Electronic device

Abstract

To provide an electronic apparatus having a resin housing with excellent heat dissipation.SOLUTION: An electronic apparatus 1 includes an electronic module 10 including an electronic component that generates heat, a resin housing 4 that houses the electronic module 10, and heat dissipation gel 5 interposed between the electronic module 10 and a part of the housing 4. The casing 4 includes the facing plate 41, which faces the electronic module 10 via the heat dissipation gel 5 and extends along the plane orthogonal to the direction in which the casing 4 faces the electronic module 10, and the projections 42, which project from the facing plate 41 toward the electronic module 10 and are in contact with the heat dissipation gel 5. The opposing-plate part 41 and the protruding part 42 each have anisotropic thermal conductivity. In the opposing plate portion 41, the thermal conductivity in one direction along the spreading direction is larger than the thermal conductivity in the thickness direction. In the protrusion 42, the thermal conductivity in the protruding direction is larger than the thermal conductivity in any direction orthogonal to the protruding direction.SELECTED DRAWING: Figure 1

Description

[Technical Field]

[0001] The present invention relates to an electronic device. [Background technology]

[0002] A heat dissipation structure having a heat-generating electronic component, a circuit board on which the electronic component is mounted, a case for accommodating the circuit board, and grease interposed between the electronic component and the case is disclosed in Patent Document 1. Patent Document 1 proposes providing a step in the case to prevent the grease from moving from a predetermined interposed position. [Prior art documents] [Patent documents]

[0003] [Patent Document 1] Japanese Patent Application Laid-Open No. 2005-5671 Summary of the Invention [Problem to be solved by the invention]

[0004] However, the heat dissipation structure of Patent Document 1 leaves room for improvement in terms of heat dissipation from electronic components when the case (i.e., housing) is made of resin. That is, considering the reduction of carbon dioxide emissions during manufacturing and weight reduction, it is desirable to change the housing from metal to resin. In this case, there is room for improvement in the heat dissipation from the electronic components through the heat dissipation gel and housing.

[0005] The present invention has been made in view of the above-mentioned problems, and aims to provide an electronic device having a resin housing with excellent heat dissipation properties. [Means for solving the problem]

[0006] One aspect of the present invention is an electronic device (1) having an electronic module (10) equipped with heat-generating electronic components, a resin housing (4) that houses the electronic module, and a heat-dissipating gel (5) interposed between the electronic module and a part of the housing, The housing has an opposing plate portion (41) that faces the electronic module via the heat dissipation gel and that is along a plane perpendicular to the facing direction of the electronic module; a plurality of protrusions (42) protruding from the opposing plate portion toward the electronic module and in contact with the heat dissipation gel; the opposing plate portion and the protrusion portion each have anisotropy in thermal conductivity, the opposing plate portion has a thermal conductivity in one direction along the expansion direction that is greater than the thermal conductivity in the thickness direction; The protrusion is in an electronic device in which the thermal conductivity in the protruding direction is greater than the thermal conductivity in any direction perpendicular to the protruding direction. [Effects of the Invention]

[0007] In the electronic device, the opposing plate and the protrusion each have the anisotropic thermal conductivity as described above. This improves heat dissipation from the electronic module through the heat dissipation gel and the housing. Therefore, excellent heat dissipation can be achieved in an electronic device having a resin housing.

[0008] As described above, according to the above aspect, it is possible to provide an electronic device having a resin housing with excellent heat dissipation properties. In addition, the symbols in parentheses in the claims and the means for solving the problems indicate the correspondence with the specific means described in the embodiments described below, and do not limit the technical scope of the present invention. [Brief explanation of the drawings]

[0009] [Figure 1] FIG. 2 is a cross-sectional view illustrating a part of the electronic device according to the first embodiment. [Figure 2] FIG. 3 is a cross-sectional explanatory view of an opposing plate portion and a protrusion portion in the first embodiment. [Figure 3] FIG. 3 is an explanatory plan view of an opposing plate portion and a protrusion portion in the first embodiment. [Figure 4] FIG. 3 is a cross-sectional view illustrating a heat dissipation path in the first embodiment. [Figure 5] FIG. 7 is an explanatory diagram of a molding die in the first embodiment, and is a cross-sectional view taken along line VV in FIG. 6. [Figure 6] FIG. 6 is an explanatory diagram of a molding die in the first embodiment, and is a cross-sectional view taken along the line VI-VI in FIG. 5. [Figure 7] FIG. 3 is a cross-sectional view illustrating the flow of molten resin in a part of the cavity in the first embodiment. DETAILED DESCRIPTION OF THE INVENTION

