WO2017159773A1

WO2017159773A1 - Flexible circuit board and method for manufacturing same

Info

Publication number: WO2017159773A1
Application number: PCT/JP2017/010599
Authority: WO
Inventors: 田嶋　久容; 博和奥薗; 町田　英明; 金子　美晴
Original assignee: 東レエンジニアリング株式会社; 東レ・デュポン株式会社; レイテック株式会社
Priority date: 2016-03-17
Filing date: 2017-03-16
Publication date: 2017-09-21
Also published as: TWI716565B; KR102312182B1; CN109076704B; JPWO2017159773A1; CN109076704A; TW201806458A; KR20180122672A; JP6955481B2

Abstract

Provided is a flexible circuit board in which a coverlay film that offers a high degree of freedom in regard to the shape and size of an opening part is laminated on an FPC, with sufficient insulation between adjacent wiring being ensured for wiring positioned in the coverlay opening part. This flexible circuit board is provided with an insulation film 22, wiring 30, 32 formed on the insulation film, and a protective film 12 that has insulating properties disposed on a portion of the insulation film and the wiring. The protective film is laminated on the insulation film and the wiring with an adhesive agent 15 interposed therebetween, and the part of the wiring on which the protective film is not disposed is exposed on the top surface, the adhesive agent being adhered on the side or periphery of said part.

Description

Flexible circuit board and manufacturing method thereof

The present invention relates to a flexible circuit board and a method for manufacturing the same.

Conventionally, a flexible wiring board (hereinafter referred to as FPC) in which circuit wiring is formed on an insulating resin film is generally used. Since various apparatuses and devices incorporating electronic components mounted on FPCs and FPCs are always required to be small, thin, and light, more thin FPCs that can be bent are used. In addition, the wiring pitch of the FPC is small, and the component mounting density on the circuit board is increasing.

As described above, in order to make electronic devices and electronic components small, thin, and light, it is necessary to prevent short circuit between circuit wirings and between circuit wirings and surrounding components and wirings. It is necessary to cover the circuit wiring with an insulating material as much as possible to maintain insulation reliability. For this purpose, it is common practice to protect portions of the FPC circuit wiring other than the connection portions with terminals and electronic components with a coverlay film or a cover coat.

The cover lay film is an insulating resin film coated with an adhesive. After opening the part corresponding to the circuit wiring connection part or component mounting part in the FPC, the cover lay film is pasted on the circuit wiring. There is (for example, Patent Document 1). Since the connection part of circuit wiring and the part mounting part in FPC correspond to the opening part of a coverlay film, it will be in the exposed state. By bonding the coverlay film, the mechanical strength of the FPC is also improved, the circuit is protected, and the resistance to bending is also improved.

The cover coat is formed by applying and curing on a portion of the circuit wiring other than the connection portion using a material that has an insulating property and is cured by heat or light.

Also, the photosensitive cover lay is a sheet of a material that has insulating properties and is cured by light, and is cured by light after being attached to circuit wiring.

JP-A-9-283895 JP-A-10-97081

However, since the coverlay film is provided with an opening in advance and then bonded to the FPC, it takes time to align the opening and a specific part of the circuit wiring in the FPC, and if the bonding position is shifted, it is a defective product. End up. In addition, due to the size of the mold for forming the opening and the physical characteristics of the material film, the shape and size of the opening are naturally limited, and the design of the circuit wiring of the FPC is limited. End up. Furthermore, in the circuit wiring of the FPC located in the opening of the cover lay film, the opposing side surfaces of the adjacent wiring are exposed and there is a possibility that a problem occurs in the insulation between the wirings as the wiring pitch becomes smaller. The wiring at this portion has low peel strength, and the wiring is easy to peel off.

On the other hand, since the cover coat is applied to the FPC by a printing method, particularly when a photosensitive material is used, the opening can be formed small, so this is an effective method for high-density mounting. There is a problem that the thickness of the FPC is not uniform and the FPC tends to curl after curing. Further, the function of increasing the mechanical strength of FPC is weak, and there is a problem in bending resistance.

Also, a process has been proposed in which a photosensitive coverlay is bonded to the circuit surface of the FPC and then cured by light to form an insulating protective film on the FPC. There are also problems of insufficient mechanical strength and insufficient bending resistance for circuit protection.

The present invention has been made in view of such points, and the object of the present invention is to provide a coverlay film having a high degree of freedom in designing the shape and size of the opening bonded to the FPC so that the coverlay It is an object of the present invention to provide a flexible circuit board in which insulation between adjacent wirings is sufficiently secured in wirings positioned in an opening.

