JP3988764B2 - Printed wiring board substrate, printed wiring board, and printed wiring board substrate manufacturing method - Google Patents

Description

  The present invention relates to a printed wiring board substrate, a printed wiring board, and a printed wiring board manufacturing method, and more particularly to a printed wiring board substrate having excellent heat dissipation characteristics.

  A metal such as aluminum has been mainly used for a base material in a conventional printed wiring board for heat dissipation. On the other hand, a substrate for a high heat dissipation printed wiring board using a carbon fiber metal, a carbon fiber sheet, or the like having a higher thermal conductivity than a metal such as aluminum has been proposed for weight reduction and thickness reduction. Here, the carbon fiber metal, the carbon fiber sheet, and the like have anisotropy in the heat conduction direction and have a feature that heat is easily conducted only in the fiber direction. For this reason, the substrate for the high heat dissipation printed wiring board is excellent in that a plurality of carbon fiber metals or carbon fiber sheets are superposed so that the heat conduction directions are orthogonal to each other, and the heat conduction direction has a two-dimensional spread. The heat dissipation characteristic was acquired (for example, refer patent document 1).

Japanese Patent Laid-Open No. 11-40902 (second page, FIG. 1)

  In a printed wiring board substrate using carbon fiber metal or carbon fiber sheet having anisotropy in the heat conduction direction, heat is conducted only in the fiber direction. For this reason, in the printed wiring board using this, the heat generated from the electronic component is conducted only in a specific direction and is not diffused throughout the board, so that the heat dissipation performance is degraded. In addition, even when a plurality of carbon fiber metals or carbon fiber sheets are overlapped so that the fiber directions are orthogonal to each other, the heat conductivity is low between the upper and lower carbon fiber metals or carbon fiber sheets, so that the heat dissipation performance is reduced. was there.

  This invention was made in order to solve the above problems, and in a printed wiring board substrate using carbon fiber metal or carbon fiber sheet, the heat conduction direction has a two-dimensional spread. An object of the present invention is to obtain a printed wiring board that achieves high heat dissipation performance and can be reduced in weight and thickness.

  The substrate for a printed wiring board according to the present invention includes a first substrate having anisotropy in a heat conduction direction, and the first substrate so as to have a heat conduction direction different from that of the first substrate. A second base material having anisotropy in the heat conduction direction, a heat conduction hole communicating the first base material and the second base material, and an inner wall of the heat conduction hole. And a heat conductive layer.

  According to the present invention, in a printed wiring board substrate using a carbon fiber metal, a carbon fiber sheet, or the like, the heat conduction holes for heat diffusion are superposed so that the heat conduction directions of the carbon fiber metal and the carbon fiber sheet are different. Since the heat conduction layer is provided in the inside of the heat conduction hole, heat conduction is generated between the superimposed carbon fiber metal and the carbon fiber sheet, and the heat generated from the electronic component can be diffused to the entire base material.

Hereinafter, the present invention will be specifically described with reference to the drawings showing embodiments thereof. In the first embodiment, a printed wiring board using the printed wiring board substrate according to the present invention will be described as an example.
Embodiment 1 FIG.
FIG. 1 is a cross-sectional view of a printed wiring board 1 according to Embodiment 1, and a printed wiring board substrate 2 according to the present invention includes a first carbon fiber sheet 3 as a first substrate, The second carbon fiber sheet 4 as a base material is overlapped and configured. The printed wiring board substrate 2 is provided with a heat diffusion hole 5 that is a heat conduction hole, and an inner wall of the heat diffusion hole 5 is provided with a first metal plating 6 that is a heat conduction layer. The inside of the heat diffusion hole 5 surrounded by the first metal plating 6 is filled with a heat conductive resin 7. Further, a second metal plating 61 is formed on the surface of the printed wiring board substrate 2, and the printed wiring board substrate 2 is sandwiched between the second metal plating 61 and the insulating resin 8, thereby A plate 1 is constructed. On the other hand, the printed wiring board 1 is provided with through holes 9 penetrating the front and back, pads 10, and thermal vias 11 reaching from the surface of the printed wiring board 1 to the second metal plating 61, and prints heat generated by the electronic component 12. Conducted to the wiring board substrate 2. A wiring pattern 13 is provided on the back surface.

