Heat sink and method for manufacturing a heat sink

Abstract

The present invention provides a heat sink that is resistant to cracking even when force is applied to bend it, and has a uniform thermal conductivity in each direction in a plan view, as well as a method for manufacturing the same. [Solution] A heat sink 100 made of a sintered body of a graphite-copper composite material containing flake-shaped graphite particles 5 laminated via a copper layer, wherein the thermal conductivity in the direction perpendicular to the lamination direction of the flake-shaped graphite particles 5 is greater than the thermal conductivity in the lamination direction, characterized in that when the heat sink 100 is divided into four sections vertically and horizontally in a plan view, the lamination direction of the flake-shaped graphite particles 5 in the upper left section 11 and the lower right section 31 intersects with the lamination direction of the flake-shaped graphite particles 5 in the upper right section 21 and the lower left section 41. The intersection angle is preferably 60 to 90 degrees.

Description

Technical Field

[0001] The present invention relates to a heat sink made of a sintered body of a graphite-copper composite material and a method for manufacturing the same.

Background Art

[0002] Conventionally, as a member of a heat sink for cooling a heat source such as a semiconductor element such as an IGBT, a heat sink for radiating heat generated from the heat source has been used. Examples of the material of the heat sink include a sintered body of a graphite-copper composite material.

[0003] Among them, there is a graphite-copper composite material that includes flaky graphite particles laminated via a copper layer, and the thermal conductivity in a direction perpendicular to the lamination direction of the flaky graphite particles is greater than the thermal conductivity in the lamination direction, and it is excellent in thermal conductivity in a specific direction.

[0004] FIG. 11 is a schematic diagram of such a graphite-copper composite material. FIG. 11(a) shows a sintered body 7 including flaky graphite particles laminated via a copper layer. Further, FIG. 11(b) shows the sintered body 7 cut out into a plate shape to form a heat sink 8.

[0005] The sintered body 7 is sintered in a state where the flaky graphite particles 5 are laminated so as to be horizontally arranged. Therefore, the thermal conductivity in the directions X and Y perpendicular to the lamination direction Z of the flaky graphite particles 5 increases, while the thermal conductivity in the lamination direction Z decreases. If the heat sink 8 cut out into a plate shape is tilted and a heat source is placed on the X-Z plane, the heat generated from the heat source is radiated in the direction Y where the thermal conductivity is high.

[0006] On the other hand, since the thermal conductivity in the lamination direction Z is low, when a heat source is placed on the X-Z plane, a large difference in thermal conductivity occurs between the direction X and the direction Z. In contrast, Patent Document 1 describes an invention in which the lamination direction Z is made oblique to the heat sink so as to equalize the thermal conductivity in the vertical direction and the thermal conductivity in the horizontal direction in a plan view.

[0007] Figure 12 is a schematic diagram showing a conventional heat sink described in Patent Document 1, in which the flake-shaped graphite particles 5 of the heat sink 9 are stacked diagonally (from the lower right to the upper left), and the thermal conductivity in the vertical direction and the thermal conductivity in the horizontal direction in a plan view are equalized. [Prior art documents] [Patent Documents]

[0008] [Patent Document 1] Japanese Patent Publication No. 2019-192890 [Overview of the project] [Problems that the invention aims to solve]

[0009] However, the heat sink described in Patent Document 1 had a problem in that it was prone to cracking along the direction horizontal to the flake-like graphite particles when force was applied to bend it. In addition, there was a problem in that there was a large difference in thermal conductivity between two intersecting diagonal directions in a plan view ("down-right to up-left direction" and "down-left to up-right direction"). Furthermore, there was a problem in that distortion occurred when cutting it with a wire saw.

[0010] The present invention solves the above-mentioned conventional problems and provides a heat sink that is less likely to crack along a specific direction even when force is applied to bend it, and has equalized thermal conductivity in each direction in a plan view, as well as a method for manufacturing the same. [Means for solving the problem]

[0011] To solve the above problems, the present invention provides a heat sink made of a sintered body of a graphite-copper composite material containing flake-shaped graphite particles laminated via a copper layer, wherein the thermal conductivity in the direction perpendicular to the lamination direction of the flake-shaped graphite particles is greater than the thermal conductivity in the lamination direction, characterized in that when the heat sink is divided into four sections vertically and horizontally in a plan view, the lamination direction of the flake-shaped graphite particles in the upper left and lower right sections intersects with the lamination direction of the flake-shaped graphite particles in the upper right and lower left sections.

