JP2005223174A - Method for manufacturing double-sided circuit board - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a method for manufacturing a double-sided circuit board which can simplify its steps, realize its micromachining operation, and have a good mass productivity. <P>SOLUTION: The method for manufacturing a double-sided circuit board includes a laser machining step of simultaneously forming a blind via hole and a through hole having arbitrary different shapes, by laser machining from one side at desired positions in a double-sided metallic laminate having metallic layers laminated on both sides of a resin layer; a metal plating step of providing a metal plated layer by metal plating a resin surface and an exposed metallic part within the through hole made by the laser machining to electrically connect both surfaces of the metallic layers; and a metallic pattern formation step of forming metallic patterns on the both surfaces. <P>COPYRIGHT: (C)2005,JPO&NCIPI

Description

The present invention relates to a method for manufacturing a double-sided circuit board, and in particular, by combining a double-sided metal laminate as a starting material and a laser processing, a blind via hole and any irregularly shaped hole processing at a desired position. The present invention relates to a method for producing a double-sided circuit board that is simultaneously performed and has a high function and excellent mass productivity in which an electromagnetic shielding function is imparted to a hole side surface such as a component hole.
In this specification, the irregularly shaped through hole means any irregularly shaped through hole having two or more different sectional shapes.

In response to recent demands for downsizing, high-density packaging, and high performance of electronic devices, there are increasing cases in which a plurality of types of holes such as component holes are provided in different shapes in addition to blind via holes.
For example, using a two-layer CCL, photoresist co on one surface of a copper foil - after the formation of the emissions, CO ₂ Le - - coating to pattern The - in pattern - a polyimide film of a portion corresponding to emissions removed After forming a blind hole and desmearing the polyimide film deposited on the bottom of the blind hole, a part of the bottom copper foil and a small amount of polyimide are removed by etching and desmearing. It is known to form blind via holes by plating (Patent Document 1).

In this case, when a through hole is provided, a through hole is formed in the copper foil and polyimide layer on both sides by drilling or punching, and when a blind via hole is provided, a hole is formed by etching in the metal foil on one side. After the processing, a blind via hole is formed by irradiating a laser such as CO ₂ , UV-YAG or excimer laser.
In these sequential opening processing methods, it is impossible to simultaneously form the blind via hole and the component hole by the reel-to-roll conveying method. In general, a blind via hole is formed by laser processing and then a part hole processing is performed by pressing.

However, according to the above method, a step of forming a blind via hole by a laser and a step of forming a component hole by a press are necessary, and two steps are required to process all the holes. It is. In addition, fine processing such as narrow part holes and release holes? In this case, it may be impossible to handle by press working. For this reason, the conventional circuit board and its manufacturing method are inferior in mass productivity in terms of uniform quality and high productivity.
For this reason, simultaneous processing by punching is proposed using a double-sided metal laminate as a starting material (Patent Document 2), and the simultaneous addition of blind via holes and component holes by laser processing 5 (Patent Document 3) has been proposed.

Japanese Patent Laid-Open No. 10-154730 (first page) JP-A-11-135577 (first page) JP 2002-252256 A (first page)

However, according to the method described in Patent Document 2, the simultaneous processing itself by punching has a problem in the productivity of the blind hole and is not applicable.
In addition, according to the method described in Patent Document 3, a portion of the metal laminate that has been removed as a component hole having a size larger than the removal capability of the device remains in the device, and the reel tool・ Continuous operation with the reel system becomes impossible.

  Accordingly, an object of the present invention is to provide a method for manufacturing a double-sided circuit board that simplifies the process, enables microfabrication, and has good mass productivity.

  According to the present invention, a blind via hole and an arbitrarily shaped through-hole are simultaneously formed at a desired position of a double-sided metal laminate in which metal layers are laminated on both sides of a resin layer by laser processing from one side. The laser processing step to be formed, the resin surface in the through-hole formed by the laser processing and the exposed metal portion are metal-plated to provide a metal plating layer, and both surfaces of the metal layer are electrically The present invention relates to a method of manufacturing a double-sided circuit board including a metal plating step for connecting to a metal pattern and a metal pattern forming step for forming a metal pattern on both sides.

