Manufacturing method of heat-dissipating circuit board structure and embedded circuit board

Abstract

This invention discloses a method for manufacturing a heat-dissipating circuit board structure and an embedded circuit board. The method for manufacturing the heat-dissipating circuit board structure includes: forming a through-hole in a circuit board, the circuit board including a substrate and a metal layer formed on the substrate; forming a receiving groove recessed from the surface of the substrate away from the metal layer to the metal layer; widening the through-hole at its center to form a deformation opening, such that a portion of the metal layer has a plurality of edge portions spaced apart from each other around the deformation opening; and inserting a heat-conducting block from the deformation opening toward the receiving groove, such that the plurality of edge portions are bent and located between the heat-conducting block and the inner wall surface of the receiving groove.

Description

TECHNICAL FIELD

[0001] The present application relates to a circuit board, in particular to a manufacturing method of a heat dissipation circuit board structure and an embedded circuit board. BACKGROUND

[0002] The existing circuit board is by digging a size corresponding to a heat conduction block of a slot hole, and then embedding the heat conduction block in the slot hole of the existing circuit board. However, the embedding method of the heat conduction block of the existing circuit board has been used for a long time, and the problems caused thereby (such as difficult rework, high processing precision requirement) have existed and are difficult to be effectively improved.

[0003] Therefore, the applicant believes that the above defects can be improved, and finally proposes the present application by means of scientific principles. SUMMARY

[0004] The present application aims to provide a manufacturing method of a heat dissipation circuit board structure and an embedded circuit board, which can effectively improve the defects that may be caused by the existing circuit board.

[0005] The embodiment of the present application discloses a manufacturing method of a heat dissipation circuit board structure, which comprises: a patterning step: forming a cross-shaped through hole in a predetermined area of a circuit board; wherein the circuit board comprises a board material and a metal layer formed on the board material, and the cross-shaped through hole penetrates the metal layer and the board material; a slot digging step: recessing a receiving slot from the surface of the board material away from the metal layer to the metal layer in the predetermined area of the circuit board, so that the cross-shaped through hole is only located in the metal layer and is connected to the receiving slot; a hole opening step: widening the center of the cross-shaped through hole of the metal layer to form a deformation port, so that the metal layer part in the predetermined area is formed with multiple edge parts arranged around the deformation port and spaced from each other; and a burying step: inserting a heat conduction block from the deformation port towards the receiving slot, so that multiple edge parts are bent between the heat conduction block and the inner wall surface of the receiving slot.

[0006] This invention also discloses a method for manufacturing a heat-dissipating circuit board structure, comprising: a patterning step: forming a through-hole in a predetermined area of ​​a circuit board; wherein the circuit board includes a substrate and a metal layer formed on the substrate, and the through-hole penetrates the metal layer and the substrate; an opening step: widening the center of the through-hole in the metal layer to form a deformation opening, so that the metal layer portion located in the predetermined area has a plurality of edge portions arranged around the deformation opening and spaced apart from each other; a groove step: forming a receiving groove in the predetermined area of ​​the circuit board from the surface of the substrate away from the metal layer to the metal layer, so that the deformation opening communicates with the receiving groove, and the plurality of edge portions are located at the bottom of the receiving groove; and an embedding step: inserting a heat-conducting block from the deformation opening toward the receiving groove, so that the plurality of edge portions are bent and located between the heat-conducting block and the inner wall surface of the receiving groove.

[0007] This invention also discloses a method for manufacturing a heat-dissipating circuit board structure, comprising: a groove-cutting step: providing a circuit board comprising a substrate and a metal layer formed on the substrate, and in a predetermined area of ​​the circuit board, a receiving groove is recessed from the surface of the substrate away from the metal layer and extending to the metal layer; a hole-opening step: forming a deformation opening in the metal layer, so that the portion of the metal layer located in the predetermined area forms an annular portion surrounding the deformation opening; a patterning step: patterning the annular portion to form a plurality of edge portions spaced apart from each other; and an embedding step: inserting a heat-conducting block from the deformation opening toward the receiving groove, so that the plurality of edge portions are bent and located between the heat-conducting block and the inner wall surface of the receiving groove.

