Printed wiring board and method of manufacturing the same

Abstract

The application discloses a printed wiring board and a preparation method thereof, and relates to the technical field of printed wiring boards.

Description

TECHNICAL FIELD

[0001] The application belongs to the technical field of processing printed circuit boards, and particularly relates to a printed circuit board and a preparation method thereof. BACKGROUND

[0002] PCB (Printed Circuit Board), also known as a printed wiring board or a printed circuit board, is an important electronic component widely used, is a support body of electronic components, and is also a carrier for electrical connection of electronic components. At present, double-sided printed circuit boards are increasingly widely used in the industry, and the quality requirements for double-sided printed circuit boards are increasingly high in the industry.

[0003] At present, the schemes for preparing double-sided conductive layers of printed circuit boards with inconsistent thicknesses include: 1. etching two surfaces respectively: etching one surface first, and then etching the other surface; and 2. designing different etching compensations based on the different thicknesses of the conductive layers, and adjusting the etching parameters accordingly.

[0004] However, the above schemes have the following problems: 1. when etching the other surface, the first-etched surface needs to be protected, and since the adhesion of the substrate after etching is poor, the first-etched surface is prone to problems such as poor protection; and 2. the differentiated compensations and the differentiated adjustment of the etching parameters are not conducive to control, and the process failure risk is high. SUMMARY

[0005] The application provides a printed circuit board and a preparation method thereof, to solve the problem that it is difficult to prepare double-sided conductive lines with inconsistent thicknesses of conductive layers in a high quality in the preparation of double-sided printed circuit boards.

[0006] To solve the above technical problems, the application provides a preparation method of a printed circuit board, which comprises: obtaining a to-be-processed board piece; thickening a first preset position of a first surface of the to-be-processed board piece to form a preset boss; covering and protecting the preset boss and a second preset position of a second surface of the to-be-processed board piece; and etching the to-be-processed board piece after the covering and protecting, to form conductive lines at the first preset position of the first surface and the second preset position of the second surface at the same time.

[0007] The step of thickening the first preset position of the first surface of the to-be-processed board piece to form the preset boss comprises: pasting a first protective film on the first surface except the first preset position and the second surface; and electroplating the to-be-processed board piece pasted with the first protective film to thicken the first preset position.

[0008] The step of electroplating the to-be-processed board piece pasted with the first protective film to thicken the first preset position is followed by: removing the first protective film.

[0009] The step of covering and protecting the preset boss and the second preset position of the second surface of the plate to be processed includes covering and protecting the preset boss and the second preset position of the second surface of the plate to be processed by a second protective film.

[0010] The step of etching the plate to be processed after covering and protecting includes removing the second protective film.

[0011] The step of obtaining the plate to be processed includes obtaining a copper-clad plate or a multilayer plate; forming at least one hole on the copper-clad plate or the multilayer plate by drilling, wherein the hole includes a through hole and a micro blind hole; and performing whole-plate electroplating on the copper-clad plate or the multilayer plate to perform metalization treatment on the hole and to thicken the copper surface of the copper-clad plate or the multilayer plate, thereby obtaining the plate to be processed.

[0012] The step of performing whole-plate electroplating on the copper-clad plate or the multilayer plate after the step of forming at least one hole on the copper-clad plate or the multilayer plate by drilling and before the step of performing whole-plate electroplating on the copper-clad plate includes sequentially performing drill dirt removal and hole treatment on the hole; and the hole treatment includes copper deposition treatment, black hole treatment or black shadow treatment.

[0013] The step of performing whole-plate electroplating on the copper-clad plate includes performing whole-plate electroplating on opposite surfaces of the copper-clad plate or the multilayer plate until the thickness of the conductive layer of the opposite surfaces meets the preset thickness requirement.

[0014] The step of performing whole-plate electroplating on the copper-clad plate includes performing whole-plate electroplating on opposite surfaces of the copper-clad plate or the multilayer plate until the thickness of the conductive layer of the opposite surfaces meets the preset thickness requirement.

[0015] To solve the above technical problems, the present application also provides a printed circuit board prepared by the preparation method of any one of the printed circuit boards.

