Heat sink and method of manufacturing the same

Abstract

The present application provides a heat sink and a manufacturing method thereof. The heat sink (101) is provided with a graphite plate (102), two base materials (103) arranged adjacent to the graphite plate, and a fixing member (106). The graphite plate is in a strip shape, has a fin portion (104) and a base portion (105) provided at one end of the fin portion, the base material has a hole portion (103A) into which the fixing member can be inserted, the base material is arranged in a manner that the fixing member is inserted into the hole portions of the two base materials and is adjacent to both sides of the thickness direction of the base portion, the base portion is in close contact with the base materials adjacent to both sides of the thickness direction of the base portion, the adjacent base materials are fixed by riveting of the fixing member in a state of close contact with each other, and in a case where the surface roughness of the fin portion is set as Ra1, the surface roughness of the base material is set as Ra2, and the surface roughness of the base portion is set as Ra3, the relationship is Ra1>Ra2≥Ra3.

Description

TECHNICAL FIELD

[0001] The present application relates to a heat sink capable of managing heat released from a heat source such as an electronic device and a manufacturing method thereof. BACKGROUND

[0002] As the demand for heat dissipation from small electronic devices increases, heat management has become an increasingly important factor in the design of electronic products. The performance (processing speed), reliability, and expected lifetime of an electronic device (e.g., a device) are inversely proportional to the component temperature of the device. For example, by reducing the component temperature of a silicon semiconductor or the like, which is a typical device, it is possible to increase the processing speed, reliability, and expected lifetime of the device. Among these, to maximize the lifetime or reliability of the device, it is most important to control the component temperature of the device during operation within the limits set by the designer of the device.

[0003] As an excellent material in such heat management, a carbon material such as graphite is attracting attention. Graphite has a thermal conductivity equivalent to that of aluminum or copper or the like, which is a typical high thermal conductivity material, and has superior heat transport properties to copper. Therefore, graphite is attracting attention as a material for heat dissipation fins used in heat spreaders for LSI chips, or heat sinks for semiconductor power modules, and the like.

[0004] In existing heat sinks using graphite, for example, a heat sink in which graphite fins are fixed to a metal base with an adhesive is disclosed in Patent Literature 1.

[0005] In addition, a heat sink in which, as shown in FIG. 1 of Patent Literature 2, in order to sandwich graphite fins 204, a groove 206 having a width larger than the thickness of the fins 204 is provided in a metal base 203, and after the fins 204 are inserted into the groove 206, a riveting groove 202 is formed in the vicinity of the groove 206, and a portion of the base 203 is pressed into the fins 204 in a wedge shape as a metal press-in portion 201. Figure 10

[0006] PRIOR ART DOCUMENTS

[0007] PATENT LITERATURE

[0008] Patent Literature 1: Japanese Patent Application Laid-Open No. 2009-505850

[0009] Patent Literature 2: Japanese Patent Application Laid-Open No. 2019-80041 SUMMARY

[0010] A heat sink of one embodiment of the present application includes:

[0011] a graphite plate;

[0012] ​two substrates respectively arranged in abutment with the graphite plate; and

[0013] a fixing member,

[0014] The graphite plate is in a strip shape and has a fin portion and a base portion provided at one end of the fin portion,

[0015] Each of the substrates has a hole portion into which the fixing member is inserted,

[0016] The two substrates are respectively arranged in abutment with both sides in a thickness direction of the base portion of the graphite plate with the fixing member inserted into the hole portions of the two substrates, and the base portion of the graphite plate is in close contact with opposing surfaces of the two substrates, and the two substrates are riveted to the graphite plate by the fixing member, whereby the two substrates are fixed in a state where the opposing surfaces of the two substrates are in close contact with each other,

[0017] In a case where a surface roughness of the fin portion of the graphite plate is set as Ra1, a surface roughness of the substrate is set as Ra2, and a surface roughness of the base portion of the graphite plate is set as Ra3,

[0018] Ra1 > Ra2 ≥ Ra3. BRIEF DESCRIPTION OF DRAWINGS

[0019] Figure 1A is a front cross-sectional view showing a schematic configuration of a heat sink according to an embodiment of the present application.

[0020] Figure 1B is a side cross-sectional view showing a schematic configuration of a heat sink according to an embodiment of the present application.

[0021] Figure 1C is a front cross-sectional view showing a schematic configuration of a graphite plate provided in a heat sink according to an embodiment of the present application.

