JP2020109790A - Thermal conductive structure and thermal diffusion device - Google Patents

Abstract

To provide a thermal conductive structure which can maintain a high thermal conductivity in the extension direction of a graphene sheet without reducing the strength, and a thermal diffusion device having the thermal conductive structure.SOLUTION: A thermal conductive structure 10 includes: a graphite structure 11; a recess part 30 in the upper surface 11A of the graphite structure 11, the recess part including an inclined surface 31 intersecting with the upper surface 11A; and a coating layer 20 formed in the inclined surface 31, the coating layer covering an edge part of the graphene sheet appearing in the inclined surface 31 by being in contact with the edge part.SELECTED DRAWING: Figure 1

Description

The present invention relates to a heat conduction structure including a graphite structure formed by stacking a plurality of graphene sheets, and a heat diffusion device including the heat conduction structure.

A graphite structure having a titanium layer formed on the surface of a graphite plate, which is a highly heat-conductive material, is known as a heat conductor that moves and dissipates heat from a heat-generating body that is the object of heat dissipation (see Patent Document 1). The graphite plate is formed by stacking a plurality of graphene sheets, and has a composition that is brittle and easily collapses. Therefore, in the above-described conventional graphite structure, by covering the surface of the graphite plate with the titanium layer, the strength is increased while realizing efficient heat conduction. Further, the above-mentioned conventional graphite structure has a through hole penetrating in a direction perpendicular to the basal surface of the graphite plate, and by forming a titanium layer on the inner surface of this through hole, the strength of the graphite plate is further improved. It is reinforced.

JP, 2013-191830, A

Since the above-mentioned conventional graphite structure has a plurality of through holes penetrating perpendicularly to the basal plane, the plurality of through holes hinder the heat conduction in the extending direction of the graphene sheet (the direction along the basal plane). To be done. Further, since a titanium compound in which carbon atoms and titanium are bonded is formed on the edge surface (side surface adjacent to the basal surface) of the graphite plate, the titanium layer and the edge surface are strongly bonded, In order to generate the same bonding force between the basal surface and the titanium layer, it is necessary to form the through holes innumerably, the strength is rather lowered, and the thermal conductivity in the extending direction of the graphene sheet is increased. Is significantly reduced.

An object of the present invention is to provide a heat conduction structure capable of maintaining a high heat conductivity in the extending direction of a graphene sheet without lowering the strength, and a heat diffusion device including the heat conduction structure. To do.

(1) A heat conducting structure of the present invention is formed on a graphite structure formed by stacking a plurality of graphene sheets and a first surface of the graphite structure on a side to which a heat transfer target is attached. A concave portion including an inclined surface that intersects the surface, and a covering portion that is formed on at least the inclined surface and covers the edge portion in close contact with the edge portion of the graphene sheet that appears on the inclined surface, Characterize. In addition, it is preferable that one or more recesses are provided on the first surface.

Since the present invention is configured as described above, the edge portion of the graphene sheet (the end portion of the graphene sheet in the basal surface direction) appears on the inclined surface. Since carbon atoms in an unsaturated state (having unbonded hands) are present at the edge portion of the graphene sheet, carbon atoms in an unsaturated state appear on the inclined surface. Therefore, by forming the covering portion so as to cover the inclined surface, the atoms, molecules, etc. contained in the covering portion are bonded to the above-mentioned unsaturated carbon atoms. As a result, the covering portion is firmly formed on the inclined surface while being in close contact with the inclined surface. Further, a plurality of edge portions appear on the inclined surface, and the gap between the edge portions brings about an anchor effect when the covering portion is formed on the inclined surface. Therefore, by forming the covering portion so as to cover the inclined surface, the material of the covering portion enters the gap between the edge portions, and the bonding force and the adhesion between the inclined surface and the covering portion are improved. As a result, the covering portion is firmly formed on the inclined surface while being in close contact with the inclined surface. As described above, in the heat conducting structure of the present invention, since the covering portion is formed in a state where the covering portion is firmly adhered to the inclined surface of the first surface, the covering portion is formed even if the graphite structure is thermally expanded. The peeling and cracking of the can be prevented. In particular, peeling or cracking of the coating portion at the end portion in the basal surface direction of the heat conducting structure of the present invention is prevented. In addition, since the graphite structure has extremely high thermal conductivity in the basal plane direction, when a heat transfer object such as a heating element is attached to the first surface side of the heat conductive structure of the present invention, When the heat of the heat transfer object is transferred to the edge part of the inclined surface through the coating part, it is quickly transferred from the edge part to the basal surface direction and diffused. Further, since it is not necessary to form a large number of through holes in the graphite structure for preventing peeling or cracking of the coating portion due to the thermal expansion, without lowering the strength of the heat conducting structure, It becomes possible to maintain high thermal conductivity in the extending direction.