The flexible circuit board of the present invention includes an insulating film, a wiring formed on the insulating film, and an insulating protective film disposed on the insulating film and a part of the wiring. Is bonded to the insulating film and the wiring via an adhesive, and a portion of the wiring where the protective film is not disposed is exposed to the side or the periphery while the upper surface is exposed. The adhesive is attached. That is, the protective film is not disposed on the wiring except for the part, and the upper surface of the wiring is exposed at that part.

The protective film is preferably made of any one of polyimide resin and polyester resin.

Another flexible circuit board of the present invention includes an insulating film, a wiring formed on the insulating film, and an insulating protective film disposed on the insulating film and a part of the wiring, The protective film is bonded to the insulating film and the wiring via an adhesive, and the adhesive adheres to the side or the periphery of the wiring in a portion where the protective film is not disposed on the protective film. The adhesive is provided on the insulating film on which the wiring is not formed, and a conductive layer made of a conductive member is placed on the surface of the adhesive and the upper surface of the wiring.

The conductive layer may be a plating layer.

The method for producing a flexible circuit board of the present invention includes a step of preparing a wiring forming film in which wiring is formed on an insulating film, and a cover sheet in which an adhesive is formed on one surface of the insulating protective film. A bonding process in which the adhesive is placed facing the wiring and placed on the wiring forming film, an adhesive exposing process of removing a part of the protective film to expose a part of the adhesive, and an exposure And a wiring exposure step of exposing an upper surface of the wiring by removing an upper portion of the part of the adhesive.

The protective film is preferably made of any one of polyimide resin and polyester resin, and the adhesive exposing step is preferably performed by etching.

The wiring exposure step is preferably performed by etching using a solution containing permanganate and sodium hydroxide. Here, the permanganate is a salt of permanganic acid and a base, and examples thereof include potassium permanganate and sodium permanganate.

The solution used in the wiring exposure step has a potassium permanganate concentration of 2 mass% to 18.15 mass% and a sodium hydroxide concentration of 20 mass% or less, or a potassium permanganate concentration of 1. % By mass or more and less than 2% by mass and the concentration of sodium hydroxide is 0.05% by mass or more and 20% by mass or less, or the concentration of potassium permanganate is 0.5% by mass or more and less than 1% by mass and the concentration of sodium hydroxide 0.05 mass% or more and less than 18 mass%, or the concentration of potassium permanganate is 0.1 mass% or more and less than 0.5 mass% and the concentration of sodium hydroxide is 1.5 mass% or more and less than 18 mass% Or the concentration of potassium permanganate is 0.05% by mass or more and less than 0.1% by mass and the concentration of sodium hydroxide is 1.5% by mass or more and less than 5% by mass. It is preferred.

The solution used in the wiring exposure step has a sodium permanganate concentration of 2 mass% to 20 mass% and a sodium hydroxide concentration of 20 mass% or less, or a sodium permanganate concentration of 1 mass%. Or more and less than 2% by mass and the concentration of sodium hydroxide is 0.05 to 20% by mass, or the concentration of sodium permanganate is 0.5 to 1% by mass and the concentration of sodium hydroxide is 0 0.05 mass% or more and less than 18 mass%, or a sodium permanganate concentration of 0.1 mass% or more and less than 0.5 mass% and a sodium hydroxide concentration of 1.5 mass% or more and less than 18 mass%. Either is preferable.

In the flexible circuit board of the present invention, since the wiring in the portion where the protective film is not disposed is surrounded by the adhesive around the side, the wiring is mechanically and electrically protected by the adhesive, and the wiring The peel strength and insulation between the wires are sufficiently secured.

It is a cross-sectional schematic diagram which shows a preparatory process. It is a cross-sectional schematic diagram which shows a bonding process. It is a cross-sectional schematic diagram which shows an adhesive agent exposure process. It is a cross-sectional schematic diagram which shows a wiring exposure process. It is a cross-sectional schematic diagram which shows the flexible circuit board which concerns on another embodiment. It is a cross-sectional schematic diagram which shows the flexible circuit board which concerns on other embodiment.

Hereinafter, embodiments of the present invention will be described in detail with reference to the drawings. The following description of the preferred embodiments is merely exemplary in nature and is not intended to limit the invention, its application, or its use. The “cover sheet” in the present invention is a type of cover lay, and refers to a sheet provided with an adhesive that ensures the peel strength of the wiring and the insulation between the wirings.

(Embodiment 1)
In Embodiment 1, an adhesive is formed on one surface of the insulating protective film, and a step (preparation step) of preparing a wiring forming film (corresponding to FPC) in which wiring is formed on the insulating film. A cover sheet is bonded to the wiring-forming film with the adhesive facing the wiring (bonding process), and a part of the protective film is removed to expose a part of the adhesive. A flexible circuit board is manufactured by a step (adhesive exposing step) and a step (wiring exposing step) of removing the upper part of the exposed part of the adhesive to expose the upper surface of the wiring.

