Heat dissipation structure and substrate unit

Abstract

This heat dissipation structure comprises a plate-form heat dissipation member that contains a carbon material and has a first surface, and a plurality of element mounting parts that are positioned on the first surface. The thermal conductivity of the heat dissipation member is higher in a specific direction than in an X direction, and is higher in a Z direction than in the X direction, where the X direction is a direction in which the plurality of element mounting parts are arranged, the specific direction is a prescribed direction inclined with respect to the X direction among directions following the first surface, and the Z direction is a direction intersecting the first surface. Furthermore, the plurality of element mounting parts include a first element mounting part, a second element mounting part that is adjacent to the first element mounting part, and a third element mounting part that is adjacent to the second element mounting part and is positioned on the side opposite from the first element mounting part. The specific direction is a direction inclined with respect to the X direction so that a straight line overlapping the first element mounting part, among straight lines extending along the specific direction, does not overlap the third element mounting part.

Description

Heat dissipation structure and board unit

[0001] The present disclosure relates to a heat dissipation structure and a substrate unit.

[0002] Cited Document 1 shows a package in which a plurality of light emitting elements are mounted side by side.

[0003] Japanese Patent Application Laid-Open No. 2022-185010

[0004] The heat dissipation structure according to the present disclosure comprises: a plate-shaped heat dissipation member including a carbon material and having a first surface; and a plurality of element mounting portions located on the first surface, wherein when the direction in which the plurality of element mounting portions are arranged is referred to as the X direction, a predetermined direction along the first surface that is inclined with respect to the X direction is referred to as the specific direction, and a direction intersecting the first surface is referred to as the Z direction, the thermal conductivity of the heat dissipation member in the specific direction is higher than the thermal conductivity in the X direction, and the thermal conductivity in the Z direction is higher than the thermal conductivity in the X direction.

[0005] The substrate unit according to the present disclosure comprises a substrate and the above-mentioned heat dissipation structure located on the substrate, wherein the element mounting portion and the substrate are thermally connected via the heat dissipation member, and the thermal conductivity of the heat dissipation member is higher than the thermal conductivity of the substrate in the Z direction.

[0006] 1A is a plan view showing a substrate unit according to a first embodiment of the present disclosure. FIG. 1B is a cross-sectional view showing a substrate unit according to a first embodiment of the present disclosure taken along line B-B in FIG. 1A. FIG. 2C is a perspective view showing a heat dissipation member according to a first embodiment of the present disclosure. FIG. 2D is a cross-sectional view showing a heat dissipation member according to a first embodiment of the present disclosure, illustrating a configuration excluding a protective layer. FIG. 2E is a cross-sectional view showing a heat dissipation member according to a first embodiment of the present disclosure, illustrating a configuration excluding a protective layer, a first plate member, and a second plate member. FIG. 2F is a cross-sectional view taken along line A-A in FIG. 2A. FIG. 2G is a diagram illustrating the properties of a graphite block. FIG. 2H is a cross-sectional view showing a first side surface of the graphite block. FIG. 2H is a cross-sectional view showing a second side surface of the graphite block. FIG. 2I is a diagram illustrating the thermal expansion characteristics of a sample, illustrating a characteristic diagram of the graphite block alone. FIG. 2I is a diagram illustrating the thermal expansion characteristics of a sample, illustrating a characteristic diagram of oxygen-free copper. FIG. 2I is a diagram illustrating the thermal expansion characteristics of a sample, illustrating a characteristic diagram of a configuration in which an oxygen-free copper plate is joined to a graphite block. FIG. 7A is a perspective view showing the sample of FIG. 7B. FIG. 7C is a perspective view showing the sample of FIG. 7C. FIG. 7D is a cross-sectional view showing an electronic device incorporating a substrate unit. FIG. 1 is a diagram showing a configuration in which the arrangement direction of the element mounting portions is parallel to the direction in which the crystal planes of the graphite block extend, and is a perspective view showing the relationship between the heat dissipation member and the element mounting portion (submount substrate). FIG. 2 is a diagram showing a configuration in which the arrangement direction of the element mounting portions is parallel to the direction in which the crystal planes of the graphite block extend, and is a plan view showing the relationship between the graphite block and the element mounting portion. FIG. 3 is a diagram showing a configuration in which the arrangement direction of the element mounting portions is perpendicular to the direction in which the crystal planes of the graphite block extend, and is a perspective view showing the relationship between the heat dissipation member and the element mounting portion (submount substrate). FIG. 4 is a diagram showing a configuration in which the arrangement direction of the element mounting portions is perpendicular to the direction in which the crystal planes of the graphite block extend, and is a plan view showing the relationship between the graphite block and the element mounting portion. FIG. 5 is a diagram showing a configuration in which the arrangement direction of the element mounting portions is inclined with respect to the direction in which the crystal planes of the graphite block extend, and is a perspective view showing the relationship between the heat dissipation member and the element mounting portion (submount substrate).1 is a diagram showing a configuration in which the arrangement direction of the element mounting portions is inclined with respect to the extension direction of the crystal planes of the graphite block, and is a plan view showing the relationship between the graphite block and the element mounting portions; FIG. 2 is a diagram showing a configuration in which the arrangement direction of the element mounting portions is inclined with respect to the extension direction of the crystal planes of the graphite block, and is a plan view for explaining the inclination angle, which is an angle at which the first heat transfer region and the second heat transfer region partially overlap, and an angle at which the first heat transfer region and the third heat transfer region do not overlap; FIG. 3 is a diagram showing a configuration in which the arrangement direction of the element mounting portions is inclined with respect to the extension direction of the crystal planes of the graphite block, and is a plan view for explaining the inclination angle, which is an angle at which the first heat transfer region does not overlap with the second heat transfer region and the third heat transfer region; FIG. 4 is a diagram showing a heat dissipation member according to a second embodiment of the present disclosure, and is a perspective view showing a configuration from which a protective layer is removed; FIG. 5 is a diagram showing a heat dissipation member according to a second embodiment of the present disclosure, and is a perspective view showing a configuration from which a protective layer and a first plate material and a second plate material are removed; and FIG. 6 is a cross-sectional view showing a portion where two graphite materials are adjacent to each other. Fig. 1 is a diagram showing a heat dissipation member according to a third embodiment of the present disclosure, and is a perspective view showing a configuration excluding a protective layer. Fig. 2 is a diagram showing a heat dissipation member according to a third embodiment of the present disclosure, and is a perspective view showing a configuration excluding a protective layer, a first plate material, and a second plate material. Fig. 3 is a diagram illustrating an example of a method for manufacturing a heat dissipation member according to the present disclosure.

[0007] Hereinafter, each embodiment of the present disclosure will be described in detail with reference to the drawings. Electronic elements such as light-emitting elements are heat sources. Therefore, there is a need for a heat dissipation structure that can be provided on a substrate unit on which the electronic elements are mounted. An object of the present disclosure is to provide a heat dissipation structure and a substrate unit having high heat dissipation performance.

[0008] 1A and 1B are diagrams showing an example of a substrate unit 10 according to a first embodiment of the present disclosure, with Fig. 1A being a plan view and Fig. 1B being a cross-sectional view taken along line B-B in Fig. 1A. The substrate unit 10 of one embodiment includes a substrate 20 on which an electronic element 310 (Fig. 9) is mounted, and a heat dissipation member 100 that removes heat from the electronic element 310.

[0009] <Substrate> The substrate 20 may be made of metal. Specifically, the substrate 20 may be made of a metal material such as copper or aluminum, or an alloy material containing copper or aluminum. This configuration enables the substrate unit 10 to be manufactured at a low cost.

[0010] The substrate 20 may have a frame portion 21 on its upper surface. With this configuration, a recess for accommodating the electronic element 310 can be formed by the upper surface of the substrate 20 and the inner surface of the frame portion 21. In other words, with this configuration, the substrate unit 10 is provided with an electronic element accommodating package having a recess for accommodating the electronic element 310. The frame portion 21 may be made of the same material as the substrate 20, or may be made of a different material than the substrate 20.

[0011] <Submount Substrate> The substrate unit 10 may further include a plurality of submount substrates 30 located in an area surrounded by the frame portion 21. Although the substrate unit 10 of one embodiment includes three submount substrates 30, the number of submount substrates 30 included in the substrate unit 10 is not limited to three and may be one, two, four or more. The submount substrate 30 may be a circuit board.

[0012] The submount substrate 30 may be made of an insulating material such as a ceramic material. This configuration ensures insulation between the heat dissipation member 100 and the electronic element 310. The material of the submount substrate 30 may be silicon nitride ceramic. This configuration ensures insulation between the heat dissipation member 100 and the electronic element 310 and also provides the submount substrate 30 with high thermal conductivity. Furthermore, this configuration provides the submount substrate 30 with high toughness, making it easy to thin the submount substrate 30. The material of the submount substrate 30 may also be alumina ceramic. This configuration ensures insulation between the heat dissipation member 100 and the electronic element 310 and also provides the submount substrate 30 with high strength. Therefore, it is easy to thin the submount substrate 30. The material of the submount substrate 30 may also be aluminum nitride ceramic. Note that the submount substrate 30 may be made of a semiconductor material such as SiC (silicon carbide).

[0013] <Third Bonding Material> The submount substrate 30 may be fixed to the heat dissipation member 100 via a third bonding material 40 located on the heat dissipation member 100. That is, the submount substrate 30 may be bonded to the upper surface 101 of the heat dissipation member 100 via the third bonding material 40 located between the lower surface of the submount substrate 30 and the upper surface 101 of the heat dissipation member 100. Solder may be used as the third bonding material 40. This configuration can reduce the inhibition of heat conduction by the third bonding material 40. The third bonding material 40 may be a thermally conductive adhesive, a thermally conductive filler (grease, etc.), or the like.

[0014] <Element Mounting Portion> The substrate unit 10 may further include an element mounting portion 50 located within the frame portion 21. The substrate unit 10 of one embodiment includes three element mounting portions 50, but the number of element mounting portions 50 included in the substrate unit 10 is not limited to three, and may be one, two, four or more.

[0015] Hereinafter, the direction in which the multiple element mounting portions 50 are arranged will be referred to as the X direction, the direction in which the element mounting portions 50 extend will be referred to as the Y direction, a plane extending in the X and Y directions will be referred to as the XY plane, and a direction intersecting (e.g., perpendicular to) the XY plane will be referred to as the Z direction. In one embodiment, the element mounting portion 50 has a dimension in the X direction that is shorter than the dimension in the Y direction, but this is not limited thereto. The dimension in the X direction may be longer than the dimension in the Y direction, or the dimensions in the X direction and the Y direction may be the same. The shape of the element mounting portion 50 in a planar view may be larger than the shape of the electronic element 310 placed on the element mounting portion 50 in a planar view. Note that the shape of the element mounting portion 50 in a planar view may be the same as the shape of the electronic element 310 placed on the element mounting portion 50 in a planar view.