  According to the present invention, a blind via hole and an arbitrarily shaped hole of any kind are provided at a desired position, and the drilling can be performed in a single step without collecting the residue generated during the drilling. High-volume production of double-sided circuit boards that have a shield function against electromagnetic waves on the side of the board with a simplified process using a one-step opening process (perforation process). Can be obtained by sex.

The preferred embodiments of the present invention are listed below.
1) The double-sided metal laminate has a heat-fusible polyimide layer in which a metal foil is thermocompression bonded to both sides of a polyimide film having a heat-fusible three-layer structure, or a polyimide precursor solution is cast on the metal foil. Two layers of a single-sided metal-clad laminate are laminated by thermocompression bonding, or a metal layer is laminated on both sides of a polyimide film by either depositing a base metal and copper on both sides of the polyimide film and then metal plating. Manufacturing method of said double-sided circuit board.
2) The method for producing a double-sided circuit board as described above, wherein the laser processing is performed by a UV-YAG laser.
3) The method for producing a double-sided circuit board as described above, wherein the laser processing is continuously performed by a reel-to-roll method.

4) After the laser processing step simultaneously forms blind via holes and arbitrarily shaped through-holes, the thin film layer with adhesive layer laminated on the other surface is peeled to remove the laser. -A method for producing a double-sided circuit board as described above, comprising the step of removing together the waste produced by the processing.
5) The metal plating step includes the following steps: cleaning in the hole, acid cleaning of the surface, formation of a conductive film in the hole, formation of a copper plating layer in the hole and on the metal layer by electrolytic copper plating Manufacturing method for double-sided circuit boards.
6) The metal pattern forming step includes forming an etching resist on both surfaces of the metal plating layer and forming a metal pattern having a desired shape by exposure, development, etching of the metal layer, and peeling of the etching resist. Manufacturing method for double-sided circuit boards.
7) The above-mentioned double-sided circuit board manufacturing method, wherein the metal pattern forming step forms a signal wiring layer on one metal layer and a ground wiring layer on the other metal layer.

7) The method for producing a double-sided circuit board according to claim 1, further comprising a step of forming a protective film such as a solder resist having a desired shape.
8) The method for producing a double-sided circuit board as described above, wherein the solder resist is a photosensitive dry film type, laminated in a vacuum, and then patterned at a predetermined position by exposure and development operation.
9) The method for producing a double-sided circuit board as described above, further comprising a step of performing metal plating such as Ni / Au or tin on the exposed metal portion.
10) The method for producing a double-sided circuit board as described above, wherein the metal plating is electrolytic nickel plating and then electrolytic gold plating.

1 is a partial schematic view showing an example of a COF to which the double-sided circuit board obtained by the method of the present invention is applied, and FIG. 1 is a partial schematic diagram of a preferred example of the process of the double-sided circuit board manufacturing method of the present invention. This will be described with reference to FIGS. 2 (showing the front part of the process) and FIG. 3 (showing the back part of the process).
In FIG. 1, a double-sided circuit board 1 includes a blind via hole 5 and a through hole 6 (not shown) formed in a double-sided metal laminate in which a metal layer 2 and a metal layer 3 are laminated on both sides of a resin layer 4. Are formed at the same time by laser processing, and a metal plating layer 7 is provided in the hole (that is, the side surface) of the through hole to prevent electromagnetic waves. Provided with a shield function, metal plating 8 is provided on the exposed metal portion, both surfaces of the metal layer are electrically connected, metal patterns are formed on both surfaces, and a solder having a desired shape is further formed. A protective layer of resist 9 is provided.

  In FIG. 2, the double-sided circuit board 1 has a (A) step: on one side of a double-sided metal laminate in which a metal layer 2 and a metal layer 3 are laminated on both sides of a resin layer (preferably a polyimide film) 4 ( B) Step of disposing the easily peelable thin film material layer 10 with adhesive, (C) Laser processing and penetrating through the non-continuous holes and resin layer that lead to the resin layer at the desired position on the other surface The step of forming the continuous hole 6, the step (D) of peeling the thin film layer with adhesive 10 in FIG. 3, (E) the step of removing together the waste generated by the opening process by this, (F) Obtained by a manufacturing method comprising a step of metal plating the inside and exposed metal portions and electrically connecting both sides of the metal layer, and (G) a step of forming metal patterns on both sides. . The double-sided circuit board 1 in FIGS. 2 and 3 is a part of a long-sized one in a reel-to-reel method, although not shown.