FIG. 1 is a view showing a cross section of the wiring forming film 20 and the cover sheet 10 in the preparation process. The wiring forming film 20 has a plurality of wirings 31 formed on the insulating film 22. The cover sheet 10 is one in which an insulating adhesive 14 is formed on one surface of an insulating protective film 12. Note that it is not necessary to provide an opening in the cover sheet 10.

As the insulating film 22, a film made of polyimide resin, polyester resin, PPS (polyphenylene sulfide) resin, aramid resin, LCP (liquid crystal polymer) or the like and having a thickness of about 5 μm to 75 μm is generally used. The wiring 31 is formed by bonding a copper foil to the insulating film 22 and patterning the copper foil by etching, or by patterning by a semi-additive method using a metalizing material, or by an additive method. Or formed by printing using conductive ink or the like. Note that there is generally a form in which an adhesive made of the same or different material as the insulating film 22 exists between the insulating film 22 and the wiring 31. As the protective film 12, a film made of polyimide resin, polyester resin, PPS (polyphenylene sulfide) resin, aramid resin, LCP (liquid crystal polymer) or the like and having a thickness of about 2.5 μm to 25 μm is generally used. From the viewpoint of heat resistance, dimensional stability, and bending resistance, a polyimide resin is preferable. The adhesive 14 is mainly composed of an epoxy resin, an acrylic resin, a polyimide resin, or the like, and is generally a thermosetting resin, but may be a photo-curing type and has a thickness of 5 μm. To about 35 μm.

Next, the wiring forming film 20 and the cover sheet 10 are bonded together (FIG. 2, bonding process). In the bonding step, the adhesive 14 formed on one surface of the cover sheet 10 is stacked facing the wiring 31 of the wiring forming film 20, and heated or irradiated with UV light while applying pressure, thereby the adhesive. 14 is cured. Since it is not necessary to provide an opening in the cover sheet 10 in the bonding step, it is not necessary to align the wiring forming film 20 with the wiring 31 (alignment between the opening and the wiring portion to be exposed), and it is easy to roll. Bonding can be performed by toe roll. In addition, you may bond the wiring formation film 20 and the cover sheet 10 in the sheet unit (what is called a sheet | seat) in which a single or several circuit is included. Also in this case, exact alignment between the opening and the exposed wiring portion is not necessary. As described above, in the present embodiment, since strict alignment at the time of bonding is not required, defective products that have failed in alignment do not occur, and the process speed can be increased, so that bonding can be performed at low cost and at high speed. it can. Although not intended to align the opening, it goes without saying that a guide hole or the like may be previously formed in the cover sheet as a guide in order to send or install the material in the bonding process.

When the bonding process is completed, all the

wirings

32 and 32a are protected by the cover sheet 10. Then, the protective film 12 existing above the portion of the wiring 32a to be exposed is removed to form the opening 40 (FIG. 3, adhesive exposing step). There are various methods for removing the protective film 12, such as a method using etching and a method using a laser. For example, the etching method uses the method disclosed in Patent Document 2 to form an etching resistant resist in a portion other than the portion where the opening is formed, and then an etching solution is applied. This step is the same as the wiring formation by etching, and can be easily performed with high accuracy. A method using a laser can also be performed with high accuracy.

In the adhesive exposing step, the opening 40 is formed in the protective film 12, but since the cured adhesive 15 is placed on the upper surface of the wiring 30a located in the opening 40, the upper surface of the wiring 30a is exposed. Not. Then, the cured adhesive 15 on the upper surface of the wiring 30a is removed (FIG. 4, wiring exposure process). Removal of the cured adhesive 15 is preferably performed using a solution that dissolves the adhesive 15, and the type of the solution may be selected depending on the type of the adhesive 15. For example, in the case of the epoxy adhesive 15, it may be dissolved using an aqueous solution of potassium permanganate and sodium hydroxide, washed with water, and then neutralized. The wiring 30a is preferably filled with the adhesive 15 and only the upper surface is exposed. For that purpose, it is preferable to control the dissolution rate by reducing the concentration of the solution in which the adhesive 15 is dissolved.

By performing the above steps, a part of the wiring 30 of the wiring forming film 20 is located in the opening 40 of the protective film 12 and is filled with the adhesive 15 so that the upper surface 39 is exposed. The other wirings 32 are embedded with the adhesive 15 and the protective film 12 is present above. That is, a part of the wirings 30 of the wiring forming film 20 is in a state where the protective film 12 is not disposed on the upper surface 39 and the adhesive 15 is present on the side or the periphery. .

In this way, since the adhesive 15 is present on the side or the periphery of the wiring 30 positioned in the opening 40 of the protective film 12, the inter-line insulation reliability between the

adjacent wirings

30 and 30 is improved. Can be kept high. In particular, the insulation reliability between lines can be kept high even when the wiring pitch is reduced. And the protective film 12 is excellent in bending resistance.