[0008] This invention discloses an embedded circuit board, comprising: a board having two surfaces located on opposite sides, wherein a receiving groove is recessed from one of the surfaces; and a metal layer formed on the other surface of the board and constituting the bottom of the receiving groove; wherein the metal layer forms a deformation opening communicating with the receiving groove; wherein the metal layer forms a plurality of edge portions surrounding the deformation opening and spaced apart from each other at a portion corresponding to the receiving groove, and each edge portion is bendable toward the inner wall of the receiving groove to form a spring arm shape.

[0009] In summary, the manufacturing method of the heat-dissipating circuit board structure and the embedded circuit board disclosed in the embodiments of the present invention, through the structural design of multiple edges that can be bent toward the receiving groove to match the heat-conducting block, thereby reducing the processing accuracy requirements of the receiving groove (or, thereby enabling the embedded circuit board to allow the heat-conducting block embedded therein to have a large range of processing errors), and also facilitating the rework of the heat-conducting block and the embedded circuit board.

[0010] To further understand the features and technical content of this invention, please refer to the following detailed description and accompanying drawings. However, these descriptions and drawings are only for illustrating the invention and are not intended to limit the scope of protection of the invention in any way. Attached Figure Description

[0011] Figure 1 This is a schematic diagram of the patterned steps of the manufacturing method of the heat-dissipating circuit board structure according to Embodiment 1 of the present invention.

[0012] Figure 2 This is a schematic diagram of the groove-cutting step in the manufacturing method of the heat-dissipating circuit board structure according to Embodiment 1 of the present invention.

[0013] Figure 3 for Figure 2 A cross-sectional view along section line III-III;

[0014] Figure 4 This is a schematic diagram of the hole-opening steps in the manufacturing method of the heat-dissipating circuit board structure according to Embodiment 1 of the present invention.

[0015] Figure 5 for Figure 4 A cross-sectional view along section line VV;

[0016] Figure 6 and Figure 7 This is a schematic diagram of the embedding steps in the manufacturing method of the heat-dissipating circuit board structure according to Embodiment 1 of the present invention;

[0017] Figure 8 This is a schematic diagram of the filling steps in the manufacturing method of the heat-dissipating circuit board structure according to Embodiment 1 of the present invention.

[0018] Figure 9 This is a schematic diagram of the hole-opening steps in the manufacturing method of the heat-dissipating circuit board structure according to Embodiment 2 of the present invention;

[0019] Figure 10 for Figure 9 A cross-sectional view along section line XX;

[0020] Figure 11 This is a schematic diagram of the groove-cutting step in the manufacturing method of the heat-dissipating circuit board structure according to Embodiment 2 of the present invention;

[0021] Figure 12 This is a schematic diagram of the groove-cutting step in the manufacturing method of the heat-dissipating circuit board structure according to Embodiment 3 of the present invention;

[0022] Figure 13 for Figure 12 A cross-sectional view along section line XIII-XIII;

[0023] Figure 14 This is a schematic diagram of the hole-opening steps in the manufacturing method of the heat-dissipating circuit board structure according to Embodiment 3 of the present invention;

[0024] Figure 15 This is a schematic diagram illustrating the patterned steps of the manufacturing method of the heat-dissipating circuit board structure according to Embodiment 3 of the present invention.

[0025] Symbol Explanation

[0026] 1000: Heat-dissipating circuit board structure

[0027] 100: Embedded circuit board

[0028] 100a: Circuit board

[0029] 1: Board material

[0030] 11a, 11b: Panel surface

[0031] 12: Reception Container

[0032] 121: Inner wall surface

[0033] 2: Metal layer

[0034] 21: Deformation Mouth

[0035] 22: Edge

[0036] 23: Circular part

[0037] 3: Cross-shaped through holes

[0038] 200: Heatsink

[0039] 201: End

[0040] 300: Fill layer

[0041] H: Thickness direction

[0042] R: Preset area

[0043] G: Gap

[0044] α: Bending angle

[0045] T: Thickness

[0046] D1: First Distance

[0047] D2: Second Distance

[0048] L: Length

[0049] S110: Patterning Steps

[0050] S130: Trenching Steps

[0051] S150: Hole Opening Procedure

[0052] S170: Embedding Steps

[0053] S190: Filling Procedure

[0054] S230: Hole Opening Procedure

[0055] S250: Trenching Steps

[0056] S310: Trenching Steps

[0057] S330: Hole Opening Procedure

[0058] S350: Patterning Steps Detailed Implementation

[0059] The following specific embodiments illustrate the implementation of the "manufacturing method of heat-dissipating circuit board structure and embedded circuit board" disclosed in this invention. Those skilled in the art can understand the advantages and effects of this invention from the content disclosed in this specification. This invention can be implemented or applied through other different specific embodiments, and various details in this specification can also be modified and changed based on different viewpoints and applications without departing from the concept of this invention. Furthermore, the accompanying drawings of this invention are for simple illustrative purposes only and are not depictions of actual dimensions; this is stated in advance. The following embodiments will further describe the relevant technical content of this invention in detail, but the disclosed content is not intended to limit the scope of protection of this invention.