[0016] The submount substrate 30 is a substrate that is interposed between the electronic element 310 and an object (substrate 20) to which the electronic element 310 is to be mounted in order to mount the electronic element 310 on a module substrate, a package, or the like. Therefore, at least a portion of the upper surface of the submount substrate 30 may be the element mounting portion 50. In FIG. 1A , the area surrounded by the two-dot chain line is the element mounting portion 50.

[0017] 2A, 2B, and 2C are diagrams illustrating an example of a heat dissipation member 100 according to a first embodiment of the present disclosure, where FIG. 2A is a perspective view of the heat dissipation member 100, FIG. 2B is a perspective view illustrating a configuration excluding the protective layer 150, and FIG. 2C is a perspective view illustrating a configuration excluding the protective layer 150, the first plate member 120, and the second plate member 130. FIG. 3 is a cross-sectional view taken along line A-A in FIG. 2A. FIG. 4 is a diagram illustrating the properties of the graphite block 110. The heat dissipation member 100 according to one embodiment has high thermal conductivity and can quickly transfer heat received at the upper surface 101 to the lower surface 102.

[0018] Heat dissipation member 100 may include graphite block 110. Graphite block 110 may have a first surface 111, a second surface 112 located opposite first surface 111, and a side surface 113 located between first surface 111 and second surface 112. Heat dissipation member 100 may further include second bonding materials 140 located on first surface 111 and second surface 112, a first plate member 120 fixed to first surface 111 via second bonding material 140, a second plate member 130 fixed to second surface 112 via second bonding material 140, and a protective layer 150 covering side surface 113.

[0019] [Graphite Block] The graphite block 110 may have a structure in which a plurality of graphenes are stacked in the first direction A1. Graphene may be a sheet-like substance in which a honeycomb structure formed by bonding carbon atoms extends in a two-dimensional direction. Adjacent graphenes may be bonded to each other by intermolecular forces, which are van der Waals forces.

[0020] The surface of graphite block 110 may have a surface where graphene spreads in a two-dimensional direction and a surface where multiple graphene layers appear. Hereinafter, the surface where graphene spreads in a two-dimensional direction will be referred to as a "crystal surface," and the surface where graphene layers appear will be referred to as a "crystal layer surface." In the drawings, the "crystal surface" will be represented by a honeycomb pattern, and the "crystal layer surface" will be represented by a striped pattern.

[0021] Graphite block 110 may have anisotropy in its brittleness. For example, as anisotropy in its brittleness, graphite block 110 may have a tendency to easily cleave along a plane in which graphene extends, i.e., a plane intersecting first direction A1, as shown in FIG. 4 . Cleavage means breaking along a certain plane. FIG. 4 shows a state in which crack E1 has occurred due to cleavage.

[0022] Furthermore, as anisotropy of the brittleness, graphite block 110 may have a property in which graphene located on a crystal plane is easily peeled off when stress is applied along the crystal plane. Furthermore, graphite block 110 may have a property in which edge portions E2 (see FIGS. 5 and 6 ) of graphene are weak and easily broken from edge portions E2.

[0023] As a specific material, graphite block 110 may be mainly composed of pyrolytic graphite. The term "main component" may mean a volume ratio of 80% or more. Pyrolytic graphite may be produced as follows: First, a resin material such as polyimide is carbonized and decomposed into hydrocarbon gas. Next, the decomposed hydrocarbon is vapor-deposited and laminated. Then, a pressure annealing process is performed to produce pyrolytic graphite. In one embodiment, graphite block 110 may be a single component.

[0024] [Each Surface of Graphite Block] The first plate member 120 and the second plate member 130 may be bonded to the first surface 111 and the second surface 112 of the graphite block 110, respectively. The first surface 111 and the second surface 112 may be surfaces extending in the first direction A1. With this configuration, the first plate member 120 and the second plate member 130 are bonded to the crystal layer surfaces. Therefore, the first plate member 120 and the second plate member 130 can reduce the force applied to the graphite block 110 in a direction that causes it to cleave.

[0025] If the first plate material 120 and the second plate material 130 were bonded to each other on their crystal planes, the graphene on the crystal planes would be easily peeled off due to stress generated during bonding. In this case, even during use, when external forces are applied to the first plate material 120 and the second plate material 130 in various directions, there is a risk that the first plate material 120 or the second plate material 130 will peel off together with the graphene on its surface. In contrast, if the first plate material 120 and the second plate material 130 are bonded to each other on their crystal layer planes, the peeling of the graphene can be suppressed. Therefore, the toughness of the heat dissipation member 100 can be improved.

[0026] Figure 5 is a cross-sectional view showing a first side surface 113a of graphite block 110. Figure 6 is a cross-sectional view showing a second side surface 113b of graphite block 110. Figure 5 shows part C1 of Figure 2A, and Figure 6 shows part C2 of Figure 2A.

[0027] The side surface 113 of the graphite block 110 may be a surface extending in a direction intersecting the first direction A1. The side surface 113 may include a first side surface 113a that is a crystal plane and a second side surface 113b that is a crystal layer plane. The first side surface 113a that is a crystal plane may be a surface extending in two directions intersecting the first direction A1. The two directions may be a second direction A2 and a third direction A3 that are perpendicular to the first direction A1 and perpendicular to each other. The second side surface 113b that is a crystal layer plane may be a surface extending in the first direction A1 and the second direction A2.

[0028] The protective layer 150 may cover the side surface 113. As shown in FIG. 5 , the first side surface 113a is a crystal plane where graphene is likely to peel off, and an edge portion E2 of the graphene that is likely to break may appear. The second side surface 113b is where the edge portion E2 of the graphene that is likely to break appears. By covering the side surface 113 with the protective layer 150, the occurrence of the above-mentioned peeling or breakage can be reduced, and the toughness of the heat dissipation member 100 can be improved.

[0029] The graphite block 110 may be rectangular, with two opposing faces being crystal planes and the remaining four faces being crystal layer planes. The first face 111 to which the first plate member 120 is bonded and the second face 112 to which the second plate member 130 is bonded may be the crystal layer plane with the largest area among the four crystal layer planes and the crystal layer plane opposite to that face. This configuration can improve the stability of mounting a heat source (such as an electronic element 310) on the heat dissipation member 100.

[0030] When two surfaces located opposite each other are referred to as a pair of surfaces, a configuration may be employed in which plate materials 120, 130 are positioned on two pairs of surfaces (i.e., four surfaces) of graphite block 110 with second bonding material 140 interposed therebetween. In this case, the remaining pair of surfaces (i.e., two surfaces) may be covered with protective layer 150. The two pairs of surfaces on which plate materials 120, 130 are positioned with second bonding material 140 interposed therebetween may be crystalline layer surfaces. The pair of surfaces covered with protective layer 150 may also be crystalline surfaces. This configuration also achieves the same effect of increasing the toughness of heat dissipation member 100 described above.

[0031] [Thermal Conductivity] The graphite block 110 may have very high thermal conductivity in directions along the crystal planes. The thermal conductivity of the graphite block 110 in the second direction A2 and the third direction A3 may be 200 W / m·K or more, while the thermal conductivity in the first direction A1 may be lower than the thermal conductivity in the second direction A2 or the third direction A3, such as 7 W / m·K. That is, the graphite block 110 may have anisotropic thermal conductivity. The thermal conductivity in the second direction A2 and the third direction A3 may be preferably 370 W / m·K or more, more preferably 450 W / m·K or more, and even more preferably 800 W / m·K or more. In one embodiment, the thermal conductivity of the graphite block 110 in the second direction A2 and the third direction A3 may be 1200 W / m·K or more, more specifically, approximately 1700 W / m·K.

[0032] The thermal conductivity of the first plate 120 and the second plate 130 may be highly isotropic compared to that of the graphite block 110. Furthermore, the thermal conductivity of the first plate 120 and the second plate 130 may be higher than the thermal conductivity of the graphite block 110 in the first direction A1. According to this configuration, when heat is applied to a portion of the first plate 120 from outside the heat dissipation member 100, the heat is isotropically dispersed in the first plate 120 and then conducted to the graphite block 110. Then, in the graphite block 110, the heat is quickly dispersed in the second direction A2 and the third direction A3, which have high thermal conductivity. The heat is then conducted to the second plate 130 and isotropically dispersed in the second plate 130. As described above, even when heat is applied to a portion of the first plate 120, the heat can be dispersed over a wide area of ​​the graphite block 110. Furthermore, since a wide area of ​​the second plate member 130 is thermally connected to the substrate 20, heat can be dissipated from a wide area of ​​the second plate member 130. Therefore, the heat dissipation member 100 can achieve efficient heat transfer performance.

[0033] The thermal conductivity of protective layer 150 may be highly isotropic compared to that of graphite block 110. The thermal conductivity of protective layer 150 may be higher than the thermal conductivity of graphite block 110 in first direction A1. This configuration provides an effect of dispersing heat in first direction A1 at second side surface 113b via protective layer 150. Therefore, the addition of this dispersion effect allows heat dissipation member 100 to achieve more efficient heat transfer performance.

[0034] [Surface Roughness of Graphite Block] As shown in Figure 5, the surface roughness of the first side surface 113a, which is a crystal plane, may be smaller than the surface roughness of the first surface 111, which is a crystal layer plane. Specifically, the surface roughness of the first surface 111 may be 20 times or more, 10 times or more but less than 20 times, or 5 times or more but less than 10 times the surface roughness of the first side surface 113a. The surface roughness refers to the arithmetic mean roughness Ra defined in JIS (Japanese Industrial Standards) B_0601:2001. The surface roughness can be measured after removing the protective layer 150 and the first plate member 120 from the heat dissipation member 100.

[0035] According to this configuration, as shown in FIG. 5 , the edge portion E2 of the graphene appearing on the first side surface 113a is reduced. Therefore, the fragility of the first side surface 113a can be reduced. Furthermore, the small surface roughness reduces the adhesion between the protective layer 150 and the first side surface 113a. The low adhesion reduces the stress applied to the second side surface 113b when the protective layer 150 is formed. Therefore, it is possible to prevent a portion of the graphene from peeling off from the graphite block 110 on the second side surface 113b.

[0036] 5 and 6, the surface roughness of the second side surface 113b, which is a crystal layer surface, may be greater than the surface roughness of the first side surface 113a. Specifically, the surface roughness of the second side surface 113b may be 20 times or more, 10 times or more but less than 20 times, or 5 times or more but less than 10 times the surface roughness of the first side surface 113a. The surface roughness refers to the arithmetic mean roughness Ra described above. The surface roughness can be measured after removing the protective layer 150 from the heat dissipation member 100.

[0037] As shown in FIG. 6 , second side surface 113b includes relatively large irregularities due to the surface roughness. The irregularities may be fine irregularities. On second side surface 113b, a portion of protective layer 150 is located within a recess F1 of the irregularities of second side surface 113b. This provides an anchor effect, improving the adhesion of protective layer 150 to second side surface 113b. This prevents protective layer 150 from peeling off from graphite block 110. Furthermore, since protective layer 150 is located within the recess F1 of the irregularities, the thermal resistance between protective layer 150 and graphite block 110 can be reduced compared to a configuration in which a gap is formed in recess F1.