[0010] (Embodiment 1) An embodiment of an electronic device will be described with reference to FIGS. As shown in Fig. 1, the electronic device 1 of this embodiment includes an electronic module 10, a resin housing 4, and a heat-dissipating gel 5. The electronic module 10 includes an electronic component 2 that generates heat. The housing 4 houses the electronic module 10. The heat-dissipating gel 5 is interposed between the electronic module 10 and a portion of the housing 4.

[0011] The housing 4 has a facing plate 41 and multiple protrusions 42. The facing plate 41 faces the electronic module 10 via the heat dissipation gel 5 and is a portion along a plane perpendicular to the facing direction of the electronic module 10. The protrusions 42 protrude from the facing plate 41 toward the electronic module 10 and come into contact with the heat dissipation gel 5.

[0012] The opposing plate portion 41 and the protrusion portion 42 each have anisotropic thermal conductivity. The opposing plate portion 41 has a higher thermal conductivity in one direction along the spreading direction than in the thickness direction. The protrusion portion 42 has a higher thermal conductivity in the protruding direction than in any direction perpendicular to the protruding direction.

[0013] In this specification, the opposing direction between the electronic module 10 and the opposing plate portion 41 will be referred to as the Z direction where appropriate.

[0014] In this embodiment, the electronic module 10 has an electronic component 2 and a circuit board 3. The electronic component 2 is mounted on the circuit board 3. In this embodiment, the electronic component 2 is formed by mounting a semiconductor chip 21 on a conductive base 22 and molding it with a resin part 23. The surface of the base 22 opposite to the semiconductor chip 21 is exposed from the resin part 23. The surface of the semiconductor chip 21 opposite to the base 22 is covered with the resin part 23.

[0015] In this embodiment, the circuit board 3 is a multilayer circuit board in which conductor patterns 321 and 322 are formed in multiple layers on an insulating base material 31. The electronic component 2 is mounted on the circuit board 3 by connecting the base 22 to the conductor pattern 322 on the surface of the circuit board 3 with solder (not shown). In addition, the terminal 24 of the electronic component 2 is connected to another conductor pattern 322 on the circuit board 3.

[0016] An electronic module 10 having a circuit board 3 and electronic components 2 mounted on the circuit board 3 is sandwiched by parts of a housing 4 on both sides in the stacking direction, i.e., the Z direction. That is, a facing plate portion 41, which is part of the housing 4, is disposed opposite the electronic module 10, and a heat-dissipating gel 5 is interposed between the facing plate portion 41 and the electronic module 10. The heat-dissipating gel 5 may be, for example, a silicone resin or the like containing a thermally conductive filler. In this embodiment, in particular, the heat-dissipating gel 5 may be one that uses silicone as a base component, is filled with zinc oxide (ZnO) as a filler in a range of 60 wt% to 90 wt%, and has a viscosity of 200 Pa·sec to 500 Pa·sec.

[0017] As shown in Figures 1 and 2, a plurality of protrusions 42 protrude from the opposing plate portion 41 toward the electronic module 10. As shown in Figure 3, each protrusion 42 is formed in a fin shape that is elongated in a direction perpendicular to the Z direction. The longitudinal direction of each protrusion 42 when viewed from the Z direction is referred to as the X direction. The direction perpendicular to both the X direction and the Z direction is referred to as the Y direction. The multiple protrusions 42 are arranged in the Y direction at predetermined intervals. A groove that is elongated in the X direction is formed between protrusions 42 adjacent to each other in the Y direction.

[0018] As shown in FIG. 2, the cross section of the protrusion 42 taken along a plane perpendicular to the X direction has a substantially trapezoidal shape. The housing 4 is made of a resin mixed with a large number of thermally conductive fillers 41f, 42f. The fillers 41f, 42f have anisotropic shapes. That is, each filler 41f, 42f has a rod-like or plate-like shape, for example. The fillers 41f, 42f may be graphite fillers, carbon fiber fillers, or the like. The resin constituting the housing 4 may be, for example, PPS (polyphenylene sulfide), PP (polypropylene), PBT (polybutylene terephthalate), PA66 (polyamide 66), or the like.