In addition, when a normal cover lay film or cover coat is used, when the width of the exposed wiring is reduced (that is, the wiring pitch is reduced), the peel strength of the wiring from the wiring forming film 20 is reduced, There is a risk that the wiring may be peeled off from the flexible circuit board or cracked due to changes in the FPC usage environment, deterioration over time, external pressure or bending from the outside. However, in the case of the flexible circuit board according to the present embodiment, the side or the periphery of the wiring 30 is surrounded by the adhesive 15, so that the peel strength can be kept sufficiently large even if the width of the wiring 30 is reduced. There is no risk of peeling from the flexible circuit board or cracking of the wiring. Furthermore, when the exposed wiring 30 is electrically connected to an external terminal using an anisotropic conductive adhesive (ACF or ACP), if it is a normal cover lay film or cover coat, the adjacent wiring (wiring) Since the anisotropic conductive adhesive also enters between the side surfaces of the conductive conductive particles in the anisotropic conductive adhesive, there is a possibility that the conductive particles in the anisotropic conductive adhesive may conduct between adjacent wirings. There is no such a fear, and also in this respect, the insulation reliability between the adjacent wirings 30 can be kept high.

In the conventional coverlay film, it is necessary to form an opening by punching before bonding to the wiring forming film. For this purpose, a mold is required. However, if the flexible circuit board of this embodiment is used, the mold is unnecessary and the cost can be reduced accordingly. In addition, in order to form the opening by punching, the size, shape, and opening ratio of the opening are limited. Therefore, it is not possible to design a small opening and the design of the opening shape is not free. If it is a flexible circuit board, the size and shape of the opening can be designed freely. In addition, if the flexible circuit board of this embodiment is used, it is not necessary to perform half-cut punching, the release film for the coverlay can be thinned, and the change in dimensional accuracy such as curl due to stress at the time of peeling is greatly increased. Therefore, the cost can be reduced. Furthermore, the flexible circuit board according to the present embodiment can easily process roll-to-roll, and can easily align the cover sheet and the wiring forming film at the time of bonding. Time can be shortened. In addition, since the conventional cover lay film is bonded after forming an opening, the adhesive oozes out in the opening, and in order to prevent it, in the bonding process, flexibility, heat resistance, peeling However, if the flexible circuit board of this embodiment is used, such a cushioning material is not necessary and the cost can be reduced.

<Polyimide film>
For the cover sheet used in the present invention, it is preferable to use a polyimide resin in view of heat resistance, dimensional stability, and bending resistance of the FPC, and it is further preferable to use a polyimide film having specific physical properties.

[Production method of polyimide film]
In obtaining a polyimide film, first, an aromatic diamine component and an aromatic acid anhydride component are polymerized in an organic solvent to obtain a polyamic acid solution (hereinafter also referred to as a polyamic acid solution).

The polyamic acid solution can be obtained by polymerizing a chemical substance mainly composed of an aromatic diamine component and an aromatic acid anhydride component in an organic solvent.

Examples of the aromatic diamine component include paraphenylene diamine, metaphenylene diamine, benzidine, paraxylylene diamine, 4,4′-diaminodiphenyl ether, 3,4′-diaminodiphenyl ether, 4,4′-diaminodiphenylmethane, 4, 4'-diaminodiphenylsulfone, 3,3'-dimethyl-4,4'-diaminodiphenylmethane, 1,5-diaminonaphthalene, 3,3'-dimethoxybenzidine, 1,4-bis (3-methyl-5-amino Phenyl) benzene and their amide-forming derivatives. These may be used individually by 1 type, and 2 or more types may be mixed and used for them.

The aromatic diamine component is preferably at least one selected from the group consisting of paraphenylenediamine and 4,4'-diaminodiphenyl ether from the viewpoint of excellent heat resistance and dimensional stability due to heat.

Specific examples of the aromatic acid anhydride component include, for example, pyromellitic acid, 3,3 ′, 4,4′-biphenyltetracarboxylic acid, 2,3 ′, 3,4′-biphenyltetracarboxylic acid, 3, 3 ′, 4,4′-benzophenonetetracarboxylic acid, 2,3,6,7-naphthalenetetracarboxylic acid, 2,2-bis (3,4-dicarboxyphenyl) ether, pyridine-2,3,5 Examples thereof include acid anhydride components of aromatic tetracarboxylic acids such as 6-tetracarboxylic acid and amide-forming derivatives thereof. These may be used individually by 1 type, and 2 or more types may be mixed and used for them.

As the aromatic acid anhydride component, pyromellitic dianhydride and / or 3,3 ′, 4,4′-biphenyltetracarboxylic dianhydride are used from the viewpoint of excellent heat resistance and dimensional stability due to heat. Is preferred.