(2) It is preferable that the inclined surface forms a predetermined angle with the first surface of the graphite structure. The inclined surface is formed, for example, by cutting the first surface with a lathe or the like and processing it into a tapered shape. Edges of each of the plurality of graphene sheets appear on the inclined surface according to the inclination angle.

(3) The predetermined angle is set within a range of 1 degree or more and 20 degrees or less.

(4) More preferably, the predetermined angle is set within a range of 8 degrees or more and 20 degrees or less.

(5) Further, the covering portion is formed so as to be in close contact with the entire area of the first surface or the outer peripheral surface of the graphite structure.

As a result, on the first surface or the entire surface of the graphite structure, the bonding force and the adhesiveness with the covering portion are improved.

(6) Further, the heat-conducting structure of the present invention has a hole formed in the bottom of the recess and perforated in a direction intersecting the first surface from the bottom. In this case, the covering portion is formed on the inner surface of the hole.

(7) Further, the recess penetrates the graphite structure from the first surface to the opposite second surface.

(8) Further, the present invention can be understood as a heat diffusion device that includes the above-described heat conduction structure and diffuses heat transmitted from a heat transfer object attached to the coating portion of the heat conduction structure. ..

Further, the present invention can be understood as a method for manufacturing a heat conductive structure to which a heat transfer target such as a heat dissipation target (cooling target) or a heating target is attached. A method for manufacturing a heat conducting structure according to the present invention, in a first surface of a graphite structure in which a plurality of graphene sheets are laminated, a plurality of recesses including inclined surfaces intersecting with the first surface are formed, At least the inclined surface is formed with a covering portion that covers the edge portion of the graphene sheet that appears on the inclined surface while being in close contact with the edge portion.

According to the present invention, it is possible to maintain high thermal conductivity in the extending direction of the graphene sheet without lowering the strength.

FIG. 1 is a perspective view schematically showing a heat conductive structure according to the first embodiment of the present invention. FIG. 2 is a perspective view schematically showing a graphite structure included in the heat conduction structure according to the first embodiment of the present invention. FIG. 3 is an enlarged cross-sectional view showing an example of the cross-sectional structure of the recess of the heat conducting structure according to the first embodiment of the present invention. FIG. 4 is an enlarged cross-sectional view showing an example of the cross-sectional structure of the recess according to the second embodiment of the present invention. FIG. 5 is an enlarged cross-sectional view showing an example of the cross-sectional structure of the recess according to the third embodiment of the present invention. FIG. 6 is an enlarged cross-sectional view showing an example of the cross-sectional structure of the recess according to the fourth embodiment of the present invention. FIG. 7 is an enlarged cross-sectional view showing an example of the cross-sectional structure of the recess according to the fifth embodiment of the present invention. FIG. 8 is an enlarged cross-sectional view showing an example of the cross-sectional structure of the recess according to the sixth embodiment of the present invention. FIG. 9 is a perspective view schematically showing a heat diffusion device to which the heat conduction structure according to the embodiment of the present invention is applied. FIG. 10 is a schematic diagram showing a test piece used for a thermal shock test and a thermal diffusivity test for each example and comparative example of the present invention. FIG. 11 is a perspective view showing another example of the heat diffusion device to which the heat conduction structure according to the embodiment of the present invention is applied. FIG. 12 is a perspective view showing another example of the heat diffusion device to which the heat conduction structure according to the embodiment of the present invention is applied.

Hereinafter, embodiments of the present invention will be described with reference to the accompanying drawings. The following embodiments are examples of embodying the present invention and do not limit the technical scope of the present invention. Further, in all the drawings of the following respective embodiments, the same or corresponding parts are designated by the same reference numerals.

[First Embodiment]
FIG. 1 is a perspective view showing a heat conductive structure 10 according to a first embodiment of the present invention and a structure in which a semiconductor element 56, which is a heat transfer object, is attached to the heat conductive structure 10. In FIG. 1, a cross-sectional view of the heat conducting structure 10 cut at the center of the semiconductor element 56 is shown. FIG. 2 is a perspective view showing the graphite structure 11 included in the heat conduction structure 10. The semiconductor element 56 is a heating element that generates heat when driven, such as a power semiconductor or a power module. Further, in the following embodiments, an example in which the heat conducting structure 10 is used for absorbing and cooling heat from the semiconductor element 56 which is a heat generating element will be described. However, heat is transferred from the heat conducting structure 10 to a heat transfer object. The heat conductive structure 10 may be used for the purpose of transmitting heat to heat the heat transfer object.

The heat conducting structure 10 is a member called a so-called heat diffusion plate or heat dissipation plate, and the semiconductor element 56 as the heating element is attached to the attachment region 10B located at the center of the upper surface 10A thereof. The heat-conducting structure 10 is used for absorbing heat from the semiconductor element 56 that is driven to generate heat and transmitting the heat in a direction along the upper surface 10A to diffuse the heat. By absorbing heat from the semiconductor element 56, the semiconductor element 56 can be dissipated and cooled. Further, since it has a high thermal conductivity in the direction along the upper surface 10A, the heat distribution in the semiconductor element 56 can be made substantially uniform.