[0022] Figure 2 is a partially enlarged view showing a state where a graphite plate and two substrates are arranged in an assembly process of a heat sink shown in Figure 1A

[0023] Figure 3 Figure 1A Figure 2

[0024] Figure 4 Figure 1A ​​​​​Assembling process of the heat sink shown and before Figure 3 The stage shown and between Figure 5 The stage shown and between the riveting of the fixing member, the partial enlarged sectional view of the case before.

[0025] Figure 5 Is the graphite plate Figure 1A The schematic configuration of the heat sink shown is enlarged and partially enlarged to show the riveting by the fixing member, the base of the graphite plate and the base material on both sides of the base are mutually adhered, and the base materials are also mutually adhered. The partial enlarged sectional view of the case.

[0026] Figure 6 Is a front view of the sectional view showing the schematic configuration of the heat sink of the present application of examples 1-3 and comparative examples 1-2.

[0027] Figure 7A Is a front view of the sectional view showing the schematic configuration of the heat sink of the present application of example 4.

[0028] Figure 7B Is a schematic diagram of the heat sink shown Figure 7A The schematic configuration of the heat sink shown is a side view of the sectional view.

[0029] Figure 8 Is the TEG schematic diagram of the thermal conductivity evaluation test in the present application and comparative examples.

[0030] Figure 9 Is a diagram showing the results of the thermal conductivity evaluation test.

[0031] Figure 10 Is a schematic configuration diagram of the heat sink of the prior art.

[0032] Explanation of reference numerals

[0033] 101: heat sink

[0034] 102: graphite plate

[0035] 103: base material

[0036] 103A: hole part

[0037] 103B: opening surface

[0038] 103C: surface opposite to heat source

[0039] 104: fin part

[0040] 105: base

[0041] 105A: non-base surface

[0042] 105B: part in contact with base material

[0043] 105C: Plane

[0044] 106: Fixed components

[0045] 106A: Riveting part

[0046] 107: Lubricating Grease

[0047] 108: Temperature Measurement Department

[0048] 109: Fan

[0049] 110: Heater

[0050] 111: Support plate

[0051] 123: (The contact surface between the base of the graphite plate and the substrate)

[0052] 131: concave part

[0053] 133: (Contact surfaces between substrates)

[0054] 145: Steps

[0055] 201: Metal Press-in Section

[0056] 202: Riveting groove

[0057] 203: Base

[0058] 204: Fins

[0059] 205: Void Detailed Implementation

[0060] In the heat sink of Patent Document 1, since the adhesive is between the fins and the base, there is a problem of reduced thermal conductivity between the fins and the base.

[0061] Additionally, in the heat sink of Patent Document 2, such as Figure 10 As shown, the metal press-in portion 201 of the metal base 203 is pressed into the graphite fin 204. However, the metal press-in portion 201 only seals a portion between the groove insertion part of the fin 204 and the side of the groove 206, creating a void 205 in the unsealed portion. That is, although the metal base 203 and the graphite fin 204 partially contact and seal after the metal press-in portion 201 is pressed in, other parts are not sealed. Therefore, there is a problem that the contact area between the fin 204 and the base 203 deviates, resulting in reduced thermal conductivity between the fin and the base.

[0062] Therefore, the purpose of this invention is to solve the above-mentioned problems and provide a heat sink and a method for manufacturing the same, which can prevent the reduction of thermal conductivity between the fins and the base.

[0063] Hereinafter, an embodiment of the present application will be described in detail based on the drawings.

[0064] (Embodiment)

[0065] The heat sink 101 of the embodiment of the present application is provided with at least one graphite sheet 102, two base materials 103, and a fixing member 106. As one example, in Figure 1A and Figure 1B , a case where the heat sink 101 is provided with one graphite sheet 102, two base materials 103, and three fixing members 106 is shown.

[0066] Hereinafter, in the description of the embodiment of the present application, the left-right direction in the paper plane of the heat sink 101 shown in Figure 1A will be set as the thickness direction, the up-down direction in the paper plane will be set as the length direction, and the direction perpendicular to the paper plane will be set as the width direction.

[0067] The graphite sheet 102 is a band-shaped member, and in Figure 1B , has a length in the width direction in the left-right direction in the paper plane that is substantially the same as the length in the width direction of the base material 103. The graphite sheet 102 has a fin portion 104 and a base portion 105, the fin portion 104 is disposed on the free end side and used for heat dissipation, and the base portion 105 is disposed on the fixed end side, is in close contact with each base material 103 between two adjacent base materials 103, and transmits heat transmitted from each base material 103 to the fin portion 104. In Figure 1B , the length in the width direction of the fin portion 104 is the same as the length in the width direction of the base portion 105 in the width direction in the left-right direction in the paper plane.