  Next, a method for manufacturing the printed wiring board 1 will be described. FIG. 2 is a cross-sectional view showing a manufacturing process of the printed wiring board 1 according to the first embodiment. First, as shown in FIG. 2 (a), the first carbon fiber sheet 3 and the second carbon fiber sheet 4 are arranged so that their fiber directions are orthogonal to each other, and adhesion of a prepreg or the like (not shown) is performed. Adhere with the material. FIG. 3 is a perspective view showing a state in which the first carbon fiber sheet 3 and the second carbon fiber sheet 4 are overlapped. In FIG. 3, if fibers are present in the solid line direction of the first carbon fiber sheet 3 and the second carbon fiber sheet 4, they are superposed so that the respective fiber directions are orthogonal to each other. The reason for superimposing them orthogonally is that the first and second carbon fiber sheets 3 and 4 have a characteristic that heat is easily conducted only in the fiber direction. The first carbon fiber sheet 3 and the second carbon fiber sheet 4 used in the first embodiment are, for example, SZ500 manufactured by Advanced Materials, Dialead (registered trademark) manufactured by Mitsubishi Chemical Corporation, and the like. The one having a thermal conductivity in the fiber direction of 450 to 600 W / mK and a specific gravity of 2 to 2.2 is used.

  Next, as shown in FIG. 2B, through holes 9a and heat diffusion holes 5 are provided in the first carbon fiber sheet 3 and the second carbon fiber sheet 4 that are overlapped by drilling or the like. At this time, a plurality of heat diffusion holes 5 are provided uniformly over the entire first carbon fiber sheet 3 and second carbon fiber sheet 4 that are overlapped. FIG. 4 is a top view of the printed wiring board substrate 2 in the first embodiment, and is a diagram showing a state in which the heat diffusion holes 5 are provided. As shown in FIG. 4, the heat diffusion holes 5 are provided uniformly over the entire surface of the printed wiring board substrate 2. Further, the hole diameter of the heat diffusion hole 5 may be any value. However, considering that the first metal plating 6 is applied inside or the heat conductive resin 7 is filled, the hole diameter is approximately 0. A value of about 2 mm to 1.0 mm is desirable. On the other hand, the through-hole 9a may be provided anywhere as long as it does not overlap with the heat diffusion hole 5, but the number, size, and the like vary depending on the type and use of the printed board 1 to be created.

  Next, as shown in FIG. 2C, a first metal plating 6 is applied to the through hole 9a, the inner walls of the heat diffusion hole 5, and the surfaces of the carbon fiber sheets 3 and 4. Further, as shown in FIG. 2D, the heat conductive resin 7 is filled in the heat diffusion hole 5 provided with the first metal plating 6 by a technique such as screen printing. Then, as shown in FIG. 2 (e), a second metal plating 61 is applied to the surfaces of the first and second carbon fiber sheets 3 and 4 and the inner wall of the through-hole 9a. In FIG. 2C and FIG. 2E, the metal to be plated is one having excellent thermal conductivity such as copper.

  Next, as shown in FIG. 2 (f), the printed wiring board substrate 2 is sandwiched between the front and back surfaces by the insulating resin 8, and the copper foil 14 is overlapped on the front and back surfaces of the insulating resin 8 and heat-pressed. At this time, the insulating resin 8 is formed not only on the front and back surfaces of the carbon fiber sheets 3 and 4 but also in the through hole 9a. Next, as shown in FIG. 2G, a hole 9b for forming a through hole 9 for conducting the front and back and a hole 11a for forming a thermal via 11 are provided by drilling or laser processing. Here, the hole 9b is pierced so as to penetrate the base material, while the hole 11a is pierced from the copper foil 14 on the surface until reaching the second metal plating 61. Next, as shown in FIG. 2 (h), a third metal plating 62 is applied to the inner walls of the holes 9b and 11a and the copper foil 14 on the front and back surfaces. Finally, as shown in FIG. 2I, the third metal plating 62 and the copper foil 14 are etched to form the pad 10, the wiring pattern 13, the thermal via 11, and the through hole 9.