As shown in FIG. 1, the heat conducting structure 10 includes a graphite structure 11 formed in a rectangular plate shape, and a coating layer 20 (a coating of the present invention) provided so as to cover the entire circumferential surface of the graphite structure 11. (An example of a part) and.

As shown in FIG. 2, the graphite structure 11 is formed in a flat plate shape and has a crystal structure in which a plurality of graphene sheets 15 are stacked in one direction. In this embodiment, a plurality of graphene sheets 15 are stacked in the vertical direction (Y-axis direction) so that the basal surfaces of the graphene sheets 15 are parallel to each other.

The graphene sheet 15 is a sheet-like graphene and is formed by covalently bonding a six-membered ring in a plane direction (basal plane direction), and has a thickness of one carbon atom (about 0.335 nm). Is. Since the layers of each graphene sheet 15 of the graphite structure 11 are bonded by Van der Waals force, the graphene sheet 15 has a property of being easily peeled in layers.

As shown in FIG. 2, the graphite structure 11 has a thickness direction in the stacking direction (Y-axis direction) in which the graphene sheets 15 are stacked, and in the present embodiment, the thickness D1 thereof is the basal plane direction (X The plate shape is thinner than the size in the axial direction and the Z-axis direction).

Specifically, when the heat conducting structure 10 is used for the purpose of absorbing and radiating heat from the semiconductor element 56 as a heating element attached to the attachment region 10B (see FIG. 1), the graphite structure 11 has a thickness D1 is formed to be 1.5 mm to 2.0 mm. Further, in this case, the graphite structure 11 is formed in a rectangular shape or a circular shape in a plan view, and for example, is formed in a square shape with one side of 30 mm to 300 mm depending on the size of the semiconductor element 56 to be radiated. It is also possible to use a circular one having a diameter of 30 mm to 300 mm or a circular one. Note that the actual thickness of the graphene sheet 15 is one carbon atom, but for convenience of description, the graphene sheet 15 represented by the actual thickness or more is shown in each drawing.

As the graphite structure 11, highly oriented pyrolytic graphite (HOPG) having higher thermal conductivity than general graphite is adopted. Specifically, MINTEQ International Inc. of the United States. The product name "PYROID" manufactured by the manufacturer is used.

The graphite structure 11 has anisotropy in thermal conductivity. That is, the graphite structure 11 is along the XZ plane rather than the thermal conductivity in the Y-axis direction (direction perpendicular to the XZ plane), that is, along the upper surface 10A of the heat conduction structure 10 in FIG. Direction (basal plane direction) thermal conductivity is extremely high. The property that the thermal conductivity varies depending on the direction of the material is called anisotropy, and the graphite structure 11 having this anisotropy is generally referred to as an anisotropic heat conductor or an anisotropic heat conduction element. It is called. Specifically, the graphite structure 11 has a thermal conductivity of about 1500 [W/mK] to 1700 [W/mK] in the direction along the XZ plane, and a thermal conductivity of 5 [W] in the Y-axis direction. /MK] to 10 [W/mK].

Further, as described above, since the graphite structure 11 is highly oriented pyrolytic graphite, the linear expansion coefficient (linear expansion coefficient) of general graphite in the stacking direction (Y-axis direction) is 4.5 [ppm]. /K] to 5.5 [ppm/K], the linear expansion coefficient of the graphite structure 11 in the stacking direction (Y-axis direction) is extremely high, and specifically, about 25 [ppm/K]. ]. In addition, in the graphite structure 11, the linear expansion coefficient in the basal plane direction (X-axis direction, Z-axis direction) is extremely low, and is substantially 0 [ppm/K].

The side end surface 16 of the graphite structure 11 is in a state where the edge portions of the plurality of graphene sheets 15 in the basal plane direction are overlapped with each other, and is generally called an edge surface. As described above, since the graphene sheet 15 is formed by covalently bonding six-membered rings, the basal plane direction (the direction along the XZ plane) in the graphene sheet 15 is a strong covalent bond due to the six-membered ring. There is a connection. However, in the side end face 16, the covalent bond in the basal plane direction due to the six-membered ring is broken, so that the carbon atom bond in the side end face 16 is in an unsaturated state. Therefore, the side end surface 16 is in an activated state in which carbon atoms easily react with other substances.

