TWI565386B - Mefhod for processing in hole of circuit board and circuit board made there from - Google Patents

Description

Method for processing inside hole of circuit board and circuit board light guiding element made thereof

The present invention relates to a circuit board, and more particularly to a method of processing a hole in a circuit board and a circuit board produced thereby.

Referring to FIG. 1, which is a conventional circuit board 100a, a board member 1a and a conductive layer 2a are included. The plate member 1a is formed with a uniform hole 11a, and at least one buried line 12a is formed in the plate member 1a, and the conductive layer 2a is formed on the hole wall of the through hole 11a. However, the conventional circuit board 100a of FIG. 1 is designed to shunt current into an operating current I _A and a delay current I _B , that is, because the delay current I _B enters the buried line 12a and the operating current _A time difference occurs between the time points when I _A enters the buried line 12a, so that the signal transmitted to the buried line 12a cannot maintain its integrity.

Accordingly, the existing improvement is to perform back drilling on the conventional circuit board 100a shown in FIG. 1, thereby forming the circuit board 100a structure as shown in FIG. 2. In more detail, by the step of back drilling, the drill hole 13a is formed in the conductive layer 2a to remove the portion that is not to be used, and the generation of the escape current I _B is reduced, thereby maintaining the integrity of the signal. Moreover, in the dense hole area of the circuit board (for example, in the vicinity of the ball grid array structure), the back drilling method is more likely to make the adjacent drill holes 13a too close or close to each other, resulting in a decrease in signal transmission quality. Accordingly, the above-mentioned method of back drilling has its limitations and may be detrimental to the subsequent development of the circuit board.

Therefore, the inventors have felt that the above-mentioned defects can be improved, and they are devoted to research and matching. With the application of the theory, a present invention which is reasonable in design and effective in improving the above-mentioned defects is finally proposed.

The embodiment of the invention provides a method for processing a hole in a circuit board and a circuit board formed thereby, which can effectively improve the limitation caused by the back drilling method of the conventional circuit board.

Embodiments of the present invention provide a method for processing a hole in a circuit board, including: providing a circuit board; wherein the circuit board is formed with a uniform hole wall, and the circuit board has a cover layer formed on the wall of the through hole The cover layer defines a through hole, and the cover layer includes a predetermined removal portion; a light guide member having an outer shape substantially corresponding to the through hole is inserted into the through hole of the circuit board; wherein the through hole is received One end portion of the light guiding member is provided with a reflecting surface; the predetermined removal portion of the covering layer is adjusted to be projected into the region formed by the through hole wall; and the opening toward the circuit board The hole emits a laser beam, and the laser beam is transmitted to the reflecting surface of the light guiding element, and the laser beam is turned to be irradiated on the predetermined removal portion of the covering layer via the reflecting surface of the light guiding element, thereby further At least a portion of the predetermined removal portion of the cover layer is removed.

Preferably, the cover layer is a conductive layer; in the step of emitting the laser beam toward the through hole of the circuit board, the laser beam is continuously emitted until the predetermined removal portion of the conductive layer is completely removed, and The conductive layer is formed into two conductive portions that are separated from each other.

Preferably, the cover layer comprises a conductive layer and a shielding layer, the conductive layer is formed on the through hole hole wall, the shielding layer is formed on the conductive layer and surrounds the through hole; facing the circuit board In the step of transmitting the laser beam by the through hole, continuously emitting the laser beam until the predetermined removal portion of the shielding layer is completely removed, so that the predetermined removal portion of the conductive layer is exposed; etching with an etching solution The predetermined removal portion of the conductive layer is such that the conductive layer forms two conductive portions separated from each other.

An embodiment of the present invention further provides a circuit board formed by the in-hole processing method of the above circuit board, comprising: a uniform hole wall; and a conductive layer formed thereon On the wall of the hole, the conductive layer is formed with a notch for exposing a portion of the wall of the through hole, and the conductive layer is separated into two conductive portions via the notch.

In summary, the in-hole processing method of the circuit board provided by the embodiment of the present invention can be processed in the through hole of the circuit board by using the cooperation of the light guiding element and the laser beam, thereby providing a different The conventional in-hole processing method and the fabricated circuit board further overcome the limitations of the conventional back-drilling method.

The detailed description of the present invention and the accompanying drawings are to be understood by the claims The scope is subject to any restrictions.