  Next, heat conduction in the printed wiring board 1 will be described with reference to the drawings. In FIG. 1, heat generated from the electronic component 12 is transmitted to the printed wiring board substrate 2 on which the second metal plating 61 is applied via the thermal via 11 or the pad 10 and the insulating resin 8, and the printed wiring board. Is diffused throughout the entire substrate 2. FIG. 5A is a cross-sectional side view showing a state of heat conduction by enlarging a part of the printed wiring board 1, and corresponds to the AA cross section of FIG. On the other hand, FIG. 5B is a cross-sectional plan view showing a state of heat conduction by enlarging a part of the printed wiring board 1, and corresponds to the BB cross section of FIG.

  As shown in (a) of FIG. 5, the heat generated from the electronic component 12 is conducted to the first carbon fiber sheet 3 through the thermal via 11 as indicated by the solid line arrow 51, for example. And in the 1st carbon fiber sheet 3, it conducts to a horizontal direction like the arrows 52 and 55 in FIG.5 (b). Therefore, the heat conducted in the direction of the arrow 52 reaches the heat diffusion hole 5 a which is one of the heat diffusion holes 5. The first metal plating 6 is applied to the inner wall of the heat diffusion hole 5a, and the inside of the heat diffusion hole 5a is filled with the heat conductive resin 7, but the first metal plating 6 and the heat conductive resin 7 are filled. Unlike the first carbon fiber sheet 3, there is no anisotropy in the heat conduction direction. Accordingly, the conducted heat is conducted to the second carbon fiber sheet 4 on the lower side of the first carbon fiber sheet 3 by the first metal plating 6 and the heat conductive resin 7.

  The heat conducted to the second carbon fiber sheet 4 has a broken arrow 53 in FIG. 5B because the fiber direction of the second carbon fiber sheet 4 is orthogonal to the fiber direction of the first carbon fiber sheet 3. As described above, conduction occurs in the vertical direction perpendicular to the arrow 52. Then, when the heat diffusion hole 5b, which is one of the other heat diffusion holes 5, is reached, the first metal plating 6 and the heat conductive resin 7 provided inside the heat diffusion hole 5b are used again. Conducted to the first carbon fiber sheet 3. Further, the first carbon fiber sheet 3 conducts again in the lateral direction as indicated by a solid arrow 54. In this way, the heat conducted through the printed wiring board substrate 2 conducts between the upper and lower carbon fiber sheets 3 and 4 in the heat diffusion hole 5, thereby spreading in a two-dimensional manner. It diffuses throughout the base material 2 for use.

  The thermal conductivity in the fiber direction of the carbon fiber sheets 3 and 4 used in the first embodiment is 450 to 600 W / mK, for example, when the above-described one is used, such as 230 W / mK for aluminum, 390 W / mK for copper, Better than. On the other hand, the thermal conductivity in the direction perpendicular to the fibers is as low as 40 W / mK, for example, by SZ500 manufactured by Advanced Materials.

  As described above, in Embodiment 1, the heat diffusion holes 5 are provided in the carbon fiber sheets 3 and 4, and the first metal plating is applied to the inner wall of the heat diffusion holes 5 and the front and back surfaces of the carbon fiber sheets 3 and 4. 6, heat conduction between the upper and lower carbon fiber sheets 3 and 4 is promoted, and heat is diffused throughout the printed wiring board substrate 2. Further, in the first embodiment, since the heat conductive resin 7 is filled in the inside of the heat diffusion hole 5 and the second metal plating 61 is applied, the laser can be placed at an arbitrary position on the printed wiring board 1. It becomes possible to provide the thermal via 11 by processing, and heat dissipation can be improved without any restriction on the component arrangement of the electronic component 12.

  In Embodiment 1, since the heat conductive resin 7 is filled in the heat diffusion hole 5, the heat conduction between the first carbon fiber sheet 3 and the second carbon fiber sheet 4 is performed. Can be promoted more. In the first embodiment, since the heat diffusion holes 5 are evenly provided on the entire surfaces of the first base material and the second base material, the heat is printed regardless of the place where the electronic component 12 is mounted. It can be diffused into the wiring board substrate 2. Further, in the first embodiment, the first carbon fiber sheet 3 and the second carbon fiber sheet 4 are overlapped so that the fiber directions are orthogonal to each other, so that the heat generated by the electronic component 12 can be efficiently generated. It can diffuse to the whole substrate 2 for use.

  In Embodiment 1 described above, the carbon fiber sheet is used as the first and second base materials. However, the carbon fiber sheet is not necessarily used. For example, a carbon fiber metal may be used instead of the carbon fiber sheet. Further, the material is not limited to the carbon fiber sheet or the carbon fiber metal, and any material may be used as long as it is made of a material having anisotropy in the heat conduction direction.