[0038] [Thermal Expansion Properties] The linear expansion coefficient of graphite block 110 may be highly anisotropic on first surface 111 and second surface 112. Specifically, the linear expansion coefficient of graphite block 110 may be 20 [10^-6 / K] or more in first direction A1 and 0.050 [10^-6 / K] or less in second direction A2 and third direction A3. Furthermore, the linear expansion coefficient of graphite block 110 may be 24 [10^-6 / K] or more in first direction A1. Furthermore, the linear expansion coefficient of graphite block 110 may be a value in the range of 27 [10^-6 / K] or less in first direction A1. Furthermore, the linear expansion coefficient of graphite block 110 in second direction A2 and third direction A3 may be a negative value, specifically, −0.001 [10^-6 / K] or less. The linear expansion coefficient of the graphite block 110 in the second direction A2 and the third direction A3 may be −1.0 [10^-6 / K] or more.

[0039] The linear expansion coefficient of the first plate material 120 may be highly isotropic compared to that of the graphite block 110. In the first direction A1, the linear expansion coefficient of the first plate material 120 may be smaller than that of the graphite block 110. In the second direction A2, the linear expansion coefficient of the first plate material 120 may be larger than that of the graphite block 110. In the third direction A3, the linear expansion coefficient of the first plate material 120 may be larger than that of the graphite block 110. The same applies to the second plate material 130. The linear expansion coefficients of the first plate material 120 and the second plate material 130 may be, for example, 4.0 [10^-6 / K] or greater and less than 20 [10^-6 / K], or may be 6.0 [10^-6 / K] or greater and less than 18 [10^-6 / K]. The first plate member 120 and the second plate member 130 may be made of a material having a linear expansion coefficient of 4.0 [10^-6 / K] or more and less than 20 [10^-6 / K], such as a metal material such as copper or stainless steel, or a ceramic material such as aluminum nitride, alumina, or zirconia. Furthermore, for example, if the linear expansion coefficient of the graphite block 110 is 24 [10^-6 / K] or more in the first direction A1, a metal material such as aluminum having a linear expansion coefficient greater than that of copper may be used as the material for the first plate member 120 and the second plate member 130.

[0040] The linear expansion coefficients of the first plate member 120 and the second plate member 130 are compared with the linear expansion coefficient of the graphite block 110 using the linear expansion coefficients measured while changing the temperature from 20°C to 100°C. The linear expansion coefficients are measured using a measurement method specified in JIS depending on the material. For example, if the first plate member 120 and the second plate member 130 are made of a metal material, the measurement method specified in JIS Z 2285:2003 is used. If the first plate member 120 and the second plate member 130 are made of a ceramic material, the measurement method specified in JIS R 1618:2002 is used. The linear expansion coefficient of the graphite block 110 is measured using the measurement method specified in JIS R 1618:2002, mutatis mutandis.

[0041] With the above configuration, the coefficient of linear expansion of upper surface 101 of heat dissipation member 100 can be made closer to an isotropic value compared to a configuration using graphite block 110 alone. Therefore, when components are mounted on upper surface 101 of heat dissipation member 100, the reliability of the mounting can be improved. The same applies to lower surface 102 of heat dissipation member 100.

[0042] Next, we will explain how the linear expansion coefficient of upper surface 101 of heat dissipation member 100 approaches an isotropic value and how the reliability of mounting is improved by the linear expansion coefficient becoming an isotropic value. Figures 7A, 7B, and 7C are diagrams illustrating the thermal expansion characteristics of three samples: Figure 7A is a characteristic diagram of a graphite block alone, Figure 7B is a characteristic diagram of oxygen-free copper, and Figure 7C is a characteristic diagram of a configuration in which an oxygen-free copper plate is joined to a graphite block. Figures 8A, 8B, and 8C are perspective views showing the samples of Figures 7A, 7B, and 7C, respectively.

[0043] The first sample 210 is a graphite block made of pyrolytic graphite alone. The first sample 210 corresponds to the graphite block 110 of the first embodiment. The top surface 211 of the first sample 210 corresponds to the first surface 111 of the graphite block 110 of the first embodiment. The second sample 220 is an oxygen-free copper plate. The third sample 230 is a member in which the first plate 120 and the second plate 130 made of oxygen-free copper are joined to the first surface 111 and the second surface 112 of the graphite block 110 made of pyrolytic graphite with a brazing material. The top surface 231 of the third sample 230 corresponds to the top surface 121 of the first plate 120.

[0044] The characteristic diagrams in Figures 7A, 7B, and 7C are vector distribution diagrams representing the thermal expansion characteristics of the top surfaces 211, 221, and 231 of the three samples 210, 220, and 230. The vectors in Figures 7A, 7B, and 7C were obtained as follows: First, digital images of each top surface 211, 221, and 231 were obtained at two different temperatures for each sample. The digital images were acquired using a CCD (Charge Coupled Device) camera. The two different temperature conditions were a standard temperature (e.g., 23°C) and a 100°C condition. The temperature was adjusted using heaters disposed above and below the samples 210, 220, and 230. This process resulted in the acquisition of two digital images for each sample, one at the standard temperature and one at 100°C. Next, the two digital images for each sample were analyzed using image correlation to measure the displacement of the same point between the two digital images. The measured displacement is then represented by a vector.

[0045] 7A, the linear expansion coefficient of the graphite block alone in first sample 210 was highly anisotropic. The linear expansion coefficient of typical pyrolytic graphite in the first direction A1 was 25 [10^-6 / K], and the linear expansion coefficients in the second direction A2 and the third direction A3 were −0.6 [10^-6 / K].

[0046] As shown in FIG. 7B , the linear expansion coefficient of the second sample 220, i.e., oxygen-free copper, was highly isotropic. As shown by comparing FIGS. 7A and 7B , the linear expansion coefficient of the first sample 210 (graphite block alone) in the first direction A1 was greater than the linear expansion coefficient of the second sample 220 (oxygen-free copper) in the first direction A1. Furthermore, the linear expansion coefficient of the first sample 210 (graphite block alone) in the third direction A3 was smaller than the linear expansion coefficient of the second sample 220 (oxygen-free copper) in the third direction A3. The linear expansion coefficient of the second sample 220 (oxygen-free copper) was 17.7 [10^-6 / K].

[0047] As shown in FIG. 8C , the third sample 230, i.e., the graphite block 110 bonded to the oxygen-free copper first and second plates 120 and 130, exhibited anisotropic linear expansion coefficients. However, the linear expansion coefficients approached a high, isotropic value compared to the first sample 210 (graphite block alone). As shown by comparing FIGS. 7A and 7C , the difference between the linear expansion coefficients of the third sample 230 in the first direction A1 and the third direction A3 was smaller than the difference between the linear expansion coefficients of the first sample 210 in the first direction A1 and the third direction A3. This characteristic was achieved by the isotropy of the linear expansion coefficients of the first and second plates 120 and 130 suppressing the anisotropy of the graphite block 110.

[0048] The heat dissipation member 100 of one embodiment includes a highly anisotropic graphite block 110. However, by adopting a structure similar to that of the third sample 230 described above, the linear expansion coefficients of the upper surface 121 and the lower surface 131 can be made closer to isotropic values. When mounting a component on an arbitrary mounting surface, if the component's linear expansion coefficient is isotropic, it is desirable that the linear expansion coefficient of the mounting surface also be close to isotropic. This is because highly anisotropic thermal expansion characteristics of the mounting surface result in anisotropic stress at the joint between the mounting surface and the component, making it more likely that the component and the mounting surface will warp due to temperature changes. Alternatively, stress is less likely to be smoothly distributed, making it more likely that areas of stress will be concentrated.

[0049] In one embodiment, the coefficient of linear expansion of the upper surface 101 of the heat dissipation member 100 is closer to an isotropic value than that of the graphite block 110 alone. Therefore, when mounting components on the upper surface 101 of the heat dissipation member 100, warping due to temperature changes can be suppressed, and mounting can be achieved with reduced stress concentration. This improves mounting reliability.

[0050] [Materials of the First Plate and the Second Plate] The material of the first plate 120 may be a copper-based metal or alloy, such as oxygen-free copper. With this configuration, the anisotropy of the linear expansion coefficient at the upper surface 121 can be reduced, as shown in FIG. 7C . Furthermore, high thermal conductivity of the first plate 120 can be obtained, thereby realizing more efficient heat transfer performance of the heat dissipation member 100. The first plate 120 may be a metal with high thermal conductivity, such as aluminum. With this configuration, the anisotropy of the thermal expansion characteristics can be reduced, as in the case of copper. Furthermore, the high thermal conductivity allows the heat dissipation member 100 to achieve efficient heat transfer performance. From the viewpoint of heat transfer, copper has better properties than aluminum.

[0051] The first plate member 120 may be made of ceramics such as alumina ceramics, silicon nitride ceramics, or aluminum nitride ceramics. This configuration also reduces the anisotropy of thermal expansion characteristics, as with copper. Furthermore, by using ceramics, insulation properties can be met when the heat dissipation member 100 requires such properties. When using ceramics, the first plate member 120 may be made of alumina ceramics or silicon nitride ceramics. By using such a material, high rigidity can be achieved to resist the residual stress of the graphite block 110. Furthermore, the first plate member 120 may be made of aluminum nitride ceramics. By using such a material, high thermal conductivity can be imparted to the first plate member 120 in addition to rigidity, thereby achieving more efficient heat transfer performance of the heat dissipation member 100.

[0052] The above-described materials for the first plate 120 can be similarly applied to the second plate 130. The second plate 130 also exhibits the same effects as when the above-described materials are applied to the first plate 120.

[0053] [Hardness] The hardness of the first plate member 120 and the second plate member 130 may be higher than the hardness of the graphite block 110. With this configuration, even if an external force is applied to the first plate member 120 and the second plate member 130, the external force is dispersed and acts on the graphite block 110. Therefore, damage to the graphite block 110 inside the first plate member 120 and the second plate member 130 can be suppressed.

[0054] The hardness may be measured by Vickers hardness. The hardness of graphite block 110 may be 10 MPa or more and 40 MPa or less in Vickers hardness. The hardness of first plate member 120 and second plate member 130 may be preferably 10 times or more, more preferably 20 times or more, the hardness of graphite block 110. The hardness of first plate member 120 and second plate member 130 may be preferably 200 MPa or more in Vickers hardness, more preferably 500 MPa or more, and even more preferably 900 MPa or more in Vickers hardness.