Examples of the metal layer in the present invention include metal foils and metal films of copper, aluminum, iron, gold and the like, or alloy foils and alloy films of these metals, preferably rolled copper foil, electrolytic copper foil, vapor deposition and / or Or a plated copper film etc. are mention | raise | lifted. As the metal foil, it is preferable that the surface roughness is not so large and not too small, preferably the Rz of the contact surface with the polyimide is 3 μm or less, particularly 0.5 to 3 μm, and of these, particularly 1.5 to 3 μm. . Such metal foils, such as copper foils, are known as VLP, LP (or HTE).
The thickness of the metal foil is preferably about 1 μm to 12 μm, particularly about 2 μm to 9 μm. The greater the thickness of the metal foil, the more disadvantageous for fine patterning.
Moreover, when Rz is small, you may use what surface-treated the metal foil surface.

The resin layer in the present invention is preferably a polyimide film, and may be a single-layer polyimide film made of polyimide having a glass transition temperature of about 275 to 375 ° C., which has both high heat resistance and flexibility, particularly glass. It has a thermocompression bonding and / or flexible polyimide layer having a glass transition temperature of about 200 to 300 ° C. on both sides of a high heat resistant polyimide layer having a transition temperature of 300 ° C. or higher, and the total thickness is about 7 to 50 μm, especially A three-layered polyimide film having a tensile modulus (25 ° C.) of about 7 to 25 μm and a tensile modulus (25 ° C.) of about 400 to 1000 kgf / mm ² is preferred from the viewpoint of high density.

The double-sided metal laminate in the present invention can be obtained by preferably laminating a metal foil and a thermocompression-bonding three-layer polyimide film, preferably by thermocompression bonding with a double belt press.
Further, the double-sided metal laminate in the present invention is a double-sided polyimide film having a flexible polyimide layer on both sides of a high heat-resistant polyimide layer or a single-layer polyimide film having both high heat resistance and flexibility. It can obtain by carrying out electro copper plating (metal vapor deposition-electro copper plating method) after carrying out metal vapor deposition to. In this case, the polyimide film is cleaned by a plasma screening process continuously after forming a concavo-convex shape having convex portions of a network structure on the treated surface subjected to the reduced-pressure discharge treatment, or after being placed in the atmosphere once after the reduced-pressure discharge treatment. Then, a metal thin film is formed by a vapor deposition method, and at least two metal thin films, in particular, a base metal vapor deposition layer and a copper vapor deposition layer on the two layers are laminated and electroplated. preferable.

  Various combinations are possible as the material of the metal thin film in the metal vapor deposition-electro copper plating method. It is good also as a 2 or more-layer structure which has a base layer and a surface vapor deposition metal layer as a metal vapor deposition film. Examples of the underlayer include chromium, tungsten, titanium, palladium, zinc, molybdenum, nickel, cobalt, zirconium, iron, nickel-chromium alloy, nickel-copper alloy, nickel-gold alloy, and nickel-molybdenum alloy. An example of the surface layer (or intermediate layer) is copper. As a material of the metal plating layer provided on the vapor deposition layer, copper, copper alloy, silver, etc., particularly copper is suitable. On both sides of the vacuum-discharged polyimide film, chromium, tungsten, titanium, palladium, zinc, tin, molybdenum, nickel, cobalt, zirconium, iron, nickel-chromium alloy, nickel-copper alloy, nickel-gold alloy, nickel- After forming a base metal layer such as molybdenum alloy and the like, and forming a copper vapor deposition layer thereon as an intermediate layer, a copper electroless plating layer is formed (the formation of an electroless plating layer is a Or the thickness of the metal deposition layer is increased, for example, 0.1 to 1.0 μm is omitted, and an electroless metal plating layer such as copper is omitted, and an electro copper plating is used as a surface layer. A layer may be formed.

In the above-mentioned electrolytic copper plating, for example, copper sulfate 50 to 200 g / l, sulfuric acid 100 to 250 g / l and a small amount of brightener, temperature 15 to 45 ° C., current density 0.1 to 10 A (ampere) / dm ² , air stirring It is preferable that the conveyance speed is 0.1 to 2 m / min, the addition of appropriate amounts of chlorine and a brightening agent, and the cathode is copper.