In the present invention, the combination of the aromatic diamine component and the acid anhydride component includes one or more aromatic diamine components selected from the group consisting of paraphenylenediamine, 4,4′-diaminodiphenyl ether and 3,4′-diaminodiphenyl ether. And a combination of pyromellitic dianhydride and / or an aromatic acid anhydride component of 3,3 ′, 4,4′-biphenyltetracarboxylic dianhydride is particularly preferable.

When the aromatic diamine component contains paraphenylene diamine and 4,4′-diaminodiphenyl ether, the molar ratio of paraphenylene diamine to 4,4′-diaminodiphenyl ether is preferably 50/50 to 0/100, More preferred is / 60 to 0/100.

When the aromatic acid anhydride component comprises pyromellitic dianhydride and 3,3 ′, 4,4′-biphenyltetracarboxylic dianhydride, pyromellitic dianhydride and 3,3 ′, 4,4 The molar ratio of '-biphenyltetracarboxylic dianhydride is preferably 100/0 to 50/50, and more preferably 100/0 to 60/40.

As a method for producing a polyimide film, for example, a method in which a polyamic acid solution is cast into a film and thermally decyclized and desolvated to obtain a polyimide film, a cyclization catalyst and a dehydrating agent are mixed in the polyamic acid solution, and a chemical is obtained. A method of obtaining a polyimide film by preparing a gel film by decyclizing it and heating and desolvating it is preferred, but the latter is preferred.

The polyimide film thus obtained can be further annealed to reduce the heat shrinkage rate (specifically, the heat shrinkage rate after heating at 200 ° C. for 60 minutes is 0.2% or less. From the viewpoint of the above. The method of annealing treatment is not particularly limited, and may be according to a conventional method. The annealing temperature is not particularly limited, but is preferably 200 to 500 ° C, more preferably 200 to 370 ° C, and particularly preferably 210 to 350 ° C. Specifically, it is preferable to carry out the annealing treatment by running the film in a furnace heated to the above temperature range under low tension. The time during which the film stays in the furnace is the processing time, but it is controlled by changing the running speed, and the processing time is preferably 5 seconds to 5 minutes. The film tension during running is preferably 10 to 50 N / m, more preferably 20 to 30 N / m.

In order to increase the dimensional accuracy of the FPC, the polyimide film has a heat shrinkage ratio after heating at 200 ° C. for 60 minutes, usually 0.2% or less (eg, 0.01 to 0.15%), preferably 0.15. % Or less (for example, 0.01 to 0.1%), preferably 0.1% or less (for example, 0.01 to 0.07%). The heat shrinkage rate after heating the polyimide film at 200 ° C. for 60 minutes is the CNC image processing system NEXIV VM- after the film size (L1) after being left in a room adjusted to 25 ° C. and 60% RH for 2 hours or more. The film dimensions (L2) after measurement using a 250 (Nikon), followed by heating at 200 ° C. for 60 minutes and then leaving again in a room adjusted to 25 ° C. and 60% RH for one day are measured with the CNC image. It can be measured using a processing apparatus system and calculated by the following formula.
Thermal contraction rate (%) =-{(L2-L1) / L1} × 100

The average linear expansion coefficient of the polyimide film is not particularly limited, but is, for example, 0 to 100 ppm / ° C., preferably 0 to 50 ppm / ° C., more preferably 3 to 35 ppm / ° C. The thermal expansion coefficient can be measured by using TMA-50 manufactured by Shimadzu Corporation under the conditions of a measurement temperature range: 50 to 200 ° C. and a temperature increase rate: 10 ° C./min.

<Example 1>
In Example 1, a cover sheet manufactured by Unon Giken Co., Ltd. was used, in which the protective film was Kapton 50EN having a thickness of 12.5 μm and an epoxy adhesive 20 μm was formed thereon. This cover sheet was affixed to a circuit-forming substrate having a circuit formed on one side under a bonding condition of 150 ° C., 3 MPa, 30 minutes.

A part of the protective film of the flexible circuit board with the cover sheet is removed by etching with a polyimide etching solution TPE3000N manufactured by Toray Engineering Co., Ltd., and 35 mm × 22 within a range including the opening from the sheet-like substrate after the removal. A test piece of 5 mm was prepared.

Using the above-mentioned test piece, the adhesive was etched in 100 g of an etching solution containing at least one of potassium permanganate and sodium hydroxide, washed with water, and then neutralized.

At that time, the etching rate until the wiring of the test piece was exposed was changed in various concentrations of potassium permanganate and sodium hydroxide contained in the etching solution.

The results are shown in Table 1. In addition, the conditions of patent 3251515 were used for the etching conditions of the protective film at this time.