[0019] The orientation direction of the plurality of fillers 41f in the opposing plate portion 41 is generally the same. The orientation direction of the plurality of fillers 41f is one direction along the XY plane. In this embodiment, the orientation direction of the plurality of fillers 41f in the opposing plate portion 41 is the Y direction. Here, the orientation direction is the direction in which the longitudinal direction of the fillers 41f faces.

[0020] On the other hand, the orientation directions of the plurality of fillers 42f in the protrusion 42 are also generally aligned with one another. The orientation direction of the plurality of fillers 42f is the Z direction.

[0021] In the resin housing 4, the direction along the orientation direction of the fillers 41f and 42f is the direction in which thermal conductivity is high. Therefore, by orienting the fillers 41f as described above, the thermal conductivity in one direction along the Y direction, i.e., the extension direction, is higher than the thermal conductivity in the Z direction, i.e., the thickness direction, in the opposing plate portion 41. Similarly, by orienting the fillers 42f as described above, the thermal conductivity in the Z direction, i.e., the protrusion direction, is higher than the thermal conductivity in the direction along the XY plane, i.e., the direction perpendicular to the protrusion direction, in the protrusion portion 42.

[0022] The protrusions 42 have a long fin shape when viewed from the Z direction. The opposing plate 41 has a higher thermal conductivity in a direction perpendicular to the longitudinal direction (i.e., the Y direction) than in the longitudinal direction (i.e., the X direction) of the protrusions 42 when viewed from the Z direction. To achieve this, the orientation direction of the filler 42f in the opposing plate 41 is along the Y direction.

[0023] In this embodiment, as described above, the opposing plate portion 41 and the protrusion portion 42 face the electronic component 2 from one side in the Z direction, and the opposing plate portion 41 and the protrusion portion 42 face the circuit board 3 from the other side in the Z direction (see FIG. 1). The heat dissipation gel 5 is interposed between the electronic component 2 and the opposing plate portion 41 and the protrusion portion 42, and the heat dissipation gel 5 is also interposed between the circuit board 3 and the opposing plate portion 41 and the protrusion portion 42.

[0024] The heat dissipating gel 5 is in contact with the entire surface of the protrusions 42, the entire surface of the opposing plate 41 between adjacent protrusions 42, and even with part of the surface of the opposing plate 41 around the protrusions 42. The heat dissipating gel 5 is also filled into the grooves formed between the multiple protrusions 42.

[0025] The heat dissipation gel 5 between the electronic component 2 and the housing 4 is in close contact with the resin portion 23 of the electronic component 2. The heat dissipation gel 5 between the circuit board 3 and the housing 4 is in close contact with the surface of the circuit board 3 opposite to the surface on which the electronic component 2 is mounted. The heat dissipation gel can also be in close contact with part of the conductor pattern on the circuit board 3. In this case, it is possible to more easily dissipate heat from the electronic component 2 to the opposing plate portion 41 on the circuit board 3 side.

[0026] 1, the opposing plate 41 facing the circuit board 3 is made thicker than the surrounding area by raising a portion of the housing 4 toward the circuit board 3. The circuit board 3 may also have a through-hole (not shown) that penetrates in the thickness direction (i.e., the Z direction) and has a conductor inside. When viewed from the Z direction, the through-hole may be provided within the overlapping area between the electronic component 2 and the heat dissipation gel 5 on the circuit board 3 side (i.e., the lower side in FIG. 1).

[0027] As described above, in this embodiment, the heat dissipation gel 5, the opposing plate portion 41, and the protrusion portion 42 are provided above and below the electronic module 10 in Fig. 1. Hereinafter, for convenience, the upper side of the electronic module 10 in Fig. 1 will be simply referred to as the upper side, and the lower side of the electronic module 10 in Fig. 1 will be simply referred to as the lower side.

[0028] As described above, the opposing plate portion 41 and the protrusion portion 42 of the housing 4 each have anisotropic thermal conductivity. The thermal conductivity in each direction of the opposing plate portion 41 and the protrusion portion 42 has the following relationship.