[知知]

100a‧‧‧ boards

1a‧‧‧Plate

11a‧‧‧Tongkong

12a‧‧‧ buried line

13a‧‧‧Drilling

2a‧‧‧ Conductive layer

I _A ‧‧‧ actuation current

I _B ‧‧‧ escape current

[Embodiment of the Invention]

100‧‧‧ boards

1‧‧‧through hole wall

11‧‧‧ Notch

2‧‧‧ Coverage

21‧‧‧through hole

211‧‧‧ first opening

212‧‧‧second opening

22‧‧‧ Conductive layer

221‧‧‧Predetermined removal site

222‧‧‧Electrical Department

223‧‧‧ gap

23‧‧‧Shielding layer

231‧‧‧Reserved removal site

232‧‧ ‧ gap

3‧‧‧Additional conductive layer

200‧‧‧Light guiding elements

201‧‧‧ Body Department

202‧‧‧End

203‧‧‧reflecting surface

300‧‧‧ Laser equipment

301‧‧‧Laser beam

Figure 1 is a schematic diagram of a conventional circuit board.

2 is a schematic view of the conventional circuit board of FIG. 1 after processing.

FIG. 3 is a schematic diagram of step S101 of the first embodiment of the method for processing the hole in the circuit board of the present invention.

4 is a schematic diagram of steps S102 and S103 of the first embodiment of the method for processing the hole in the circuit board of the present invention.

FIG. 5 is a schematic diagram of step S104 of the first embodiment of the method for processing the hole in the circuit board of the present invention.

FIG. 6 is a schematic diagram of step S105 of the first embodiment of the method for processing the hole in the circuit board of the present invention.

Fig. 7 is a schematic view showing the step S104' of the first embodiment of the method for processing the hole in the circuit board of the present invention.

FIG. 8 is a schematic diagram of step S201 of the first embodiment of the method for processing the hole in the circuit board of the present invention.

FIG. 9 is a schematic diagram of steps S202 and S203 of the first embodiment of the method for processing the hole in the circuit board of the present invention.

10 is a step S204 of the first embodiment of the method for processing a hole in a circuit board according to the present invention; intention.

Figure 11 is a schematic view showing the step S205 of the first embodiment of the method for processing the hole in the circuit board of the present invention.

FIG. 12 is a schematic diagram of step S206 of the first embodiment of the method for processing the hole in the circuit board of the present invention.

Figure 13 is a schematic view showing the step S204' of the first embodiment of the method for processing the hole in the circuit board of the present invention.

[First Embodiment]

Please refer to FIG. 3 to FIG. 7 , which are the first embodiment of the present invention. It should be noted that the related quantity and appearance mentioned in the embodiment are only used to specifically describe the implementation of the present invention. The manner in which the content is understood is not to be construed as limiting the scope of the invention.

This embodiment provides a method for processing a hole in a circuit board. For ease of understanding, this embodiment takes a unit area of the circuit board as an example, and a cross-sectional view of each step is used for explanation. In addition, when referring to the drawings corresponding to each step, please refer to the drawings of other steps as needed. The steps of the method for processing the hole in the circuit board of the embodiment are as follows:

Step S101: As shown in FIG. 3, a circuit board 100 is provided; wherein the circuit board 100 is formed with a uniform aperture wall 1 and the circuit board 100 has a cover layer 2 formed on the through hole wall 1. The cover layer 2 surrounds a through hole 21 defining a circular surface, and the cover layer 2 defines a first opening 211 and a second opening 212 defined on opposite sides of the through hole 21; and the cover layer 2 includes There is a predetermined removal portion 221 (in the present embodiment, the predetermined removal portion 221 is substantially the central portion of the cover layer 2).

In more detail, the cover layer 2 is a conductive layer 22 in this embodiment, In the following description, the cover layer 2 is directly represented by the conductive layer 22, and the thickness of the above-described conductive layer 22 is smaller than a predetermined thickness required for the circuit board 100 in practical use. The conductive layer 22 is preferably a black-browned copper layer to facilitate absorption of the laser beam in subsequent steps and is easily removed by etching.

