JP2002141640A - Flexible printed-wiring board, and its manufacturing method - Google Patents

Abstract

PROBLEM TO BE SOLVED: To obtain a flexible printed-wiring board that can form fine wiring, has a wiring pattern near the center in a thickness direction, and can obtain a contact for connection from both the front and rear. SOLUTION: The wiring pattern 3 is formed by electrolytic plate with a metal plate 1 as a lead for electrolytic plating, an insulating resin 4 is formed on it, an opening 5 is formed at an insulating covering so that the wiring pattern is exposed partially. The metal plate is removed by etching, the insulating covering 4 is formed also on a surface where the metal plate is removed, and an opening is formed also on the insulating covering.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a flexible printed wiring board, capable of forming fine wiring, having a wiring pattern near the center in the thickness direction, and obtaining electrical connection contacts from both front and back surfaces. The present invention relates to a flexible printed wiring board and a method for manufacturing the same.

[0002]

2. Description of the Related Art In recent years, with the demand for higher functionality and lighter, thinner and smaller electronic devices, high-density integration of electronic components and further high-density mounting have been promoted. Fine wiring is also being advanced in flexible printed wiring boards. Also, due to a demand for high-density mounting, components are mounted on both front and back surfaces of a flexible printed wiring board.

A conventional flexible printed wiring board is formed by laminating an insulating resin film such as polyester or polyimide with a copper foil using an adhesive such as epoxy or acrylic.
After forming a circuit by etching a copper foil, a film with an adhesive, which has been drilled in necessary places in advance, is pasted on the circuit to produce an insulating coating. However, in such a flexible printed wiring board, since a circuit is formed by etching a copper foil, it has been difficult to form fine wiring.

The bending property required of a flexible printed wiring board is evaluated as the bending resistance of the copper circuit when the bending is repeated. It is known that it is improved so that it is located at the center in the thickness direction of the copper circuit, that is, the insulating resin layers on the front and back surfaces of the copper circuit have the same thickness, and preferably the insulating resin having the same elastic modulus is used on the front and back surfaces. ing. However, in the above-mentioned conventional flexible printed wiring board, since an adhesive film that becomes an insulating coating is attached onto the copper circuit, the insulating coating is not flattened due to the unevenness of the circuit, and the copper circuit becomes thicker than the flexible printed wiring board. The folding endurance was not good because it was deviated in either direction.

Further, in order to form a connection hole on the insulating resin film side, a method of opening the hole with a laser or etching the insulating resin with a strong alkali is used. You can do fine processing,
Processing time is required, and there is a problem that a fine hole cannot be formed by resin etching.

As a technology for manufacturing a flexible printed wiring board capable of processing fine circuits and openings, TAB (Tape)
Automated Bonding) is known. In TAB, an insulating resin film that has been previously opened is bonded to a thin copper foil, and the opening is once filled with another resin, and then a fine circuit is etched into the copper foil. afterwards,
By removing the filled resin, a part of the copper circuit is exposed from the insulating resin film. A metal mold is usually used to form a hole in the insulating resin film, but a method of making a fine hole with high precision using a laser is also used.

In the TAB technology, circuit processing is performed by a dedicated etching apparatus, and it is said that a circuit having a line width of 15 μm can be manufactured at present. However, further miniaturization will not be easy in the future. There is no. Further, the processing steps are complicated, for example, the insulating resin film once drilled is filled with resin, the circuit processing is performed, and the resin is removed again after processing.

[0008] Also, a cover coat of an insulating resin is usually formed on the copper circuit surface, but the ink type cover coat is thinner than the insulating resin film used for TAB. Greatly deviates from the center in the thickness direction. In the case of a film-type cover coat with an adhesive, the thickness and elastic modulus of the insulating resin film used for TAB and the insulating resin film used for the cover coat are reduced. In other words, the copper circuit is displaced from the center in the thickness direction, and the elastic modulus of the insulating resin layer is different between the front and back of the copper circuit, and in each case, there is a problem that the folding resistance is not good.

[0009]

SUMMARY OF THE INVENTION The present invention has been made in view of the above-mentioned problems in a flexible printed wiring board, and allows fine wiring to be formed, and has a wiring pattern near the center in the thickness direction. It is an object of the present invention to provide a flexible printed circuit board and a method for manufacturing the same, in which contacts for electrical connection can be obtained from both sides.