[0029] In the opposing plate portion 41, the thermal conductivity in one direction along the expansion direction where the thermal conductivity is maximum (in this embodiment, the Y direction) is defined as λ1a, and the thermal conductivity in the thickness direction (i.e., the Z direction) is defined as λ1b. In addition, in the protrusion portion 42, the thermal conductivity in the protruding direction (i.e., the Z direction) is defined as λ2a, and the thermal conductivity in the direction perpendicular to the protruding direction where the thermal conductivity is maximum is defined as λ2b. In this case, it is preferable that the relationships of the following formulas (1) and (2) are satisfied (see Experimental Example 1 described later). λ1b / λ1a≦0.5 (1) λ2b / λ2a≦0.5 (2)

[0030] Furthermore, making λ1b / λ1a and λ2b / λ2a extremely small may be disadvantageous in terms of difficulty in manufacturing, reduced strength, etc. From this perspective, for example, the following may be satisfied: 0.1≦λ1b / λ1a≦0.5, 0.1≦λ2b / λ2a≦0.5. Note that the thermal conductivities λ1a and λ1b are each the average thermal conductivities of the entire opposing plate portion 41, and the thermal conductivities λ2a and λ2b are each the average thermal conductivities of the multiple protrusions 42.

[0031] In this embodiment, the thermal conductivity of the heat dissipating gel 5 can be set to, for example, 0.2 to 20 W / m·K. The thermal conductivity λ1a can be set to, for example, 1 to 100 W / m·K. The thermal conductivity λ1b can be set to, for example, 0.5 to 50 W / m·K. The thermal conductivity λ2a can be set to, for example, 1 to 100 W / m·K. The thermal conductivity λ2b can be set to, for example, 0.5 to 50 W / m·K.

[0032] Furthermore, the height h of the protrusion 42 in the Z direction can be, for example, 0.05 to 10 mm, more preferably 0.1 to 5 mm. If the height h is too small, there is a concern that the function of the protrusion 42 to retain the heat-dissipating gel 5 will be reduced. If the height h is too large, there is a concern that the distance between the opposing plate 41 and the electronic module 10 will be too large, which will reduce heat dissipation.

[0033] 3, the protrusions 42 have a fin shape that is elongated in the X direction when viewed from the erection direction (i.e., the Z direction). The width w of the protrusions 42 in the Y direction at the base can be, for example, 0.05 to 10 mm, more preferably 0.1 to 5 mm. If the width w is too small, it may be difficult to form the protrusions 42 or to ensure the strength of the protrusions 42. If the width w is too large, it may be difficult to secure a sufficient contact area between the heat dissipation gel 5 and the housing 4, which may result in a decrease in heat dissipation performance.

[0034] The housing 4 has a plurality of protrusions 42, and the interval c between adjacent protrusions 42 in the Y direction can be, for example, 0.9 to 5 mm. If the interval c is too small, there is a concern that it will be difficult to process the protrusions 42. If the interval c is too large, there is a concern that it will be difficult to secure a sufficient contact area between the heat dissipation gel 5 and the housing 4, which may result in a decrease in heat dissipation performance.

[0035] The thickness t of the opposing plate portion 41 in the Z direction can be set to, for example, 0.2 to 10 mm. If the thickness t is too small, it may be difficult to process the opposing plate portion 41. If the thickness t is too large, it may be difficult to orient the filler 41f.

[0036] In this embodiment, the opposing plate portion 41 and the plurality of protrusions 42 are integrally formed. An example of a method for molding the portion of the housing 4 that includes the opposing plate portion 41 and the plurality of protrusions 42 will be described below with reference to Figures 5 to 7. In Figures 5 to 7, arrows F indicate the flow of molten resin.

[0037] Molten resin mixed with a large number of fillers is injected into a mold shown in Figures 5 and 6 for injection molding. The mold cavity 40 has a plate-shaped space 410 for molding the opposing plate portion 41 and a plurality of protruding spaces 420 for molding the protruding portions 42. The protruding spaces 420 are formed long in the X direction.

[0038] The plate-shaped space 410 has a substantially rectangular outer shape, and the film gate 401 is connected to one side of the rectangular outer shape (specifically, one side on one end side in the Y direction). As shown in FIG. 5, the thickness of the film gate 401 in the Z direction is smaller than that of the plate-shaped space 410. As shown in FIG. 6, the film gate 401 has a shape such that the width in the X direction decreases as it moves away from the plate-shaped space 410 in the Y direction. The end of the film gate 401 opposite the plate-shaped space 410 is connected to the resin supply path 402.