In addition, the circuit board 100 may be a laminated board, that is, the circuit board 100 has a plurality of stacked boards (not shown) and a colloid (not shown) bonded to any two-phase stacked board, at least the above-mentioned circuit board 100 One of the plates is formed with at least one conductive line (not shown) for signal transmission. Wherein, the plate body is usually formed by a preimpregnated material, and the prepreg material layer may be a glass fiber prepreg or a carbon fiber prepreg according to different reinforcing materials. Carbon fiber prepreg), epoxy resin (Epoxy resin) and other materials. However, the plate body can also be formed by a soft plate material, that is, the plate body is mostly composed of a polyester material (Polyester, PET) or a polyimine resin (Polyimide, PI) without glass. Fiber, carbon fiber, etc. However, embodiments of the invention do not limit the material of the plate.

Step S102: As shown in FIG. 4, a light guiding element 200 is inserted into the through hole 21 via the first opening 211 of the circuit board 100. The light guiding element 200 includes a substantially cylindrical body portion 201 and a self-body portion. A distal end portion 202 of the 201 end edge (the top end edge of the body portion 201 as shown in FIG. 4) is integrally extended. The outer shape of the main body portion 201 corresponds to the through hole 21, that is, the cross-sectional shape of the main body portion 201 perpendicular to the long axis direction is substantially the same as the cross-sectional shape of the through hole 21 in which the main body portion 201 is inserted, so that the light guiding member 200 is inserted into the through hole. After 21, the side surface of the body portion 201 of the light guiding element 200 can exhibit a gap-free arrangement substantially between the conductive layer 22. Furthermore, the end portion 202 of the light guiding element 200 is received in the through hole 21 and is provided (for example, plated) with a conical reflecting surface 203.

In more detail, the distal end portion 202 of the light guiding element 200 is a cone in this embodiment, and the maximum diameter of the distal end portion 202 is not greater than (e.g., substantially equal to) the diameter of the body portion 201, and the distal end portion 202 is The edge of the body portion 201 is along the body portion 201 The long axis direction is formed by gradually decreasing the diameter. Furthermore, the reflecting surface 203 is the outer surface of the end portion 202 and is preferably a smooth mirror surface, thereby achieving the effect of completely reflecting the laser beam.

Step S103: As shown in FIG. 4, the predetermined removal portion 221 of the conductive layer 22 is adjusted so that the reflection surface 203 is projected onto the region formed by the through hole wall 1. In more detail, by moving the light guiding element 200 or the circuit board 100 to adjust the relative positions of the light guiding element 200 or the circuit board 100, the predetermined removal portion 221 of the conductive layer 22 is located outside the reflecting surface 203. .

Step S104: As shown in FIG. 5, a laser beam 301 is emitted from a laser device 300 toward the through hole 21 of the circuit board 100, and the laser beam 301 is incident on the through hole 21 of the circuit board 100 via the second opening 212. The laser beam 301 is transmitted to the reflective surface 203 of the light guiding element 200, whereby the laser beam 301 is radially deflected and irradiated onto the predetermined removal portion 221 of the conductive layer 22 via the reflecting surface 203 of the light guiding element 200. The predetermined removal portion 221 of the conductive layer 22 is removed. The laser device 300 continuously emits the laser beam 301 until the predetermined removal portion 221 of the conductive layer 22 is completely removed, so that the conductive layer 22 forms the two conductive portions 222 separated from each other.

It should be noted that the intensity of the laser beam 301 reflected by the reflecting surface 203 is gradually weakened from the direction away from the body portion 201 toward the body portion 201 (that is, from the top end to the bottom end of the reflecting surface 203 in FIG. 5). Therefore, the predetermined removal portion 221 corresponding to the portion of the reflection surface 203 remote from the body portion 201 is completely removed first, thereby continuously etching the through hole hole wall 1 until the portion of the reflection surface 203 adjacent to the body portion 201 corresponds to The predetermined removal portion 221 is completely removed. According to this, after the predetermined removal portion 221 is completely removed, the through-hole hole wall 1 will form an annular recess 11 and the depth of the above-described recess 11 gradually narrows away from the body portion 201 toward the body portion 201.

In addition, the above steps are exemplified by the formation of the two conductive portions 222 separated from each other by the conductive layer 22, but it is not excluded that the conductive layer 22 is formed by more than two conductive portions (not shown) separated from each other. For example, after the step S104, one of the conductive portions 222 of the two conductive portions 222 is further provided with a predetermined removal portion (not shown), and then the above steps S102 to S104 are repeatedly performed to make the conductive layer 22. Three mutually separated conductive portions are formed (not shown).