[0068] The band-shaped member of the graphite sheet 102 is formed by stacking a plurality of high molecular films and performing graphitization while controlling the applied pressure. If graphite powder is compressed to form the graphite sheet 102, the graphite sheet 102 becomes brittle, and it is difficult to adjust the surface roughness described later, so the graphite sheet 102 is preferably formed of a high molecular film.

[0069] The high molecular film constituting the graphite sheet 102 can be at least one of polyoxadiazole, polybenzothiazole, polybenzodithiazole, polybenzoxazole, polybenzodioxazole, polybenzimidazole, aramid, polyphenylene benzimidazole, polyphenylene benzobisimidazole, polythiazole, and poly-p-phenylenevinylene.

[0070] As shown in Figure 1C , in the faces of the substance graphitized using a plurality of high molecular films, the portion 105B in contact with each base material 103 is partially peeled off in the face opposite to each base material 103, respectively, to form the base portion 105. That is, the face of the graphite sheet 102 peeled off to form the base portion 105 is the face disposed on both sides in the thickness direction of the graphite sheet 102.

[0071] The portion of the graphite plate 102 other than the base 105 is the fin portion 104. At the boundary between the fin portion 104 and the base 105, a step 145 is formed such that the thickness of the base 105 is less than the thickness of the fin portion 104. If the thinner base 105 is sandwiched between two substrates 103, while the thicker fin portion 104 is not sandwiched between the two substrates 103 and is exposed, the step 145 allows for easy positioning of the graphite plate 102 and the substrates 103. In this way, the fin portion 104 and the base 105 are integrally formed to create the graphite plate 102.

[0072] The graphite plate 102 has a base 105 with planes 105C on both sides in the thickness direction. Additionally, the graphite plate 102 has a non-base plane 105A at its free end in the length direction of the base 105, perpendicular to the six-membered ring structure of the graphite crystals. When the base 105 has the same length as the substrate 103 described later in the length direction, the non-base plane 105A is disposed flush with the surface 103C of the substrate 103 opposite the heat source. It should be noted that "flush" includes approximately flush.

[0073] The substrate 103 is made of metals such as copper, aluminum, stainless steel, or die-casting alloys. Figure 1B As shown, the substrate 103 is composed of a cuboid component, and as an example, it has three holes 103A extending along the thickness direction of the substrate 103. Each hole 103A extends in such a way that the fixing member 106, described later, can be inserted. Figure 1B In the width direction (left-right) within the paper, the holes 103A are spaced apart near the center and near both ends in the width direction of the substrate 103. Furthermore, the substrate 103 has an opening surface 103B (opposing surface) including the openings of the holes 103A, and a surface 103C opposite to the heat source. The opening surface 103B and the surface 103C opposite to the heat source of the substrate 103 are planar.

[0074] The fixing member 106 is, for example, a rod-shaped member such as a tube made of metals like copper, iron, or SUS, and is particularly preferably made of copper, which has high thermal conductivity. The fixing member 106 can be inserted into the holes 103A provided in each substrate 103. Figure 1B In this example, three fixing members 106 are inserted into three holes 103A. The axial length of the fixing member 106 is greater than the sum of the axial lengths of the holes 103A of the two substrates 103.

[0075] That is, if the fixing member 106 is inserted in a state where the two substrates 103 are in contact with each other, the both end portions of the fixing member 106 can be made to protrude from the two substrates 103, and by caulking the both end portions of the fixing member 106, a caulking portion 106A that expands radially outward from the opening edge of the hole portion 103A can be provided to fix the two substrates 103.

[0076] As shown in FIG. 1, the heat sink 101 of the embodiment is configured by combining the graphite sheet 102, the two substrates 103, and the fixing member 106. In addition, the heat sink 101 has a contact surface 123 configured by the graphite sheet 102 being in close contact with each of the substrates 103, and has a contact surface 133 configured by the substrates 103 being in close contact with each other. The present application has the following features in order to prevent a decrease in the thermal conductivity of these contact surfaces 123 and 133. Figure 1A Figure 1B As shown in FIG. 1, the heat sink 101 of the embodiment is configured by combining the graphite sheet 102, the two substrates 103, and the fixing member 106. In addition, the heat sink 101 has a contact surface 123 configured by the graphite sheet 102 being in close contact with each of the substrates 103, and has a contact surface 133 configured by the substrates 103 being in close contact with each other. The present application has the following features in order to prevent a decrease in the thermal conductivity of these contact surfaces 123 and 133.