[0012] Preferably, the stacking direction of the flake-shaped graphite particles in the upper left and lower right is from the lower left to the upper right, and the stacking direction of the flake-shaped graphite particles in the upper right and lower left is from the lower right to the upper left.

[0013] Preferably, the stacking direction of the flaky graphite particles in the upper left and lower right is from the lower right to the upper left, and the stacking direction of the flaky graphite particles in the upper right and lower left is from the lower left to the upper right.

[0014] Preferably, the intersection angle between the stacking direction of the flaky graphite particles in the upper left and lower right portions and the stacking direction of the flaky graphite particles in the upper right and lower left portions is 60 to 90 degrees.

[0015] Furthermore, the present invention relates to a method for manufacturing a heat sink, comprising a sintered body of a graphite-copper composite material containing flake-shaped graphite particles laminated via a copper layer, wherein the thermal conductivity in the direction perpendicular to the lamination direction of the flake-shaped graphite particles is greater than the thermal conductivity in the lamination direction, characterized in that when the heat sink is divided into four sections vertically and horizontally in a plan view, the four sintered bodies are arranged and joined together such that the lamination direction of the flake-shaped graphite particles in the upper left and lower right sections intersects with the lamination direction of the flake-shaped graphite particles in the upper right and lower left sections. [Effects of the Invention]

[0016] The heat sink of the present invention is a heat sink made of a sintered body of a graphite-copper composite material containing flake-shaped graphite particles laminated via a copper layer, wherein the thermal conductivity in the direction perpendicular to the lamination direction of the flake-shaped graphite particles is greater than the thermal conductivity in the lamination direction. Furthermore, when the heat sink is divided into four sections vertically and horizontally in a plan view, the lamination direction of the flake-shaped graphite particles in the upper left and lower right sections intersects with the lamination direction of the flake-shaped graphite particles in the upper right and lower left sections. Therefore, even when force is applied to bend it, it does not tend to crack along a specific direction. In addition, the thermal conductivity in each direction in a plan view is leveled out in the vertical, horizontal, and diagonal directions.

[0017] Furthermore, when the layering direction of the flake-like graphite particles in the upper left and lower right is from lower left to upper right, and the layering direction of the flake-like graphite particles in the upper right and lower left is from lower right to upper left, it is effective against diagonal bending forces at the corners.

[0018] Furthermore, when the stacking direction of the flake-like graphite particles in the upper left and lower right is from the lower right to the upper left, and the stacking direction of the flake-like graphite particles in the upper right and lower left is from the lower left to the upper right, it is effective against diagonal bending forces toward the center.

[0019] Furthermore, when the intersection angle between the stacking direction of the flake-like graphite particles in the upper left and lower right sections and the stacking direction of the flake-like graphite particles in the upper right and lower left sections is between 60 and 90 degrees, the resistance to cracking and the leveling of thermal conductivity are good.

[0020] Furthermore, the present invention provides a method for manufacturing a heat sink, which comprises a sintered body of a graphite-copper composite material containing flake-shaped graphite particles laminated via a copper layer, wherein the thermal conductivity in the direction perpendicular to the lamination direction of the flake-shaped graphite particles is greater than the thermal conductivity in the lamination direction. When the heat sink is divided into four sections vertically and horizontally in a plan view, the four sintered bodies are arranged and joined so that the lamination directions of the flake-shaped graphite particles in the upper left and lower right sections intersect with those of the flake-shaped graphite particles in the upper right and lower left sections. Therefore, even when force is applied to bend the heat sink, it is not prone to cracking along a specific direction. In addition, the thermal conductivity in each direction in a plan view is equalized in the vertical, horizontal, and diagonal directions.