[0016] The present application has the following advantages: Different from the prior art, the present application thickens the first preset position of the first surface of the plate to be processed to form a preset boss, covers and protects the preset boss and the second preset position of the second surface of the plate to be processed, and then etches the plate to be processed after covering and protecting to jointly form a conductive circuit at the first preset position of the first surface and the second preset position of the second surface, thereby realizing one-time preparation of the double-sided conductive circuit of the printed circuit board, avoiding separate etching or adjusting etching parameters for the first surface and the second surface, improving the controllability of the preparation of the conductive circuit, reducing the failure risk of the preparation of the conductive circuit, improving the quality of the conductive circuit, and further improving the quality and reliability of the printed circuit board. BRIEF DESCRIPTION OF DRAWINGS

[0017] Figure 1is a flowchart of an embodiment of the method for manufacturing the printed circuit board provided by the present application;

[0018] Figure 2 is a flowchart of another embodiment of the method for manufacturing the printed circuit board provided by the present application;

[0019] Figure 3a is a structural diagram of an embodiment of the multilayer board after drilling in step S21;

[0020] Figure 3b is a structural diagram of an embodiment of the board to be processed in step S22;

[0021] Figure 3c is a structural diagram of an embodiment of the board to be processed after removing the first protective film in step S23;

[0022] Figure 3d is a structural diagram of an embodiment of the board to be processed after pasting the second protective film in step S24;

[0023] Figure 4 is a structural diagram of an embodiment of the printed circuit board provided by the present application. DETAILED DESCRIPTION

[0024] The technical solutions in the embodiments of the present application will be clearly and completely described below with reference to the drawings in the embodiments of the present application. Obviously, the described embodiments are only some of the embodiments of the present application, but not all the embodiments of the present application. Based on the embodiments in the present application, all other embodiments obtained by those of ordinary skill in the art without creative work fall within the scope of protection of the present application.

[0025] It should be noted that if the embodiments of the present application involve directional indications (such as up, down, left, right, front, back, etc.), the directional indications are only used to explain the relative positional relationship, movement condition, etc. between components in a certain posture (as shown in the drawings), and if the certain posture changes, the directional indications also change accordingly.

[0026] In addition, if the embodiments of the present application involve descriptions of “first”, “second”, etc., the descriptions of “first”, “second”, etc. are only for description purposes, and cannot be understood as indicating or implying the relative importance of the indicated technical features or implicitly indicating the number of the indicated technical features. Therefore, the features limited by “first” and “second” can explicitly or implicitly include at least one of the features. In addition, the technical solutions of the various embodiments can be combined with each other, but it must be based on the fact that a person of ordinary skill in the art can realize it, and when the combination of technical solutions contradicts each other or cannot be realized, it should be considered that the combination of technical solutions does not exist and is not within the scope of protection claimed by the present application.

[0027] Referring to Figure 1 , Figure 1 is a flowchart of an embodiment of a method for manufacturing a printed circuit board provided by the present application. The printed circuit board of the embodiment is a printed circuit board with a design requirement of inconsistent thickness of double-sided conductive lines.

[0028] Step S11: Obtain a to-be-processed board piece.

[0029] In a specific application scenario, the to-be-processed board piece can be a copper-clad board or a multi-layer board that has been laminated in the processing process. The copper-clad board (CCL) refers to a raw board-shaped material made by impregnating electronic glass fiber cloth or other reinforcing materials with resin, and covering one or both sides with copper foil and then hot pressing. The multi-layer board can include hard board printed circuit board, soft and hard combined printed circuit board, pure soft board, and other intermediate multi-layer board pieces in the manufacturing process of various printed circuit boards.

[0030] Step S12: Thicken the first preset position of the first surface of the to-be-processed board piece to form a preset boss.

[0031] Thicken the first preset position of the first surface of the to-be-processed board piece to form a preset boss at the first preset position of the first surface. That is, to achieve specified position thickening at the first preset position.

[0032] In a specific application scenario, electroplating can be performed at the first preset position of the first surface of the to-be-processed board piece to thicken the first preset position and form a preset boss on the first preset position. The first preset position is the position on the first surface of the to-be-processed board piece where the conductive line needs to be prepared, and the specific position and number can be set based on the actual requirements of the conductive line on the first surface. Before electroplating, copper deposition, blackening, or electroplating liquid coating can be performed at the first preset position to improve the efficiency and accuracy of electroplating.

[0033] In a specific application scenario, the first preset position can also be thickened by welding a conductive block at the first preset position to form a preset boss.