Step S105: performing electroplating on at least one of the two conductive portions 222 to form a supplementary conductive layer 3, wherein the material of the supplementary conductive layer 3 is the same as the conductive layer 22, as shown in FIG. The material, and the total thickness of both the conductive layer 3 and the conductive portion 222 to which it is attached, is the predetermined thickness required for the circuit board 100 to be used.

It should be noted that in the present embodiment, only the conductive portion 222 located above in FIG. 6 is plated as an example, but it is not excluded that the two conductive portions 222 are simultaneously plated, or only in the lower portion of FIG. The conductive portion 222 is plated.

After the steps S101 to S105 described above are implemented, the circuit board 100 shown in FIG. 6 can be completed, but in actual application, the steps do not exclude replacement with a reasonable change. For example, as shown in FIG. 7, this is the changing step S104' of step S104, in which the light guiding element 200 is a transparent light guiding body, and the end portion 202 of the light guiding element 200 is a conical groove. Therefore, the laser device 300 is such that the laser beam 301 is incident on the light guiding element 200 and is transmitted to the reflecting surface 203 of the light guiding element 200.

In addition, when the aperture of the through hole 21 is too large, the laser device 300 can be rotated with the central axis of the light guiding element 200 as the axis, so that the laser beam 301 emitted by the laser device 300 is irradiated along the circular path. On the reflecting surface 203. Furthermore, when the aperture of the through hole 21 is small, the light guiding element 200 can also be a member like an optical fiber.

Further, although the structure of the light guiding element 200 of the present embodiment is exemplified above, it may be changed according to the designer's request. For example, in another embodiment not shown The end portion of the light guiding element may form a single beveled reflecting surface and transmit the light guiding element to achieve the effect that the reflecting surface reflects the laser beam in an annular manner.

Next, a description will be given of a structural technical feature for the circuit board 100 shown in FIG. 6 as follows. Among them, since many configurations have been mentioned in the above manufacturing method, some of the similarities will not be repeated. The circuit board 100 includes a uniform aperture wall 1, a conductive layer 22 formed on the via hole wall 1, and a supplemental conductive layer 3 formed on at least a portion of the conductive layer. The conductive layer 22 is formed with a notch 223 for exposing a portion of the through-hole hole wall 1, and the conductive layer 22 is separated into two conductive portions 222 via the notch 223, and the supplementary conductive layer 3 is formed on the two conductive portions. At least one of 222.

[Second embodiment]

Please refer to FIG. 8 to FIG. 13 , which are the second embodiment of the present invention. It should be noted that the related quantities and appearances mentioned in the embodiment are only used to specifically describe the implementation of the present invention. The manner in which the content is understood is not to be construed as limiting the scope of the invention.

This embodiment also provides a method for processing a hole in a circuit board, and the same as the first embodiment will not be described again. The steps of the method for processing the hole in the circuit board of the embodiment are as follows:

Step S201: As shown in FIG. 8, a circuit board 100 is provided; wherein the circuit board 100 is formed with a uniform aperture wall 1 and the circuit board 100 has a cover layer 2 formed on the through hole wall 1. The cover layer 2 surrounds a through hole 21 defining a circular surface, and the cover layer 2 defines a first opening 211 and a second opening 212 defined on opposite sides of the through hole 21; and the cover layer 2 includes The predetermined removal portions 221, 231 are predetermined (in the present embodiment, the predetermined removal portions 221, 231 are substantially the cover layer 2 Central part).

In more detail, the cover layer 2 is a conductive layer 22 and a shielding layer 23 in the embodiment. The conductive layer 22 is formed on the through hole hole wall 1. The shielding layer 23 is formed on the conductive layer 22 and is defined by The through hole 21 is formed. The conductive layer 22 is preferably a copper layer and the thickness thereof is a predetermined thickness required for the circuit board 100 in practical applications, and the shielding layer 23 is preferably adapted to absorb the laser beam and is easily removed. The material is, for example, an organic material (such as a resin) or a metal material (such as tin).

