TW201806458A - Flexible circuit board and method for manufacturing the same - Google Patents

Abstract

The object of the invention is to provide a flexible circuit board, of which on a FPC, a cover film having a high degree of design freedom in size and shape of an opening is adhered, thereby insulation between adjacent wirings located in the opening of the cover film is accordingly sufficiently assured. The flexible circuit board of the invention includes an insulating film 22, wirings 30 and 32 formed on the insulating film and an insulating protective film 12 disposed on a part of the insulating film and the wiring. The protective film is adhered to the insulating film and the wiring through an adhesive agent 15. The upper surface of the wiring in which the portion of the protective film is not disposed is exposed, and an adhesive is adhered onto the side or surrounding of the wirings.

Description

Flexible circuit board and manufacturing method thereof

The present invention relates to a flexible circuit board and a method of fabricating the same.

Conventionally, a flexible circuit board (hereinafter referred to as FPC) in which circuit wiring is formed on an insulating resin film is generally used. Various devices and devices that are internally assembled with FPCs and electronic components mounted on the FPC are often required to be small, thin, and light, so that thin and bendable FPCs are increasingly used, and FPCs are also available. The wiring pitch is getting smaller and smaller, and the component packaging density on the circuit substrate is getting higher and higher.

As described above, in order to make the electronic device and the electronic component small, thin, and light, it is necessary to prevent a short circuit between the circuit wiring, the circuit wiring, and the surrounding components and wiring, etc., and it is necessary to use the insulating material as much as possible for the FPC. The circuit wiring is covered to maintain insulation reliability. In order to achieve the above object, a coverlay film and a cover coat are generally used to protect portions of the circuit wiring of the FPC other than the connection portion to which the terminal and the electronic component are connected.

The cover film is formed by applying an adhesive to the insulating resin film, and is attached to the circuit wiring after the portion corresponding to the connection portion of the circuit wiring in the FPC and the component package portion is opened (for example, patent document) 1). The connection portion of the circuit wiring and the component package portion in the FPC correspond to the opening portion of the cover film, and thus are exposed. By laminating the cover film, the mechanical strength of the FPC is improved, the circuit is protected, and the bending resistance is also improved.

The surface layer is formed by curing a portion other than the joint portion of the circuit wiring which is made of an insulating material and which is cured by light or the like.

The photosensitive development cover film is a sheet which is prepared in advance by a material which is insulating and which is cured by light, and is bonded to the circuit wiring and cured by light. [Patent Document 1] Japanese Laid-Open Patent Publication No. Hei 9-283895 (Patent Document 2)

[Technical problems to be solved by the invention]

However, since the cover film is provided with the opening portion in advance and then attached to the FPC, it is time-consuming and time-consuming to align the position of the opening portion and the specific portion of the circuit wiring in the FPC, and the defective position may occur when the bonding position is deviated. . Further, depending on the size of the mold forming the opening, the physical properties of the film material, and the like, the shape and size of the opening are naturally limited, and the design of the circuit wiring of the FPC is limited. Further, in the circuit wiring of the FPC located in the opening portion of the cover film, the side faces of the adjacent wirings are exposed, and the smaller the wiring pitch, the more the insulation between the wirings may cause problems, and the wiring of the portion is peeled off. The strength is low and the wiring is easily peeled off.

On the other hand, since the surface layer is applied to the FPC by a printing method, particularly when a photosensitive material is used, since the opening portion can be formed small, printing is an effective method when performing high-density packaging, but There may be a problem that the thickness of the insulating material is not uniform and the FPC is easily curled after curing. Further, there is a problem in that the effect of improving the mechanical strength of the FPC is poor and the bending resistance is improved.

A solution has also been proposed in which a photosensitive developing cover film is attached to a circuit surface of an FPC, and then cured by light to form an insulating protective film on the FPC. However, at this time, there is a problem that it is easy to curl after curing, and there is also a problem that the mechanical strength of the circuit protection is insufficient and the bending resistance is insufficient.