According to this result, when potassium permanganate is not included, any concentration of sodium hydroxide or potassium permanganate is 1.2 mass% or less and sodium hydroxide is not present. If less than 0.05% by weight, or if potassium permanganate is 0.1% by weight or less and sodium hydroxide is less than 1.5% by weight, or if potassium permanganate is less than 1% by weight And when sodium hydroxide is 18% by mass or more, or when potassium permanganate is less than 0.1% by mass and sodium hydroxide is 5% by mass or more, the adhesive may be etched. could not.

On the other hand, the concentration of potassium permanganate is 2% by mass or more and 18.15% by mass or less and the concentration of sodium hydroxide is 20% by mass or less, or the concentration of potassium permanganate is 1% by mass or more and less than 2% by mass and water. The concentration of sodium oxide is 0.05% by mass or more and 20% by mass or less, or the concentration of potassium permanganate is 0.5% by mass or more and less than 1% by mass, and the concentration of sodium hydroxide is 0.05% by mass or more and 18% by mass. %, Or the concentration of potassium permanganate is 0.1% by mass or more and less than 0.5% by mass and the concentration of sodium hydroxide is 1.5% by mass or more and less than 18% by mass, or the concentration of potassium permanganate Was 0.05 mass% or more and less than 0.1 mass% and the concentration of sodium hydroxide was 1.5 mass% or more and less than 5 mass%, the adhesive could be etched.

Therefore, in the conditions indicated by numbers in the table and the conditions indicated by ◯, that is, the range surrounded by the thick line, the 10 μm thick adhesive can be etched within 60 minutes, and cannot be etched in the table. Alternatively, it is presumed that the adhesive having a thickness of 10 μm cannot be etched within 60 minutes under the conditions indicated by “x”.

In addition, the etching time was shorter as the concentration of each chemical solution was higher in the etching conditions.

<Example 2>
In Example 2, the same test piece as in Example 1 was used, and the adhesive was etched using a solution containing at least one of sodium permanganate and sodium hydroxide as an adhesive etchant. That is, in this example, unlike in Example 1, the permanganate contained in the etching solution is sodium permanganate.

The results are shown in Table 2. In addition, the conditions of patent 3251515 were used for the etching conditions of the protective film at this time.

According to this result, when sodium permanganate is 0.05% by mass, any concentration of sodium hydroxide or sodium permanganate is 1.2% by mass or less and When sodium is not contained, or when sodium permanganate is 0.1 mass% or less and sodium hydroxide is less than 1.5 mass%, or sodium permanganate is 0.5 mass% or less However, when the amount of sodium hydroxide was 18% by mass or more, the adhesive could not be etched.

On the other hand, the concentration of sodium permanganate is 2% by mass to 20% by mass and the concentration of sodium hydroxide is 20% by mass or less, or the concentration of sodium permanganate is 1% by mass to less than 2% by mass and sodium hydroxide Concentration of 0.05% to 20% by mass, or sodium permanganate concentration of 0.5% to less than 1% by mass and sodium hydroxide concentration of 0.05% to less than 18% by mass Alternatively, the adhesive can be etched when the concentration of sodium permanganate is 0.1% by weight or more and less than 0.5% by weight and the concentration of sodium hydroxide is 1.5% by weight or more and less than 18% by weight. It was.

<Example 3>
In Example 3, etching was performed using two types of cover sheets.

First, as the first cover sheet, a cover sheet manufactured by Unon Giken Co., Ltd. was used, in which the protective film was Kapton 50EN having a thickness of 12.5 μm and an epoxy adhesive 20 μm was formed thereon. This cover sheet was affixed on both surfaces of the circuit formation board in which the circuit was formed in both surfaces. This adhesive is made of a material different from that of the cover sheet of Example 1. The pasting conditions are the same as those in the first embodiment.

A part of the protective film of the flexible circuit board with cover sheet is removed by etching with a polyimide etching solution TPE3000N manufactured by Toray Engineering Co., Ltd., and 40 mm × 90 mm within a range including the opening from the sheet-like substrate after the removal. A test piece was prepared.

Next, as a second cover sheet, a cover sheet made by Nikkan Kogyo Co., Ltd., in which the protective film is Kapton 50H having a thickness of 12.5 μm and an epoxy adhesive 20 μm formed thereon, is used. The cover sheet was affixed to both sides of a circuit-forming substrate on which circuits were formed on both sides. The bonding conditions were 160 ° C., 3 MPa, and 40 minutes.

The adhesive was etched in 100 g of an etching solution containing sodium permanganate and sodium hydroxide using the above-mentioned two types of test pieces, washed with water, and then neutralized.

The results are shown in Table 3. In addition, the conditions of patent 3251515 were used for the etching conditions of the protective film at this time.

According to this result, the adhesive could be etched although the etching time was different at a concentration of 8.5% by mass of sodium permanganate and 5% by mass of sodium hydroxide.