  In the first embodiment, the heat diffusion holes 5 have been described as being arranged in a grid pattern on the printed wiring board substrate 2, but this need not necessarily be a grid pattern. For example, an oblique grid shape as shown in FIG. 6A or a concentric circle shape as shown in FIG.

  In the first embodiment, the shape of the heat diffusion hole 5 is described as being circular. However, the heat diffusion hole 5 is not necessarily a circular hole. Any shape may be used as long as heat is conducted, and it may be oval or square.

  In the first embodiment, the heat diffusion holes 5 are described as being uniformly provided in the printed wiring board substrate 2, but this need not necessarily be uniform. For example, a large number of heat diffusion holes 5 may be provided under a component that generates a large amount of heat, and the heat diffusion of the component may be promoted.

Embodiment 2. FIG.
In the first embodiment, the case where the heat conductive resin 7 is filled in the heat diffusion hole 5 and the second metal plating 61 is applied on the heat conductive resin 7 has been described. However, the heat conductive resin is not necessarily provided. 7 need not be filled. In this case, the process of filling the heat conductive resin 7 and the process of applying the second metal plating 61 are not required, and the manufacture becomes easy, and the manufacturing cost of the printed wiring board 1 can be reduced.

  FIG. 7 is a cross-sectional view showing the printed wiring board 1 according to the second embodiment. Compared with FIG. 1 according to the first embodiment, FIG. 7 does not fill the heat diffusion hole 5 with the heat conductive resin 7. The point which is filled with the insulating resin 8 is different. In FIG. 7, the same or corresponding parts as in FIG. In the second embodiment, the heat generated in the electronic component 12 is conducted to the first carbon fiber sheet 3 through the first metal plating 6 by the thermal via 11. Next, the heat conducted to the first carbon fiber sheet 3 is lowered by the first metal plating 6 applied to the inner wall of the heat diffusion hole 5 formed in the printed wiring board substrate 2. Conducted to the second carbon fiber sheet 4. Since the subsequent heat conduction is the same as that of the first embodiment, the description thereof is omitted.

  Next, the manufacturing method of the printed wiring board 1 in Embodiment 2 is demonstrated. FIG. 8 is a cross-sectional view showing the manufacturing process of the printed wiring board 1 in the second embodiment, and corresponds to FIG. 2 in the first embodiment. Since Embodiment 2 does not fill the inside of the thermal diffusion hole 5 with the heat conductive resin 7, in FIG. 8, the step of filling the heat conductive resin 7 shown in FIG. The difference is that the step of applying the second metal plating 61 shown in e) can be omitted.

  First, as shown to (a) of FIG. 8, the 1st carbon fiber sheet 3 and the 2nd carbon fiber sheet 4 are arrange | positioned so that each fiber direction may orthogonally cross, and it adhere | attaches with adhesives, such as a prepreg. Next, as shown in FIG. 8B, through holes 9a and heat diffusion holes 5 are provided in the overlapped first carbon fiber sheet 3 and second carbon fiber sheet 4 by drilling or the like. Similar to the first embodiment, a plurality of heat diffusion holes 5 are provided uniformly over the entire carbon fiber sheet. And as shown in FIG.8 (c), the 1st metal plating 6 is given to the inner surface of the through-hole 9a and the hole 5 for thermal diffusion, and the surface of the carbon fiber sheets 3 and 4. As shown in FIG.

  Next, in Embodiment 2, the steps shown in (d) and (e) of FIG. 2 are omitted as described above, and the printed wiring board substrate 2 is viewed from the front and back as shown in (d) of FIG. It is sandwiched between the insulating resins 8, and the copper foil 14 is overlapped on the front and back surfaces of the insulating resin 8 and heat-pressed. For this reason, in the second embodiment, the insulating resin 8 is formed not only in the through hole 9a but also in the heat diffusion hole 5. Next, as shown in FIG. 8E, a hole 9b for forming the through hole 9 and a hole 11a for forming the thermal via 11 are provided by drilling or laser processing. Next, as shown in FIG. 8F, a third metal plating 62 is applied to the inner walls of the holes 9b and 11a and the copper foils 14 on the front and back surfaces. Finally, as shown in FIG. 8G, the third metal plating 62 and the copper foil 14 are etched to form the pad 10, the wiring pattern 13, the thermal via 11, and the through hole 9.