The present invention has been made in view of the above problems, and an object thereof is to provide a flexible circuit board in which a cover film having a shape and a large degree of freedom in designing an opening portion is attached to an FPC, and the cover film is sufficiently ensured. Insulation between adjacent wirings in the wiring of the opening.

[Technical means for solving technical problems]

The flexible circuit board of the present invention has a structure including an insulating film, a wiring formed on the insulating film, and an insulating protective film disposed on the insulating film and a portion of the wiring, the protective film being permeable to an adhesive The upper surface of the portion of the wiring in which the protective film is not disposed is exposed and the adhesive is adhered to the side or the periphery thereof. That is, a protective film is not disposed above the portion other than the portion of the wiring, and the upper surface of the wiring of the portion is exposed.

The protective film is preferably composed of one of a polyimide resin and a polyester resin.

Other flexible circuit boards of the present invention include an insulating film, wiring formed on the insulating film, and an insulating protective film disposed on the insulating film and a portion of the wiring. The protective film is adhered to the insulating film and the wiring through an adhesive, and the adhesive is disposed on the side or the periphery of the wiring in a portion where the protective film is not disposed, and is not formed. The adhesive film is provided on the insulating film of the wiring, and a surface of the adhesive and an upper surface of the wiring are covered with a conductive layer made of a conductive material.

The conductive layer may be a plating layer.

A method of manufacturing a flexible circuit board according to the present invention includes: a process of preparing a wiring forming film which is a film in which a wiring is formed on an insulating film; and a bonding process in which an adhesive film is formed on one side of the insulating protective film a cover sheet of the agent, wherein the cover sheet is placed on the wiring forming film in such a manner that the adhesive is applied to the wiring, and the adhesive is exposed to the process to remove a part of the protective film. A part of the adhesive is exposed; a wiring exposure process is performed, and an upper portion of the portion of the adhesive exposed is removed to expose an upper surface of the wiring.

Preferably, the protective film is composed of one of a polyimide resin and a polyester resin, and the adhesive exposure process is performed by etching.

Preferably, the wiring exposure process is performed by etching, and a solution containing permanganate and sodium hydroxide is used for the etching. The permanganate herein is a salt formed of permanganic acid and a salt group, and examples thereof include potassium permanganate, sodium permanganate, and the like.

Preferably, the solution used in the wiring exposure process satisfies one of the following conditions: 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; 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 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. Alternatively, 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.

Preferably, the solution used in the wiring exposure process satisfies one of the following conditions: 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; or 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 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 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. %.

[Effects of the Invention]

In the flexible circuit board of the present invention, the side of the wiring on which the portion of the protective film is not disposed is surrounded by the adhesive. Therefore, the wiring is mechanically and electrically protected by the adhesive, and the peeling strength of the wiring and the wiring compartment are The insulation is also fully guaranteed.

Hereinafter, embodiments of the present invention will be described in detail based on the drawings. The following description of the preferred embodiments is an essential example and is not intended to limit the invention, its application, or its use. In addition, the "cover sheet" in the present invention is a type of a cover film, and is a cover film provided with an adhesive which can ensure the peeling strength of the wiring and the insulation between the wirings.

(First embodiment)

In the first embodiment, a flexible circuit board is manufactured by a process of preparing a wiring forming film (equivalent to FPC) which is a film in which a wiring is formed on an insulating film, and an insulating property. a cover sheet in which an adhesive is formed on one surface of the protective film, and the adhesive sheet is placed on the wiring forming film to conform to the wiring, and the bonding process is performed (bonding process) a process of removing a part of the protective film to expose a part of the adhesive (adhesive exposure process); removing an upper portion of the exposed portion of the adhesive to expose an upper surface of the wiring Process (wiring exposes the process).