[0055] The Vickers hardness of the first plate member 120 and the second plate member 130 can be measured using the measurement method specified in JIS Z 2244:2009. The Vickers hardness of the graphite block 110 is a value converted from the measurement results of a nanoindentation test with a load of 20 mN / 10 seconds. Examples of materials having a hardness 10 times or more that of the graphite block 110 include various metal materials such as copper, aluminum, and stainless steel, and ceramic materials such as aluminum nitride, alumina, and zirconia. Furthermore, materials having a hardness 10 times or more that of the graphite block 110 are not limited to metal materials and ceramic materials, and various materials such as resin materials may also be used. In this disclosure, the Vickers hardness is expressed as a value obtained by converting the unit HV into pressure.

[0056] [Second Bonding Material] The first plate member 120 may be bonded to the first surface 111 via the second bonding material 140. The second plate member 130 may be bonded to the second surface 112 via the second bonding material 140. A brazing material may be used for the second bonding material 140. The second bonding material 140 may be configured to cover the bonding surfaces of the first plate member 120 and the second plate member 130 (i.e., clad) during the manufacturing stage of the heat dissipation member 100. This configuration allows the bonding material to be thinner after bonding. Therefore, the thermal resistance of the second bonding material 140 can be reduced.

[0057] Second bonding material 140 may be configured to be formed into a sheet shape during the manufacturing process of heat dissipation member 100. In this configuration, sheet-shaped second bonding material 140 may be sandwiched between first plate member 120 and graphite block 110 and then subjected to a heating process and a cooling process to exert a brazing effect. The same applies to second plate member 130. With this configuration, even if first surface 111 and second surface 112 of graphite block 110 have large areas, the adhesion between first plate member 120 and graphite block 110 via second bonding material 140 can be improved. Similarly, the adhesion between second plate member 130 and graphite block 110 via second bonding material 140 can be improved. The improved adhesion can reduce the thermal resistance between first plate member 120 and graphite block 110 and the thermal resistance between second plate member 130 and graphite block 110 compared to a configuration in which a gap is present.

[0058] The second bonding material 140 may be referred to as an intervening layer. The second bonding material 140 may be located only in a partial region of the first surface 111 and only in a partial region of the second surface 112. When the second bonding material 140 is located only in a partial region of the first surface 111, a range of the first surface 111 other than the region where the second bonding material 140 is located may be filled with thermally conductive grease or the like as an intervening layer. Furthermore, when the second bonding material 140 is located only in a partial region of the second surface 112, a range of the second surface 112 other than the region where the second bonding material 140 is located may be filled with thermally conductive grease or the like as an intervening layer.

[0059] [Protective Layer] The protective layer 150 may be a plating layer or a resin film. By employing a plating layer, the protective layer 150 can be realized with high thermal conductivity, which contributes to the efficient heat transfer performance of the heat dissipation member 100. Furthermore, when the heat dissipation member 100 is required to be electrically conductive, this requirement can be met. Furthermore, when an insulator such as ceramic is used for the first plate member 120 and the second plate member 130, a metal layer may be formed on the insulator, and then a plating layer may be formed as the protective layer 150.

[0060] In addition to the side surface 113, the protective layer 150 may cover the side surface 122 of the first plate 120 (see FIGS. 2B and 3 ) and the side surface 132 of the second plate 130 (see FIGS. 2B and 3 ). Peeling of the protective layer 150 is more likely to occur at the edges than at other locations. On the other hand, the protective layer 150 is more likely to adhere to the side surface 122 of the first plate 120 and the side surface 132 of the second plate 130 with higher strength than to the side surface 113 of the graphite block 110. Therefore, by having the protective layer 150 cover a portion of the first plate 120 and the second plate 130, the edges of the protective layer 150 are positioned on the surfaces of the first plate 120 and the second plate 130, thereby preventing peeling of the protective layer 150. Furthermore, the protective layer 150 is continuous from the surfaces of the first plate 120 and the second plate 130 to the side surface 113 of the graphite block 110. Therefore, peeling of the protective layer 150 can be suppressed, including the region of the side surface 113 of the graphite block 110 .

[0061] Protective layer 150 may further cover a portion of upper surface 121 of first plate 120. Protective layer 150 may further cover a portion of lower surface 131 of second plate 130. Upper surface 121 of first plate 120 is the surface opposite to the surface facing graphite block 110. Lower surface 131 of second plate 130 is the surface opposite to the surface facing graphite block 110. Even with this configuration, peeling of protective layer 150 can be suppressed as described above.

[0062] When the protective layer 150 covers the upper surface 121 of the first plate 120, the upper surface 101 of the heat dissipation member 100 may correspond to the surface of the protective layer 150. When the protective layer 150 does not cover the upper surface 121 of the first plate 120, the upper surface 101 of the heat dissipation member 100 may correspond to the upper surface 121 of the first plate 120. When the protective layer 150 covers the lower surface 131 of the second plate 130, the lower surface 102 of the heat dissipation member 100 may correspond to the surface of the protective layer 150. When the protective layer 150 does not cover the lower surface 131 of the second plate 130, the lower surface 102 of the heat dissipation member 100 may correspond to the lower surface 131 of the second plate 130.

[0063] The protective layer 150 may further cover the entire side surface 122 and the upper surface 121 of the first plate 120, the entire side surface 113 of the graphite block 110, and the entire side surface 132 and the lower surface 131 of the second plate 130. Figures 2A and 3 show this configuration. This configuration reduces (e.g., eliminates) the edge portions of the protective layer 150, thereby further preventing peeling and damage of the protective layer 150. Furthermore, this configuration reduces the complexity of the process of forming the protective layer 150.

[0064] When the protective layer 150 covers at least a portion of the upper surface 121 of the first plate 120 and the lower surface 131 of the second plate 130, a material with high thermal conductivity, such as a metal plating layer, may be applied to the protective layer 150. With this configuration, even when a heat source (such as an electronic element 310) comes into contact with the heat dissipation member 100 via the protective layer 150, heat can be quickly conducted to the first plate 120 or the second plate 130 via the protective layer 150.

[0065] <First Bonding Material> The heat dissipation member 100 may be fixed to the substrate 20 via a first bonding material 60 located on the substrate 20. That is, the heat dissipation member 100 may be bonded to the upper surface of the substrate 20 via the first bonding material 60 located between the lower surface 102 of the heat dissipation member 100 and the upper surface of the substrate 20. Solder may be used as the first bonding material 60. This configuration can reduce the inhibition of heat conduction by the first bonding material 60. The first bonding material 60 may be a thermally conductive adhesive, a thermally conductive filler (grease, etc.), or the like.

[0066] <Substrate Unit> The substrate unit 10 may include a substrate 20, a heat dissipation member 100 containing a carbon material and located on the substrate 20, and an element mounting portion 50 located on the opposite side of the substrate 20 with respect to the heat dissipation member 100. The element mounting portion 50 and the substrate 20 may be thermally connected via the heat dissipation member 100. Furthermore, the thermal conductivity of the heat dissipation member 100 may be higher than the thermal conductivity of the substrate 20 in the direction in which the substrate 20 and the heat dissipation member 100 are aligned (Z direction, second direction A2). With this configuration, the heat dissipation member 100, which has high thermal conductivity in the Z direction, is disposed along the heat transfer path from the element mounting portion 50 to the substrate 20 (heat transfer path parallel to the Z direction). This allows heat to be transferred more quickly from the electronic element 310, which serves as a heat source, than when the heat dissipation member 100 is not disposed between the substrate 20 and the element mounting portion 50.

[0067] The substrate unit 10 may have an element mounting portion 50 on the first surface 111 of the heat dissipation member 100 (i.e., above the first surface 111 when the second surface 112 faces downward and the first surface 111 faces upward). That is, the heat dissipation member 100 may be bonded to the upper surface of the substrate 20 via a first bonding material 60 with the second surface 112 facing downward and the first surface 111 facing upward, and a submount substrate 30 may be bonded to the upper surface 101 via a third bonding material 40. The element mounting portion 50 may be a part of the upper surface 101 of the heat dissipation member 100. That is, the substrate unit 10 may not be provided with a submount substrate 30. The substrate unit 10 may have an element mounting portion 50 on the second surface 112 of the heat dissipation member 100 (i.e., above the second surface 112 when the first surface 111 faces downward and the second surface 112 faces upward). The element mounting portion 50 may be a part of the lower surface 102 of the heat dissipation member 100 .

[0068] In the substrate unit 10, the heat dissipation member 100 may include a graphite block 110 with anisotropic thermal conductivity and a protective portion (first plate 120, second plate 130, protective layer 150) covering the graphite block 110. This configuration protects the relatively fragile graphite block 110. Furthermore, in the substrate unit 10, the substrate 20 may be made of metal. This configuration prevents deformation of the substrate 20 because the graphite block 110 is disposed on the metal substrate 20 (the bottom of the metal package). For example, if the substrate is made of a graphite block, heat can be rapidly transferred from the heat source electronic element 310 without disposing the heat dissipation member 100 between the substrate (graphite block) and the element mounting portion 50. However, this configuration may result in deformation of the substrate due to the anisotropic thermal expansion characteristics of the substrate (graphite block) itself. The substrate 20 may also be made of ceramic.

[0069] In the substrate unit 10, the thermal conductivity of the graphite block 110 in the alignment direction (Z direction, second direction A2) of the substrate 20 and the heat dissipation member 100 may be higher than the thermal conductivity of the graphite block 110 in a direction (first direction A1) intersecting (e.g., perpendicular to) the alignment direction. Furthermore, in the alignment direction (Z direction, second direction A2), the thermal conductivity of the heat dissipation member 100 may be higher than the thermal conductivity of the protective portion (first plate member 120, second plate member 130, protective layer 150). Additionally, in the one direction (first direction A1), the thermal conductivity of the substrate 20 may be higher than that of the heat dissipation member 100, and the thermal conductivity of the protective portion may be higher than that of the heat dissipation member 100. According to this configuration, the substrate 20 and the protective portion (first plate material 120, second plate material 130, protective layer 150) have the effect of dispersing heat in the one direction (first direction A1), thereby reducing the anisotropy of thermal conduction of the graphite block 110.

[0070] The protective portion that protects graphite block 110 may be made of plating alone. That is, first surface 111, second surface 112, and side surface 113 of graphite block 110 may be covered with plating without providing first plate member 120 or second plate member 130. The protective portion that protects graphite block 110 may be made of an organic material or a ceramic material.

[0071] Furthermore, in one direction (first direction A1) intersecting (e.g., perpendicular to) the arrangement direction of substrate 20 and heat dissipation member 100, first bonding material 60 bonding substrate 20 and heat dissipation member 100 may have a higher thermal conductivity than graphite block 110. According to this configuration, the inhibition of heat conduction by first bonding material 60 can be reduced compared to when the thermal conductivity of first bonding material 60 is lower than the thermal conductivity of graphite block 110 in the one direction (first direction A1).

[0072] Furthermore, in one direction (first direction A1) intersecting (e.g., perpendicular to) the arrangement direction of substrate 20 and heat dissipation member 100, second bonding material 140 bonding graphite block 110 and protective portion (first plate member 120, second plate member 130) may have a thermal conductivity higher than that of graphite block 110. According to this configuration, the inhibition of heat conduction by second bonding material 140 can be reduced compared to when the thermal conductivity of second bonding material 140 is lower than the thermal conductivity of graphite block 110 in the one direction (first direction A1).