[0077] In addition, the surface roughness of the fin portion 104 of the graphite sheet 102 is set to Ra1, the surface roughness of the substrate 103 is set to Ra2, and the surface roughness of the base portion 105 of the graphite sheet 102 is set to Ra3. Hereinafter, in the description of the embodiment of the present application, the surface roughness refers to the arithmetic average roughness (Ra) defined in JIS (Japanese Industrial Standards) B0601 (2013).

[0078] The fin portion 104 of the graphite sheet 102 included in the heat sink 101 receives wind generated by a fan (not shown) for the purpose of heat dissipation, and thus it is preferable that the surface area be as large as possible. In the embodiment of the present application, the value of the surface roughness Ra1 of the fin portion 104 is preferably in the range of 2.0 μm > Ra1 ≥ 1.0 μm, and particularly preferably in the range of 2.0 μm > Ra1 ≥ 1.5 μm, from the characteristics of the manufacturing of the graphite sheet 102.

[0079] In addition, the value of the surface roughness Ra3 of the base portion 105 of the graphite sheet 102 is preferably in the range of 0.5 μm ≥ Ra3 ≥ 0.2 μm, and particularly preferably in the range of 0.5 μm ≥ Ra3 ≥ 0.4 μm.

[0080] The substrate 103 is formed so that the value of the surface roughness Ra2 of the substrate 103 is close to the value of the surface roughness Ra3 of the base portion 105 of the graphite sheet 102 and is not lower than the value of the surface roughness Ra3 of the base portion 105 of the graphite sheet 102.

[0081] ​With this configuration, when the two ends of the fixing member 106 are riveted together, the formation of tiny voids on the contact surface 123 between the base 105 of the graphite plate 102 and each substrate 103 can be suppressed, preventing a decrease in thermal conductivity. Furthermore, when the two ends of the fixing member 106 are riveted together, since the surface of the substrate 103 is at least as rough as the surface of the base 105, the crushing of the graphite on the surface of the base 105 can be suppressed, preventing a decrease in thermal conductivity. Specifically, the surface roughness Ra2 of the substrate 103 is formed such that its value is greater than or equal to the surface roughness Ra3 of the base 105 of the graphite plate 102 but less than the surface roughness Ra1 of the fin portion 104. Therefore, the range of the surface roughness Ra2 of the substrate 103 is preferably 1.0 μm > Ra2 ≥ 0.5 μm, and particularly preferably 0.7 μm ≥ Ra2 ≥ 0.5 μm.

[0082] By employing three surface roughness ranges Ra1, Ra2, and Ra3, heat transferred to the substrate 103 of the heat sink 101 is efficiently transferred to the fin portion 104 via the base 105 of the graphite plate 102. Therefore, it is possible to prevent a decrease in the thermal conductivity of the heat sink 101.

[0083] The manufacturing method, i.e. the assembly method, of the radiator 101 will be described below in the order of assembly.

[0084] First of all, Figure 1C In the steps shown, the graphite plate 102 is formed by stacking multiple polymer films and firing them while controlling the applied pressure. Furthermore, the graphite that forms the base 105 of the graphite plate 102 is partially peeled off from the end of the graphite plate 102 along the length direction by a predetermined size to form the base 105 with a surface roughness Ra3 where Ra1 > Ra3.

[0085] Next, in Figure 2 In the steps shown, the graphite plate 102 is arranged such that each substrate 103 having a surface roughness Ra2 with the formula Ra1>Ra2≥Ra3 is adjacent to each other on both sides of the base 105 in the thickness direction. The length of each substrate 103 in the longitudinal direction is pre-adjusted to take into account its contact with the base 105 of the graphite plate 102, which will be described later. The planes 105C on both sides of the base 105 in the thickness direction and the opening surfaces 103B of each substrate 103 are respectively arranged opposite each other.

[0086] That is, in Figure 2 In the steps shown, the graphite plate 102 and each substrate 103 are arranged such that the planes 105C on both sides of the base 105 in the thickness direction of the graphite plate 102 are adjacent to the opening surfaces 103B of each substrate 103.

[0087] Furthermore, the graphite plate 102 is arranged such that the base 105 does not close the holes 103A of each substrate 103. By making the step 145 at the boundary between the fin portion 104 and the base 105 of the graphite plate 102 contact the upper surfaces of the two substrates 103, the base 105, which has a smaller thickness, is sandwiched between the two substrates 103, while the fin portion 104, which has a larger thickness, is not sandwiched between the two substrates 103 and is exposed. The graphite plate 102 and the substrates 103 are positioned in this manner. In a subsequent step, the fixing member 106 is inserted into the hole 103A.