  As described above, in the second embodiment, the first metal plating 6 applied to the inner wall of the heat diffusion hole 5 is interposed between the first and second carbon fiber sheets instead of the heat conductive resin 7. It plays a role in conducting heat. In the second embodiment, it is not necessary to fill the inside of the heat diffusion hole 5 with the heat conductive resin 7 and to apply the second metal plating 61. Therefore, the step of filling the heat conductive resin 7 and the second step The step of applying the metal plating 61 can be omitted, the manufacture is facilitated, and the manufacturing cost of the printed wiring board 1 can be reduced.

Embodiment 3 FIG.
In the first embodiment, the first carbon fiber sheet 3 and the second carbon fiber sheet 4 are used as constituents of the printed wiring board substrate 2 and are stacked so that their fiber directions are orthogonal to each other. Although described as being combined, it is not always necessary to overlap two carbon fiber sheets. That is, the number of carbon fiber sheets may be one, and in this case, the printed wiring board 1 can be reduced in thickness and weight.

  FIG. 9 is a cross-sectional view showing printed wiring board 1 according to the third embodiment. Compared with FIG. 1 according to the first embodiment, FIG. 9 shows only the first carbon fiber sheet 3 without overlapping two carbon fiber sheets. The only difference is that they are only used. In FIG. 9, the same or corresponding parts as in FIG. Also in the third embodiment, the heat generated by the electronic component 12 is conducted to the first carbon fiber sheet 3 through the second metal plating 61 by the thermal via 11. In the third embodiment, since only one first carbon fiber sheet 3 is used, heat is conducted only in the fiber direction of the first carbon fiber sheet 3 in the printed wiring board substrate 2.

  In the third embodiment, the heat conduction in the direction orthogonal to the first carbon fiber sheet 3 is performed by the first metal plating 6 and the second metal plating 61. That is, the first metal plating 6, the second metal plating 61, and the first carbon fiber sheet 3 realize thermal diffusion having a spread in a two-dimensional direction. In the case of the third embodiment, the necessary heat dissipation characteristics can be obtained by changing the thicknesses of the first metal plating 6 and the second metal plating 61.

  As described above, in the third embodiment, instead of the second carbon fiber sheet 4, the first metal plating 6 and the second metal plating 61 are heated in a direction orthogonal to the first carbon fiber sheet 3. It plays a role of conducting. In Embodiment 3, since only one carbon fiber sheet is required, the printed wiring board 1 can be made thinner and lighter.

Embodiment 4 FIG.
In the first to third embodiments, it has been described that the heat is spread in the two-dimensional direction in the printed wiring board substrate 2, but the printed wiring board 1 is further spread from the printed wiring board substrate 2. It is also possible to dissipate heat to the housing on which is mounted.

  10 is a cross-sectional view showing the printed wiring board 1 according to the fourth embodiment. Compared with FIG. 1 according to the first embodiment, FIG. 10 shows a plurality of thermal vias 11b provided on the printed wiring board 1 and the printed wiring board. 1 is different in that it is in contact with the housing 15 on which 1 is mounted. In FIG. 10, the same or corresponding parts as in FIG. Also in the fourth embodiment, the heat generated by the electronic component 12 is transmitted to the printed wiring board substrate 2 through the second metal plating 61 by the thermal via 11 and spreads and diffuses in the two-dimensional direction. In the fourth embodiment, the inside of the thermal diffusion hole 5 is filled with the thermal conductive resin 7, the second metal plating 61 is applied on the thermal conductive resin 7, and the thermal via 11b is further provided thereon. Thus, the housing 15 is in contact. With such a configuration, the heat diffused by the printed wiring board substrate 2 is conducted to the casing 15 through the thermal via 11b and radiated.

  As described above, in the fourth embodiment, the heat generated by the electronic component 12 is diffused by the printed wiring board substrate 2 and radiated to the housing 15 by the thermal via 11b. In the fourth embodiment, since the thermal via 11b can be arranged at an arbitrary position in accordance with the shape of the portion in contact with the casing 15, the heat of the printed wiring board 1 can be obtained without removing the insulating resin 7 by machining or the like. Can be radiated to the housing 15.