[0073] Furthermore, the melting point of the first bonding material 60 that bonds the substrate 20 and the heat dissipation member 100 may be lower than the melting point of the second bonding material 140 that bonds the graphite block 110 and the protective portion (first plate member 120, second plate member 130). This configuration facilitates temperature control during mounting of the heat dissipation member 100 compared to when the melting point of the first bonding material 60 is higher than the melting point of the second bonding material 140. For example, if the melting point of the first bonding material 60 is higher than the melting point of the second bonding material 140, there is a possibility that the second bonding material 140 will melt when the heat dissipation member 100 is fixed to the substrate 20 by the first bonding material 60, thereby releasing the bond between the graphite block 110 and the protective portion (first plate member 120, second plate member 130). Therefore, temperature control is required to avoid melting of the second bonding material 140. In other words, the first bonding material 60 may be a bonding material with a relatively low melting point, such as a solder material. The second bonding material 140 may also be a bonding material with a relatively high melting point, such as a metal brazing filler metal (for example, a copper brazing filler metal).

[0074] Furthermore, the melting point of the first bonding material 60 that bonds the substrate 20 and the heat dissipation member 100 may be lower than the melting point of the bonding material included in the package (e.g., the bonding material that bonds the substrate 20 and the frame 21). This configuration facilitates temperature control during mounting of the heat dissipation member 100 compared to when the melting point of the first bonding material 60 is higher than the melting point of the bonding material included in the package. For example, if the melting point of the first bonding material 60 is higher than the melting point of the bonding material included in the package, there is a possibility that the bonding material included in the package will melt and damage the package (e.g., the bonding between the substrate 20 and the frame 21 will be released) when the heat dissipation member 100 is fixed to the substrate 20 by the first bonding material 60. Therefore, temperature control is required to avoid melting of the bonding material included in the package. In other words, the first bonding material 60 may be a bonding material with a relatively low melting point, such as a solder material. Furthermore, the bonding material included in the package may be a bonding material with a relatively high melting point, such as a metal-based brazing filler metal (e.g., a copper brazing filler metal).

[0075] Furthermore, in the substrate unit 10, the element mounting portion 50 may be located on the heat dissipation member 100 via a submount substrate 30 containing an insulating material. This configuration ensures insulation between the heat dissipation member 100 and the electronic element 310. Although the substrate unit 10 shown in FIGS. 1A and 1B includes a submount substrate 30, the substrate unit 10 does not necessarily have to include the submount substrate 30. In this configuration, the submount substrate 30 and the electronic element 310 may be mounted on the substrate unit 10 when the electronic device 300 is manufactured.

[0076] Furthermore, the melting point of the third bonding material 40 that bonds the heat dissipation member 100 and the submount substrate 30 may be lower than the melting point of the second bonding material 140 that bonds the graphite block 110 and the protective portion (first plate member 120, second plate member 130). This configuration facilitates temperature control during mounting of the submount substrate 30 compared to when the melting point of the third bonding material 40 is higher than that of the second bonding material 140. For example, if the melting point of the third bonding material 40 is higher than that of the second bonding material 140, there is a possibility that the second bonding material 140 will melt when the submount substrate 30 is fixed to the heat dissipation member 100 with the third bonding material 40, thereby releasing the bond between the graphite block 110 and the protective portion (first plate member 120, second plate member 130). Therefore, temperature control is required to avoid melting of the second bonding material 140. In other words, the third bonding material 40 may be a bonding material with a relatively low melting point, such as a solder material. The second bonding material 140 may also be a bonding material with a relatively high melting point, such as a metal brazing filler metal (for example, a copper brazing filler metal).

[0077] Furthermore, the melting point of the third bonding material 40 that bonds the heat dissipation member 100 and the submount substrate 30 may be lower than the melting point of the bonding material included in the package (e.g., the bonding material that bonds the substrate 20 and the frame 21). This configuration facilitates temperature control during mounting of the submount substrate 30 compared to when the melting point of the third bonding material 40 is higher than the melting point of the bonding material included in the package. For example, if the melting point of the third bonding material 40 is higher than the melting point of the bonding material included in the package, there is a possibility that the bonding material included in the package will melt and damage the package (e.g., the bonding between the substrate 20 and the frame 21 will be released) when the submount substrate 30 is fixed to the heat dissipation member 100 by the third bonding material 40. Therefore, temperature control is required to avoid melting of the bonding material included in the package. In other words, the third bonding material 40 may be a bonding material with a relatively low melting point, such as a solder material. Furthermore, the bonding material included in the package may be a bonding material with a relatively high melting point, such as a metal-based brazing filler metal (e.g., a copper brazing filler metal).

[0078] Furthermore, the melting point of the third bonding material 40 that bonds the heat dissipation member 100 and the submount substrate 30 may be lower than the melting point of the first bonding material 60 that bonds the substrate 20 and the heat dissipation member 100. This configuration makes temperature control during mounting of the submount substrate 30 easier than when the melting point of the third bonding material 40 is higher than that of the first bonding material 60. For example, if the melting point of the third bonding material 40 is higher than that of the first bonding material 60, there is a possibility that the first bonding material 60 will melt when the submount substrate 30 is fixed to the heat dissipation member 100 by the third bonding material 40, causing the bond between the substrate 20 and the heat dissipation member 100 to be released. Therefore, temperature control is required to avoid melting of the first bonding material 60. The melting point of the third bonding material 40 may be the same as that of the first bonding material 60. For example, if the first bonding material 60 is a solder material such as a gold-based solder material whose melting point differs before and after bonding (specifically, a solder material whose melting point is higher after bonding than before bonding), even if the melting point of the third bonding material 40 is the same as the melting point of the first bonding material 60 (the melting point before bonding), when the third bonding material 40 is used (when the submount substrate 30 is mounted), the melting point of the first bonding material 60 is higher than the melting point of the third bonding material 40, so temperature control to avoid melting of the first bonding material 60 is not necessary.

[0079] Furthermore, in the alignment direction (Z direction, second direction A2) of the submount substrate 30 and the heat dissipation member 100, the thermal conductivity of the heat dissipation member 100 may be higher than the thermal conductivity of the submount substrate 30. Furthermore, the thermal conductivity of the heat dissipation member 100 in the first direction A1 (the stacking direction of graphene) may be lower than the thermal conductivity of the submount substrate 30 in the X direction and the Y direction. Furthermore, the thermal conductivity of the submount substrate 30 may be highly isotropic compared to the graphite block 110.

[0080] Furthermore, in the alignment direction (Z direction, second direction A2) of the substrate 20 and the heat dissipation member 100, the thermal conductivity of the heat dissipation member 100 may be higher than the thermal conductivity of the substrate 20. Furthermore, the thermal conductivity of the heat dissipation member 100 in the first direction A1 (the stacking direction of graphene) may be lower than the thermal conductivity of the substrate 20 in the X direction and the Y direction. Furthermore, the thermal conductivity of the substrate 20 may be highly isotropic compared to that of the graphite block 110.

[0081] <Electronic Device> Fig. 9 is a cross-sectional view showing an example of an electronic device 300 incorporating a substrate unit 10. The heat dissipation member 100 may be substituted for the heat dissipation members 100A and 100B of embodiments 2 and 3 described below. As shown in Fig. 9, the electronic device 300 according to an embodiment of the present disclosure includes the substrate unit 10 and an electronic element 310 located on an element mounting portion 50 of the substrate unit 10. The electronic element 310 may be mounted on the element mounting portion 50 via a bonding material 320 such as solder. This configuration allows heat from the electronic element 310 to be quickly conducted to the substrate 20 via the heat dissipation member 100.

[0082] In the electronic device 300, the melting point of the third bonding material 40 that bonds the heat dissipation member 100 and the submount substrate 30 may be lower than the melting point of the bonding material 320 that bonds the electronic element 310 and the submount substrate 30. This configuration facilitates temperature control during mounting of the submount substrate 30 compared to when the melting point of the third bonding material 40 is higher than that of the bonding material 320. For example, if the melting point of the third bonding material 40 is higher than that of the bonding material 320, there is a possibility that the bonding material 320 will melt and release the bond between the submount substrate 30 and the electronic element 310 when the submount substrate 30 (the submount substrate 30 with the electronic element 310 fixed thereto) is fixed to the heat dissipation member 100 by the third bonding material 40, and therefore temperature control is required to avoid melting of the bonding material 320. The melting point of the third bonding material 40 may be the same as that of the bonding material 320. For example, if the bonding material 320 is a solder material such as a gold-based solder material whose melting point differs before and after bonding (specifically, a solder material whose melting point is higher after bonding than before bonding due to a change in the alloy state before and after bonding), even if the melting point of the third bonding material 40 is the same as the melting point of the bonding material 320 (the melting point before bonding), when the third bonding material 40 is used (when the submount substrate 30 is mounted), the melting point of the bonding material 320 is higher than the melting point of the third bonding material 40, so temperature control to avoid melting of the bonding material 320 is not necessary.

[0083] The electronic device 300 may be mounted on a module substrate having a heat dissipation function to form an electronic module. Specifically, the bottom surface of the electronic device 300 (specifically, the bottom surface of the substrate 20) may be mounted on the module substrate via a bonding material such as solder. The heat dissipation member 100 may then be thermally connected to a heat sink via the module substrate. With this configuration, heat from the electronic element 310 can be quickly conducted to the module substrate and the heat sink via the heat dissipation member 100 and dissipated from the heat sink.

[0084] A heat source other than the electronic element 310 may be mounted on the element mounting portion 50. That is, various heat sources such as the electronic element 310, a heat pipe for exhausting heat, and a heater for heating can be mounted on the element mounting portion 50. When a heater is mounted on the element mounting portion 50 as a heat source, an object to be heated may be placed on the lower surface 102 of the heat dissipation member 100. With this configuration, it is possible to equalize the heat variations in each part of the heater and transfer heat to the object to be heated.

[0085] The board unit 10 may be used as a component for an optical communication module. Specifically, the board unit 10 may be used as a package for an optical communication module such as a laser / photodiode module, an LN / EA modulator, or a multiplexer / demultiplexer (mux / demux). The board unit 10 may also be used as a component for a wireless communication device such as a package for an RF power transistor.

[0086] The electronic device 300 shown in Fig. 9 has a directional light-emitting element (optical element) such as a laser diode (semiconductor laser) mounted as the electronic element 310 on the element mounting portion 50 of the substrate unit 10. As shown in Fig. 9, the substrate unit 10 may have a lens L such as a condenser lens mounted on a portion facing the emission portion of the light-emitting element (electronic element 310). Note that optical components other than the lens L, such as a mirror, a filter, a prism, etc., may also be mounted on the substrate unit 10.