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

The insulating film 22 is generally a film made of a polyimide resin, a polyester resin, a PPS (polyphenylene sulfide) resin, an aromatic polyamide resin, an LCP (liquid crystal polymer) or the like and having a thickness of about 5 μm to 75 μm. The wiring 31 is formed by bonding a copper foil to the insulating film 22, patterning the copper foil by etching, or patterning by a semi-additive process using a metal spray material. It is formed by molding, or formed by a fully-additive process, or formed by printing using a conductive ink or the like. In addition, a form in which an adhesive composed of a material of the same or different kind as the insulating film 22 exists between the insulating film 22 and the wiring 31 is also generally present. The protective film 12 is generally a film composed of a polyimide resin, a polyester resin, a PPS (polyphenylene sulfide) resin, an aromatic polyamide resin, an LCP (liquid crystal polymer), or the like and having a thickness of about 2.5 μm to 25 μm. . From the viewpoint of heat resistance, dimensional stability, and bending resistance, a polyimide resin is preferred. 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. However, the adhesive 14 may be photocurable, and the thickness of the adhesive 14 is about 5 μm to 35 μm.

Then, the wiring forming film 20 and the cover sheet 10 are bonded together (FIG. 2, bonding process). In the bonding process, the adhesive 14 formed on one surface of the cover sheet 10 is superposed on the wiring 31 of the wiring forming film 20, and while applying pressure, the UV light is heated or irradiated to cure the adhesive 14. In the bonding process, since it is not necessary to provide the opening portion in the cover sheet 10, the alignment position with the wiring 31 of the wiring forming film 20 (aligning the opening portion and the position of the wiring portion to be exposed) is not required, and the winding can be easily performed. Fit the roll-to-roll style. In addition, the wiring forming film 20 and the cover sheet 10 may be bonded together in units of sheets (so-called lobes) included in a single or plural circuit. At this time, it is not necessary to precisely align the position of the opening portion and the wiring portion to be exposed. As described above, since it is not necessary to precisely align the position at the time of bonding in the present embodiment, the defective product in which the alignment failure has occurred does not occur, and the process speed is also improved, so that the bonding can be performed at a low cost and at a high speed. In addition, although the alignment of the opening is not intended, in order to guide the feeding or setting of the material in the bonding process, it is of course possible to open a guide hole or the like on the cover sheet in advance.

After the bonding process is completed, all of the wirings 32, 32a are in a state of being protected by the cover sheet 10. Then, the protective film 12 existing over the portion of the wiring 32a to be exposed is removed to form the opening 40 (Fig. 3, adhesive exposing process). The protective film 12 has various removal methods such as a method of removing by etching, a method of removing by laser, and the like. By the method of etching removal, for example, the etching resist is formed outside the portion where the opening is formed by the method disclosed in Patent Document 2, and then the etching liquid acts. This process is the same as the process of forming wiring by etching, and can be performed easily and with high precision. The method of removing by laser can also be performed with high precision.

In the adhesive exposure process, although the opening 40 is formed in the protective film 12, the cured adhesive 15 is formed on the upper surface of the wiring 30a in the opening 40, and therefore the upper surface of the wiring 30a is not exposed. Then, the cured adhesive 15 on the upper surface of the wiring 30a is removed (Fig. 4, wiring exposure process). When the cured adhesive 15 is removed, it is preferred to use a solution capable of dissolving the adhesive 15, as long as the type of the solution is selected depending on the type of the adhesive 15. For example, when the adhesive 15 is an epoxy system, it is dissolved in an aqueous solution of potassium permanganate and sodium hydroxide, washed with water, and then neutralized. It is to be noted that it is preferable that the wiring 30a is buried in the adhesive 15 and only the upper surface is exposed. For this reason, it is preferred to lower the concentration of the solution in which the adhesive 15 is dissolved and to control the dissolution rate.

By performing the above process, the wiring 30 which is a part of the wiring forming film 20 is placed in the opening 40 of the protective film 12, and is buried under the adhesive 15 and the upper surface 39 is exposed, and the other wiring 32 is buried in the adhesive. 15 and the protective film 12 is present above. That is, the state of the wiring 30 which is a part of the wiring forming film 20 is such that the protective film 12 is not disposed above, the upper surface 39 is exposed, and the adhesive 15 is present on the side or the periphery.