[0021] Thus, according to the present invention, it is possible to provide a heat sink that is less likely to crack along a specific direction even when force is applied to bend it, and which has equalized thermal conductivity in each direction in a plan view, as well as a method for manufacturing the same. [Brief explanation of the drawing]

[0022] [Figure 1] This is a front view showing a heat sink according to Embodiment 1 of the present invention. [Figure 2] This is a plan view showing the intersection angle of the heat sink according to Embodiment 1. [Figure 3] It is a diagram showing the manufacturing process of the heat dissipation plate. [Figure 4] It is a diagram showing the manufacturing process of the heat dissipation plate. [Figure 5] It is a diagram showing the manufacturing process of the heat dissipation plate. [Figure 6] It is a diagram showing the manufacturing process of the heat dissipation plate. [Figure 7] It is a plan view showing the crossing angle of the heat dissipation plate according to Embodiment 2. [Figure 8] It is a plan view showing the crossing angle of the heat dissipation plate according to Embodiment 3. [Figure 9] It is a plan view showing the crossing angle of the heat dissipation plate according to Embodiment 4. [Figure 10] It is a diagram showing the configurations of the examples and comparative examples. [Figure 11] It is a schematic diagram of the graphite - copper composite material. [Figure 12] It is a schematic diagram showing the heat dissipation plate according to the conventional example.

Mode for Carrying Out the Invention

[0023] The heat dissipation plate and its manufacturing method according to the embodiment of the present invention will be described. The heat dissipation plate in this embodiment is composed of a sintered body of a graphite - copper composite material containing flaky graphite particles laminated via a copper layer, and the thermal conductivity in the direction perpendicular to the lamination direction of the flaky graphite particles is greater than the thermal conductivity in the lamination direction.

[0024] The electric sintering device for sintering the graphite - copper composite material in this embodiment will be described. The electric sintering device sinter the powder material placed in the mold in the vacuum container by applying pressure with a vertical pressure shaft having an upper punch and a lower punch while passing an electric current through the mold.

[0025] Electrically conductive sintering apparatuses are classified into two types based on the method of current application: single-axis electrically conductive sintering apparatuses, which use the same axis for both pressure application and current application in the vertical direction, and multi-axis electrically conductive sintering apparatuses, which separate the pressure application and current application axes and apply current in the horizontal direction. Single-axis electrically conductive sintering apparatuses use the same axis for both pressure application and current application, which tends to result in an uneven temperature distribution in the radial (horizontal) direction of the sintered area. To improve upon this drawback, multi-axis electrically conductive sintering apparatuses separate the pressure application and current application axes. In this embodiment, it is possible to use a single-axis electrically conductive sintering apparatus, but from the viewpoint of achieving a uniform temperature distribution, it is more preferable to use a multi-axis electrically conductive sintering apparatus.

[0026] (Embodiment 1) Next, a heat sink according to Embodiment 1 of the present invention will be described with reference to Figure 1-2. Figure 1 is a front view showing the heat sink 100 according to Embodiment 1. Figure 2 is a plan view showing the intersection angle of the heat sink 100 according to Embodiment 1. In the following embodiments, the intersection angle will be expressed as an acute angle of 90 degrees or less.

[0027] The heat sink 100 is divided into four sections vertically and horizontally in a plan view. The upper left section 11, upper right section 21, lower right section 31, and lower left section 41 are joined together to form a single heat sink 100. Reference numeral 5 schematically indicates the stacking direction of the flake-shaped graphite particles.

[0028] The outer perimeter of the heat sink 100 is surrounded by a copper plate 1 and copper square bars 2, which reinforces its strength and makes it easier to handle. Holes are provided in the copper square bars 2 at the corners for attachment to a heat sink or the like.

[0029] As shown in Figure 2(a), the stacking direction of the flake-like graphite particles 5 in the upper left 11 (hereinafter simply referred to as "stacking direction") is 11z, and the stacking direction in the lower right 31 is 31z, both of which are in the direction from lower left to upper right. Also, the stacking direction in the upper right 21 is 21z, and the stacking direction in the lower left 41 is 41z, both of which are in the direction from lower right to upper left.

[0030] As shown in Figure 2(b), the stacking directions 11z and 31z of the upper left 11 and lower right 31 intersect at an intersection angle A. The intersection angle A is 90 degrees.