[0088] Next, in Figure 3 In the steps shown, rod-shaped fixing members 106 are inserted into the holes 103A of each substrate 103. For adjacent substrates 103, the fixing members 106 axially align the holes 103A of each substrate 103 in a row via the holes 103A. Furthermore, Figure 4 express Figure 3 The steps shown are the same as the following. Figure 5 The state between the steps shown. Figure 4 In the process, the graphite plate 102 is in contact with the substrate 103, but the substrates 103 are not in contact with each other.

[0089] Furthermore, next, in Figure 5 In the steps shown, the two ends of the fixing member 106 are deformed in the axial direction to rivet the substrates 103 and the graphite plate 102 together to form a heat sink 101. When the substrates 103 and the graphite plate 102 are riveted together, the planes 105C on both sides of the base 105 of the graphite plate 102 in the thickness direction are respectively in close contact with the opening surfaces 103B of the adjacent substrates 103, forming riveting portions 106A at both ends of the fixing member 106. In addition, the base 105 of the graphite plate 102 is in close contact with the substrate 103, forming a recess 131 in the substrate 103. In other words, the contact surface 123 between the base 105 of the graphite plate 102 and the substrate 103 is the side surface of the recess 131 formed by the base 105 of the graphite plate 102 through which the substrate 103 with the base 105 is inserted. The contact surface 123 is also the surface where the planes 105C on both sides of the base 105 in the thickness direction are in close contact with the opening surface 103B of the substrate 103. In addition, the contact surface 133 is also the surface where the opening surfaces 103B of each substrate 103 are in close contact with each other.

[0090] Furthermore, the boundary between the fin portion 104 and the base 105 of the graphite plate 102 is approximately flush with the end of one end of each substrate 103 along its length. That is, the graphite plate 102 is positioned relative to the substrate 103 by means of the step 145.

[0091] That is, in the heat sink 101 of the embodiment of the present application, the base portion 105 of the graphite sheet 102 is bonded to the opposing surface (opening surface 103B) of each of the substrates 103 between the substrates 103 adjacent to both sides in the thickness direction of the base portion 105. Further, the two adjacent substrates 103 are configured so that the opposing surfaces (opening surfaces 103B) thereof are bonded to each other.

[0092] Further, the heat sink 101 of the embodiment of the present application is configured so that the surface roughness Ra1 of the fin portion 104 of the graphite sheet 102, the surface roughness Ra2 of the substrate 103, and the surface roughness Ra3 of the base portion 105 satisfy the relationship of Ra1 > Ra2 > Ra3.

[0093] Therefore, the heat sink 101 of the embodiment of the present application does not require an adhesive, and the contact surface 123 between the metal substrate 103 and the graphite sheet 102 is bonded without being easily hollowed, and thus the heat conductivity of the contact surface 123 can be prevented from being reduced.

[0094] Further, the value of the surface roughness Ra2 of the substrate 103 is equal to or greater than the value of the surface roughness Ra3 of the base portion 105 of the graphite sheet 102, and in the contact surface 123 where the base portion 105 and the substrate 103 are bonded, the graphite of the surface of the base portion 105 is not easily crushed, and thus the reduction in the heat conductivity can be prevented. Further, the value of the surface roughness Ra1 of the fin portion 104 of the graphite sheet 102 is greater than the value of the surface roughness Ra2 of the substrate 103. That is, heat is easily transferred from the upstream to the downstream of the heat transfer path, and thus the heat sink 101 of the embodiment of the present application can prevent the reduction in the heat conductivity.

[0095] Further, according to the above-described assembly method, it is not necessary to form a recess for receiving the base portion 105 in the substrate 103 in advance, and the positioning of the substrate 103 and the graphite sheet 102 is also easily performed by the step 145. Further, the above-described predetermined relationship of the surface roughness between the fin portion 104 and the base portion 105 of the graphite sheet 102 can be easily formed by the partial peeling of the graphite.

[0096] Hereinafter, the present application will be further described by showing examples and comparative examples.

[0097] (Example 1)

[0098] As the heat sink 101 of the present application, Example 1, as shown in FIG. 1, was produced. Figure 6As shown, eight graphite plates 102, each 50 mm long, 55 mm wide, and 0.2 mm thick, were used. Each graphite plate 102 was formed by stacking multiple layers of a polyphenylene benzobisimidazole film as a polymer film and firing it under controlled pressure. A 5 mm portion of graphite from the base portion 105 of the graphite plate 102 was partially peeled off from its longitudinal end. The surface roughness of the fin portion 104 and the base portion 105 are Ra1 = 1.7 μm and Ra3 = 0.5 μm, respectively.