[0034] Step S13: Cover and protect the preset boss and the second preset position of the second surface of the to-be-processed board piece.

[0035] The preset boss covers and protects the second preset position of the second surface of the plate to be processed, and other positions of the plate to be processed except the preset boss and the second preset position are exposed, so that subsequent etching can be facilitated. The second preset position refers to a position on the second surface of the plate to be processed where the conductive circuit needs to be prepared, and the specific position and quantity can be set based on the demand of the conductive circuit on the second surface.

[0036] Step S14: Etching the plate to be processed after covering and protecting to form conductive circuits at the first preset position of the first surface and the second preset position of the second surface at the same time.

[0037] The plate to be processed after covering and protecting is etched to remove the exposed positions of the plate to be processed except the preset boss and the second preset position, so that the conductive layers of the preset boss and the second preset position on the plate to be processed are separated, and the required conductive circuit is formed. Since the thicknesses of the conductive layers of the preset boss and the second preset position are inconsistent, the thicknesses of the conductive circuits on the first surface and the second surface after etching are also different, thereby realizing the preparation of the printed circuit board with inconsistent thicknesses of the double-sided conductive circuits.

[0038] In this step, the etching can etch the double-sided conductive layers of the plate to be processed at one time to prepare the double-sided conductive circuits with different thicknesses at the same time, avoiding separate etching or adjusting the etching parameters for the first surface and the second surface, improving the controllability of the preparation of the double-sided conductive circuits, and reducing the failure risk of the preparation of the double-sided conductive circuits.

[0039] Through the above method, the preparation method of the printed circuit board of the embodiment can thicken the first preset position of the first surface of the plate to be processed to form a preset boss, cover and protect the preset boss and the second preset position of the second surface of the plate to be processed, and then etch the plate to be processed after covering and protecting to form conductive circuits at the first preset position of the first surface and the second preset position of the second surface at the same time, so that the preparation of the double-sided conductive circuits of the printed circuit board can be completed at one time, avoiding separate etching or adjusting the etching parameters for the first surface and the second surface, improving the controllability of the preparation of the conductive circuits, reducing the failure risk of the preparation of the conductive circuits, realizing the preparation of the printed circuit board with inconsistent thicknesses of the double-sided conductive circuits, improving the quality of the conductive circuits, and further improving the quality and reliability of the printed circuit board.

[0040] Please refer to Figure 2 , Figure 2 is a flowchart of another embodiment of the preparation method of the printed circuit board provided by the present application. The printed circuit board of the embodiment is a printed circuit board with inconsistent thicknesses of double-sided conductive circuits.

[0041] Step S21: Obtain a copper-clad plate or a multi-layer plate, and form at least one hole on the copper-clad plate or the multi-layer plate by drilling.

[0042] A copper-clad plate or a multi-layer plate is obtained. The copper-clad plate includes a dielectric layer and a conductive layer. When the copper-clad plate is used to prepare the to-be-processed plate, the conductive layer covers the two surfaces of the copper-clad plate. When the multi-layer plate is used to prepare the to-be-processed plate, the conductive layer also covers the two surfaces of the multi-layer plate.

[0043] The copper-clad plate or the multi-layer plate is drilled to form at least one hole on the copper-clad plate or the multi-layer plate. In a specific application scenario, the copper-clad plate or the multi-layer plate can be drilled by mechanical drilling to form at least one hole on the copper-clad plate. In a specific application scenario, the copper-clad plate or the multi-layer plate can also be drilled by laser drilling to form at least one hole on the copper-clad plate or the multi-layer plate. Laser drilling refers to irradiating a high-power-density laser beam on a specific material to heat the material to a vaporization temperature in a very short time, and evaporating to form a hole.

[0044] The hole in this step includes a through hole and a micro blind hole. The through hole refers to a hole that penetrates two or more layers and extends vertically. The micro blind hole refers to a conductive hole that connects adjacent two layers without penetrating. The copper-clad plate or the multi-layer plate is drilled to form at least one hole on the copper-clad plate or the multi-layer plate. In a specific application scenario, multiple holes can be drilled on the copper-clad plate or the multi-layer plate, for example, 3, 5, or 10 holes. The specific number of holes can be set according to the conductive requirements of the printed circuit board, which is not limited herein. When the copper-clad plate is used to prepare the to-be-processed plate, the hole can include a through hole or a micro blind hole. When the multi-layer plate is used to prepare the to-be-processed plate, the hole can only include a micro blind hole, which is used to prepare a micro blind hole on the outermost copper layer or connect the holes that have been metallized in the intermediate layer through the blind hole, so as to connect the through holes on the entire plate.