  In the fourth embodiment, the thermal via 11b radiates heat to the housing 15. However, this is not necessarily the thermal via 11b, and may be a heat radiating through hole. FIG. 11 is a cross-sectional view showing the printed wiring board 1 when the through-hole 16 for heat dissipation is provided in place of the thermal via 11b that contacts the housing 15 in the fourth embodiment. As shown in FIG. 11, in a portion in contact with the casing 15, a through-hole 16 for heat dissipation that does not provide the through-hole portion hole 9 a is formed in the printed wiring board substrate 2, and the printed wiring board substrate 2 The heat dissipation through-hole 16 is brought into contact. Thereby, the heat conducted by the printed wiring board substrate 2 can be radiated to the housing 15 through the heat radiating through hole 16.

  As described above, with the configuration shown in FIG. 11, even in the printed wiring board 1 not provided with the thermal via 11b, the heat of the printed wiring board 1 is removed without removing the insulating resin 7 by machining or the like. Heat can be radiated to the housing 15 with a small thermal resistance.

It is sectional drawing of the printed wiring board used for Embodiment 1 of this invention. It is a figure explaining the manufacturing method of the printed wiring board in Embodiment 1 of this invention. It is a perspective view which shows a mode that the 1st carbon fiber sheet and 2nd carbon fiber sheet in Embodiment 1 of this invention are piled up. It is a figure which shows a mode that the hole for thermal diffusion used for Embodiment 1 of this invention is provided. It is a figure explaining a mode that heat | fever conducts the printed wiring board in Embodiment 1 of this invention. It is a top view of the base material for printed wiring boards used for Embodiment 1 of this invention. It is sectional drawing of the printed wiring board used for Embodiment 2 of this invention. It is a figure explaining the manufacturing method of the printed wiring board in Embodiment 2 of this invention. It is sectional drawing of the printed wiring board used for Embodiment 3 of this invention. It is sectional drawing of the printed wiring board used for Embodiment 4 of this invention. It is sectional drawing of the printed wiring board used for Embodiment 4 of this invention.

Explanation of symbols

DESCRIPTION OF SYMBOLS 1 Printed wiring board 2 Base material 3 for printed wiring boards The 1st carbon fiber sheet 4 which is a 1st base material The 2nd carbon fiber sheet 5 which is a 2nd base material The hole 6 for thermal diffusion which is a heat conduction hole 1st metal plating which is a heat conductive layer 7 heat conductive resin 8 insulating resin

Claims (8)

  A first base material having anisotropy in the heat conduction direction and an anisotropy in the heat conduction direction superimposed on the first base material so as to have a different heat conduction direction from the first base material A heat conductive hole communicating with the first base material and the second base material, and a heat conductive layer provided on an inner wall of the heat conductive hole. Base material for printed wiring boards.   The printed wiring board substrate according to claim 1, wherein a heat conductive resin is provided inside the heat conductive hole surrounded by the heat conductive layer.   2. The printed wiring board substrate according to claim 1, wherein the first or second substrate having anisotropy in a heat conduction direction is a carbon fiber metal or a carbon fiber sheet, respectively.   The printed wiring board substrate according to claim 1, wherein the heat conduction holes are provided uniformly over the entire surfaces of the first substrate and the second substrate.   2. The printed wiring board substrate according to claim 1, wherein the first substrate and the second substrate are overlapped so that their heat conduction directions are orthogonal to each other.   A printed wiring board comprising the printed wiring board substrate according to claim 1 and an insulating resin sandwiching the printed wiring board substrate.   A second base material having anisotropy in the heat conduction direction is superimposed on the first base material having anisotropy in the heat conduction direction so that the heat conduction direction is different from that of the first base material. And a step of drilling a heat conduction hole communicating with the first base material and the second base material, and a step of providing a heat conduction layer on the inner wall of the drilled heat conduction hole. A method for producing a printed wiring board substrate.   The step of superimposing the second base material having anisotropy in the heat conduction direction on the first base material having anisotropy in the heat conduction direction so that the heat conduction direction is orthogonal to the first base material. A step of drilling a heat conduction hole communicating with the first base material and the second base material, a step of providing a heat conduction layer on the inner wall of the drilled heat conduction hole, and the heat conduction layer And a step of providing a heat conductive resin inside the heat conductive hole.

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