[0039] When molding a portion of the housing 4 that includes the opposing plate portion 41 and the multiple protrusions 42, first, molten resin containing a filler is injected into the cavity 40 from the resin supply path 402. The molten resin then passes through the film gate 401 and is introduced into the plate-shaped space 410. The film gate 401 has a shape that is thin in the Z direction and gradually widens in width in the X direction. Therefore, the molten resin is introduced into the plate-shaped space 410 through the film gate 401 while spreading across the entire width of the plate-shaped space 410 in the X direction. The resin introduced into the plate-shaped space 410 from the portion spanning the entire width in the X direction flows through the plate-shaped space 410 along the Y direction, filling it. Then, a portion of the resin flowing through the plate-shaped space 410 toward the opposite side of the film gate 401 is also introduced into the protrusion space 420, as shown in FIG. 7 . The flow vector of the resin introduced into the protrusion space 420 is oriented in the Z direction.

[0040] In this manner, the molten resin flows through the cavity 40 and fills the cavity 40. A large number of fillers in the molten resin are oriented along the flow direction. In this manner, the fillers are oriented generally along the Y direction in the plate-shaped space 410, and the fillers are oriented generally along the Z direction in the protruding space 420. By solidifying the molten resin in this state, a portion of the housing 4 including the opposing plate portion 41 and the plurality of protrusions 42 can be molded. The portion including the opposing plate portion 41 and the plurality of protrusions 42 molded as described above can be joined to, for example, another component separately manufactured to form the housing 4.

[0041] Next, the effects of this embodiment will be described. In the electronic device 1, the opposing plate portion 41 and the protrusion portion 42 each have the anisotropy of thermal conductivity as described above, which can improve heat dissipation from the electronic module 10 through the heat dissipation gel 5 and the housing 4.

[0042] That is, the thermal conductivity of the protrusion 42 in the protruding direction is greater than the thermal conductivity in any direction perpendicular to the protruding direction. Therefore, heat transferred from the heat-dissipating gel 5 to the protrusion 42 is easily transferred to the opposing plate 41 along the protruding direction Z, as shown in FIG. 4 . The thermal conductivity of the opposing plate 41 in one direction along its expansion direction is greater than the thermal conductivity in its thickness direction. This allows heat transferred to the opposing plate 41 to easily diffuse along the expansion direction of the opposing plate 41. As a result, heat from the electronic module 10 is easily dissipated to the outside via the heat-dissipating gel 5 and the housing 4. Therefore, an electronic device 1 having a resin housing 4 can achieve excellent heat dissipation (see Experimental Example 1, described later). Note that the arrow H in FIG. 4 indicates the direction of heat transfer.

[0043] Furthermore, the thermal conductivity of the opposing plate portion 41 is greater in the Y direction than in the X direction. In this case, in order to orient the filler 41f in the opposing plate portion 41 along the Y direction, it is conceivable that during molding, the flow of resin in the plate-shaped space 410 is oriented along the Y direction, as shown in FIGS. 6 and 7. In this way, as shown in FIG. 7, the flow of resin flowing into the protruding space 420 tends to be oriented in the Z direction. As a result, the orientation direction of the filler 42f in the protrusion portion 42 tends to be oriented in the Z direction, and as a result, the thermal conductivity of the protrusion portion 42 in the Z direction tends to be large.

[0044] As described above, according to this embodiment, it is possible to provide an electronic device having a resin housing with excellent heat dissipation properties.

[0045] (Experimental Example 1) This example is an example in which the relationship between λ1b / λ1a and λ2b / λ2a and heat dissipation properties in the electronic device 1 shown in the first embodiment is investigated. In this example, this relationship was analyzed by simulation using Ansys (registered trademark), a thermal analysis simulation software from Ansys, Inc.

[0046] The analysis conditions were as follows: the configuration of the electronic device 1 was the basic configuration shown in the first embodiment, and the dimensions of the protrusion 42 (see FIG. 2) were as follows: h = 15 mm, w = 2.1 mm, c = 0.9 mm. The thickness t of the upper opposing plate 41 was 2 mm, and the thickness t of the lower opposing plate 41 was 2.5 mm.

[0047] Various changes were assumed for the ratios of the thermal conductivities λ1b / λ1a and λ2b / λ2a of the opposing plate portion 41 and the protrusion portion 42 of the housing 4. The changes in λ1b / λ1a and λ2b / λ2a were made under the assumption that the average values ​​of λ1b and λ1a, and the average values ​​of λ2b and λ2a were kept constant. The thermal conductivity of the heat dissipation gel 5 was set to 3 W / m K. It was also assumed that the outside of the housing 4 was in contact with the air at room temperature.