As described above, since the wiring 30 located in the opening 40 of the protective film 12 has the adhesive 15 on the side or the periphery thereof, it is possible to maintain high insulation reliability between the adjacent wirings 30 and 30. In particular, it is possible to maintain high insulation reliability between wires even when the wiring pitch is small. Further, the protective film 12 is excellent in bending resistance.

When a normal cover film and a surface layer are used, if the width of the exposed wiring is small (that is, the wiring pitch is small), the peeling strength required for the wiring to be peeled off from the wiring forming film 20 is low, and the use environment of the FPC is low. The change, the deterioration over time, the external pressure and the bending from the outside may cause the wiring to be peeled off or broken from the flexible circuit board. However, in the flexible circuit board of the present embodiment, the side or the periphery of the wiring 30 is surrounded by the adhesive 15. Therefore, even if the width of the wiring 30 is small, a large peeling strength can be ensured, and there is no need to worry about wiring. 30 is peeled off from the flexible circuit board or the wiring 30 is broken. Further, when the exposed wiring 30 and the external terminal are electrically connected by an anisotropic conductive adhesive (ACF or ACP), the anisotropic conductive adhesive also enters the adjacent layer if it is a usual cover film and a surface layer. Between the wirings (between the sides of the wiring), the conductive particles in the anisotropic conductive adhesive may cause conduction between adjacent wirings, but there is no such concern in the flexible circuit board of the present embodiment. At this point as well, high inter-line insulation reliability can be maintained between adjacent wirings 30, 30.

The previous cover film needs to be formed by punching before it is attached to the wiring forming film, and it is necessary to use a mold for this purpose. However, the flexible circuit board of the present embodiment does not require the use of a mold, so that the corresponding cost can be reduced. Further, in order to form an opening by punching, the size, shape, and aperture ratio of the opening are restricted, so that the opening cannot be designed to be small, and the design of the opening shape is not free. However, in the case of the flexible circuit board of the present embodiment, the size, shape, and the like of the opening can be freely designed. Further, in the flexible circuit board of the present embodiment, it is possible to make the release film for the cover film thin, and to achieve dimensional accuracy such as curl due to stress at the time of peeling, without performing half die cutting. The changes are greatly reduced, so the cost can be reduced. Further, according to the flexible circuit board of the present embodiment, the winding-to-roll processing can be easily performed, and the position of the cover sheet and the wiring forming film can be easily aligned at the time of bonding. Therefore, the cost can be reduced and the manufacturing time can be shortened. Since the previous cover film is formed by forming an opening and then adhering, an adhesive may be oozing out at the opening portion. In order to prevent this problem, it is necessary to have both flexibility, heat resistance, peelability, and the like in the bonding process. The cushioning material of a complicated structure is not required for the flexible circuit board of the present embodiment, and the cost can be reduced.

<Polyimide film>

The cover sheet used in the present invention is preferably a polyimide resin, which is preferred from the viewpoints of heat resistance, dimensional stability, and bending resistance of the FPC, and a polyimide film having specific physical properties is more preferable.

[Method for producing polyimine film]

In order to obtain a polyimide film, first, an aromatic diamine component and an aromatic acid anhydride component are polymerized in an organic solvent to obtain a polyaminic acid solution (hereinafter also referred to as a polyamine solution).

The polyaminic acid solution can be obtained by polymerizing a chemical substance containing an aromatic diamine component and an aromatic acid anhydride component as a main component in an organic solvent.

Examples of the aromatic diamine component include p-phenylenediamine, m-phenylenediamine, benzidine, p-xylylenediamine, 4,4'-diaminodiphenyl ether, and 3,4'-diamino group. Diphenyl ether, 4,4'-diaminodiphenylmethane, 4,4'-Diaminodiphenyl sulfone, 3,3'-dimethyl-4,4' -diaminodiphenylmethane, 1,5-naphthalenediamine, 3,3'-dimethoxybenzidine, 1,4'-bis(3-methyl-5-aminophenyl)benzene (1,4 - bis (3-methyl-5-aminophenyl) benzene) and a guanamine-forming derivative of the above. These may be used alone or in combination of two or more.