[0010]

SUMMARY OF THE INVENTION According to the present invention, there is provided a wiring board in which a gap between a plurality of wiring patterns formed on the same plane is filled with a resin, on both front and back surfaces of the wiring board so as to cover the wiring pattern and the resin; An insulating coating is formed so as to have the same thickness on both sides, and an opening is provided in the insulating coating so that a part of the wiring pattern is exposed.

The present invention also provides a step of forming a wiring pattern by electrolytic plating using a metal plate as a lead for electrolytic plating, a step of forming an insulating film on the wiring pattern,
Forming an opening in the insulating coating so that a part of the wiring pattern is exposed, removing the metal plate by etching, and forming an insulating coating on the surface from which the metal plate has been removed. A method for manufacturing a flexible printed wiring board, characterized in that:

Further, the present invention provides, in addition to the above-mentioned manufacturing process,
A method for manufacturing a flexible printed wiring board, comprising a step of forming a resist metal by electrolytic plating between a metal plate and a wiring pattern using the metal plate as a lead for electrolytic plating.

In the present invention, the wiring pattern is formed by electrolytic plating using a metal plate as a lead for electrolytic plating. In electrolytic plating, a plating resist is formed on a metal plate, an opening corresponding to a wiring pattern is formed in the plating resist, and a metal is deposited in the opening by electrolytic plating to form a wiring pattern. In the method of forming by etching the copper foil, the cross section of the obtained wiring pattern is trapezoidal, but in the case of electrolytic plating, the wiring pattern with the same line width can be formed with the same shape as the verticality of the cross section of the plating resist. When formed, especially in a fine circuit, the wiring cross-sectional area can be increased, and a fine wiring with low wiring resistance can be formed.

Further, by forming the wiring pattern by electrolytic plating, the thickness of the wiring pattern can be formed to an arbitrary thickness by controlling the plating time, and the impedance control required in the high-frequency circuit can be controlled more precisely. There is also an advantage that can be.

After a wiring pattern is formed by electrolytic plating by using a photosensitive insulating resin as a plating resist, the photosensitive insulating resin layer is directly filled with a resin for filling a gap between wiring patterns of a flexible printed wiring board. Can be used as

A resist metal may be formed between the metal plate and the wiring pattern by electrolytic plating. In this case, when the metal plate described below is removed, etching stops at the resist metal layer. The metal plate can be removed while leaving the wiring pattern stably.

After a wiring pattern is formed on a metal plate, a method of forming an insulating coating serving as a cover coat on the wiring pattern includes a method of coating and laminating a dry film. An opening for electrical connection is formed in the formed insulating coating, but the opening can be precisely formed by using a photosensitive insulating coating.

Next, the metal plate is removed by etching to obtain a flexible printed wiring board with insulation coating.
After the metal plate is removed, the gap between the wiring patterns of the flexible printed wiring board is filled with resin, and the wiring pattern and the resin in the gap are flush with each other.

Further, on the surface from which the metal plate has been removed, an insulating coating serving as a cover coat is formed in the same manner as described above, and thereafter, an opening for electrical connection is formed in the formed insulating coating. By forming the thickness of the insulating coating to be the same as the thickness of the insulating coating previously formed on the opposite surface of the wiring pattern, the wiring pattern can be arranged at the center in the thickness direction of the flexible printed wiring board. A flexible printed wiring board having excellent folding resistance can be obtained.

[0020]

DESCRIPTION OF THE PREFERRED EMBODIMENTS Hereinafter, embodiments of the present invention will be described with reference to the drawings, but the present invention is not limited thereto. FIG. 1 is a cross-sectional view illustrating an example of a method for manufacturing a flexible printed wiring board according to an embodiment of the present invention. FIG. 2 is a cross-sectional view for explaining an example in which a resist metal is formed between a metal plate and a wiring pattern.

In the method of manufacturing a flexible printed wiring board according to the present invention, first, a plating resist 2 is formed on a metal plate 1 (FIG. 1A). The plating resist 2 can be formed by, for example, forming an ultraviolet-sensitive insulating resin film on the metal plate 1 by coating or laminating, selectively exposing it to light using a negative film or the like, and then developing it. Alternatively, a commercially available ultraviolet-sensitive dry film type plating resist may be laminated and exposed and developed in the same manner as described above. However, by using a photosensitive insulating resin, the flexible printed wiring of the present invention can be used. It is suitable because it can be used as a resin to fill the gaps between the wiring patterns of the board.