[0048] Then, the temperature of the electronic component 2 of each sample was analyzed when a predetermined power (4 W) was continuously supplied to the electronic component 2. That is, when a predetermined amount of time has passed after continuously supplying a predetermined power to the electronic component 2, a balance is achieved between heat generation and heat dissipation, and an equilibrium state is reached. The temperature of the electronic component 2 in this equilibrium state was analyzed. The temperature is the temperature at the position of the electronic component 2 where the temperature is highest. The analysis results are shown in Table 1.

[0049] [Table 1]

[0050] In Table 1 above, for samples where λ1b / λ1a = λ2b / λ2a = 1, there is no anisotropy in thermal conductivity in the opposing plate portion 41 and the protrusion portion 42, and the temperature at this point (i.e., 114°C) is used as the reference temperature. Hereinafter, this temperature will be referred to as the reference temperature where appropriate. As can be seen from the table, for samples that satisfy λ1b / λ1a ≦ 0.5 and λ2b / λ2a ≦ 0.5, the temperature is 10°C or more lower than the reference temperature. Furthermore, for samples that satisfy λ1b / λ1a ≦ 0.25 and λ2b / λ2a ≦ 0.25, the temperature is 16°C or more lower than the reference temperature. As such, it can be confirmed that the heat dissipation performance of the electronic component 2 can be improved by appropriately providing anisotropy in thermal conductivity in the opposing plate portion 41 and the protrusion portion 42.

[0051] In the above embodiment, the configuration in which the opposing plate portion 41, the multiple protrusions 42, and the heat dissipating gel 5 are arranged on both sides of the electronic module 10 in the Z direction has been shown, but the configuration in which the opposing plate portion 41, the multiple protrusions 42, and the heat dissipating gel 5 are arranged on one side of the electronic module 10 in the Z direction is also possible. That is, for example, the configuration in which the opposing plate portion 41, the multiple protrusions 42, and the heat dissipating gel 5 are arranged only on the side facing the electronic component 2, or the configuration in which the opposing plate portion 41, the multiple protrusions 42, and the heat dissipating gel 5 are arranged only on the side facing the circuit board 3 is also possible.

[0052] The present invention is not limited to the above-described embodiments, and can be applied to various embodiments within the scope of the present invention. [Explanation of symbols]

[0053] 1...electronic device, 10...electronic module, 2...electronic component, 3...circuit board, 4...casing, 41...opposing plate portion, 42...protrusion portion, 5...heat dissipation gel

Claims

1. An electronic device (1) having an electronic module (10) equipped with heat-generating electronic components, a resin housing (4) that houses the electronic module, and a heat-dissipating gel (5) interposed between the electronic module and a part of the housing, The housing has a facing plate portion (41) that faces the electronic module via the heat dissipation gel and that is along a plane perpendicular to the facing direction of the electronic module; a plurality of protrusions (42) protruding from the opposing plate portion toward the electronic module and in contact with the heat dissipation gel; the opposing plate portion and the protrusion portion each have anisotropy in thermal conductivity, the opposing plate portion has a thermal conductivity in one direction along the expansion direction that is greater than the thermal conductivity in the thickness direction; The protrusion has a thermal conductivity in a protruding direction that is greater than the thermal conductivity in any direction perpendicular to the protruding direction.

2. In the opposing plate portion, the thermal conductivity in one direction along the spreading direction where the thermal conductivity is maximum is λ1a, the thermal conductivity in the thickness direction is λ1b, When the thermal conductivity of the protrusion in the protruding direction is λ2a and the thermal conductivity in the direction perpendicular to the protruding direction where the thermal conductivity is maximum is λ2b, λ1b / λ1a≦0.5 and λ2b / λ2a≦0.5, The electronic device according to claim 1 , wherein

3. 3. The electronic device described in claim 1 or 2, wherein the protrusion portion has a fin shape that is elongated when viewed from the thickness direction of the opposing plate portion, and the opposing plate portion has a thermal conductivity in a direction perpendicular to the longitudinal direction of the protrusion portion when viewed from the thickness direction that is greater than the thermal conductivity along the longitudinal direction of the protrusion portion.

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