[0045] In a specific application scenario, after the copper-clad plate or the multi-layer plate is drilled by laser drilling or mechanical drilling, and at least one hole is formed on the copper-clad plate or the multi-layer plate, the hole on the copper-clad plate can be left with drill dirt such as resin slag and copper slag. Therefore, the hole on the copper-clad plate or the multi-layer plate needs to be cleaned in this step.

[0046] After the drilling, the holes on the copper-clad plate are subjected to hole processing to obtain the plate to be processed of the embodiment. The hole processing includes copper deposition processing, black hole processing or black shadow processing. The holes on the copper-clad plate are subjected to hole processing to cover a layer of conductive material on the hole wall and / or hole bottom, which facilitates subsequent hole filling and electroplating. The black hole processing refers to that fine graphite or carbon black paint (black hole liquid) is dip-coated on the hole wall and / or hole bottom to form a conductive layer; the black shadow processing refers to that black shadow liquid containing unique additives and conductive gel-like substances is dip-coated on the hole wall and / or hole bottom to form a conductive layer; and the copper deposition processing refers to that a thin layer of chemical copper is deposited on the hole wall and / or hole bottom by a chemical method to serve as a substrate for electroplating.

[0047] Referring to Figure 3a , Figure 3a is a structural schematic diagram of the copper-clad plate after drilling in step S21 of the embodiment. The embodiment will be described in the case that the plate to be processed is prepared from the multi-layer plate. The case that the plate to be processed is prepared from the copper-clad plate is similar to the embodiment and will not be described herein. The plate to be processed of the embodiment includes a base layer, an upper conductive layer and a lower conductive layer. Figures 3a-3d is a schematic diagram of each step of the preparation method of the printed circuit board of the embodiment.

[0048] The plate to be processed 100 of the embodiment includes a base layer 104, an upper conductive layer 101 and a lower conductive layer 102. The upper conductive layer 101 is arranged on one side of the plate to be processed 100, and the lower conductive layer 102 is arranged on the other opposite side of the plate to be processed 100. A plurality of holes 103 are further arranged on the two surfaces of the plate to be processed 100.

[0049] The base layer 104 of the embodiment is a multi-layer plate prepared from single-layer plates by sequentially performing bottom drilling, bottom hole metallization, bottom circuit preparation, pressing and the like, and then after drilling.

[0050] Step S22: The opposite two surfaces of the copper-clad plate or multi-layer plate are subjected to whole-plate electroplating until the thickness of the conductive layer of the opposite two surfaces meets the preset thickness requirement.

[0051] The opposite two surfaces of the copper-clad plate or multi-layer plate are subjected to whole-plate electroplating to perform metallization on the holes drilled in step S21 and to thicken the conductive layer of the opposite two surfaces of the copper-clad plate or multi-layer plate until the thickness of the conductive layer of the opposite two surfaces meets the preset thickness requirement, thereby obtaining the plate to be processed of the embodiment. The preset thickness requirement refers to the thinner thickness requirement in the different conductive layers of the finished printed circuit board, i.e. the thickness requirement of the conductive circuit of the second surface of the embodiment.

[0052] Referring to Figure 3b , Figure 3bis a structural schematic diagram of an embodiment of the plate to be processed in step S22.

[0053] The plate to be processed 200 in this embodiment includes an upper conductive layer 201 and a lower conductive layer 202 arranged oppositely. The thickness of the upper conductive layer 201 and the lower conductive layer 202 is the same, both being a preset thickness requirement S.

[0054] Step S23: Paste the first protective film on the first surface except the first preset position and the second surface, and electroplate the plate to be processed with the first protective film to thicken the first preset position.

[0055] The first protective film is pasted on the first surface of the plate to be processed except the first preset position and the second surface to expose the first preset position, and then the plate to be processed with the first protective film is electroplated to thicken the first preset position, thereby forming a preset boss at the first preset position. The total thickness of the preset boss and the conductive layer of the first surface is the thickness requirement of the thicker one in the differential conductive layer in the finished printed circuit board, that is, the thickness requirement of the conductive circuit of the first surface in this embodiment.