[0087] 10A and 10B are diagrams showing an example of a configuration in which the arrangement direction (X direction) of the element mounting portions 50 is parallel to the extension direction (third direction A3) of the crystal planes in the graphite block 110. Figures 11A and 11B are diagrams showing an example of a configuration in which the arrangement direction (X direction) of the element mounting portions 50 is perpendicular to the extension direction (third direction A3) of the crystal planes in the graphite block 110. Figures 12A and 12B are diagrams showing an example of a configuration in which the arrangement direction (X direction) of the element mounting portions 50 is inclined with respect to the extension direction (third direction A3) of the crystal planes in the graphite block 110. 10A , 10B , 11A , 11B , 12A , and 12B , FIGS. 10A , 11A , and 12A are perspective views showing the relationship between the heat dissipation member 100 and the element mounting portion 50 (submount substrate 30), and FIGS. 10B , 11B , and 12B are plan views showing the relationship between the graphite block 110 and the element mounting portion 50. FIGS. 13A and 13B are plan views showing an example of a configuration in which the arrangement direction (X direction) of the element mounting portions 50 is inclined with respect to the direction in which the crystal planes of the graphite block 110 extend (third direction A3), and are used to explain the inclination angle θ. In FIGS. 10A , 10B , 11A , 11B , 12A , 12B , 13A , and 13B , the dot-hatched regions indicate regions (heat transfer regions R) through which heat from the electronic element 310 mounted on the element mounting portion 50 moves. Figures 10A, 10B, 11A, 11B, 12A, 12B, 13A, and 13B show the heat transfer region R when the effect of the first plate material 120, the second plate material 130, and the protective layer 150 in dispersing heat in the first direction A1 is ignored.

[0088] When the substrate unit 10 has multiple element mounting portions 50, if the arrangement direction (X direction) of the element mounting portions 50 is parallel to the direction in which the crystal plane extends (third direction A3), the cooling effect of the heat dissipation member 100 may not be fully exerted. Specifically, when the arrangement direction (X direction) of the element mounting portions 50 is parallel to the direction in which the crystal plane extends (third direction A3), as shown in FIGS. 10A and 10B , the heat transfer region R through which heat from an electronic element 310 mounted on one element mounting portion 50 moves coincides with the heat transfer region R through which heat from an electronic element 310 mounted on another element mounting portion 50 moves. Therefore, in this configuration, only a narrow area of ​​the graphite block 110 can be used as the heat transfer region R, and the heat dissipation member 100 cannot achieve efficient heat transfer performance. Furthermore, in this configuration, a portion of the heat from the electronic element 310 mounted on one element mounting portion 50 moves toward the electronic elements 310 mounted on the other element mounting portions 50. Therefore, if this configuration is adopted when the substrate unit 10 has three or more element mounting sections 50, the heat from multiple electronic elements 310 will affect one electronic element 310, and there is a risk that the electronic element 310 will be deformed due to abnormal heat generation, etc.

[0089] When the substrate unit 10 has a plurality of element mounting portions 50, the arrangement direction (X direction) of the element mounting portions 50 may be perpendicular to the direction in which the crystal plane extends (third direction A3). With this configuration, as shown in Figures 11A and 11B, the heat transfer region R through which heat of the electronic element 310 mounted on one element mounting portion 50 moves does not coincide with the heat transfer region R through which heat of the electronic element 310 mounted on another element mounting portion 50 moves. That is, the total number of graphene layers that face the element mounting portions 50, among the graphene constituting the graphite block 110, is greater than the case in which the arrangement direction (X direction) of the element mounting portions 50 is parallel to the direction in which the crystal plane extends (third direction A3) (as in Figures 10A and 10B). Therefore, a wider area of ​​the graphite block 110 can be used as the heat transfer region R than in this case (the case of FIGS. 10A and 10B ), thereby realizing more efficient heat transfer performance of the heat dissipation member 100 and improving the cooling effect of the heat dissipation member 100. Furthermore, with this configuration, the heat of one electronic element 310 is not affected by the heat of other electronic elements 310, so that even if the board unit 10 has three or more element mounting portions 50, abnormal heat generation does not occur.

[0090] When the substrate unit 10 has a plurality of element mounting portions 50, the arrangement direction (X direction) of the element mounting portions 50 may be inclined with respect to the direction in which the crystal plane extends (third direction A3). With this configuration, as shown in FIGS. 12A and 12B , the total number of inter-graphene layers of the graphene constituting the graphite block 110 that face the element mounting portions 50 is greater than when the arrangement direction (X direction) of the element mounting portions 50 is parallel (as in FIGS. 10A and 10B ) or perpendicular (as in FIGS. 11A and 11B ) to the direction in which the crystal plane extends (third direction A3). Therefore, a wider area of ​​the graphite block 110 can be used as the heat transfer region R than in these cases (as in FIGS. 10A and 10B , and as in FIGS. 11A and 11B ). This allows for more efficient heat transfer performance of the heat dissipation member 100, thereby further improving the cooling effect of the heat dissipation member 100.

[0091] That is, when the substrate unit 10 has a plurality of element mounting portions 50, the arrangement direction (X direction) of the element mounting portions 50 may preferably be a direction perpendicular to the direction in which the crystal plane of the graphite block 110 extends (third direction A3), or more preferably, may be a direction inclined (a direction that is neither parallel nor perpendicular) to the direction in which the crystal plane of the graphite block 110 extends (third direction A3).

[0092] When the arrangement direction (X direction) of the element mounting portions 50 is inclined with respect to the direction in which the crystal plane of the graphite block 110 extends (third direction A3), the inclination angle θ may be preferably 30° to 60°, and more preferably 45°. The inclination angle θ can be changed as appropriate depending on the shape and size of the element mounting portions 50, the spacing between the element mounting portions 50, etc.

[0093] Here, when the substrate unit 10 has three or more element mounting portions 50, one of these element mounting portions 50 is referred to as the first element mounting portion 50a, the element mounting portion 50 located adjacent to the first element mounting portion 50a is referred to as the second element mounting portion 50b, and the element mounting portion 50 located adjacent to the second element mounting portion 50b and on the opposite side of the first element mounting portion 50a is referred to as the third element mounting portion 50c. The heat transfer region R through which heat of the electronic element 310 mounted on the first element mounting portion 50a moves is referred to as the first heat transfer region Ra, the heat transfer region R through which heat of the electronic element 310 mounted on the second element mounting portion 50b moves is referred to as the second heat transfer region Rb, and the heat transfer region R through which heat of the electronic element 310 mounted on the third element mounting portion 50c moves is referred to as the third heat transfer region Rc.

[0094] When the arrangement direction (X direction) of three or more element mounting portions 50 is tilted with respect to the direction of extension of the crystal plane (third direction A3), the tilt angle θ may be an angle at which the first heat transfer region Ra and the second heat transfer region Rb partially overlap, but at which the first heat transfer region Ra and the third heat transfer region Rc do not overlap, as shown in FIG. 13A . With this configuration, a wider area of ​​the graphite block 110 can be used as the heat transfer region R compared to when the first heat transfer region Ra and the third heat transfer region Rc partially overlap, thereby achieving more efficient heat transfer performance of the heat dissipation member 100 and further improving the cooling effect of the heat dissipation member 100. Furthermore, with this configuration, the heat from multiple electronic elements 310 does not affect a single electronic element 310, preventing abnormal heat generation. Note that the second heat transfer region Rb is not shown in FIG. 13A .

[0095] When the arrangement direction (X direction) of three or more element mounting portions 50 is tilted with respect to the direction in which the crystal plane extends (third direction A3), the tilt angle θ may be an angle at which the first heat transfer region Ra and the second heat transfer region Rb do not overlap, as shown in FIG. 13B . That is, the first heat transfer region Ra may be an angle at which the first heat transfer region Ra does not overlap with the second heat transfer region Rb and the third heat transfer region Rc. With this configuration, heat from one electronic element 310 does not affect another electronic element 310, so abnormal heat generation does not occur even when the substrate unit 10 has three or more element mounting portions 50.

[0096] The angle at which the first heat transfer region Ra and the second heat transfer region Rb do not overlap may include the angle at which the first heat transfer region Ra and the second heat transfer region Rb contact each other. The angle at which the first heat transfer region Ra and the third heat transfer region Rc do not overlap may also include the angle at which the first heat transfer region Ra and the third heat transfer region Rc contact each other. The angle at which the first heat transfer region Ra and the second heat transfer region Rb contact each other may also be the angle at which the boundary surface between the first heat transfer region Ra and the other region (a plane extending in the second direction A2 and the third direction A3) contacts the boundary surface between the second heat transfer region Rb and the other region (a plane extending in the second direction A2 and the third direction A3). The same applies to the angle at which the first heat transfer region Ra and the third heat transfer region Rc contact each other.

[0097] That is, when the arrangement direction (X direction) of three or more element mounting portions 50 is tilted with respect to the direction in which the crystal plane extends (third direction A3), the tilt angle θ may preferably be an angle at which the first heat transfer region Ra and the third heat transfer region Rc do not overlap, or more preferably an angle at which the heat transfer region R is maximized. Furthermore, for example, in addition to the tilt angle θ, the shape and size of the element mounting portions 50, the spacing between the element mounting portions 50, and the like may be set so as to satisfy the condition that the first heat transfer region Ra and the third heat transfer region Rc do not overlap.

[0098] Furthermore, when the substrate unit 10 has two element mounting portions 50, the heat transfer region R through which heat from the electronic element 310 mounted on one element mounting portion 50 moves does not have to overlap with the heat transfer region R through which heat from the electronic element 310 mounted on the other element mounting portion 50 moves. With this configuration, a wider area of ​​the graphite block 110 can be used as the heat transfer region R compared to when these two heat transfer regions R overlap even partially, thereby achieving efficient heat transfer performance of the heat dissipation member 100 and further improving the cooling effect of the heat dissipation member 100.

[0099] 12A , 12B , 13A , and 13B , a heat dissipation structure 400 according to an embodiment of the present disclosure may include a plate-shaped heat dissipation member 100 containing a carbon material and having a first surface 111, and a plurality of element mounting portions 50 positioned on the first surface 111. The direction in which the plurality of element mounting portions 50 are arranged is referred to as the X direction, a predetermined direction along the first surface 111 that is inclined with respect to the X direction is referred to as a specific direction (the direction in which the crystal plane extends (third direction A3)), and a direction intersecting the first surface 111 is referred to as the Z direction. The thermal conductivity of the heat dissipation member 100 in the specific direction may be higher than the thermal conductivity in the X direction, and the thermal conductivity in the Z direction may be higher than the thermal conductivity in the X direction. This configuration can reduce heat transfer in the heat dissipation member 100 in the direction in which the plurality of element mounting portions 50 are arranged (the X direction), thereby preventing deformation of the electronic element 310 due to abnormal heat generation or the like. Furthermore, with this configuration, it is possible to cool the electronic element 310 (transfer heat from the electronic element 310, which is a heat source) using a wider area of ​​the heat dissipation member 100 (graphite block 110) than when the thermal conductivity is high in the direction (X direction) in which the multiple element mounting portions 50 are arranged. Therefore, efficient cooling by the heat dissipation member 100 can be achieved.