In the present invention, an easily peelable thin film material layer with an adhesive is disposed on one surface of the double-sided metal laminate, and a blind via hole and a through hole are simultaneously formed by laser processing. It is necessary.
By the above-described opening process, an irregularly shaped continuous or discontinuous hole having an arbitrary shape is formed.
Examples of the irregularly shaped hole include a device hole and a release hole for external trimming.

As the pressure-sensitive adhesive (or adhesive) for the thin film material layer with pressure-sensitive adhesive, a one-part silicone rubber pressure-sensitive adhesive (trade name: RTV rubber KE3417 / manufactured by Shin-Etsu Silicone), a two-part silicone rubber pressure-sensitive adhesive (product) Name: RTV Rubber KE1204 / manufactured by Shin-Etsu Silicone Co., Ltd., two-component epoxy adhesive (trade name: Cemedine High-Super-5 / produced by Cemedine), two-component epoxy adhesive (product name: Cemedine EP001 / Cemedine) (Manufactured by Co., Ltd.), two-component urethane adhesive, acrylic pressure-sensitive adhesive, and the like can be suitably used.
Moreover, as a thin film substance layer with an adhesive, what provided the said adhesive on support bodies, such as plastic films, such as metal foil, a polyimide film, and a polyester film, is mentioned.

Examples of the laser processing method include laser processing such as CO ₂ laser, UV-YAG laser, and excimer laser, preferably UV-YAG.
With the UV-YAG laser, a laser in the ultraviolet region having an oscillation wavelength in the range of about 260 to 400 nm can be used.
In the laser processing, a laser is irradiated to a desired position of at least one metal layer of the double-sided metal laminate to form a hole of preferably 20 to 100 μmφ, particularly about 30 to 100 μmφ. . At the same time, the holes can be formed by irradiating a laser in the same shape on the polyimide film layer.

In the present invention, a non-continuous hole penetrating to the resin layer (polyimide layer) and a continuous hole penetrating through the resin layer are formed at a desired position on the other surface of the double-sided metal laminate by the laser processing. Then, the thin film layer with the adhesive is peeled off.
According to the above method, the buffing method and the drive last method for removing the metal burrs generated in the via forming process in the conventional process are not necessary, and the polyimide portion in the via is cleaned (desmeared). Therefore, the wet desmear method using an alkaline permanganate aqueous solution is not essential, so that relatively large elongation is likely to occur only in the conveying direction in the buffing method, and anisotropy occurs in the dimensional change of the processed substrate. Problems, cleaning of the polyimide part in the via hole by the desmear process, problems of dust generation in the drive last method, and residual abrasive grains do not cause poor resist adhesion in the photolithography process.

After the waste generated by the opening process is removed together, the inside of the hole is metal-plated to electrically connect both sides of the metal layer.
As a metal plating method, it can carry out by the method described in Unexamined-Japanese-Patent No. 11-51425, for example.
For example, a method of activating a Pd—Sn film in a via hole or the like to increase conductivity and metal plating, preferably electrolytic copper plating can be used.

That is, this is a method for improving the conductivity of a palladium-tin coating by immersing a palladium-tin coating formed by using a palladium-tin colloidal catalyst in an alkaline accelerator bath containing a reducing agent.
The palladium-tin coating is a coating obtained by using a palladium-tin colloidal catalyst, and this coating is generally performed in a so-called DPS (Direct Plating System) method.

A specific DPS method is implemented as follows. First, using monoethanolamine, nonionic surfactant, cationic surfactant, etc., degrease the metal and polyimide in the pores, desmear with an alkaline permanganate solution, then use persulfate soda. After soft etching, pre-dip into sodium chloride, hydrochloric acid, etc. After these steps, a Pd-Sn film is formed by an activating step of immersing in a palladium-tin colloid solution, and finally an alkaline accelerator bath containing sulfuric acid carbonate, potassium carbonate and copper ions, and sulfuric acid. When activated with an acidic accelerator bath containing, a reducing agent may be added to the alkaline accelerator bath used for activation. Examples of the reducing agent that can be added include aldehydes such as formaldehyde, acetaldehyde, propionaldehyde, and benzaldehyde, catechol, resorcin, ascorbic acid, and the like. As the alkaline accelerator bath to which the reducing agent is added, those containing sodium carbonate, potassium carbonate and copper ions are preferable.
By the above method, a coating having a low resistance value made of Pd—Sn can be obtained, and the coating time by electrolytic copper plating in the next step can be shortened.