[0056] In a specific application scenario, the first protective film can be a photosensitive anti-plating film or other photosensitive film. The photosensitive anti-plating film is a kind of high molecular compound which can form a stable substance attached to the surface of the plate after irradiation by a specific light source to achieve the function of blocking electroplating.

[0057] After electroplating, the first protective film on the plate to be processed is removed.

[0058] Please refer to Figure 3c , Figure 3c is a structural schematic diagram of an embodiment of the plate to be processed after removing the first protective film in step S23.

[0059] The first surface 302 of the plate to be processed 300 in this embodiment forms a plurality of preset bosses 303, while the second surface 301 of the plate to be processed 300 does not change. The total thickness of the preset boss 303 and the lower conductive layer is the thickness of the conductive circuit to be prepared on the first surface.

[0060] Step S24: Cover and protect the preset boss and the second preset position of the second surface of the plate to be processed by the second protective film.

[0061] After forming the preset boss on the first surface, the preset boss and the second preset position of the second surface of the plate to be processed are covered and protected by the second protective film. The second preset position refers to the position on the second surface of the plate to be processed where the conductive circuit is to be formed, which can be set based on actual conditions.

[0062] Further, the second protective film can cover all surfaces of the preset boss exposed, i.e. the top surface and all side surfaces of the preset boss away from the second surface of the to-be-processed board, to further improve the etching resistance of the preset boss, and further improve the quality of the conductive circuit finally formed on the first surface.

[0063] The second protective film includes a photosensitive resist film or other resist film. The photosensitive resist film is a high-molecular compound that can generate a polymerization reaction (a reaction process of synthesizing a polymer from a monomer) to form a stable substance attached to the board surface after irradiation by a specific light source, thereby achieving the function of blocking etching.

[0064] Please refer to Figure 3d , Figure 3d is a structural schematic diagram of an embodiment of the to-be-processed board of step S24 pasting the second protective film.

[0065] In this embodiment, the first surface 402 of the to-be-processed board 400 has a plurality of preset bosses 403 formed thereon, each of which is pasted with a second protective film 404, and the second preset positions 405 on the second surface 401 of the to-be-processed board 400 are also pasted with the second protective film 404, and the second protective film 404 on the second surface 401 corresponds to the second preset positions 405 one by one, so as to protect the preset bosses 403 and the second preset positions 405 by the second protective film 404.

[0066] Step S25: etching the to-be-processed board covered by the second protective film to form a conductive circuit at the first preset positions on the first surface and the second preset positions on the second surface.

[0067] The to-be-processed board covered by the second protective film is etched to form a conductive circuit at the first preset positions on the first surface and the second preset positions on the second surface at the same time.

[0068] After etching, the second protective film pasted on the preset boss and the second preset position is removed to complete the preparation of the printed circuit board. At this time, the preparation of the printed circuit board with inconsistent thickness of the double-sided conductive circuit can be completed.

[0069] Based on the design requirement of the differentiated conductive circuit thickness of the product, the smaller specification of the conductive circuit thickness is taken as the reference, the thicker conductive circuit is only used for the conductor pattern position that needs to be reserved, and the specific process is used for directional thickening, and the thickness of the conductive layer that needs to be etched away is consistent with the smaller thickness specification, so that the differentiated conductive circuit thickness can be completed by etching once, the preparation efficiency of the printed circuit board is improved under the condition of ensuring the quality of the conductive circuit.

[0070] Through the above method, the preparation method of the printed circuit board of the embodiment can be applied to various processed or unprocessed board pieces by preparing the unprocessed board piece based on the copper-clad board or the multi-layer board piece, thereby improving the application range of the preparation method of the printed circuit board. Furthermore, after obtaining the unprocessed board piece, the first protective film is pasted on the positions except the first preset position on the first surface and the second surface, the unprocessed board piece with the pasted first protective film is electroplated to thicken the first preset position to form a preset boss with a larger thickness, the second protective film is used to cover and protect the preset boss and the second preset position on the second surface of the unprocessed board piece, and finally the etching is performed on the covered and protected unprocessed board piece to jointly form the conductive circuit at the first preset position on the first surface and the second preset position on the second surface. Thus, the one-time preparation of the printed circuit board with the conductive circuit with inconsistent thicknesses on two surfaces can be realized, the separate etching or adjustment of etching parameters on the first surface and the second surface is avoided, the controllability of the preparation of the conductive circuit is improved, the failure risk of the preparation of the conductive circuit is reduced, the preparation of the printed circuit board with the conductive circuit with inconsistent thicknesses on two surfaces is realized, and the quality of the conductive circuit is improved, thereby improving the quality and reliability of the printed circuit board.