As shown in FIG. 2, a plurality of recesses 30 are formed on the upper surface 11A of the graphite structure 11. The upper surface 11A is a surface on the side of the graphite structure 11 to which the semiconductor element 56 (heat transfer target) as a heating element is attached, and is an example of the first surface of the present invention. The concave portion 30 is formed in a circular shape in a plan view, and is formed in a tapered shape toward the bottom portion 32 (see FIG. 3). The recess 30 is formed by cutting from the upper surface 11A to the inside of the graphite structure 11. A plurality of recesses 30 are arranged on the upper surface 11A so as to be arranged at equal intervals in the X-axis direction and the Z-axis direction.

The intervals between the recesses 30 in the X-axis direction and the Z-axis direction can be determined in accordance with the type and size of the heat transfer target to be mounted in the mounting region 10B, the size and thickness of the graphite structure 11, and the like. , 0.5 mm to 50 mm. The number of the recesses 30 per unit area can also be determined in accordance with the type and size of the heat transfer target to be mounted in the mounting region 10B, the size and thickness of the graphite structure 11, and the like. The arrangement direction of the plurality of recesses 30 is not limited to the X-axis direction and the Z-axis direction. On the upper surface 11A, the plurality of recesses 30 may be arranged in an equilateral triangle shape (triangle arrangement) so as to be equally spaced in all directions.

FIG. 3 is an enlarged cross-sectional view showing an example of the cross-sectional structure of the recess 30. As shown in FIG. 3, the inner peripheral surface of the recess 30 is an inclined surface 31 that intersects the upper surface 11A at a predetermined inclination angle. That is, the concave portion 30 has the inclined surface 31 that is inclined at a predetermined angle with respect to the upper surface 11A. In the recess 30, the depth D2 from the upper surface 11A to the bottom 32 is such that the edge portions of the plurality of graphene sheets 15 appear on the inclined surface 31 and is sufficiently shorter than the thickness D1 of the graphite structure 11. That is, since the concave portion 30 is formed on the upper surface 11A, an edge surface in which the edge portions of the plurality of graphene sheets 15 are superposed on each other appears in the inclined surface 31.

Here, the size of the opening of the concave portion 30, the internal shape of the concave portion 30, and the inclination angle of the inclined surface 31 depend on the thickness of the coating layer 20, the type of coating material of the coating layer 20 described later, the thickness D1 of the graphite structure 11, and the like. Based on this, it is set to an appropriate value according to the application of the heat conducting structure 10.

The recess 30 can be formed on the upper surface 11A of the graphite structure 11 by mechanical processing such as cutting, electric discharge processing, or laser processing. It is also possible to form the recess 30 by masking a region on the upper surface 11A of the graphite structure 11 other than the area where the recess 30 is formed, and then performing a blast treatment on the upper surface 11A. It is also possible to form the recess 30 in the upper surface 11A by wet etching or dry etching. Here, in the wet etching, the region other than the place where the concave portion 30 is formed is masked on the upper surface 11A of the graphite structure 11, and then the corrosive liquid is supplied to the upper surface 11A to corrode the exposed portion, whereby the concave portion 30 is formed. Can be formed. Similarly, in the dry etching as well, a region other than the portion where the recess 30 is formed is masked on the upper surface 11A, and a reaction gas (etching gas) that reacts with carbon such as oxygen gas or hydrogen gas is supplied to the upper surface 11A. The recess 30 can be formed on the upper surface 11A by reacting with the carbon of the exposed portion.

As described above, the heat conducting structure 10 has the coating layer 20 provided so as to cover the entire peripheral surface of the graphite structure 11. The coating layer 20 is formed so as to be in close contact with the entire peripheral surface of the graphite structure 11. In the present embodiment, the coating layer 20 is a coating layer formed by coating the entire peripheral surface of the graphite structure 11 with a coating material. Since the coating layer 20 is formed on the entire peripheral surface of the graphite structure 11, the coating layer 20 is also formed in a state of being in close contact with the inclined surface 31 and the bottom portion 32 of the inner periphery of the recess 30.

Specifically, the coating layer 20 includes, for example, a coating material containing a metal element capable of forming a compound by bonding to carbon atoms in an unsaturated state (state having dangling bonds) appearing on the inclined surface 31. And a coating formed on at least the inclined surface 31 by the coating material. As the metal element, for example, so-called active metal such as nickel or titanium can be applied. Nickel and titanium have extremely high wettability with respect to the inclined surface 31, which is the bonding surface, that is, bond reactivity with unsaturated carbon atoms. The metal element preferably has a linear expansion coefficient smaller than the linear expansion coefficient (about 25 [ppm/K]) of the graphite structure 11 in the stacking direction, and in addition to nickel and titanium described above, iron and aluminum. , Gold, silver, copper, zinc, chromium, tin, lead, tungsten, tantalum, SUS304, SUS430, or alloys containing these metals are preferable.