<Example 4>
In Example 4, etching was performed using two types of cover sheets.

First, as the first cover sheet, a cover sheet made of Kyocera Chemical Co., Ltd. was used, in which the protective film was Kapton 50ENC having a thickness of 12.5 μm and an epoxy adhesive 25 μm was formed thereon. This cover sheet was affixed on both surfaces of the circuit formation board in which the circuit was formed in both surfaces. This adhesive is different in material from the adhesives of the cover sheets of Examples 1 and 2. The pasting conditions are the same as those in the first embodiment.

A part of the protective film of the flexible circuit board with cover sheet is removed by etching with a polyimide etching solution TPE3000N manufactured by Toray Engineering Co., Ltd., and 20 mm × 20 mm within the range including the opening from the sheet-like substrate after the removal. A test piece was prepared.

Next, as the second cover sheet, a cover sheet made by Kyocera Chemical Co., Ltd., in which the protective film is Kapton 50ENC having a thickness of 12.5 μm and an epoxy adhesive 25 μm formed thereon, is used. The cover sheet was affixed to both sides of a circuit-forming substrate on which circuits were formed on both sides. The bonding conditions are the same as in Example 1. The cover sheet adhesive is different in material from the cover sheets of Examples 1 and 2 and the first cover sheet of this example.

The results are shown in Table 4. In addition, the conditions of patent 3251515 were used for the etching conditions of the protective film at this time.

(Embodiment 2)
The flexible circuit board according to the second embodiment is shown in FIG. 5 in the part of the flexible circuit board shown in FIG. 4 from which the adhesive 15 is removed in the opening formed in the protective film 12 and the wiring exposure process. Thus, the conductive layer 50 made of a conductive member is formed. The conductive layer 50 is placed on the upper surface 39 of the wiring 33 and is formed so as to fill the entire depression formed in the adhesive exposing step and the wiring exposing step. The conductive layer 50 can be formed by applying a conductive paste or plating. In addition, after mounting members other than the conductive layer 50 on a part of the adhesive layer 15 and the wiring 30 of the flexible circuit board according to Embodiment 1 shown in FIG. 4, the conductive layer 50 is formed so as to cover them. It doesn't matter.

(Embodiment 3)
The flexible circuit board according to the third embodiment is shown in FIG. 6 in the part of the flexible circuit board shown in FIG. 4 where the adhesive 15 is removed in the opening formed in the protective film 12 and the wiring exposure process. Thus, a conductive layer 52 made of a conductive member is formed, and this conductive layer 52 is a plating layer. The conductive layer 52 is placed on the upper surface 39 of the wiring 34 and is formed so as to cover the entire bottom surface and side surfaces of the recess formed in the adhesive exposing step and the wiring exposing step. The plating method for forming the conductive layer 52 that is a plating layer is not particularly limited. In addition, after mounting members other than the conductive layer 52 on a part of the adhesive layer 15 and the wiring 30 of the flexible circuit board according to Embodiment 1 shown in FIG. 4, the conductive layer 52 is formed so as to cover them. It doesn't matter.

(Other embodiments)
The above-described embodiment is an exemplification of the present invention, and the present invention is not limited to these examples, and these examples may be combined or partially replaced with known techniques, common techniques, and known techniques. Also, modified inventions easily conceived by those skilled in the art are included in the present invention.

The material and thickness of the insulating film and the protective film may be any material as long as they have insulating properties and satisfy various characteristics as a flexible circuit board. For example, a polyester resin film may be used as the protective film. In this case, the polyester resin film may be etched using an alkaline solution (for example, an aqueous hydrazine solution). The material is not particularly limited as long as the adhesive is also used for the cover sheet.

Also, the type of the adhesive is not particularly limited as long as it has insulating properties.

It is preferable that only the upper surface of the wiring where the protective film is not disposed is exposed, but the upper part of the side surface may be partially exposed. If at least half of the side surface is surrounded by the adhesive (that is, at least half of the side surface of the wiring is buried in the adhesive), an effect of insulation and mechanical strength is obtained.

After removing the protective film, the adhesive on the wiring may be removed using a laser. Further, the adhesive may be removed using a sand blast method.

Also, if the wiring of the flexible circuit board is divided into a high-definition part and other parts, this technology is applied only to the high-definition part, and the other parts are provided with a conventional cover coat and an opening in advance. It is also possible to use a composite (so-called hybrid type) that uses the covered cover.

Also, the flexible circuit board may be a type in which wiring is formed on one side, a type in which wiring is formed on both sides, or a multilayer type having three or more circuit layers. At this time, in the type in which the wiring is formed on one side, the cover sheet is formed on the surface on which the wiring is formed, and in the double-sided wiring type, the cover sheet is formed on both sides. In the case of the multi-layer type, depending on the laminating method, the single-sided type may be laminated, the double-sided type may be laminated, or the single-sided and double-sided may be laminated together. Cover sheets are formed on the circuit surfaces of the outer layer and the inner layer.