[0100] In the heat dissipation structure 400, the multiple element mounting portions 50 may include a first element mounting portion 50a, a second element mounting portion 50b adjacent to the first element mounting portion 50a, and a third element mounting portion 50c adjacent to the second element mounting portion 50b and located on the opposite side of the first element mounting portion 50a. The specific direction (the direction in which the crystal plane extends (third direction A3)) may be inclined with respect to the X direction so that lines extending along the specific direction that overlap the first element mounting portion 50a do not overlap the third element mounting portion 50c. Among the lines extending along the specific direction, the line that overlaps the first element mounting portion 50a may be a line extending along the specific direction that is located within the first heat transfer region Ra. This configuration prevents heat from three or more electronic elements 310 from being transferred to a portion of the heat dissipation member 100 (graphite block 110). Therefore, abnormal heat generation can be suppressed, and heat management becomes easier. For example, if a line extending in a specific direction that overlaps the first element mounting portion 50a also overlaps the third element mounting portion 50c, i.e., if the first heat transfer region Ra and the third heat transfer region Rc overlap, heat from three or more electronic elements 310 will be transferred to the overlapping portion (a part of the graphite block 110), which may cause deformation of the electronic elements 310 due to abnormal heat generation. Therefore, some kind of countermeasure is necessary.

[0101] 14A and 14B are diagrams showing an example of a heat dissipation member 100A according to a second embodiment. FIG. 14A is a perspective view showing the configuration excluding the protective layer 150, and FIG. 14B is a perspective view showing the configuration excluding the protective layer 150, the first plate member 120, and the second plate member 130. FIG. 15 is a cross-sectional view showing a location where two graphite members are adjacent to each other in the heat dissipation member 100A according to the second embodiment. The heat dissipation member 100A according to the second embodiment differs from that according to the first embodiment in the configuration of the graphite block 110A, but may otherwise be similar to that according to the first embodiment. The differences will be described in detail below. That is, the substrate unit according to the second embodiment differs from that according to the first embodiment in the configuration of the heat dissipation member 100A (specifically, the graphite block 110A), but may otherwise be similar to that according to the first embodiment.

[0102] Graphite block 110A may include multiple graphite pieces 110u. Graphite piece 110u refers to a single structure that remains when the bond to the surrounding area by the bonding material is released. It is not easy to prepare a single large graphite block. In the second embodiment, by adopting a structure in which graphite block 110A includes multiple graphite pieces 110u, the dimensions of heat dissipation member 100A can be increased, thereby increasing the design flexibility of heat dissipation member 100A.

[0103] The number of the graphite materials 110u is not particularly limited, but may be five or less. By having five or less graphite materials, the proportion of the graphite block 110A occupied by regions with low thermal conductivity can be reduced. The regions with low thermal conductivity are gaps G1 formed between a pair of adjacent graphite materials 110u or bonding materials 141 located in the gaps G1 (see FIG. 15 ).

[0104] As shown in FIG. 14B , the plurality of graphite materials 110u may be arranged in a first direction A1 in which graphene is stacked. More specifically, the graphite block 110A may include a first graphite material 110u1, a second graphite material 110u2 arranged in a first direction A1 relative to the first graphite material 110u1, and a bonding material 141 positioned between the first graphite material 110u1 and the second graphite material 110u2 and bonding the first graphite material 110u1 and the second graphite material 110u2. Gaps G1 are generated between the plurality of graphite materials 110u. However, by arranging the plurality of graphite materials 110u in the first direction A1, it is possible to reduce the possibility that the gaps G1 will block the heat conduction path in the directions (the second direction A2 and the third direction A3) in which the thermal conductivity of the graphite material 110u is high. Therefore, the influence of the gap G1 on the thermal conduction performance of the heat dissipation member 100A can be reduced.

[0105] Furthermore, a direction of low thermal conductivity (i.e., first direction A1) can be generated throughout graphite block 110A, as in embodiment 1. Therefore, when devices or the like that should not be affected by heat are placed to the sides of graphite block 110A, the effects of heat from graphite block 110A on the devices or the like can be reduced by placing the devices or the like in the direction of low thermal conductivity. This makes it possible to eliminate or simplify the heat insulation structure for reducing the effects of heat on the devices or the like.

[0106] The gap G1 may be an air gap. Alternatively, a bonding material 141 may be located in at least a portion of the gap G1. Alternatively, the bonding material 141 may substantially fill the gap G1 (e.g., it may be located in 90% or more of the cross section). The bonding material 141 may be a brazing material, a solder material, or a resin material. Furthermore, the bonding material 141 may be made of the same material as the second bonding material 140 that bonds the first plate member 120 and the second plate member 130 to the graphite block 110A. The direction in which adjacent pairs of the plurality of graphite materials 110u face each other is not limited to the above direction. The plurality of graphite materials 110u may be arranged to face each other in a direction different from the direction in which the graphene is stacked (e.g., the second direction A2 or the third direction A3).

[0107] [Relationship Between Crystal Plane and Element Mounting Portion] In one embodiment, similarly to the first embodiment, when the substrate unit 10 has a plurality of element mounting portions 50, the arrangement direction (X direction) of the element mounting portions 50 may preferably be a direction perpendicular to the direction in which the crystal plane of the graphite block 110A extends (third direction A3), or more preferably may be a direction inclined (a direction that is neither parallel nor perpendicular) to the direction in which the crystal plane of the graphite block 110A extends (third direction A3).

[0108] Furthermore, as in the first embodiment, when the arrangement direction (X direction) of three or more element mounting portions 50 is inclined with respect to the direction in which the crystal plane extends (third direction A3), the inclination angle θ may preferably be an angle at which the first heat transfer region Ra and the third heat transfer region Rc do not overlap, or more preferably an angle at which the heat transfer region R is maximized. Furthermore, for example, in addition to the inclination angle θ, the shape and size of the element mounting portions 50, the spacing between the element mounting portions 50, and the like may be set so as to satisfy the condition that the first heat transfer region Ra and the third heat transfer region Rc do not overlap. Furthermore, as in the first embodiment, when the substrate unit 10 has two element mounting portions 50, the heat transfer region R to which the heat of the electronic element 310 mounted on one element mounting portion 50 moves and the heat transfer region R to which the heat of the electronic element 310 mounted on the other element mounting portion 50 moves may not overlap.

[0109] 16A and 16B are diagrams showing an example of a heat dissipation member 100B of embodiment 3, where FIG. 16A is a perspective view showing the configuration excluding protective layer 150, and FIG. 16B is a perspective view showing the configuration excluding protective layer 150, first plate member 120, and second plate member 130. Heat dissipation member 100B of embodiment 3 may differ from embodiments 1 and 2 in the configuration of graphite block 110B, but may otherwise be similar to embodiments 1 and 2. The differences will be described in detail below. That is, the substrate unit of embodiment 3 may differ from embodiments 1 and 2 in the configuration of heat dissipation member 100B (specifically, graphite block 110B), but may otherwise be similar to embodiments 1 and 2.

[0110] Graphite block 110B may include a plurality of graphite pieces 110u. As shown in Fig. 16A , the plurality of graphite pieces 110u may be arranged in parallel in second direction A2. This configuration allows the dimensions of heat dissipation member 100B to be increased in second direction A2 (i.e., the direction from first plate member 120 to second plate member 130), thereby increasing the design flexibility of heat dissipation member 100B.

[0111] When the graphite materials 110u are arranged in parallel in the second direction A2, they may be arranged so as to face each other in any one direction along the crystal plane (i.e., the second direction A2, the third direction A3, etc., which have high thermal conductivity). This configuration enables rapid heat conduction from the first plate material 120 to the second plate material 130.

[0112] Furthermore, the first direction A1 in which graphene is stacked and the second direction A2 and third direction A3 along the crystal plane may not coincide among the multiple graphite materials 110u. Here, a pair of adjacent graphite materials 110u will be referred to as a first graphite material 110u and a second graphite material 110u. In this case, the direction A1a in which graphene is stacked in the first graphite material 110u and the direction A1b in which graphene is stacked in the second graphite material 110u may be twisted relative to each other. Furthermore, the multiple graphite materials 110u may be bonded together via a bonding material.

[0113] According to this configuration, when heat is conducted from a portion of the first plate member 120 to the second plate member 130, the heat spreads in the third direction A3a in the graphite member 110u closest to the first plate member 120 and is then conducted to the next graphite member 110u. Then, in the next graphite member 110u, the heat spreads in the third direction A3b and is then conducted to the next graphite member 110u. As a result, the heat is dispersed in the third directions A3a and A3b, which intersect with each other in a planar view. Therefore, the anisotropy of the thermal conduction of the heat dissipation member 100B is reduced, and heat can be conducted through a larger area of ​​the heat dissipation member 100B. This allows for efficient heat transfer performance.

[0114] [Relationship Between Crystal Plane and Element Mounting Portion] In one embodiment, when the substrate unit 10 has a plurality of element mounting portions 50, the arrangement direction (X direction) of the element mounting portions 50 may preferably be a direction perpendicular to the extending direction (e.g., third direction A3a) of the crystal plane of the graphite material 110u closest to the element mounting portion 50, or more preferably may be a direction inclined (a direction that is neither parallel nor perpendicular) to the extending direction (e.g., third direction A3a) of the crystal plane of the graphite material 110u closest to the element mounting portion 50.

[0115] Furthermore, when the arrangement direction (X direction) of three or more element mounting portions 50 is inclined with respect to the direction in which the crystal plane of the graphite material 110u closest to the element mounting portion 50 extends (e.g., third direction A3a), the inclination angle θ may preferably be an angle at which the first heat transfer region Ra and the third heat transfer region Rc do not overlap in the graphite material 110u closest to the element mounting portion 50, or more preferably an angle at which the heat transfer region R is maximized. Furthermore, in addition to the inclination angle θ, the shape and size of the element mounting portions 50, the spacing between the element mounting portions 50, and the like may be set so as to satisfy the condition that the first heat transfer region Ra and the third heat transfer region Rc do not overlap in the graphite material 110u closest to the element mounting portion 50. Furthermore, when the substrate unit 10 has two element mounting portions 50, in the graphite material 110u closest to the element mounting portion 50, the heat transfer region R through which the heat of the electronic element 310 mounted on one element mounting portion 50 moves and the heat transfer region R through which the heat of the electronic element 310 mounted on the other element mounting portion 50 moves do not have to overlap.

[0116] 17 shows an example of a method for manufacturing a heat dissipation member. The following describes a method for manufacturing the heat dissipation member 100A of embodiment 2. The manufacturing method includes a graphite processing step J1, a graphite material combining and joining step J2, a cutting step J3, and a plating step J4.