[0060] It should be understood that while terms such as "first," "second," and "third" may be used in this document to describe various components or signals, these components or signals should not be limited by these terms. These terms are primarily used to distinguish one component from another, or one signal from another. Furthermore, the term "or" as used herein should, as appropriate, include any combination of one or more of the associated listed items.

[0061] [Example 1]

[0062] Please see Figures 1 to 8As shown, this is an embodiment of the present invention. This embodiment discloses a method for manufacturing a heat-dissipating circuit board structure, which sequentially includes a patterning step S110, a grooving step S130, an opening step S150, an embedding step S170, and a filling step S190. The specific implementation of the above steps will be described below. However, it should be noted that the implementation order or implementation method of the above steps can be adjusted according to design requirements, or some steps can be omitted (e.g., the filling step S190 can be omitted), so it is not limited to the content of this embodiment.

[0063] The patterning step S110: as follows Figure 1 As shown, a through-hole 3 is formed in a predetermined region R (along a thickness direction H) of a circuit board 100a. In this embodiment, the cross-section of the predetermined region R (e.g., a cross-section of the predetermined region R perpendicular to the thickness direction H) is polygonal (e.g., quadrilateral), and the through-hole 3 is formed by recessing along multiple diagonal faces of the predetermined region R. Furthermore, the circuit board 100a includes a substrate 1 and a metal layer 2 formed on the substrate 1, and the through-hole 3 penetrates the metal layer 2 and the substrate 1.

[0064] The trenching step S130: as follows Figure 2 and Figure 3 As shown, in the preset area R of the circuit board 100a, a receiving groove 12 is recessed from the surface 11a of the plate 1 away from the metal layer 2 (along the thickness direction H) and extends to the metal layer 2, so that the cross-shaped through hole 3 is located only in the metal layer 2 and communicates with the receiving groove 12.

[0065] The opening step S150: as follows: Figure 4 and Figure 5 As shown, the center of the cross-shaped through hole 3 in the metal layer 2 is widened to form a deformation opening 21, so that the portion of the metal layer 2 located in the preset region R has a plurality of edge portions 22 that surround the deformation opening 21 and are spaced apart from each other, thereby forming an embedded circuit board 100a.

[0066] In this embodiment, each side of the cross-section of the preset region R is provided with an edge portion 22, and each edge portion 22 is approximately trapezoidal. Furthermore, each edge portion 22 of the embedded circuit board 100 can be bent toward the inner wall surface 121 of the receiving groove 12 to form a spring arm shape.

[0067] The embedding step S170: as follows Figure 6 and Figure 7As shown, a heat-conducting block 200 is inserted into the receiving groove 12 through the deformation opening 21 (along the thickness direction H), so that a plurality of edge portions 22 are bent and positioned between the heat-conducting block 200 and the inner wall surface 121 of the receiving groove 12. Each edge portion 22 (after being bent) is spring-loaded and elastically abuts against the heat-conducting block 200, so that the heat-conducting block 200 is held and positioned by the plurality of edge portions 22.

[0068] It should be further noted that one end 201 of the heat-conducting block 200 is clamped and positioned on a plurality of the edge portions 22, and the cross-section of the preset region R is larger than the cross-section of the end 201 of the heat-conducting block 200, while the size of the deformation port 21 is smaller than the cross-section of the end 201 of the heat-conducting block 200.

[0069] In other words, the specific shape and size of the preset region R and the deformation port 21 in this embodiment can be defined or shaped based on the heat-conducting block 200. Furthermore, the heat-conducting block 200 is described as a block in this embodiment, but the invention is not limited thereto. For example, in other embodiments not shown in the invention, the heat-conducting block 200 may have the largest cross-section at the end 201, while the cross-sections of the remaining portions are smaller than the cross-section of the end 201.