In addition, the coating layer 20 has a coating material including a synthetic resin that adheres to the edge portion of the graphene sheet 15 that appears on the inclined surface 31, and is formed by the coating material so as to adhere to the entire peripheral surface including the inclined surface 31. It may be a film. The synthetic resin is preferably an engineering plastic having a heat resistance of 150° C. or higher, and examples thereof include polytetrafluoroethylene (PTFE), perfluoroalkoxyalkane (PFA), perfluoroethylenepropene copolymer (FEP), and ethylenetetrafluoroethylene copolymer. Fluorine resin such as (ETFE), polyimide, polyamideimide, polyetherimide, polybenzimidazole, parylene, polysulfone, polyethersulfone, polyphenylene sulfide, liquid crystal polymer, epoxy resin, silicone resin, etc. can be applied. ..

In addition, the coating layer 20 has a coating material containing an inorganic compound that adheres to the edge portion of the graphene sheet 15 that appears on the inclined surface 31, and is formed by the coating material to adhere to the entire peripheral surface including the inclined surface 31. It may be a film. As the inorganic compound, glass made of a polymer or low-molecular-weight silane as a raw material, a ceramic such as a nitride such as silicon nitride or an oxide such as alumina, and a carbon-based diamond-like carbon can be applied.

Further, the coating layer 20 may be formed in close contact with the entire peripheral surface including the inclined surface 31 with a coating agent such as a silane coupling agent or a metal-based coupling agent.

As a method for forming the coating layer 20, for example, a dry coating method such as sputtering, thermal spraying, vapor deposition, or a wet coating method such as plating or liquid coating method (for example, dipping) is used to form a film on the entire peripheral surface including the inclined surface 31. Can be used.

In the present embodiment, the coating layer formed on the surface of the graphite structure 11 is illustrated as an example of the coating portion 20, but the coating portion 20 is not limited to the coating layer. For example, the covering portion 20 is a plate member (for example, a copper plate or an aluminum plate) containing the above-mentioned metal element bonded to the upper surface 11A or the entire peripheral surface of the graphite structure 11, a plate member containing the above-mentioned synthetic resin, and the above-mentioned plate member. It may be a plate member (for example, a ceramic plate) containing an inorganic compound. Further, the covering portion 20 may be formed by forming a thermal interface material (TIM material) such as a heat dissipation grease, a heat conduction sheet, or a gap filler on the surface of the graphite structure 11. The covering portion 20 can also be formed by casting, for example, so that the graphite structure 11 is arranged at the center of the metal block containing the above-mentioned metal element.

From the above, in the heat conduction structure 10, first, the plurality of recesses 30 are formed in the upper surface 11A of the graphite structure 11, and the coating layer 20 is formed on the entire peripheral surface including the inclined surface 31 by the above-described forming method. By doing so, it can be manufactured.

Since the heat-conducting structure 10 is configured in this manner, the covering layer 20 is firmly formed on the inclined surface 31 with the edge portion of the graphene sheet 15 exposed, in a state in which the coating layer 20 is in close contact with the inclined surface 31. To be done. Moreover, since a plurality of edge portions appear on the inclined surface 31, a so-called anchor effect can be obtained on the inclined surface 31. Therefore, the adhesion between the inclined surface 31 and the coating layer 20 is improved by the anchor effect due to the coating material entering the gap between the edge portions when the coating layer 20 is formed. Thereby, even if the graphite structure 11 and the coding layer 20 are thermally expanded, the coating layer 20 is prevented from peeling off or cracking in the heat conducting structure 10. In particular, peeling or cracking of the coding layer 20 at the end of the heat conducting structure 10 in the basal plane direction is prevented. Further, when a heat transfer object such as a heating element is attached to the upper surface 10A, if the heat of the heat transfer object is transferred to the edge portion appearing on the inclined surface 31 through the coating layer 20, the edge portion To quickly spread in the direction of the basal plane. Further, since it is not necessary to form a large number of through holes in the graphite structure 11 to prevent the coating layer 20 from peeling or cracking due to the thermal expansion, the graphite structure 11 becomes brittle by forming a plurality of through holes. Can be prevented. That is, it is possible to maintain high thermal conductivity in the basal plane direction of the graphene sheet 15 without lowering the strength of the heat conductive structure 10.

As described above, the heat conducting structure 10 is mainly used for heat dissipation or soaking of the semiconductor element 56 as a heat generating element such as a power semiconductor or a power module. Hereinafter, with reference to FIG. 9, a cooling diffusion device 50 (an example of the thermal diffusion device of the present invention) including the above-described heat conduction structure 10, and a semiconductor module 60 (a book) including the cooling diffusion device 50 and the semiconductor element 56. An example of the heat diffusion device of the invention will be described.

As shown in FIG. 9, the cooling diffusion device 50 includes the heat conductive structure 10 and a heat radiator 57 such as a heat sink.