Step S202: As shown in FIG. 9, a light guiding element 200 is inserted into the through hole 21 via the first opening 211 of the circuit board 100. The light guiding element 200 includes a substantially cylindrical body portion 201 and a self-body portion. A distal end portion 202 of the 201 end edge (the top end edge of the body portion 201 as shown in FIG. 9) is integrally extended. The outer shape of the main body portion 201 corresponds to the through hole 21, that is, the cross-sectional shape of the main body portion 201 perpendicular to the long axis direction is substantially the same as the cross-sectional shape of the through hole 21 in which the main body portion 201 is inserted, so that the light guiding member 200 is inserted into the through hole. After 21, the side surface of the body portion 201 of the light guiding element 200 can be provided with a gap-free arrangement substantially between the shielding layer 23. Furthermore, the end portion 202 of the light guiding element 200 is received in the through hole 21 and is provided (for example, plated) with a conical reflecting surface 203. It should be noted that the light guiding element 200 of the present embodiment has a substantially the same configuration as the light guiding element 200 of the first embodiment.

Step S203: As shown in FIG. 9, the predetermined removal portions 221, 231 of the cover layer 2 are adjusted so that the reflection surface 203 is projected onto the region formed by the through hole wall 1. In more detail, by moving the light guiding element 200 or the circuit board 100 to adjust the relative positions of the light guiding element 200 or the circuit board 100, the predetermined removal portion 231 of the shielding layer 23 is located outside the reflecting surface 203. .

Step S204: As shown in FIG. 10, a laser beam 301 is emitted from a laser device 300 toward the through hole 21 of the circuit board 100, and the laser beam 301 is transmitted through the second opening. 212 is incident on the through hole 21 of the circuit board 100, and the laser beam 301 is transmitted to the reflecting surface 203 of the light guiding element 200, whereby the laser beam 301 is radially turned by the reflecting surface 203 of the light guiding element 200. The predetermined removal portion 231 of the shielding layer 23 is irradiated, and the predetermined removal portion 231 of the shielding layer 23 is removed. The laser device 300 continuously emits the laser beam 301 until the predetermined removal portion 231 of the shielding layer 23 is completely removed, so that the shielding layer 23 is formed with a notch 232, and the predetermined removal portion 221 of the conductive layer 22 passes through the gap 232. Exposed to the outside.

Step S205: As shown in FIG. 11, the predetermined removal portion 221 of the conductive layer 22 is etched with an etching solution, so that the conductive layer 22 forms the two conductive portions 222 separated from each other. In the process of etching the conductive layer 22 by the etching solution, a portion other than the predetermined removed portion 221 of the conductive layer 22 is protected by the covering layer 23, thereby avoiding etching by the etching liquid.

In addition, the above steps are exemplified by the formation of the two conductive portions 222 separated from each other by the conductive layer 22, but it is not excluded that the conductive layer 22 is formed by more than two conductive portions (not shown) separated from each other. For example, after the step S203, a predetermined removal portion (not shown) is further disposed on the remaining shielding layer 23, and then the above steps S202 and S203 are repeatedly performed, so that the shielding layer 23 is further formed with a gap ( BRIEF DESCRIPTION OF THE DRAWINGS Further, in step S204, the conductive layer 22 can be formed into three mutually separated conductive portions (not shown).

Step S206: As shown in FIG. 12, after the conductive layer 22 forms the two conductive portions 222 separated from each other, the shielding layer 23 is removed.

After the steps S201 to S206 described above are implemented, the circuit board 100 shown in FIG. 12 can be completed. However, in practical applications, the steps do not exclude replacement with a reasonable change. For example, as shown in FIG. 13, this is the changing step S204' of step S204, wherein the light guiding element 200 is a transparent light guiding body, and is guided. The distal end portion 202 of the optical element 200 has a conical groove. Therefore, the laser device 300 is such that the laser beam 301 is incident on the light guiding element 200 and is transmitted to the reflecting surface 203 of the light guiding element 200.

Next, a description will be given of a structural technical feature for the circuit board 100 shown in FIG. Among them, since many configurations have been mentioned in the above manufacturing method, some of the similarities will not be repeated. The circuit board 100 includes a uniform aperture wall 1 and a conductive layer 22 formed on the aperture aperture wall 1. The conductive layer 22 is formed with a notch 223 for exposing a portion of the through-hole hole wall 1, and the conductive layer 22 is separated into two conductive portions 222 via the notch 223.