[0070] More specifically, the thickness T of any of the edge portions 22, two edge portions 22 facing each other are separated by a first distance D1 at their adjacent end edges and by a second distance D2 at their far end edges; any of the edges has a length L, and the length L of any of the edges satisfies the following relationship: (D2-2T)>L>D1.

[0071] Furthermore, the heat-conducting block 200 and the inner wall surface 121 of the receiving groove 12 are spaced apart and form a gap G. The size of the gap G depends on the bending angle α of the plurality of edge portions 22. In this embodiment, the bending angle α of each edge portion 22 is preferably between 60 degrees and 90 degrees, but the present invention is not limited thereto. That is, depending on the size difference between the heat-conducting block 200 and the receiving groove 12, each edge portion 22 can be bent with a different bending angle α, so that there can be a large allowable error range between the heat-conducting block 200 and the receiving groove 12.

[0072] The filling step S190: as follows Figure 8As shown, a filling layer 300 is formed to fill the gap G. The material of the filling layer 300 can be adjusted according to design requirements. For example, electroplating can be performed within the gap G to form the filling layer 300 (e.g., a conductive filling layer); or, an insulating material can be filled within the gap G to form the filling layer 300 (e.g., an insulating filling layer).

[0073] The manufacturing method of the heat dissipation circuit board structure described above in this embodiment can be achieved by implementing the above-mentioned multiple steps. Figure 8 The illustrated heat-dissipating circuit board structure 1000 includes the embedded circuit board 100, the heat-conducting block 200 embedded within the embedded circuit board 100, and the filler layer 300 filling the embedded circuit board 100. However, the present invention is not limited thereto. For example, in other embodiments of the present invention not shown, the heat-dissipating circuit board structure 1000 may be manufactured by performing other steps or omit the filler layer 300 (e.g.: Figure 7 Alternatively, the embedded circuit board 100 can be used alone (e.g., for sale) or in combination with other components.

[0074] The following is a brief description of the specific structure of the heat dissipation circuit board structure 1000 in this embodiment, and please refer to the description in the above-described manufacturing method of the heat dissipation circuit board structure when appropriate (that is, the technical features already described in the above-described manufacturing method of the heat dissipation circuit board structure will not be repeated here).

[0075] like Figure 8 As shown, the embedded circuit board 100 includes a substrate 1 and a metal layer 2 formed on the substrate 1. The substrate 1 has two surfaces 11a and 11b located on opposite sides, and a receiving groove 12 is recessed from one of the surfaces 11a of the substrate 1. The metal layer 2 is formed on the other surface 11b of the substrate 1 and forms the bottom of the receiving groove 12. The metal layer 2 has a deformation opening 21 communicating with the receiving groove 12, and the metal layer 2 has a plurality of edge portions 22 arranged around the deformation opening 21 and spaced apart from each other at the portion corresponding to the receiving groove 12. Furthermore, the heat-conducting block 200 is inserted into the embedded circuit board 100 from the deformation opening 21 of the metal layer 2 toward the receiving groove 12, and the plurality of edge portions 22 are bent and located between the heat-conducting block 200 and the inner wall surface 121 of the receiving groove 12.

[0076] More specifically, one end 201 of the heat-conducting block 200 is clamped and positioned on a plurality of the edge portions 22, and the size of the deformation port 21 is smaller than the cross-section of the end 201 of the heat-conducting block 200. The cross-section of the end 201 is polygonal (e.g., quadrilateral), and the positions of the plurality of edge portions 22 correspond to a plurality of sides (e.g., four sides) of the cross-section, but the invention is not limited thereto. For example, in other embodiments of the invention not illustrated, the number of the plurality of edge portions 22 may also be less than the number of sides of the cross-section.

[0077] The filling layer 300 may be a conductive filling layer that fills the gap G by electroplating. Furthermore, the metal layer 2, the heat-conducting block 200, and the filling layer 300 (e.g., the conductive filling layer) are all made of the same material, so that the plurality of edge portions 22 and the heat-conducting block 200 are integrally connected to each other through the filling layer 300 (e.g., the conductive filling layer). Alternatively, the filling layer 300 may also be an insulating filling layer that fills the gap G by filling the gap G with an insulating material.