A semiconductor element 56 as a heating element such as a power semiconductor or a power module is attached to the center of the upper surface 10A of the heat conducting structure 10. By mounting the semiconductor element 56 on the upper surface 10A, a semiconductor module 60 including the cooling diffusion device 50 and the semiconductor element 56 is configured.

A heat radiator 57 such as a heat sink is attached to the lower surface 10C of the heat conducting structure 10. Thereby, the cooling diffusion device 50 can efficiently radiate heat from the semiconductor element 56 attached to the upper surface 10A of the heat conducting structure 10 through the heat conducting structure 10 and the heat radiator 57. Further, even if the heat distribution in the semiconductor element 56 is uneven, the heat conducting structure 10 absorbs the heat of the semiconductor element 56 from the upper surface 10A and then quickly transfers it in the direction along the upper surface 10A. The heat distribution in can be made uniform.

As another example of the heat diffusion device of the present invention, for example, as shown in FIG. 11, a plurality of heat transfer tubes 711 through which a cooling medium flows, and a plurality of fins 712 that transfer heat from the heat transfer tubes 711. A heat exchanger 71 having In the heat exchanger 71, the plurality of fins 712 are composed of the heat conductive structure 10 described above. With this configuration, quick and efficient heat exchange can be realized between the fins 712 and the fluid (for example, air or water) passing around the fins 712.

Further, as another example of the heat diffusion device of the present invention, for example, as shown in FIG. 12, a plurality of flow paths 721 through which a cooling medium flows therein are formed inside a rectangular parallelepiped block 722 made of metal such as aluminum. A heat exchanger 72 can be considered. In the heat exchanger 72, the heat conducting structure 10 is attached in close contact with the upper surface and the lower surface of the block 722. That is, the heat exchanger 72 includes the pair of heat conducting structures 10. With this configuration, the heat transferred from the flow path 721 and transferred to the upper surface or the lower surface of the block 722 can be quickly and efficiently transferred to the fluid passing therethrough. As a modification of the heat exchanger 72, the block 722 is made of a graphite structure instead of a metal such as aluminum, and a pipe made of a metal such as aluminum or copper for forming the flow passage 721 is provided therein. The configuration may be considered. In this case, the above-described recess 30 is formed on the outer peripheral surface of the block 722.

[Effect confirmation test]
Hereinafter, with reference to Table 1, the test results of the test (thermal shock test and thermal diffusivity test) for confirming the effect of the heat conductive structure 10 according to the first embodiment will be described. Here, Table 1 shows Examples 1 to 6 of the heat conducting structure 10 and inclination angles of Comparative Examples 1 to 3 for comparing the effects of the heat conducting structure 10 and the results of each test.

For each of Examples 1 to 6 and Comparative Examples 1 to 3 shown in Table 1, test pieces described below were prepared, and a thermal shock test and a thermal diffusivity test were performed on each of these test pieces.

Here, the test piece is the one shown in FIG. 10, and a cubic graphite block having a side of 10 mm is prepared, and one of the corners on the upper surface thereof has Examples 1 to 6 and Comparative Examples 1 to 3, respectively. The graphite block is turned using an end mill in a lathe to form an inclined surface K1 and an inclined surface K2 of 45 degrees is formed at the other corner so that the inclined angle θ corresponds to (see Table 1). After that, a nickel coating having a thickness of 37.5 [μm] is formed on the peripheral surface of the graphite block by plating. The nickel coating is an example of the coating layer 20 described above. As shown in Table 1, the angle of the inclined surface of Comparative Example 1 was 0 degree. In addition, the tilt angle θ in Example 1 was set to 1 degree. Moreover, the inclination angle θ of each of Examples 2 to 6 was set to 3 degrees, 5 degrees, 8 degrees, 10 degrees, and 20 degrees. The inclination angles θ of Comparative Examples 2 and 3 were set to 30 degrees and 40 degrees. In addition, in order to ensure a fair evaluation in the thermal diffusivity test described later, all the test pieces have the same volume.

In the thermal shock test, each test piece of Examples 1 to 6 and Comparative Examples 1 to 3 was heated from 20°C to 350°C with a hot plate stirrer (C-MAG HS7 manufactured by IKA of Germany), and then tested. The piece was placed on an aluminum tray and cooled to room temperature (about 20° C.). Then, the presence or absence of swelling or cracking of the nickel coating of the test piece was determined by visually confirming and tentatively confirming the cooled test piece, and the thermal shock test was evaluated. The evaluation results are shown in Table 1. Here, if swelling can be confirmed visually or by tentacles, it is determined as “blistered”, and if cracking can be confirmed by visual observation or tentacles, it is determined as “cracked”, and examples based on these determination results Evaluation was performed on 1 to 6 and Comparative Examples 1 to 3. In addition, when cracks could be confirmed, it was evaluated as "x (Poor: bad)", and when there was swelling but no cracks was evaluated as "△ (Fair: medium)", neither swelling nor cracking was confirmed. The case was evaluated as “◯ (Good: Good)”.