In addition, the present technology can be used as an inner cover sheet structure even in a so-called rigid flex board in which a flexible circuit board and a printed board are combined.

A plurality of flexible circuit boards according to the above embodiment may be stacked to electrically connect the wirings of two adjacent flexible circuit boards. As a conduction method, for example, the wiring reaches an insulating film. A through hole is formed, and the conductive member is embedded in the through hole, and at the same time, the conductive member is protruded on the side opposite to the surface on which the wiring of the insulating film is arranged, and the protruding portion and another flexible circuit board Although the method of making it contact with wiring is mentioned, It is not limited to this method.

DESCRIPTION OF SYMBOLS 10 Cover sheet 12

Protective film

14, 15 Adhesive 20 Wiring formation film 22 Insulating

film

30, 30a Wiring 31

Wiring

32, 32a Wiring 33 Wiring 34 Wiring 39

Upper surface

50, 52 Conductive layer

Claims

Insulating film, wiring formed on the insulating film, and an insulating protective film disposed on a part of the insulating film and the wiring,
The protective film is bonded to the insulating film and the wiring via an adhesive,
Of the wiring, the portion where the protective film is not disposed on the upper surface is exposed, and the adhesive is attached to the side or the periphery.
The flexible circuit board according to claim 1, wherein the protective film is made of any one of a polyimide resin and a polyester resin.
Insulating film, wiring formed on the insulating film, and an insulating protective film disposed on a part of the insulating film and the wiring,
The protective film is bonded to the insulating film and the wiring via an adhesive,
In the portion where the protective film is not disposed on, the adhesive is attached to the side or the periphery of the wiring, and the adhesive is provided on the insulating film where the wiring is not formed. And a flexible circuit board on which a conductive layer made of a conductive member is placed on the surface of the adhesive and the upper surface of the wiring.
The flexible circuit board according to claim 3, wherein the conductive layer is a plating layer.
Preparing a wiring forming film in which wiring is formed on an insulating film;
A bonding step in which an adhesive is formed on one surface of the insulating protective film, and a bonding step in which the adhesive is placed on the wiring forming film so that the adhesive faces the wiring.
An adhesive exposing step of removing a part of the protective film to expose a part of the adhesive;
And a wiring exposing step of removing an upper part of the exposed part of the adhesive to expose an upper surface of the wiring.
The method for manufacturing a flexible circuit board according to claim 5, wherein the protective film is made of any one of a polyimide resin and a polyester resin, and the adhesive exposing step is performed by etching.
The method for manufacturing a flexible circuit board according to claim 5 or 6, wherein the wiring exposure step is performed by etching using a solution containing a permanganate.
The method for manufacturing a flexible circuit board according to claim 7, wherein the solution used in the wiring exposure step further contains sodium hydroxide.
The solution used in the wiring exposure step is
The concentration of potassium permanganate is 2% by mass or more and 18.15% by mass or less, and the concentration of sodium hydroxide is 20% by mass or less,
Or the concentration of potassium permanganate is 1% by mass or more and less than 2% by mass and the concentration of sodium hydroxide is 0.05% by mass or more and 20% by mass or less,
Alternatively, the concentration of potassium permanganate is 0.5% by mass or more and less than 1% by mass and the concentration of sodium hydroxide is 0.05% by mass or more and less than 18% by mass,
Or the concentration of potassium permanganate is 0.1% by mass or more and less than 0.5% by mass and the concentration of sodium hydroxide is 1.5% by mass or more and less than 18% by mass,
Or the concentration of potassium permanganate is 0.05% by weight or more and less than 0.1% by weight and the concentration of sodium hydroxide is 1.5% by weight or more and less than 5% by weight,
The method for producing a flexible circuit board according to claim 7, which is any one of the above.
The solution used in the wiring exposure step is
The concentration of sodium permanganate is 2% by mass or more and 20% by mass or less, and the concentration of sodium hydroxide is 20% by mass or less,
Alternatively, the concentration of sodium permanganate is 1% by mass or more and less than 2% by mass and the concentration of sodium hydroxide is 0.05% by mass or more and 20% by mass or less,
Or the concentration of sodium permanganate is 0.5% by weight or more and less than 1% by weight and the concentration of sodium hydroxide is 0.05% by weight or more and less than 18% by weight,
Or, the concentration of sodium permanganate is 0.1% by mass or more and less than 0.5% by mass and the concentration of sodium hydroxide is 1.5% by mass or more and less than 18% by mass,
The method for producing a flexible circuit board according to claim 7, which is any one of the above.