[0099] The substrate 103 is made of aluminum and has dimensions of □50 × 4.8 × (thickness t = 5) mm. The surface roughness of the substrate 103 is Ra2 = 0.6 μm. The substrate 103 has a hole 103A for inserting a copper tube with an outer diameter of 1 mm, which serves as a fixing member 106. Nine sheets of substrate 103 are used.

[0100] The heat sink 101 was fabricated by riveting such a graphite plate 102 to a substrate 103 using a copper tube 106, and its performance was evaluated by a thermal conductivity test described later.

[0101] It should be noted that in the surface roughness measurement in the examples and comparative examples, the KEYENCE LK-G80 was used, and the reference length L was set to 1 mm.

[0102] (Example 2)

[0103] In Example 2, a heat sink 101 with Ra1 = 1.9 μm and other conditions the same as in Example 1 was fabricated.

[0104] (Example 3)

[0105] In Example 3, a heat sink 101 with Ra2 = Ra3 = 0.2 μm and other conditions the same as in Example 1 was fabricated.

[0106] (Example 4)

[0107] In Example 4, as Figure 7A and Figure 7B As shown, a heat sink 101 was fabricated in which a graphite plate 102 extends through to the heat-source-opposing surface 103C of a substrate 103, with the non-base surface 105A flush with the surface 103C opposite the heat source 112. In the graphite plate 102, as an example, three fixing members 106 are inserted into each of the three holes 103A. In Embodiment 4, a heat sink 101 was fabricated with all other conditions identical to those in Embodiment 1. With this configuration, sufficient contact area relative to the heat source 112 is achieved, and heat is easily transferred via the non-base surface 105A. It should be noted that "flush" includes approximately flush.

[0108] (Comparative Example 1)

[0109] As Comparative Example 1, a heat sink 101 was produced in which Ra2 = 2 μm and the other conditions were the same as in Example 1.

[0110] (Comparative Example 2)

[0111] As Comparative Example 2, a heat sink 101 was produced in which Ra2 = Ra3 = 1.9 μm and the other conditions were the same as in Example 1.

[0112] (Thermal Conductivity Evaluation Test)

[0113] Thermal conductivity evaluation tests were performed on the samples produced in the examples and comparative examples under a forced cooling environment. The thermal conductivity evaluation TEG is shown in Figure 8 . Directly below the center of the heat sink 101 produced in the above examples and comparative examples, a temperature measuring portion 108 (□ 10 mm, (thickness t = 5) mm, copper) and a heater 110 (□ 10 mm, (thickness t = 1) mm, ceramic) were supported and bonded with a support plate 111. Grease 107 was applied to a thickness of 0.3 mm between the base material 103 and the temperature measuring portion 108, between the temperature measuring portion 108 and the heater 110, and between the heater 110 and the support plate 111. In addition, a fan 109 (Model UDQF56C11CET (Panasonic)) of size □ 50 mm was provided directly above the heat sink 101.

[0114] With the thermal conductivity evaluation TEG thus configured, the temperature between the heater and the heat sink when the heater and the fan were operated at an input voltage of 11 V was measured and evaluated.

[0115] (Evaluation Results)

[0116] The evaluation results of the thermal conductivities of Examples 1 to 4 and Comparative Examples 1 and 2 are shown in Figure 9 . The thermal conductivity evaluation was determined by comparison with the results obtained by the same evaluation test performed on a conventional aluminum heat sink and a metal press-in heat sink as shown in Figure 10 . The thermal conductivity evaluation obtained in the conventional aluminum heat sink and the metal press-in heat sink was 50.5 degrees Celsius and 43.6 degrees Celsius, respectively. That is, in the case where the thermal conductivity evaluation obtained was lower than the thermal conductivity evaluation obtained in the metal press-in heat sink, i.e., 43.6 degrees Celsius, B was indicated as the comprehensive evaluation, and in the case where the lowest temperature was obtained, A was indicated. Note that, in the case where the thermal conductivity evaluation obtained exceeded the thermal conductivity evaluation obtained in the metal press-in heat sink, i.e., 43.6 degrees Celsius, C was indicated.

[0117] With respect to the comprehensive evaluation of the heat sink 101 in Examples 1 to 3, the thermal conductivity evaluation was 41.6 degrees Celsius, 41.1 degrees Celsius, and 40.4 degrees Celsius, respectively, and was B evaluation in each case. In each of Examples 1 to 3, the surface roughness Ra1 of the fin portion 104 of the graphite sheet 102 was rough, and the surface roughness Ra2 of the base material 103 and the surface roughness Ra3 of the base portion 105 of the graphite sheet 102 were close in value. Therefore, the wind from the fan could be effectively received, and the thermal conductivity between the base material 103 and the graphite sheet 102 was high, and thus a heat sink 101 having a higher thermal conductivity as a whole could be formed.