In the thermal diffusivity test, a heater chip H1 of 25 [W] (see FIG. 10) was attached to the inclined surface K1 (see FIG. 10) of each test piece of Examples 1 to 6 and Comparative Examples 1 to 5 for 5 minutes. It is performed by heating and measuring the temperature change and temperature distribution of the upper surface (including the inclined surfaces K1 and K2) of the test piece by thermography (testo 870 manufactured by Testo, Germany), and measuring the in-plane temperature difference on the upper surface. It was Specifically, on the upper surface, the temperature difference in the range from the heater chip H1 on the inclined surface K1 to the inclined surface K2 (the area indicated by the dotted line in FIG. 10) was measured. Table 1 shows the measured value of the in-plane temperature difference and its evaluation. Here, when the in-plane temperature difference was 14° C. or more, it was evaluated as “x (Poor: bad)”, and when the in-plane temperature difference was less than 14° C., it was evaluated as “◯ (Good: good)”.

As shown in Table 1, Comparative Example 1 was poorly evaluated in the thermal shock test and was also poorly evaluated in the thermal diffusivity test, and thus was evaluated as "x (Poor: bad)" overall.

In Examples 1 to 3, the thermal shock test was evaluated to be moderate, but the thermal diffusivity test was evaluated to be good. Therefore, Examples 1 to 3 were comprehensively evaluated as “Good (Good)”.

In Examples 4 to 6, the thermal shock test and the thermal diffusivity test were both evaluated favorably, and thus were evaluated as "⊚ (Best: best)" comprehensively.

For Comparative Examples 2 and 3, cracks were confirmed in the thermal shock test, and the evaluation of the test was “× (Poor: bad)”. X (Poor: bad)" was evaluated.

According to the above evaluation results, it can be seen that when the inclination angle θ of the inclined surface of the test piece is in the range of 1 degree or more and 20 degrees or less, "○ (Good: Good)" or more can be obtained as the comprehensive evaluation. .. Therefore, in the above-described first embodiment, it is preferable that the inclined surface 31 of the graphite structure 11 of the heat conduction structure 10 has an inclination angle θ with respect to the upper surface 11A of 1 degree or more and 20 degrees or less. I can say.

Further, it can be seen that when the inclination angle θ of the inclined surface of the test piece is in the range of 8 degrees or more and 20 degrees or less, “∘ (Best: best)” can be obtained as the comprehensive evaluation. Therefore, in the above-described first embodiment, it is more preferable that the inclined surface 31 of the graphite structure 11 of the heat conduction structure 10 has an inclination angle θ with respect to the upper surface 11A of 8 degrees or more and 20 degrees or less. Can be said.

In the above-described first embodiment, an example in which the coating layer 20 is formed on the entire peripheral surface of the graphite structure 11 has been described, but the present invention is not limited to this configuration. For example, the present invention can be applied to a configuration in which the coating layer 20 is formed only on the upper surface 11A of the graphite structure 11.

[Second Embodiment]
Hereinafter, the second embodiment of the present invention will be described with reference to FIG. In the heat conduction structure 10 according to the second embodiment, a recess 30A is formed on the upper surface 11A of the graphite structure 11 instead of the recess 30. The recess 30A is formed in a circular shape in plan view, and is formed by cutting the upper surface 11A toward the inside of the graphite structure 11 into a tapered conical shape. Other configurations are similar to those of the first embodiment.

[Third Embodiment]
Hereinafter, the third embodiment of the present invention will be described with reference to FIG. In the heat conducting structure 10 according to the third embodiment, the hole 35 is punched from the bottom 32 of the recess 30 toward the lower surface 10C of the heat conducting structure 10. The inner diameter of the hole 35 is a size sufficiently smaller than the diameter of the recess 30 and is, for example, a size defined within the range of 0.5 mm to 1.0 mm. The holes 35 penetrate the graphite structure 11 in the stacking direction of the graphene sheets 15. Therefore, on the inner surface of the hole portion 35, an edge surface in which the edge portions of the plurality of graphene sheets 15 are overlapped in multiple layers appears. In the present embodiment, the coating layer 20 is also formed on the inner surface of the hole 35. As long as the coating layer 20 is formed so as to cover the inner surface of the hole 35, a cavity extending in the stacking direction (Y-axis direction) may be formed at the center of the hole 35, or the hole may be formed. 35 may be filled with the coating layer 20. Note that the other configurations are similar to those of the first embodiment.

[Fourth Embodiment]
Hereinafter, a fourth embodiment of the present invention will be described with reference to FIG. In the heat conducting structure 10 according to the fourth embodiment, the graphite structure 11 is provided with a hole 35A from the bottom 32 of the recess 30 toward the lower surface 10C of the heat conducting structure 10. The hole portion 35A is different from the above-described hole portion 35 in that it extends in a direction inclined at a predetermined angle with respect to the upper surface 11A. Here, the predetermined angle is determined based on one or both of the thickness of the coating layer 20 and the thickness D1 of the graphite structure 11. The other configurations are the same as those of the hole portion 35 of the third embodiment.