[0078] As described above, the manufacturing method of the heat-dissipating circuit board structure and the embedded circuit board 100 (or the heat-dissipating circuit board structure 1000 disclosed in the embodiments of the present invention) are designed to accommodate the heat-conducting block 200 by means of a plurality of edge portions 22 that can be bent toward the receiving groove 12, thereby reducing the processing accuracy requirements of the receiving groove 12 (or, thereby enabling the embedded circuit board 100 to allow the heat-conducting block 200 embedded therein to have a large range of processing errors).

[0079] Furthermore, the manufacturing method of the heat-dissipating circuit board structure and the embedded circuit board 100 disclosed in the embodiments of the present invention (or the heat-dissipating circuit board structure 1000 disclosed in the embodiments of the present invention) can also facilitate the rework of the heat-conducting block 200 and the embedded circuit board 100 (e.g., the heat-conducting block 200 can be pressed and moved away from the metal layer 2 and separated from the embedded circuit board 100).

[0080] [Example 2]

[0081] Please see Figures 9 to 11As shown, this is Embodiment 2 of the present invention. Since this embodiment is similar to Embodiment 1 above, the similarities between the two embodiments will not be repeated (e.g., the patterning step S350, the embedding step S170, and the filling step S190). The main difference between this embodiment and Embodiment 1 is that the manufacturing method of the heat-dissipating circuit board structure in this embodiment first performs an opening step S230, and then performs a trenching step S250, the order of which is reversed compared to Embodiment 1. The opening step S230 and the trenching step S250 in this embodiment will be described below:

[0082] The opening step S230: as follows: Figure 9 and Figure 10 As shown, the center of the cross-shaped through hole 3 in the metal layer 2 is widened to form a deformation opening 21, so that the portion of the metal layer 2 located in the preset region R has a plurality of edge portions 22 that surround the deformation opening 21 and are spaced apart from each other.

[0083] The trenching step S250: as follows Figure 11 As shown, in the preset area R of the circuit board 100a, a receiving groove 12 is recessed from the plate surface 11a of the plate 1 away from the metal layer 2 and extends to the metal layer 2, so that the deformation port 21 is connected to the receiving groove 12 and the plurality of edge portions 22 are located at the bottom of the receiving groove 12.

[0084] [Example 3]

[0085] Please see Figures 12 to 15 As shown, this is Embodiment 3 of the present invention. Since this embodiment is similar to Embodiment 1 above, the similarities between the two embodiments will not be repeated (e.g., the embedding step S170 and the filling step S190). The main difference between this embodiment and Embodiment 1 is that the manufacturing method of the heat-dissipating circuit board structure in this embodiment first performs a trenching step S310, followed by a hole-opening step S330 and a patterning step S350 in sequence, which is different from the implementation order in Embodiment 1. The trenching step S310, the hole-opening step S330, and the patterning step S350 in this embodiment will be described below:

[0086] The trenching step S310: as follows Figure 12 and Figure 13 As shown, a circuit board 100a is provided, which includes a substrate 1 and a metal layer 2 formed on the substrate 1. In a predetermined region R of the circuit board 100a, a receiving groove 12 is recessed from the surface 11a of the substrate 1 away from the metal layer 2 and extends to the metal layer 2.

[0087] The opening step S330: as follows: Figure 14 As shown, a deformation opening 21 is formed in the metal layer 2, so that a ring-shaped portion 23 is formed around the deformation opening 21 in the portion of the metal layer 2 located in the preset region R.

[0088] The patterning step S350: as follows Figure 14 and Figure 15 As shown, the annular portion 23 is patterned to form a plurality of edge portions 22 spaced apart from each other.

[0089] [Technical Effects of the Embodiments of the Invention]

[0090] In summary, the manufacturing method of the heat-dissipating circuit board structure and the embedded circuit board (or the heat-dissipating circuit board structure disclosed in the embodiments of the present invention) are designed to bend towards the receiving groove and are matched with the heat-conducting block, thereby reducing the processing accuracy requirements of the receiving groove (or enabling the embedded circuit board to allow the heat-conducting block embedded therein to have a large range of processing errors), and also facilitating the rework of the heat-conducting block and the embedded circuit board.

[0091] The content disclosed above is only a preferred and feasible embodiment of the present invention, and is not intended to limit the patent scope of the present invention. Therefore, all equivalent technical changes made based on the content of the present invention specification and drawings are included within the patent scope of the present invention.