[Possible effects of the embodiments of the present invention]

In summary, the in-hole processing method of the circuit board provided by the embodiment of the present invention is processed in the through hole of the circuit board by using the cooperation of the light guiding element and the laser beam to make the circuit board pass through. The conductive layer on the wall of the hole can be separated into two conductive portions, thereby providing a method different from the conventional in-hole processing method and the fabricated circuit board, thereby overcoming the limitations of the conventional back-drilling method.

Furthermore, since the conductive layer on the wall of the through hole of the circuit board can be separated into a plurality of conductive portions, and the conductive portions can each have a function of conducting, thereby achieving the effect of saving processing cost and increasing wiring density.

The above are only the preferred embodiments of the present invention, and are not intended to limit the scope of the invention, and the equivalent variations and modifications of the scope of the invention are intended to be within the scope of the invention.

1‧‧‧through hole wall

11‧‧‧ Notch

21‧‧‧through hole

212‧‧‧second opening

22‧‧‧ Conductive layer

222‧‧‧Electrical Department

200‧‧‧Light guiding elements

201‧‧‧ Body Department

202‧‧‧End

203‧‧‧reflecting surface

300‧‧‧ Laser equipment

301‧‧‧Laser beam

Claims (9)

A method for processing a hole in a circuit board, comprising: providing a circuit board; wherein the circuit board is formed with a uniform hole wall, and the circuit board has a cover layer formed on the wall of the through hole, the cover layer surrounding Defining a through hole, and the cover layer includes a predetermined removal portion; inserting a light guide element substantially corresponding to the through hole into the through hole of the circuit board; wherein the light guide received in the through hole One end portion of the component is provided with a reflecting surface; the predetermined removal portion of the covering layer is adjusted to be projected into the region formed by the through hole wall; and a laser is emitted toward the through hole of the circuit board And transmitting, by the light beam, the laser beam to the reflective surface of the light guiding element, and rotating the laser beam to a predetermined removal portion of the cover layer via the reflective surface of the light guiding element, thereby removing at least part of the The cover layer is intended to be removed. The method of processing a hole in a circuit board according to claim 1, wherein the cover layer is a conductive layer; in the step of emitting the laser beam toward the through hole of the circuit board, the laser beam is continuously emitted until The predetermined removal portion of the conductive layer is completely removed, and the conductive layer is formed into two conductive portions separated from each other. The in-hole processing method of the circuit board of claim 2, wherein after the conductive layers form the two conductive portions separated from each other, electroplating is performed on at least one of the two conductive portions to form a supplementary conductive layer. Wherein the total thickness of both the supplemental conductive layer and the conductive portion to which it is attached is a predetermined thickness. The method for processing a hole in a circuit board according to claim 3, wherein the conductive layer is made of the same material as the material of the supplementary conductive layer. The method of processing a hole in a circuit board according to claim 1, wherein the cover layer comprises a conductive layer and a shielding layer, the conductive layer is formed on the through hole wall, and the shielding layer is formed on the conductive layer. And surrounding the defining the through hole; in the step of emitting the laser beam toward the through hole of the circuit board, continuously emitting the laser beam, straight The predetermined removal portion to the shielding layer is completely removed to expose the predetermined removal portion of the conductive layer to the outside; the predetermined removal portion of the conductive layer is etched with an etching solution to form the conductive layer to form two conductive layers separated from each other unit. The in-hole processing method of the circuit board of claim 5, wherein the conductive layer has a thickness of a predetermined thickness; after the conductive layer forms the two conductive portions separated from each other, the shielding layer is removed. The in-hole processing method of the circuit board of any one of claims 1 to 6, wherein the end portion of the light guiding element is a cone, and the covering layer is defined to be located on opposite sides of the through hole. a first opening and a second opening; the light guiding element is a through hole inserted into the circuit board through the first opening, and the laser beam is incident on the through hole of the circuit board through the second opening. The method of processing a hole in a circuit board according to any one of claims 1 to 6, wherein the light guiding element is a transparent light guiding body, and the end portion of the light guiding element is a conical groove; The laser beam is incident on the light guiding element and is transmitted to the reflecting surface of the light guiding element. A circuit board produced by the method of processing a hole in a circuit board according to claim 2 or 5, comprising: a constant hole wall; and a conductive layer formed on the wall of the through hole, the conductive layer being formed A notch is formed for exposing a portion of the through hole wall, and the conductive layer is separated into two conductive portions via the notch.