[0031] Next, the manufacturing method of the heat sink 100 will be described with reference to Figure 3-6. First, as shown in Figure 3, a cylindrical body 3 is obtained by sintering a graphite-copper composite material using an energized sintering apparatus. The cylindrical body 3 is in a state where flake-shaped graphite particles 5 are arranged horizontally through a copper layer. Then, a plate body 4 is cut out from the cylindrical body 3.

[0032] Next, as shown in Figure 4, multiple plates 4 (three in this embodiment) are arranged and joined together to obtain a rectangular parallelepiped 50. If the thickness of the plates 4 is sufficient, multiple plates can be used as they are without joining them together. Then, the triangular prisms 50a, 50b, 50c, and 50d at the four corners are cut off to obtain the upper left rectangular parallelepiped 10. The upper left rectangular parallelepiped 10 is a component that corresponds to the upper left part 11 of the heat sink 100. The size and shape of the triangular prisms 50a, 50b, 50c, and 50d are determined by the size and shape of the target upper left rectangular parallelepiped 10. Alternatively, the removed triangular prisms 50a, 50b, 50c, and 50d can be combined and joined together, and the unnecessary parts can be removed for use.

[0033] Next, as shown in Figure 5, the corner 10a of the obtained upper left rectangular parallelepiped 10 is removed. This is a notch for fitting the copper square bar 2, which will be described later. The stacking direction of the upper left rectangular parallelepiped 10 is from the lower left to the upper right.

[0034] Similarly, an upper right rectangular prism 20 corresponding to the upper right part 21 of the heat sink 100, a lower right rectangular prism 30 corresponding to the lower right part 31, and a lower left rectangular prism 40 corresponding to the lower left part 41 are obtained.

[0035] Next, as shown in Figure 6, the four resulting rectangular parallelepipeds are joined together in an arrangement such that the stacking direction of the upper left rectangular parallelepiped 10 and the lower right rectangular parallelepiped 30 intersects with the stacking direction of the upper right rectangular parallelepiped 20 and the lower left rectangular parallelepiped 40. Then, the copper plate 1 and the copper square bar 2 are joined to the outer circumference of the resulting rectangular parallelepiped 500. The joining of sintered bodies to each other and the joining of sintered bodies to copper members can be done by brazing.

[0036] Next, the rectangular prism 500 is cut to the required thickness using a wire saw or similar tool to complete the heat sink 100.

[0037] The heat sink 100 according to this embodiment is a heat sink made of a sintered body of graphite-copper composite material, which includes flake-shaped graphite particles 5 laminated via a copper layer, and the thermal conductivity in the direction perpendicular to the lamination direction of the flake-shaped graphite particles 5 is greater than the thermal conductivity in the lamination direction. When the heat sink 100 is divided into four sections vertically and horizontally in a plan view, the lamination directions 11z, 31z of the flake-shaped graphite particles 5 in the upper left section 11 and lower right section 31 intersect with the lamination directions 21z, 41z of the flake-shaped graphite particles 5 in the upper right section 21 and lower left section 41. Therefore, even if force is applied to bend it, it is not prone to cracking along a specific direction. Furthermore, the thermal conductivity in each direction in a plan view is leveled in the vertical, horizontal, and diagonal directions.

[0038] Furthermore, since the stacking directions 11z and 31z of the flake-shaped graphite particles 5 in the upper left 11 and lower right 31 are in the direction from lower left to upper right, and the stacking directions 21z and 41z of the flake-shaped graphite particles 5 in the upper right 21 and lower left 41 are in the direction from lower right to upper left, it is effective against diagonal bending forces at the corners.

[0039] Furthermore, the heat sink manufacturing method according to this embodiment is a method for manufacturing a heat sink made of a sintered body of graphite-copper composite material in which flake-shaped graphite particles 5 are laminated via a copper layer, and the thermal conductivity in the direction perpendicular to the lamination direction of the flake-shaped graphite particles 5 is greater than the thermal conductivity in the lamination direction. When the heat sink is divided into four sections vertically and horizontally in a plan view, the four sintered bodies are arranged and joined so that the lamination directions 11z, 31z of the flake-shaped graphite particles 5 in the upper left section 11 and lower right section 31 intersect with the lamination directions 21z, 41z of the flake-shaped graphite particles 5 in the upper right section 21 and lower left section 41. Therefore, even if force is applied to bend it, it does not tend to crack along a specific direction. In addition, the thermal conductivity in each direction in a plan view is leveled in the vertical, horizontal, and diagonal directions.