The aromatic diamine component is preferably one or more selected from the group consisting of p-phenylenediamine and 4,4'-diaminodiphenyl ether, from the viewpoint of excellent heat resistance and thermal dimensional stability.

Specific examples of the aromatic acid anhydride component include an acid anhydride component of an aromatic tetracarboxylic acid such as the following acid and a guanamine-forming derivative of the following acid: pyromellitic acid, 3,3', 4,4'-linked Benzenetetracarboxylic acid (3,3',4,4'-biphenyltetracarboxylic acid), 2,3',3,4'-biphenyltetracarboxylic acid, 3,3',4,4'-benzophenone Carboxylic acid, 2,3,6,7-naphthalenetetracarboxylic acid, 2,2-bis(3,4-dicarboxyphenyl)ether (2,2-bis ( 3,4-dicarboxyphenyl)ether), pyridine-2,3,5,6-tetracarboxylic acid. These may be used alone or in combination of two or more.

From the viewpoint of excellent heat resistance and thermal dimensional stability, the aromatic acid anhydride component is preferably pyromellitic dianhydride and/or 3,3',4,4'-biphenyltetracarboxylic dianhydride.

In the present invention, the combination of the aromatic diamine component and the acid anhydride component is preferably selected from the following: the aromatic diamine component is derived from p-phenylenediamine, 4,4'-diaminodiphenyl ether and 3,4'- One or more selected from the group consisting of diaminodiphenyl ether, the aromatic acid anhydride component is pyromellitic dianhydride and/or 3,3',4,4'-biphenyltetracarboxylic dianhydride.

When the aromatic diamine component contains p-phenylenediamine and 4,4'-diaminodiphenyl ether, the molar ratio of p-phenylenediamine to 4,4'-diaminodiphenyl ether is 50/50 to 0. /100 is better, 40/60 to 0/100 is better.

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

The method for producing a polyimide film is, for example, a method in which a polyaminic acid solution is cast into a film form, which is thermally dehydrated and cyclized to remove a solvent to obtain a polyimide film; a ring is added to the polyamid acid solution. A method in which a catalyst and a dehydrating agent are chemically dehydrated and cyclized to prepare a gel film, and the film is heated to remove a solvent, thereby obtaining a polyimide film. The latter is preferred.

The polyimide film obtained as described above is further annealed from the viewpoint of being able to reduce the heat shrinkage rate (specifically, the heat shrinkage rate after heating at 200 ° C for 60 minutes) is 0.2% or less. Preferably. The method of the annealing treatment is not particularly limited and can be carried out in accordance with a conventional method. The temperature of the annealing treatment is not particularly limited, and is preferably 200 to 500 ° C, more preferably 200 to 370 ° C, and particularly preferably 210 to 350 ° C. Specifically, it is preferred to heat the furnace to the above temperature range and allow the film to pass through the furnace under low tension for annealing. The time during which the film stays in the furnace is the processing time, and the processing time can be controlled by changing the passing speed. The processing time is preferably 5 seconds to 5 minutes. Further, the film tension at the time of passage is preferably 10 to 50 N/m, more preferably 20 to 30 N/m.

In order to improve the dimensional accuracy of the FPC, the heat shrinkage rate of the polyimide film after heating at 200 ° C for 60 minutes is usually 0.2% or less (for example, 0.01 to 0.15%), preferably 0.15% or less (for example, 0.01 to 0.1%). It is preferably 0.1% or less (for example, 0.01 to 0.07%). After the polyimide film was allowed to stand in a room adjusted to 25 ° C and 60% RH for 2 hours or more, the film size L1 was measured with a CNC image processing apparatus system NEXIV VM-250 (manufactured by Nikon), and then heated at 200 ° C. After being placed again in the room adjusted to 25 ° C and 60% RH for 1 day, the film size L2 was measured by the CNC image processing apparatus system, and the heat shrinkage rate of the polyimide film after heating at 200 ° C for 60 minutes. It can be calculated by the following mathematical formula.