[0071] Please refer to Figure 4 , Figure 4 is a structural schematic diagram of an embodiment of the printed circuit board.

[0072] The printed circuit board 500 of the embodiment includes a base layer 503, a first conductive circuit 502, and a second conductive circuit 501. The first conductive circuit 502 is arranged on one side surface of the base layer 503, the second conductive circuit 501 is arranged on the other side surface of the base layer 503, and the first conductive circuit 502 and the second conductive circuit 501 are arranged opposite to each other.

[0073] The thickness of the first conductive circuit 502 of the embodiment is greater than that of the second conductive circuit 501 because the first conductive circuit 502 is prepared on the basis of the preset boss and the original conductive layer, and the second conductive circuit 501 is prepared on the basis of the original conductive layer. Therefore, the printed circuit board 500 of the embodiment can be applied to printed circuit boards with differentiated copper thickness design requirements.

[0074] Through the above structure, the conductive circuit on the two surfaces of the printed circuit board of the embodiment has clear and full lines, and the quality is excellent. Furthermore, the printed circuit board of the embodiment has excellent quality and high reliability.

[0075] The above merely describes the embodiments of the present application, and does not limit the patent scope of the present application, and any equivalent structure or equivalent process transformation made by using the content of the present application specification and drawings, or directly or indirectly applied in other related technical fields, are also included in the patent protection scope of the present application.

Claims

1. A method for producing a printed wiring board, characterized by, The preparation method of the printed circuit board comprises: obtaining a to-be-processed board piece; wherein, a copper-clad plate or a multi-layer board piece is obtained; at least one hole is formed on the copper-clad plate or the multi-layer board piece through drilling, wherein the hole comprises a through hole; the copper-clad plate or the multi-layer board piece is subjected to whole-board electroplating to perform metallization treatment on the hole and to thicken the copper surface of the copper-clad plate or the multi-layer board piece, so as to obtain the to-be-processed board piece; wherein, the opposite surfaces of the copper-clad plate or the multi-layer board piece are subjected to whole-board electroplating until the thickness of the conductive layer of the opposite surfaces meets a preset thickness requirement; thickening a first preset position of a first surface of the to-be-processed board piece to form a preset boss; covering and protecting the preset boss and a second preset position of a second surface of the to-be-processed board piece; wherein, the preset boss and the second preset position of the second surface of the to-be-processed board piece are covered and protected by a second protective film, and the second protective film comprises a photosensitive etching resist film; wherein, the preset thickness requirement is a thickness requirement of a conductive circuit on the second surface; double-sided etching the to-be-processed board piece after covering and protecting to simultaneously form conductive circuits at the first preset position of the first surface and the second preset position of the second surface.

2. The method of producing a printed wiring board according to claim 1, wherein The step of thickening the first preset position of the first surface of the to-be-processed board piece to form a preset boss comprises: pasting a first protective film on the first surface except the first preset position and the second surface; electroplating the to-be-processed board piece pasted with the first protective film to thicken the first preset position.

3. The method of producing a printed wiring board according to claim 2, wherein The step of electroplating the to-be-processed board piece pasted with the first protective film to thicken the first preset position is followed by: removing the first protective film.

4. The method of producing a printed wiring board according to claim 1, wherein The step of double-sided etching the to-be-processed board piece after covering and protecting is followed by: removing the second protective film.

5. The method of producing a printed wiring board according to claim 1, wherein After the step of forming at least one hole on the copper-clad plate or the multi-layer board piece through drilling, and before the step of electroplating the copper-clad plate or the multi-layer board piece, the following step is included: sequentially performing drill dirt removal and hole treatment on the hole; wherein, the hole treatment comprises copper deposition treatment, black hole treatment or black shadow treatment.

6. The preparation method of the printed circuit board according to claim 1, wherein the thicknesses of the conductive layers of the opposite surfaces of the copper-clad plate or the multi-layer board piece after whole-board electroplating are the same.

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