[0040] (Embodiment 2) Next, with reference to Figure 7, a heat sink according to Embodiment 2 of the present invention will be described. In the following embodiments, parts identical to those of the heat sink 100 according to Embodiment 1 are denoted by the same reference numerals and their descriptions are omitted. Furthermore, the manufacturing method can be the same as that of Embodiment 1. Figure 7 is a plan view showing the intersection angle of the heat sink 200 according to Embodiment 2.

[0041] The heat sink 200 is divided into four sections horizontally and vertically in a plan view. The upper left section 12, upper right section 22, lower right section 32, and lower left section 42 are joined together to form a single heat sink 200.

[0042] As shown in Figure 7(a), the stacking direction at the upper left 12 is 12z, and the stacking direction at the lower right 32 is 32z, both of which are in the direction from lower left to upper right. Also, the stacking direction at the upper right 22 is 22z, and the stacking direction at the lower left 42 is 42z, both of which are in the direction from lower right to upper left.

[0043] As shown in Figure 7(b), the stacking directions 12z and 32z of the upper left 12 and lower right 32 intersect at an intersection angle B. The intersection angle B is 60 degrees.

[0044] (Embodiment 3) Next, with reference to Figure 8, a heat sink according to Embodiment 3 of the present invention will be described. Figure 8 is a plan view showing the intersection angle of the heat sink 300 according to Embodiment 3.

[0045] The heat sink 300 is divided into four sections vertically and horizontally in a plan view. The upper left section 13, upper right section 23, lower right section 33, and lower left section 43 are joined together to form a single heat sink 300.

[0046] As shown in Figure 8(a), the stacking direction at the upper left 13 is 13z, and the stacking direction at the lower right 33 is 33z, both of which are in the direction from lower left to upper right. Also, the stacking direction at the upper right 23 is 23z, and the stacking direction at the lower left 43 is 43z, both of which are in the direction from lower right to upper left.

[0047] As shown in Figure 8(b), the stacking directions 13z and 33z of the upper left 13 and lower right 33 intersect at an intersection angle C. The intersection angle C is 60 degrees.

[0048] Even when the intersection angle is less than 90 degrees, as in the heat sink 200 according to Embodiment 2 and the heat sink 300 according to Embodiment 3, the effects of resistance to cracking and equalization of thermal conductivity can be expected. However, the intersection angle is preferably 30 to 90 degrees, more preferably 60 to 90 degrees, and even more preferably 90 degrees.

[0049] (Embodiment 4) Next, with reference to Figure 9, a heat sink according to Embodiment 4 of the present invention will be described. Figure 9 is a plan view showing the intersection angle of the heat sink 400 according to Embodiment 4.

[0050] The heat sink 400 is divided into four sections vertically and horizontally in a plan view. The upper left section 14, upper right section 24, lower right section 34, and lower left section 44 are joined together to form a single heat sink 400.

[0051] As shown in Figure 9(a), the stacking direction at the upper left 14 is 14z, and the stacking direction at the lower right 34 is 34z, both of which are in the direction from the lower right to the upper left. Also, the stacking direction at the upper right 24 is 24z, and the stacking direction at the lower left 44 is 44z, both of which are in the direction from the lower left to the upper right.

[0052] As shown in Figure 9(b), the stacking directions 14z and 34z of the upper left 14 and lower right 34 intersect at an intersection angle D. The intersection angle D is 90 degrees.

[0053] In the heat sink 400 according to this embodiment, the stacking directions 14z and 34z of the flake-shaped graphite particles 5 in the upper left 14 and lower right 34 are in the direction of lower right to upper left, and the stacking directions 24z and 44z of the flake-shaped graphite particles 5 in the upper right 24 and lower left 44 are in the direction of lower left to upper right, so it is effective against diagonal bending forces toward the center portion.