Heat shrinkage rate (%) = -[(L2-L1)/L1] × 100

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

<Example 1>

A cover sheet manufactured by UNON-GIKEN CO., LTD. was used in Example 1. The protective film was a kapton 50EN having a thickness of 12.5 μm, and a 20 μm epoxy-based adhesive was formed thereon. The cover sheet was bonded to a circuit-formed substrate on which a circuit was formed on one side under a bonding condition of 150 ° C, 3 MPa, and 30 minutes.

A portion of the protective film of the flexible circuit board with the cover sheet is removed by etching with a polyimine etchant TPE3000N manufactured by Toray Engineering Co., Ltd., and the removed sheet-like substrate is prepared in a range including the opening portion. A test piece having a size of 35 mm × 22.5 mm was produced.

The test piece was taken, and the adhesive was removed by etching in 100 g of an etching solution containing at least one of potassium permanganate and sodium hydroxide, washed with water, and neutralized.

At this time, the etching rate until the wiring of the test piece was exposed was changed, and the concentrations of potassium permanganate and sodium hydroxide contained in the etching liquid were also changed.

The above results are shown in Table 1. In addition, the etching conditions of the protective film at this time were the conditions of Japanese Patent No. 3251515.

<Table 1>

According to the results, when potassium permanganate is not contained, the adhesive cannot be removed by etching regardless of the concentration of sodium hydroxide; or, when potassium permanganate is 1.2% by mass or less and sodium hydroxide is less than 0.05% by mass, The adhesive cannot be removed by etching; or when the potassium permanganate is 0.1% by mass or less and the sodium hydroxide is less than 1.5% by mass, the adhesive cannot be removed by etching; or, potassium permanganate is less than 1% by mass and oxidized When the amount of sodium is 18% by mass or more, the adhesive cannot be removed by etching; or when the potassium permanganate is less than 0.1% by mass and the sodium hydroxide is 5% by mass or more, the adhesive cannot be removed by etching.

On the other hand, when 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, the adhesive can be removed by etching; or the concentration of potassium permanganate is 1 mass. When the content is less than 2% by mass and the concentration of the sodium hydroxide is 0.05% by mass or more and 20% by mass or less, the adhesive can be removed by etching; or the concentration of potassium permanganate is 0.5% by mass or more and less than 1% by mass. When the concentration of sodium hydroxide is 0.05% by mass or more and less than 18% by mass, the adhesive can be removed by etching; 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. When the mass% or more is less than 18% by mass, the adhesive can be removed by etching; 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. When % is used, the adhesive can be removed by etching.

Therefore, it is estimated that the condition shown as a number in the table and the condition shown as ○, that is, the range in which the thick coil is used, can remove the adhesive having a thickness of 10 μm by etching within 60 minutes, and the condition shown in the table is that etching or X cannot be performed. It is impossible to remove the adhesive having a thickness of 10 μm by etching within 60 minutes.

Further, in the conditions capable of etching, the higher the concentration of at least one of the respective chemical solutions, the shorter the etching time.

<Example 2>

In Example 2, using the same test piece as in Example 1, a solution containing at least one of sodium permanganate and sodium hydroxide was used as an etchant for the adhesive, and the adhesive was removed by etching. That is, in the present embodiment, the permanganate contained in the etching liquid is sodium permanganate, which is different from that of the first embodiment.

The above results are shown in Table 2. In addition, the etching conditions of the protective film at this time were the conditions of Japanese Patent No. 3251515.

<Table 2>

According to the results, when the amount of sodium permanganate is 0.05% by mass, the adhesive cannot be removed by etching regardless of the concentration of sodium hydroxide; or when the amount of sodium permanganate is 1.2% by mass or less and sodium hydroxide is not contained, The adhesive is removed by etching; or when the sodium permanganate is 0.1% by mass or less and the sodium hydroxide is less than 1.5%, the adhesive cannot be removed by etching; or, the sodium permanganate is 0.5% by mass or less and the sodium hydroxide is When the amount is 18% by mass or more, the adhesive cannot be removed by etching.