[0117] In the graphite processing step J1, graphite element 501 is cut using a processing machine such as a wire saw to produce a plurality of graphite materials 501u. Graphite element 501 generally has two crystal planes, and the dimensions of the crystal planes are greater than the dimensions in the direction perpendicular to the crystal planes. The cut graphite material 501u may be cut so that the minimum width of the crystal planes is smaller than the minimum width of the cut surfaces (i.e., crystal layer surfaces).

[0118] In the graphite material assembling and joining process J2, the plurality of graphite materials 501u are arranged in parallel in the orientation shown in embodiment 2. Furthermore, a first plate member 520 and a second plate member 530 are placed on the plurality of graphite materials 501u with a joining material sandwiched therebetween, and the joining material is applied by heating and cooling. At this stage, the first plate member 520 and the second plate member 530 are joined to the plurality of graphite materials 501u, and the joining material may enter gaps G1 (see FIG. 15 ) between the plurality of graphite materials 501u to join the plurality of graphite materials 501u to one another.

[0119] In the cutting process J3, the first plate material 520, the plurality of graphite materials 501u, and the second plate material 530, which are joined together, are cut to the dimensions of the first plate material 120, the graphite block 110A, and the second plate material 130 of the heat dissipation member 100A. Note that, when the arrangement direction (X direction) of the element mounting portions 50 is inclined with respect to the direction in which the crystal plane of the graphite block 110A extends (third direction A3), the cutting direction in the cutting process J3 may be inclined with respect to the third direction A3.

[0120] In the plating step J4, plating is applied to the outside of the structure cut in the cutting step J3. The plating is performed so as to cover at least the side surface 113 of the graphite block 110A. The plating may be performed on the entire surface, including the outer surfaces of the first plate material 120 and the second plate material 130. As a result, the plating layer becomes the protective layer 150. By performing the above steps J1 to J4, the heat dissipation member 100A is manufactured.

[0121] Other Embodiments The heat dissipation member is not limited to the above-described configuration. For example, in other embodiments, the linear expansion coefficients of the first and second plates may be greater than the linear expansion coefficient of the graphite block in both the first and second directions. Resin materials such as ABS resin and polybutylene terephthalate (PBT) may be used as the materials for the first and second plates. When the linear expansion coefficient of the graphite block 110 is less than 24 [10^-6 / K] in the first direction A1, metal materials such as aluminum having a linear expansion coefficient greater than that of copper may be used as the materials for the first and second plates 120 and 130. Even in this case, the same or similar configuration as the above-described embodiment provides the same effects.

[0122] The above describes the embodiments of the present disclosure. However, the heat dissipation member and substrate unit of the present disclosure are not limited to the heat dissipation members 100, 100A, and 100B and the substrate unit 10 of the above-described embodiments. For example, the details shown in the embodiments can be modified as appropriate without departing from the spirit of the invention. According to the present disclosure, a heat dissipation structure and substrate unit with high heat dissipation performance can be obtained.

[0123] In one embodiment, (1) a heat dissipation structure includes a plate-shaped heat dissipation member including a carbon material and having a first surface, and a plurality of element mounting portions located on the first surface, wherein when the direction in which the plurality of element mounting portions are arranged is referred to as an X direction, a predetermined direction along the first surface that is inclined with respect to the X direction is referred to as a specific direction, and a direction intersecting the first surface is referred to as a Z direction, the thermal conductivity of the heat dissipation member in the specific direction is higher than the thermal conductivity in the X direction, and the thermal conductivity in the Z direction is higher than the thermal conductivity in the X direction.

[0124] (2) The heat dissipation structure of (1) above is such that the plurality of element mounting portions include a first element mounting portion, a second element mounting portion adjacent to the first element mounting portion, and a third element mounting portion adjacent to the second element mounting portion and located on the opposite side of the first element mounting portion, and the specific direction is a direction inclined with respect to the X direction such that, among straight lines extending along the specific direction, a straight line that overlaps with the first element mounting portion does not overlap with the third element mounting portion.

[0125] (3) The substrate unit comprises a substrate and a heat dissipation structure of (1) or (2) located on the substrate, wherein the element mounting portion and the substrate are thermally connected via the heat dissipation member, and the thermal conductivity of the heat dissipation member is higher than the thermal conductivity of the substrate in the Z direction.

[0126] (4) The substrate unit of (3) above is configured such that the plurality of element mounting portions include a first element mounting portion, a second element mounting portion adjacent to the first element mounting portion, and a third element mounting portion adjacent to the second element mounting portion and located on the opposite side of the first element mounting portion, and the specific direction is a direction inclined with respect to the X direction such that, among straight lines extending along the specific direction, a straight line that overlaps with the first element mounting portion does not overlap with the third element mounting portion.

[0127] (5) In the substrate unit of (3) or (4) above, the heat dissipation member includes a graphite block having anisotropic thermal conductivity and a protective portion covering the graphite block, and the thermal conductivity of the graphite block in the Z direction is higher than the thermal conductivity of the graphite block in one direction intersecting the Z direction, the thermal conductivity of the heat dissipation member in the Z direction is higher than the thermal conductivity of the protective portion, and the thermal conductivity of the substrate in the one direction is higher than the thermal conductivity of the heat dissipation member, and the thermal conductivity of the protective portion is higher than the thermal conductivity of the heat dissipation member.

[0128] (6) The substrate unit of (5) above further includes a bonding material positioned between the substrate and the heat dissipation member to bond the substrate and the heat dissipation member, and the thermal conductivity of the bonding material is higher than the thermal conductivity of the graphite block in the one direction.

[0129] (7) The substrate unit of (6) above is characterized in that the bonding material is a first bonding material, the heat dissipation member further includes a second bonding material located between the graphite block and the protective portion and bonding the graphite block and the protective portion, the thermal conductivity of the second bonding material is higher than the thermal conductivity of the graphite block in the one direction, and the melting point of the first bonding material is lower than the melting point of the second bonding material.

[0130] (8) Any of the substrate units (5) to (7) above further includes a submount substrate located on the heat dissipation member and containing an insulating material, the protective portion of the heat dissipation member contains metal, and the element mounting portion is located on the heat dissipation member via the submount substrate.

[0131] (9) The substrate unit of (7) above further comprises: a submount substrate located on the heat dissipation member and containing an insulating material; and a third bonding material located between the heat dissipation member and the submount substrate and bonding the heat dissipation member to the submount substrate, wherein the protective portion of the heat dissipation member contains metal, the element mounting portion is located on the heat dissipation member via the submount substrate, and the melting point of the third bonding material is lower than the melting point of the second bonding material.

[0132] The present disclosure can be used as a heat dissipation structure and a substrate unit.

[0133] REFERENCE SIGNS LIST 10 Substrate unit 20 Substrate 30 Submount substrate 40 Third bonding material 50 Element mounting portion 50a First element mounting portion 50b Second element mounting portion 50c Third element mounting portion 60 First bonding material 100, 100A, 100B Heat dissipation member 110, 110A, 110B Graphite block 110u Graphite material 110u1 First graphite material 110u2 Second graphite material 111 First surface 112 Second surface 113 Side surface 113a First side surface 113b Second side surface 120 First plate material (protective portion) 130 Second plate material (protective portion) 140 Second bonding material 141 Bonding material 150 Protective layer (protective portion) 300 Electronic device 310 Electronic element 400 Heat dissipation structure A1 First direction A2 Second direction A3 Third direction F1 Recessed part

Claims

1. A heat dissipation structure comprising: a plate-shaped heat dissipation member containing a carbon material and having a first surface; and a plurality of element mounting portions located on the first surface, wherein when the direction in which the plurality of element mounting portions are arranged is called the X direction, a specific direction along the first surface that is inclined with respect to the X direction is called the specific direction, and a direction intersecting the first surface is called the Z direction, the thermal conductivity of the heat dissipation member in the specific direction is higher than the thermal conductivity in the X direction, and the thermal conductivity in the Z direction is higher than the thermal conductivity in the X direction.

2. The heat dissipation structure according to claim 1, wherein the plurality of element mounting portions include a first element mounting portion, a second element mounting portion adjacent to the first element mounting portion, and a third element mounting portion adjacent to the second element mounting portion and located on the opposite side of the first element mounting portion, and the specific direction is a direction that is inclined with respect to the X direction such that, among straight lines extending along the specific direction, a straight line that overlaps with the first element mounting portion does not overlap with the third element mounting portion.

3. A substrate unit comprising: a substrate; and a heat dissipation structure according to claim 1 or 2 located on the substrate, wherein the element mounting portion and the substrate are thermally connected via the heat dissipation member; and in the Z direction, the thermal conductivity of the heat dissipation member is higher than the thermal conductivity of the substrate.

4. A substrate unit as described in claim 3, wherein the plurality of element mounting portions include a first element mounting portion, a second element mounting portion adjacent to the first element mounting portion, and a third element mounting portion adjacent to the second element mounting portion and located on the opposite side of the first element mounting portion, and the specific direction is a direction inclined with respect to the X direction such that, among straight lines extending along the specific direction, a straight line that overlaps with the first element mounting portion does not overlap with the third element mounting portion.

5. A substrate unit as described in claim 3 or 4, wherein the heat dissipation member includes a graphite block having anisotropic thermal conductivity and a protective part covering the graphite block, the thermal conductivity of the graphite block in the Z direction is higher than the thermal conductivity of the graphite block in one direction intersecting the Z direction, the thermal conductivity of the heat dissipation member in the Z direction is higher than the thermal conductivity of the protective part, and the thermal conductivity of the substrate is higher than the thermal conductivity of the heat dissipation member and the thermal conductivity of the protective part is higher than the thermal conductivity of the heat dissipation member in the one direction.

6. The substrate unit according to claim 5, further comprising a bonding material located between said substrate and said heat dissipation member and bonding said substrate and said heat dissipation member, wherein the thermal conductivity of said bonding material is higher than the thermal conductivity of said graphite block in said one direction.

7. The substrate unit of claim 6, wherein the bonding material is a first bonding material, the heat dissipation member further includes a second bonding material located between the graphite block and the protective portion and bonding the graphite block and the protective portion, the thermal conductivity of the second bonding material is higher than the thermal conductivity of the graphite block in the one direction, and the melting point of the first bonding material is lower than the melting point of the second bonding material.

8. A substrate unit as described in any one of claims 5 to 7, further comprising a submount substrate located on the heat dissipation member and containing an insulating material, the protective portion of the heat dissipation member containing metal, and the element mounting portion being located on the heat dissipation member via the submount substrate.

9. A substrate unit as described in claim 7, further comprising: a submount substrate located on the heat dissipation member and containing an insulating material; and a third bonding material located between the heat dissipation member and the submount substrate and bonding the heat dissipation member and the submount substrate, wherein the protective portion of the heat dissipation member contains a metal, the element mounting portion is located on the heat dissipation member via the submount substrate, and the melting point of the third bonding material is lower than the melting point of the second bonding material.

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