Claims

1. A method for manufacturing a heat dissipating circuit board structure, comprising: a patterning step of forming a cross-shaped through-hole in a predetermined region of a circuit board, wherein the circuit board comprises a board material and a metal layer formed on the board material, and the cross-shaped through-hole penetrates the metal layer and the board material; a slotting step of recessing a receiving slot from a surface of the board material away from the metal layer to the metal layer in the predetermined region of the circuit board, so that the cross-shaped through-hole is located only on the metal layer and is connected to the receiving slot; a hole opening step of widening the cross-shaped through-hole of the metal layer at a center of the cross-shaped through-hole to form a deformation hole, so that the metal layer in the predetermined region is formed with a plurality of edge portions arranged around the deformation hole and spaced apart from each other; and a burying step of inserting a heat-conducting block from the deformation hole toward the receiving slot, so that the plurality of edge portions are bent and located between the heat-conducting block and an inner wall surface of the receiving slot.

2. The manufacturing method of the heat dissipating circuit board structure according to claim 1, wherein, In the burying step, the heat-conducting block and the inner wall surface of the receiving slot are spaced apart and form a gap, each of the edge portions is in the form of a spring arm and elastically abuts against the heat-conducting block, so that the heat-conducting block is clamped and positioned by the plurality of edge portions.

3. The manufacturing method of the heat dissipating circuit board structure according to claim 2, wherein, After the burying step, the method further comprises a filling step of electroplating in the gap to form a conductive filling layer that fills the gap.

4. The manufacturing method of the heat dissipating circuit board structure according to claim 2, wherein, After the burying step, the method further comprises a filling step of filling an insulating material in the gap to form an insulating filling layer that fills the gap.

5. The manufacturing method of the heat dissipating circuit board structure according to claim 2, wherein, One end of the heat-conducting block is clamped and positioned by the plurality of edge portions, a cross section of the predetermined region is larger than a cross section of the end of the heat-conducting block, and a size of the deformation hole is smaller than the cross section of the end of the heat-conducting block.

6. The manufacturing method of the heat dissipating circuit board structure according to claim 1, wherein, The cross section of the predetermined region is a polygon, and each side of the cross section of the predetermined region corresponds to one of the edge portions.

7. The manufacturing method of the heat dissipating circuit board structure according to claim 5, wherein, In the patterning step, the cross-shaped through-hole is recessed along a plurality of diagonal surfaces of the predetermined region.

8. A method for manufacturing a heat dissipating circuit board structure, comprising: a patterning step of forming a cross-shaped through-hole in a predetermined region of a circuit board, wherein the circuit board comprises a board material and a metal layer formed on the board material, and the cross-shaped through-hole penetrates the metal layer and the board material; a hole opening step of widening the cross-shaped through-hole of the metal layer at a center of the cross-shaped through-hole to form a deformation hole, so that the metal layer in the predetermined region is formed with a plurality of edge portions arranged around the deformation hole and spaced apart from each other; a slotting step of recessing a receiving slot from a surface of the board material away from the metal layer to the metal layer in the predetermined region of the circuit board, so that the deformation hole is connected to the receiving slot, and the plurality of edge portions are located on a slot bottom of the receiving slot; and Embedding step: inserting a heat-conducting block from the deformation opening toward the receiving groove, so that the multiple edge portions are bent to be located between the heat-conducting block and the inner wall surface of the receiving groove.

9. A method for manufacturing a heat-dissipating circuit board structure, comprising: Grooving step: providing a circuit board including a board material and a metal layer formed on the board material, and in a predetermined region of the circuit board, a receiving groove is formed in the board material away from the metal layer to the metal layer; Hole opening step: forming a deformation opening in the metal layer, so that the metal layer portion in the predetermined region forms a ring portion surrounding the deformation opening; Patternizing step: patterning the ring portion to form multiple edge portions arranged at intervals; and Embedding step: inserting a heat-conducting block from the deformation opening toward the receiving groove, so that the multiple edge portions are bent to be located between the heat-conducting block and the inner wall surface of the receiving groove.

10. An embedded circuit board, comprising: a board material having two board surfaces on opposite sides, and the board material is recessed to form a receiving groove from one of the board surfaces; and a metal layer formed on the other of the board surfaces of the board material and constituting a groove bottom of the receiving groove; wherein the metal layer forms multiple edge portions surrounding the deformation opening and arranged at intervals, and each of the edge portions can be bent toward the inner wall surface of the receiving groove to be in a spring arm shape. ​

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