[0118] In addition, with respect to the comprehensive evaluation of the heat sink 101 in Example 4, the thermal conductivity evaluation was 39.8 degrees Celsius, and was A evaluation. As in Example 4, in the case where the graphite sheet 102 penetrates to the surface 103C of the base material 103 that opposes the heat source, and the non-base surface 105A and the surface 103C that opposes the heat source are flush, the graphite can directly receive the heat from the heat source and flow to the fin portion 104, and thus it can be said that the heat can be more efficiently transferred.

[0119] On the other hand, with respect to the comprehensive evaluation of the heat sink 101 in Comparative Examples 1 and 2, the thermal conductivity evaluation was 45.8 degrees Celsius and 46.1 degrees Celsius, respectively, and was C evaluation in each case. In Comparative Example 1, the surface roughness Ra2 of the base material 103 and the surface roughness Ra3 of the base portion 105 of the graphite sheet 102 were greatly different. In addition, if the surface roughness Ra2 of the base material 103 is rougher than the surface roughness Ra1 of the fin portion 104, the thermal conductivity from the base material 103 to the graphite sheet 102 decreases, and thus the thermal conductivity of the heat sink 101 decreases.

[0120] In addition, in Comparative Example 2, the surface roughness Ra2 of the base material 103 and the surface roughness Ra3 of the base portion 105 of the graphite sheet 102 were the same in value, and were 1.9 μm. However, the surface roughness Ra1 of the fin portion 104 was 1.7 μm. That is, the surface area of the base portion 105, which is the input portion, is larger than the surface area of the fin portion 104, which is the output portion of the heat transfer in the graphite sheet 102, and thus the thermal conductivity of the graphite sheet 102 decreases. Therefore, the thermal conductivity of the heat sink 101 decreases.

[0121] That is, in a case where the surface roughness Ra1 of the fin portion 104, the surface roughness Ra2 of the base material 103, and the surface roughness Ra3 of the base portion 105 each have a value of 0.2 μm or more and less than 2.0 and satisfy the relation of Ra1 > Ra2 ≥ Ra3, the temperature of the thermal conductivity evaluation of the heat sink 101 is a temperature lower than the temperature of the thermal conductivity evaluation of the heat sink based on the related art. In addition, in a case where the surface roughness Ra1 of the fin portion 104, the surface roughness Ra2 of the base material 103, and the surface roughness Ra3 of the base portion 105 do not satisfy the relation of Ra1 > Ra2 ≥ Ra3, the temperature of the thermal conductivity evaluation of the heat sink 101 is a temperature higher than the temperature of the thermal conductivity evaluation of the heat sink based on the related art.

[0122] That is, in the heat sink 101, by the values of the surface roughness Ra1 of the fin portion 104, the surface roughness Ra2 of the base material 103, and the surface roughness Ra3 of the base portion 105 satisfying the relation of Ra1 > Ra2 ≥ Ra3, heat can be efficiently transferred. In other words, heat input to the base material 103 is transferred to the fin portion 104 via the base portion 105, and is easily dissipated from the fin portion 104 having the largest surface area, and thus the transfer of heat is smoothly performed. Therefore, in the heat sink 101, a decrease in thermal conductivity can be prevented.

[0123] According to one embodiment of the present application, the base portion of the graphite sheet is bonded to the base material on both sides in the thickness direction adjacent to the base portion, and the adjacent base materials are fixed by riveting with a fixing member in a state of being bonded to each other. With this configuration, an adhesive for fixing the graphite sheet to the base material is not required. In addition, the contact portions of the graphite sheet and the base material are bonded, and thus voids are less likely to occur.

[0124] In addition, the value of the surface roughness Ra2 of the base material is equal to or greater than the value of the surface roughness Ra3 of the base portion of the graphite sheet. With this configuration, when the both end portions of the fixing member are riveted, graphite of the surface of the base portion of the graphite sheet is less likely to be crushed. Therefore, heat of the base material is easily transferred to the graphite sheet via the base portion of the graphite sheet.

[0125] In addition, the value of the surface roughness Ra1 of the fin portion of the graphite sheet is greater than the value of the surface roughness Ra2 of the base material and the value of the surface roughness Ra3 of the base portion of the graphite sheet. Therefore, the surface area of the fin portion of the graphite sheet is greater than the surface area of the base portion, and heat dissipation is easy.