Next, after acid cleaning, electrolytic copper plating is performed.
In electroplating, the current density is set to ² A / dm ² to 8 A / dm ² , copper sulfate is 180 to 240 g / l, sulfuric acid is 45 to 60 g / l, chloride ion is 20 to 80 g / l, and thiourea as an additive It is preferable to carry out by adding dextrin or thiourea and molasses.
By the above method, a copper plating layer having a thickness of 3 to 30 μm can be formed, and a via hole or a through hole having a hole diameter of about 30 to 100 μm can be formed.

Next, a ground wiring layer having a predetermined pattern is formed on the plated metal layer on one side by a photo process and etching, and a signal having a predetermined pattern is formed on the metal layer on the other side by a photo process and etching. It is preferable to form a wiring layer.
A dry film type photosensitive solder resist is preferably laminated on the both sides or at least the ground wiring layer side on which the hole is formed, preferably by a vacuum laminator, and exposed and developed. A double-sided circuit board can be obtained by forming a solder resist layer having a desired pattern by operation together with the ground wiring layer and the signal wiring layer.

  Examples of the photosensitive solder resist include ink-type photosensitive solder resist, for example, a polyimide (precursor) -based photosensitive resin composition, preferably an imidosiloxane-based resin described in JP-A No. 2000-212446. It may be a photosensitive resin composition or an epoxy acrylate-based photosensitive thermosetting resin composition described in JP-A-2000-109541, preferably a dry film type photosensitive solder. A resist.

In particular, a solder resist having a tensile modulus of 100 kgf / mm ² or less as a simple substance after curing can be used as a protective film that does not substantially warp. As a dry film type photosensitive solder resist that can be used as a protective film after curing, a dry film solder mask for FPC manufactured by Nippon Polytech Co., Ltd. (based on urethane rubber and epoxy acrylate, flame retardant) And an epoxy acrylate resin described in Japanese Patent Application No. 2001-359790 of Ube Industries, Ltd., and a photosensitive resin composition containing an initiator, which exhibits a tensile elastic modulus of about 40 kgf / mm ² after curing. Resin composition comprising an oligomer which is a reaction product of asymmetric aromatic tetracarboxylic dianhydride with α, ω-bis (3-aminopropyl) polydimethylsiloxane, an epoxy resin and a photopolymerization initiator A dry film (which exhibits a tensile modulus of about 60 kgf / mm ² after curing) is preferred.
According to the above-mentioned dry film type photosensitive solder resist, compared to the conventional cover-lay type, there are effects such as good plating resistance, no blanking, miniaturization, and no adhesive exudation. can get.

  After that, usually, by forming an electrolytic nickel / gold plating layer or an electroless tin plating layer by a well-known method on the copper layer of the solder resist opening portion, a double-sided circuit board is formed by gold plating or tin plating. Can be obtained.

  EXAMPLES Hereinafter, the present invention will be specifically described with reference to examples, but the present invention is not limited to these examples.

Double-sided metal foil laminate in which electrolytic copper foil (thickness: 9 μm, product name: USLPR2) is thermocompression bonded to both surfaces of a polyimide film (thickness: 25 μm) with thermocompression bonding on both surfaces ( One side of Ube Industries, Ltd. (trade name: Iupicel N) is coated with an easily peelable adhesive-attached copper foil (thickness 25 μm, rolled copper foil) at a press temperature of 80 ° C. and a pressure of 0 with a continuous laminator. Laminate at .35 MPa, conveyance speed of 1.0 m / min, and UV-YAG laser [manufactured by Electro Scientific Industries (ESI), model: 5220, wavelength: 355 nm] The copper foil layer and the polyimide film layer were directly perforated to form blind via holes and four types of irregularly shaped component holes: through holes. Subsequently, the copper foil with pressure-sensitive adhesive was peeled off, and an unnecessary double-sided metal foil laminate of the component hole portion removed by laser processing was collected while being attached to the copper foil. Subsequently, the copper foil surface and the inside of a hole were cleaned with the continuous surface treatment apparatus. Subsequently, after the surface was washed with phosphoric acid, a conductive film was formed in the hole by a DPS process, and a copper plating layer having a thickness of 12 μm was formed on the copper foil layer by electrolytic copper plating and a thickness of 10 μm was formed on the opened side surface. . Next, a dry film resist (product name: SUNFORT, model number: AQ-3096) with a thickness of 30 μm is laminated on the plated copper layer (both sides), and the photo process and etching (the hole portion is tented). The signal wiring layer having a predetermined pattern was formed on the copper foil layer 3 and the ground wiring layer having a predetermined pattern was formed on the copper foil layer 2 by the protection by a ting method. Next, electrolytic nickel plating (thickness 0.5 μm) and electrolytic gold plating (thickness 0.3 μm) were applied, and a desired double-sided wiring board was produced by a reel-to-roll method.
A COF was obtained using the above double-sided wiring board. A schematic diagram of this COF is shown in FIG.