On the other hand, when 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, the adhesive can be removed by etching; or the concentration of sodium permanganate is 1 mass. When the content is less than 2% by mass and the concentration of the sodium hydroxide is 0.05% by mass or more and 20% by mass or less, the adhesive can be removed by etching; or the concentration of the sodium permanganate is 0.5% by mass or more and less than 1% by mass. When the concentration of sodium hydroxide is 0.05% by mass or more and less than 18% by mass, the adhesive can be removed by etching; 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. When the mass% or more is less than 18% by mass, the adhesive can be removed by etching.

<Example 3>

In Example 3, etching was performed using two cover sheets.

First, the first cover sheet used was a cover sheet manufactured by UNON-GIKEN CO., LTD.: The protective film was a kapton 50EN having a thickness of 12.5 μm, and a 20 μm epoxy-based adhesive was formed thereon. The cover sheet is bonded to both sides of the circuit-formed substrate on which the circuit is formed on both sides. It should be noted that the adhesive is different from the adhesive material of the cover sheet of Example 1. The bonding conditions were the same as in Example 1.

A portion of the protective film of the flexible circuit board with the cover sheet is removed by etching with a polyimine etchant TPE3000N manufactured by Toray Engineering Co., Ltd., and the removed sheet-like substrate is prepared in a range including the opening portion. A test piece having a size of 40 mm × 90 mm was produced.

Then, the second cover sheet used was a cover sheet manufactured by NIKKAN INDUSTRIES CO., LTD.: The protective film was kapton 50H having a thickness of 12.5 μm, and a 20 μm epoxy-based adhesive was formed thereon. The cover sheet is bonded to both sides of the circuit-formed substrate on which the circuit is formed on both sides. The bonding conditions were set at 160 ° C, 3 MPa, and 40 minutes.

A portion of the protective film of the flexible circuit board with the cover sheet is removed by etching with a polyimine etchant TPE3000N manufactured by Toray Engineering Co., Ltd., and the removed sheet-like substrate is prepared in a range including the opening portion. A test piece having a size of 40 mm × 90 mm was produced.

The above two test pieces were taken, and the adhesive was removed by etching in 100 g of an etching solution containing sodium permanganate and sodium hydroxide, and washed with water to carry out neutralization.

The above results are shown in Table 3. In addition, the etching conditions of the protective film at this time were the conditions of Japanese Patent No. 3251515.

<Table 3>

According to the results, when the concentration of sodium permanganate is 8.5% by mass and the concentration of sodium hydroxide is 5% by mass, the etching time can be removed, but the adhesive can be removed by etching.

<Example 4>

In Example 4, etching was performed using two cover sheets.

First, the first cover sheet used was a cover sheet manufactured by KYOCERA Chemical Corporation: the protective film was kapton 50ENC having a thickness of 12.5 μm, and a 25 μm epoxy-based adhesive was formed thereon. The cover sheet is bonded to both sides of the circuit-formed substrate on which the circuit is formed on both sides. In addition, this adhesive differs from the adhesive material of the cover sheets of Examples 1 and 2. The bonding conditions were the same as in Example 1.

A portion of the protective film of the flexible circuit board with the cover sheet is removed by etching with a polyimine etchant TPE3000N manufactured by Toray Engineering Co., Ltd., and the removed sheet-like substrate is prepared in a range including the opening portion. A test piece having a size of 20 mm × 20 mm was produced.

Then, the second cover sheet used was a cover sheet manufactured by KYOCERA Chemical Corporation: the protective film was kapton 50ENC having a thickness of 12.5 μm, and a 25 μm epoxy-based adhesive was formed thereon. The cover sheet is bonded to both sides of the circuit-formed substrate on which the circuit is formed on both sides. The bonding conditions were the same as in Example 1. It should be noted that the adhesive of the cover sheet is different from the adhesive materials of the cover sheets of Examples 1 and 2 and the first cover sheet of the present embodiment.