[0126] Therefore, heat generated from a heat source is easily dissipated, and thus a decrease in thermal conductivity of a heat sink can be prevented.

[0127] In addition, the above-described prescribed relation of the surface roughness between the fin portion and the base portion of the graphite sheet can be easily formed by local exfoliation of graphite.

[0128] Industrial Applicability

[0129] The heat sink of the above-described aspect of the present application and the manufacturing method thereof can be applied, for example, to heat dissipation of a heat generating portion in industrial equipment and vehicle-mounted fields.

Claims

1. A heat sink comprising: a graphite sheet; two base materials each disposed in contact with the graphite sheet; and a fixing member, wherein the graphite sheet is in a strip shape and has a fin portion and a base portion provided at one end of the fin portion, each of the base materials has a hole portion into which the fixing member is inserted, the two base materials are each disposed in contact with both sides in a thickness direction of the base portion of the graphite sheet with the fixing member inserted into the hole portion of each of the two base materials, the base portion of the graphite sheet is in close contact with opposing surfaces of each of the two base materials between the base materials in contact with both sides in the thickness direction, and the two base materials are fixed to the graphite sheet by the fixing member, wherein, when a surface roughness of the fin portion of the graphite sheet is set as Ra1, a surface roughness of the base material is set as Ra2, and a surface roughness of the base portion of the graphite sheet is set as Ra3, a relationship of Ra1 > Ra2 > Ra3 is established, a contact surface of the base portion of the graphite sheet and the base material is a side surface of a recess portion of the base material into which the base portion is inserted, and the base portion is in close contact with a surface of the recess portion.

3. The heat sink according to claim 1 or 2, wherein the Ra1 is 2.0 μm > Ra1 > 1.0 μm, the Ra2 is 1.0 μm > Ra2 > 0.5 μm, and the Ra3 is 0.5 μm > Ra3 > 0.2 μm.

4. The heat sink according to claim 1 or 2, wherein the Ra1 is 2.0 μm > Ra1 > 1.5 μm, the Ra2 is 0.7 μm > Ra2 > 0.5 μm, and the Ra3 is 0.5 μm > Ra3 > 0.4 μm.

5. The heat sink according to claim 1 or 2, wherein the graphite sheet is formed by stacking a plurality of polymer films and graphitizing the stacked polymer films.

6. The heat sink according to claim 1 or 2, wherein a non-base surface of the graphite sheet is flush with a surface of the base material that faces a heat source, and the graphite sheet is disposed so as to be in contact with the heat source.

7. The heat sink according to claim 1 or 2, wherein the polymer film is at least one of polyoxadiazole, polybenzothiazole, polybenzobisthiazole, polybenzoxazole, polybenzobisoxazole, polybenzimidazole, aramid, polyphenylene benzimidazole, polyphenylene benzobisimidazole, polythiazole, and poly-p-phenylenevinylene.

8. The heat sink according to claim 1 or 2, wherein the fixing member is a copper pipe.

9. The heat sink according to claim 1 or 2, wherein a step is provided at a boundary between the fin portion and the base portion.

10. The heat sink according to claim 1 or 2, wherein the graphite sheet is formed by stacking a plurality of polymer films and performing baking while controlling an applied pressure, and a graphite portion of a portion of the graphite sheet that is formed as the base portion is peeled off from an end portion in a length direction of the graphite sheet by a predetermined size, and the base portion having the surface roughness Ra3 of the relationship Ra1 > Ra3 is formed.

2. The heat spreader of claim 1, wherein, ​ ​ ​ ​ ​ ​ ​ ​ ​ 5. The heat spreader of claim 1 or 2, wherein, ​ 6. The heat spreader of claim 1 or 2, wherein, ​ 7. The heat spreader of claim 5, wherein, ​ 8. The heat spreader of claim 1 or 2, wherein, ​ 9. The heat spreader of claim 1 or 2, wherein, ​ 10. A method of manufacturing a heat sink according to any one of claims 1 to 9, wherein ​ The graphite plate is arranged to be sandwiched by two substrates in a manner that the two sides of the graphite plate in the thickness direction of the base portion abut the planes of the substrates that oppose the planes of the substrates, respectively, and the fixing member is inserted into the hole portions of the substrates, In a state in which the substrates, the graphite plate, and the substrates are arranged in abutment in this order, the two end portions of the fixing member that protrude from the substrates are deformed, the base portion is caulked while forming recesses in the substrates, and the substrates and the graphite plate are fixed as one body, the surfaces of the base portion of the graphite plate and the side surfaces of the recesses of the substrates that abut each other are in close contact with each other, and the substrates that abut each other are in close contact with each other.

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