As the photosensitive insulating resin, photosensitive insulating resins such as epoxy acrylate, urethane acrylate, cresol novolak type photosensitive resin, photosensitive polyimide, and polybenzoxazole can be used.

When a commercially available plating resist is used, after forming a wiring pattern by electrolytic plating, the plating resist is removed, and another insulating resin is applied or laminated on the obtained wiring pattern. Then, it is necessary to fill the gap between the wiring patterns. In this case, by forming the insulating resin thickly so as to cover the wiring pattern, it is possible to double as the insulating coating 4 serving as a cover coat described below.

The material of the metal plate 1 may be any material as long as it is suitable for this manufacturing method. In particular, the material is resistant to the chemical used, and is finally removed by etching. It needs to be possible. Examples of the material of such a metal plate 1 include copper, copper alloy, 42 alloy, nickel and the like.

Next, a wiring pattern 3 is formed by electrolytic plating using the metal plate 1 as a lead (electrode for power supply) for electrolytic plating (FIG. 1B). By this electrolytic plating, a portion where the plating resist 2 is not formed on the metal plate 1 is
The wiring pattern 3 is formed. Examples of the material of the wiring pattern 3 include copper, nickel, gold, tin, and silver. Furthermore, by using copper, a low-resistance and stable wiring pattern 3 can be obtained.

At this time, before forming the wiring pattern,
A thin metal other than the wiring pattern is formed on the resist metal 6
(FIG. 2). The purpose of forming the resist metal 6 is to prevent the wiring pattern 3 from being eroded and corroded by a chemical used when etching the metal plate 1. Therefore, when the wiring pattern 3 has resistance to the chemical used when etching the metal plate 1, the resist metal 6 is unnecessary. The resist metal 6 does not need to be the same pattern as the wiring pattern 3, and the resist metal may be formed on the entire surface of the metal plate 1 before forming the plating resist 2 on the metal plate 1. The material of the resist metal 6 may be any material as long as it is suitable for this manufacturing method. In particular, the resist metal 6 must be resistant to a chemical used when the metal plate 1 is finally removed by etching. is necessary. For example,
Examples include nickel, gold, tin, silver, solder, and palladium.

Next, an insulating coating 4 is formed on the formed wiring pattern 3 (FIG. 1C). As the resin forming the insulating coating 4, any resin suitable for this manufacturing method can be used. The insulating coating 4 may be formed by a method suitable for the resin to be used. For example, a resin varnish may be directly applied by printing, curtain coating, bar coating, or the like, or a dry film type resin may be vacuum-laminated.
A method of laminating by a method such as a vacuum press is used.

Next, an opening 5 is formed in the formed insulating coating 4 (FIG. 1D). The method for forming the opening 5 may be any method as long as it is suitable for this manufacturing method. Dry etching using laser or plasma, chemical etching or the like can be used. The insulating coating 4 can be selectively exposed to light and developed to form the opening 5 precisely, which is suitable for the method for manufacturing a flexible printed wiring board of the present invention.

Next, the metal plate 1 is removed by etching (FIG. 1E). At this time, when the above-described resist metal 6 is not formed between the metal plate 1 and the wiring pattern 3 and the chemical pattern used when the metal plate 1 is removed by etching, the wiring pattern is If the wiring pattern 3 does not have resistance, it is necessary to control the etching time so that the wiring pattern 3 is not eroded by the etching solution for the metal plate 1.

When the above-described resist metal 6 is not formed between the metal plate 1 and the wiring pattern 3,
If the wiring pattern has resistance to the chemical used for removing the metal plate 1 by etching,
Since the wiring pattern is not eroded by the etching solution of the metal plate 1, only the metal plate 1 can be easily removed.

When the resist metal 6 is formed between the metal plate 1 and the wiring pattern 3, the resist metal has resistance to a chemical used when the metal plate 1 is removed by etching. Therefore, even if the metal plate 1 is etched, the resist metal is not eroded or corroded, and as a result, the wiring pattern 3 is not eroded or corroded. Therefore, only the metal plate 1 is easily removed. You can do it. When the material of the metal plate 1 is copper and the material of the resist metal is nickel, tin or solder, a commercially available ammonia-based etchant can be used. When the material of the metal plate 1 is copper and the material of the resist metal is gold, almost any etching solution can be used, including a ferric chloride solution and a cupric chloride solution.

