative Example <NUM> were measured, and the results are shown in Table <NUM>.

The tensile strength and elongation were measured under tensile strength test conditions including a tensile speed of <NUM>/s and according to a test method specified in Korean Standard No. <NUM> (standard for test specimens). The Vickers hardness was measured under conditions of <NUM> and <NUM> seconds.

Referring to Table <NUM>, the aluminum-based clad heat sinks manufactured as in the examples had both of improved strength and improved ductility as compared with the aluminum-based clad heat sinks made from a rigid material (for example, Al6063) and a soft material (for example, Al3003).

The aluminum-based clad heat sink according to Comparative Example <NUM> had a high Vickers hardness but a very low elongation.

The corrosion resistance characteristics of the aluminum-based clad heat sinks manufactured as in the examples and the comparative examples were measured, and the results are shown in Table <NUM>.

The characteristics were measured by a seawater spraying method for specimens with a size of <NUM> x <NUM> and a thickness of <NUM> prepared according to the CASS standard.

Referring to Table <NUM>, the aluminum-based clad heat sink prepared as in the example exhibited improved corrosion resistance even with a small amount of CNT added, as compared to the aluminum-based clad heat sinks made from a rigid material (A6063) and a soft material (A3003). In addition, the aluminum-based clad heat sink prepared as in Comparative Example <NUM> exhibited a higher value than the pure aluminum alloy but exhibited a lower value than the aluminum-based clad heat sink prepared as in Example <NUM>.

The density, heat capacity, diffusivity, and thermal conductivity of the aluminum-based clad heat sinks prepared as in the examples and the comparative example Examples were measured and the results are shown in Table <NUM> below.

The density of the aluminum-based clad heat sink was measured on the principle of Archimedes according to the ISO standard. The heat capacity and diffusivity were measured by using a laser flash method using a specimen having a size of <NUM> x <NUM> and a thickness of <NUM>. The thermal conductivity was obtained as the product of measured density x heat capacity x diffusivity.

Referring to Table <NUM>, the aluminum-based clad heat sinks prepared in the examples exhibited a greatly improved thermal conductivity although it contains a small amount of CNT as compared with the aluminum-based clad heat sinks respectively made from a rigid material (A6063) and a soft and highly-conductive material (A1005) which is pure aluminum.

In addition, the aluminum-based clad heat sink prepared as in Comparative Example <NUM> exhibited a higher value than the pure aluminum alloy but exhibited a lower value than the aluminum-based clad heat sink prepared as in Example <NUM>.

While the present invention has been illustrated and described with reference to exemplary embodiments thereof, it is to be understood by those skilled in the art that the present invention is not limited to the disclosed exemplary embodiments but rather various modifications and improvements are possible without departing from the basic concept of the present invention. Thus, it should be understood that the modifications, improvements, and equivalents also fall within the scope of the present invention defined by the appended claims.

Claim 1:
A method of manufacturing an aluminum clad heat sink, the method comprising:
(A) preparing a composite powder by ball-milling (i) aluminum or aluminum-alloy powder and (ii) carbon nanotubes (CNT);
(B) preparing a multilayer billet comprising the composite powder; and
(C) directly extruding the multilayer billet using an extrusion die to produce a heat sink,
wherein the multilayer billet comprises a can-shaped first billet serving as a second shell layer; a second billet disposed inside the first billet and serving as a first shell layer; and a third billet disposed inside the second billet and serving as a core layer;
wherein the first billet is made of aluminum, and the second billet and the third billet comprise the composite powder, and
wherein the second billet comprises the carbon nanotubes in an amount of <NUM> to <NUM> parts by volume with respect to <NUM> parts by volume of the aluminum or aluminum-alloy powder, and the third billet comprises the carbon nanotubes <NUM> part by volume with respect to <NUM> parts by volume of the aluminum or aluminum-alloy powder.