FIG. 1 is a schematic view showing an example of a COF to which a double-sided circuit board obtained by the method of the present invention is applied. FIG. 2 is a schematic view of a preferred example (steps (A) to (C)) of each step of the method for manufacturing a double-sided circuit board according to the present invention. FIG. 3 is a schematic view of a preferred example (steps (D) to (G)) of the steps of the method for producing a double-sided circuit board according to the present invention.

Explanation of symbols

1: Double-sided circuit board 2: Metal layer 3: Metal layer 4: Resin layer 5: Blind via hole 6: Through hole 7: Metal plating layer 8: Metal plating layer 9: Solder resist 10: Thin film with adhesive Layer 11: Terminal plating layer 12: Silicon chip 13: Sensor part 14: Gold bump 15: Sensing hole

Claims (12)

A layer in which a blind via hole and an arbitrarily shaped through hole are simultaneously formed at a desired position of a double-sided metal laminate in which metal layers are laminated on both sides of a resin layer by laser processing from one side. A metal for electrically connecting both surfaces of the metal layer by providing a metal plating layer on the resin surface in the through-hole formed by the laser processing and the exposed metal portion and providing a metal plating layer A method for producing a double-sided circuit board, comprising a plating step and then a metal pattern forming step for forming a metal pattern on both sides. Double-sided metal laminate is a single-sided metal having a heat-fusible polyimide layer in which a metal foil is thermocompression bonded to both sides of a polyimide film having a heat-fusible three-layer structure, or a polyimide precursor solution is cast on the metal foil. A metal layer is laminated on both sides of the polyimide film by either laminating two of the tension laminates by thermocompression bonding or by metal plating after depositing a base metal and copper on both sides of the polyimide film. 2. A method for producing a double-sided circuit board according to 1. 2. The method for manufacturing a double-sided circuit board according to claim 1, wherein the laser processing is performed by a UV-YAG laser. 2. The method for manufacturing a double-sided circuit board according to claim 1, wherein the laser processing is continuously performed by a reel-to-roll method. After the laser processing step simultaneously forms the blind via hole and any irregularly shaped through-hole, the laser peeling process is performed by peeling the thin film layer with an easily peelable adhesive laminated on the other surface. The method for producing a double-sided circuit board according to claim 1, further comprising a step of removing waste generated by the processing together. The metal plating step includes the following steps: cleaning in the hole, acid cleaning of the surface, formation of a conductive film in the hole, formation of a copper plating layer in the hole and on the metal layer by electrolytic copper plating. A method for producing a double-sided circuit board as described in 1. 2. The metal pattern forming step comprises forming an etching resist on both surfaces of the metal plating layer and forming a metal pattern having a desired shape by exposure, development, etching of the metal layer, and peeling of the etching resist. A method for producing a double-sided circuit board as described in 1. 2. The method for manufacturing a double-sided circuit board according to claim 1, wherein the metal pattern forming step forms the signal wiring layer on the metal layer on one side and the ground wiring layer on the metal layer on the other side. Furthermore, the manufacturing method of the double-sided circuit board of Claim 1 which has the process of forming protective films, such as solder resist of desired shape. 2. The double-sided circuit board according to claim 1, wherein the solder resist is a photosensitive dry film type, which is laminated at a predetermined position by exposure and development after laminating under vacuum. Law. Furthermore, the manufacturing method of the double-sided circuit board of Claim 1 which has the process of performing metal plating, such as Ni / Au or tin, to the exposed metal part. The method for producing a double-sided circuit board according to claim 11, wherein the metal plating is electrolytic nickel plating and then electrolytic gold plating.

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