[0054] The following explanation is based on an example. [Examples]

[0055] As shown in Figure 10, the bending strength was measured for test specimens 60 (Example 1), 70 (Comparative Example 1), 80 (Comparative Example 2), and 90 (Comparative Example 3) using a four-point system with four support points 6. Each test specimen had dimensions of 30 mm in length, 5 mm in width, and 3 mm in thickness.

[0056] Example 1 corresponds to the heat sink 100 according to Embodiment 1, and the intersection angle is 90 degrees. Comparative Example 1 has a stacking direction of the entire test specimen in the width direction. Comparative Example 2 has a stacking direction of the entire test specimen in the length direction. Comparative Example 3 has a stacking direction of the entire test specimen in the diagonal direction.

[0057] Table 1 shows the measurement results for Example 1 and Comparative Examples 1-3.

[0058] [Table 1]

[0059] Example 1 showed values ​​between Comparative Example 2 and Comparative Example 3. Considering that Comparative Example 3 tends to crack along the direction horizontal to the flaky graphite particles when force is applied at an angle, Example 1 does not tend to crack along any particular direction, and the test results are considered good.

[0060] Thus, the heat sink according to this embodiment is less likely to crack along a specific direction even when force is applied to bend it, and the thermal conductivity in each direction in a plan view can be equalized.

[0061] Although the heat sink and its manufacturing method according to the embodiments of the present invention have been described above, the present invention is not limited to the embodiments described above, and various other modifications are possible. [Explanation of Symbols]

[0062] 1 copper plate 2 Copper square material 3 Cylinder 4 Plates 5. Scale-like graphite particles 6 fulcrum 7 Sintered body 8 Heat sink 9 Heat sink 10 Upper left cuboid 11 Upper left 12 Upper left 13 Upper left 14 Upper left 20 Right-hand rectangular prism 21 Upper right 22 Upper right 23 Upper right 24 Upper right 30 Lower right cuboid 31 Lower right 32 Lower right 33 Lower right 34 Lower right 40. Lower left rectangular prism 41 Lower left 42 Lower left 43 Lower left 44 Lower left 50 rectangular prisms 60 test specimens 70 test specimens 80 test specimens 90 test specimens 100 Heat sink 500 rectangular prisms

Claims

1. A heat sink made of a sintered body of a graphite-copper composite material containing flake-shaped graphite particles laminated via a copper layer, wherein the thermal conductivity in the direction perpendicular to the lamination direction of the flake-shaped graphite particles is greater than the thermal conductivity in the lamination direction, A heat sink characterized in that, when the heat sink is divided into four sections vertically and horizontally in a plan view, the stacking direction of the flake-shaped graphite particles in the upper left and lower right sections intersects with the stacking direction of the flake-shaped graphite particles in the upper right and lower left sections.

2. The heat sink according to claim 1, characterized in that the stacking direction of the flake-shaped graphite particles in the upper left and lower right is from the lower left to the upper right, and the stacking direction of the flake-shaped graphite particles in the upper right and lower left is from the lower right to the upper left.

3. The heat sink according to claim 1, characterized in that the stacking direction of the flake-shaped graphite particles in the upper left and lower right is in the direction of lower right to upper left, and the stacking direction of the flake-shaped graphite particles in the upper right and lower left is in the direction of lower left to upper right.

4. The heat sink according to claim 1, characterized in that the intersection angle between the stacking direction of the flaky graphite particles in the upper left and lower right portions and the stacking direction of the flaky graphite particles in the upper right and lower left portions is 60 to 90 degrees.

5. A method for manufacturing a heat sink made of a sintered body of a graphite-copper composite material containing flake-shaped graphite particles laminated via a copper layer, wherein the thermal conductivity in the direction perpendicular to the lamination direction of the flake-shaped graphite particles is greater than the thermal conductivity in the lamination direction, A method for manufacturing a heat sink, characterized in that when the heat sink is divided into four sections vertically and horizontally in a plan view, four sintered bodies are arranged and joined together such that the stacking direction of the flake-shaped graphite particles in the upper left and lower right sections intersects with the stacking direction of the flake-shaped graphite particles in the upper right and lower left sections.

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