[Fifth Embodiment]
Hereinafter, the fifth embodiment of the present invention will be described with reference to FIG. 7. In the heat conduction structure 10 according to the fifth embodiment, the recess 30 is formed on the upper surface 11A of the graphite structure 11, and the recess is also formed on the lower surface 11B of the graphite structure 11 (an example of the second surface of the present invention). A recess 30B similar to 30 is formed. Then, a hole 35 that penetrates the bottom 32 of the recess 30 and the bottom 32 of the recess 30B is formed in the graphite structure 11. Other configurations are similar to those of the first and third embodiments.

[Sixth Embodiment]
Hereinafter, a sixth embodiment of the present invention will be described with reference to FIG. The heat conducting structure 10 according to the sixth embodiment is provided with a plurality of recesses 30C that penetrate the graphite structure 11 in the thickness direction (Y-axis direction). The plurality of recesses 30C include a recess 30C1 formed in a tapered shape from the upper surface 11A of the graphite structure 11 toward the opposite lower surface 11B and a recess 30C2 formed in a tapered shape from the lower surface 11B to the upper surface 11A. Including. In this embodiment, the adjacent recesses 30C are arranged so that the taper directions thereof are different from each other. Note that the other configurations are similar to those of the first embodiment.

Even in the heat conduction structure 10 configured as in the second to sixth embodiments described above, the coating layer 20 is firmly formed on the inclined surface 31 in a state in which the coating layer 20 is in close contact with the inclined surface 31. The joining force between the inclined surface 31 and the coating layer 20 is increased, and the adhesion is also improved. As a result, it is possible to maintain the same effect as that of the above-described first embodiment, that is, maintain the high thermal conductivity in the basal plane direction of the graphene sheet 15 without reducing the strength of the thermal conductive structure 10. is there.

Note that, in each of the above-described embodiments, the configuration in which the plurality of recesses 30 (30A, 30B, 30C) are arranged on the upper surface 11A of the graphite structure 11 at equal intervals is illustrated, but the present invention is not limited to this configuration. .. For example, the plurality of recesses 30 may not be arranged at equal intervals and may be arranged irregularly on the upper surface 11A. Further, in each of the plurality of recesses 30 (30A, 30B, 30C), the size of the recess 30 and the inclination angle of the inclined surface 31 are equal, but, for example, the size of the recess 30 and the inclination angle of the inclined surface 31 are different. The recesses 30 may be different from each other.

10: Thermal conductive structure 10A: Upper surface 10B: Mounting area 10C: Lower surface 10mm: One side 11: Graphite structure 11A: Upper surface 11B: Lower surface 15: Graphene sheet 16: Side end surface 20: Coating layer 30: Recess 30A: Recess 30B: Recessed portion 30C: Recessed portion 30C1: Recessed portion 30C2: Recessed portion 31: Inclined surface 32: Bottom portion 35: Hole portion 35A: Hole portion 50: Cooling diffusion device 56: Semiconductor element 57: Radiator 60: Semiconductor module 71: Heat exchanger 72: Heat Exchanger 711: Heat transfer tube 712: Fin 721: Flow path 722: Block

Claims (8)

A graphite structure formed by stacking a plurality of graphene sheets,
A recess formed on the first surface of the graphite structure on the side where the heat transfer target is attached, the recess including an inclined surface intersecting the first surface;
A heat conduction structure, comprising: a coating portion that is formed on at least the inclined surface and that covers the edge portion of the graphene sheet that appears on the inclined surface and is in close contact with the edge portion. The heat conductive structure according to claim 1, wherein the inclined surface forms a predetermined angle with the first surface of the graphite structure. The heat conducting structure according to claim 2, wherein the predetermined angle is defined within a range of 1 degree to 20 degrees. The heat conducting structure according to claim 2, wherein the predetermined angle is set within a range of 8 degrees or more and 20 degrees or less. The heat conducting structure according to claim 1, wherein the covering portion is formed so as to be in close contact with the entire area of the first surface or the outer peripheral surface of the graphite structure. A hole formed in the bottom of the recess, the hole being bored in a direction intersecting the first surface from the bottom,
The heat conductive structure according to claim 1, wherein the covering portion is formed on an inner surface of the hole. The heat conduction structure according to claim 1, wherein the recess penetrates the graphite structure from the first surface to a second surface opposite to the first surface. A heat conducting structure according to any one of claims 1 to 7,
A heat diffusion device for diffusing heat transferred from a heat transfer object attached to the coating portion of the heat conductive structure.

Images