If a resist metal is used, then:
The resist metal 6 is removed by etching. Since the wiring pattern 3 has resistance to the chemical used when the resist metal is removed by etching, the wiring pattern 3 is not eroded or corroded. Therefore, the wiring pattern 3 is exposed by removing the resist metal 6. When the material of the wiring pattern 3 is copper and the material of the resist metal is nickel, tin or solder, a commercially available solder / nickel release agent (for example, Mitsubishi Gas Chemical, trade name Pewta)
x) can be used. When the material of the wiring pattern 3 is copper and the material of the resist metal is gold, it is difficult to etch the resist metal 6 without eroding or corroding the wiring pattern 3. In this case, the step of etching the resist metal 6 may be omitted.

Next, on the surface from which the metal plate 1 has been removed,
An insulating coating 4 is formed (FIG. 1F). As the insulating coating, a resin may be applied, or a film-shaped one may be laminated. It is preferable that the thickness of the insulating coating is the same as that of the insulating coating previously formed on the wiring pattern. If the thickness is different, the wiring pattern will be biased to either surface from the center in the thickness direction of the flexible printed wiring board,
Since the stress applied to the wiring when bent becomes asymmetric,
Poor folding resistance. It is preferable that the same kind of resin is used on both sides of the insulating resin used for the insulating coating 4.
When different resins are used, particularly when the elastic moduli are largely different, the stress applied to the wiring at the time of bending becomes asymmetric, and the folding resistance is not good.

Next, the flexible printed wiring board of the present invention is obtained by providing an opening in the insulating coating 4 formed on the surface on the side from which the metal plate has been removed so that a part of the wiring pattern is exposed (see FIG. 4). FIG. 1 (g)). Laser or chemical etching can also be used to form the opening, but by using a photosensitive insulating coating resin and forming it by exposure and development, a fine opening can be formed with high accuracy. It is suitable for a method for manufacturing a flexible printed wiring board.

[0035]

According to the present invention, a fine wiring pattern can be formed, and the wiring pattern is arranged at the center in the thickness direction of the flexible printed wiring board, so that it has excellent folding resistance and can easily be electrically connected from both sides. And a flexible printed wiring board from which a contact can be obtained.

[Brief description of the drawings]

FIG. 1 is a sectional view showing an example of a method for manufacturing a flexible printed wiring board according to an embodiment of the present invention.

FIG. 2 is a cross-sectional view illustrating a case where a resist metal is formed in the method for manufacturing a flexible printed wiring board according to the embodiment of the present invention.

[Explanation of symbols]

 DESCRIPTION OF SYMBOLS 1 Metal plate 2 Plating resist 3 Wiring pattern 4 Insulation coating 5 Opening 6 Resist metal

 ────────────────────────────────────────────────── ─── Continuation of front page (72) Inventor Hiroyuki Sawai 2-5-8 Higashishinagawa, Shinagawa-ku, Tokyo Sumitomo Bakelite Co., Ltd. F-term (reference) 5E314 AA24 BB02 BB11 CC01 CC15 FF01 FF06 FF17 GG24 5E338 AA01 AA12 BB19 BB63 CC01 CD13 EE32 5E343 AA02 AA12 AA33 BB15 BB24 BB71 CC67 DD43 ER21 ER25 GG08 GG20

Claims (3)

[Claims] 1. A wiring board in which gaps between a plurality of wiring patterns formed on the same plane are filled with resin so as to cover the wiring patterns and the resin on both the front and back surfaces, and to have the same thickness on both sides. A flexible printed wiring board, wherein an insulating coating is formed on the insulating coating, and an opening is provided in the insulating coating so that a part of the wiring pattern is exposed. 2. A step of forming a wiring pattern by electrolytic plating using a metal plate as a lead for electrolytic plating, a step of forming an insulating coating on the wiring pattern, and a step of forming an insulating coating on the wiring pattern so that a part of the wiring pattern is exposed. Manufacturing a flexible printed wiring board, comprising: a step of forming an opening in the substrate; a step of removing the metal plate by etching; and a step of forming an insulating coating on the surface from which the metal plate has been removed. Method. 3. A step of forming a resist metal by electrolytic plating between a metal plate and a wiring pattern using the metal plate as a lead for electrolytic plating.
A method for manufacturing a flexible printed wiring board according to claim 2.