A portion of the protective film of the flexible circuit board with the cover sheet is removed by etching with a polyimine etchant TPE3000N manufactured by Toray Engineering Co., Ltd., and the removed sheet-like substrate is prepared in a range including the opening portion. A test piece having a size of 20 mm × 20 mm was produced.

The above two test pieces were taken, and the adhesive was removed by etching in 100 g of an etching solution containing sodium permanganate and sodium hydroxide, and washed with water to carry out neutralization.

The above results are shown in Table 4. In addition, the etching conditions of the protective film at this time were the conditions of Japanese Patent No. 3251515.

<Table 4>

According to the results, when the concentration of sodium permanganate is 8.5% by mass and the concentration of sodium hydroxide is 5% by mass, the etching time can be removed, but the adhesive can be removed by etching.

(Second embodiment)

The flexible circuit board according to the second embodiment is as follows: an opening formed on the protective film 12 of the flexible circuit board shown in FIG. 4 and a portion of the flexible circuit board after a part of the adhesive 15 is removed in the wiring exposure process. A conductive layer 50 composed of a conductive material is formed as shown in FIG. The conductive layer 50 is provided on the upper surface 39 of the wiring 33, and is formed to fill the entire depression formed in the adhesive exposure process and the wiring exposure process. The conductive layer 50 can be formed by applying a conductive paste, plating, or the like. In addition, a material other than the conductive layer 50 may be provided on the adhesive layer 15 of the flexible circuit board according to the first embodiment shown in FIG. 4 and a part of the wiring 30, and then the material may be covered. A conductive layer 50 is formed.

(Third embodiment)

The flexible circuit board according to the third embodiment is as follows: an opening formed on the protective film 12 of the flexible circuit board shown in FIG. 4 and a portion of the flexible circuit board after a part of the adhesive 15 is removed in the wiring exposure process. A conductive layer 52 composed of a conductive material is formed, which is a plating layer as shown in FIG. The conductive layer 52 is provided on the upper surface 39 of the wiring 34, and is formed to cover the entire bottom surface and side surfaces of the recess formed in the adhesive exposure process and the wiring exposure process. The plating method of forming the plating layer, that is, the conductive layer 52 is not particularly limited. In addition, a material other than the conductive layer 52 may be provided on the adhesive layer 15 of the flexible circuit board according to the first embodiment shown in FIG. 4 and a part of the wiring 30, and then the material may be covered. A conductive layer 52 is formed.

(Other embodiments)

The above-described embodiments are examples of the present invention, and the present invention is not limited to the above examples, and known techniques, conventional techniques, well-known techniques, and the above examples may be combined, or the above-described examples may be replaced by known techniques, conventional techniques, and well-known techniques. portion. Further, a modified invention which is easily conceived by those skilled in the art to which the present invention pertains is also included in the present invention.

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

Further, the adhesive is not particularly limited as long as it has insulating properties.

The wiring on the upper portion where the protective film is not disposed is preferable, but only the upper surface is preferably exposed, but a part of the upper side may be exposed. As long as 1/2 or more 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), the insulating property and the mechanical strength are exerted.

After removing the protective film, the adhesive on the wiring can also be removed by laser. In addition, the adhesive can also be removed by sand blasting.

If the wiring of the flexible circuit board is divided into a portion other than the high-definition portion and the high-definition portion, the circuit board can also be a composite body (ie, a composite type): the present technology is applied only in the high-definition portion, and the portion other than the high-definition portion A cover film having a top layer and a pre-opening portion is provided using the prior art.

Further, the flexible circuit board may be a board in which wiring is formed on one surface, a board formed on both sides, or a multilayer board having three or more circuit layers. At this time, the wiring is formed on one surface of the board, the cover sheet is formed on the surface on which the wiring is formed, and the cover sheet is formed on both sides of the double-sided wiring. As for the multi-layer board, depending on the lamination method, there are cases of laminating a single panel, a case of laminating a double panel, and a case of mixing a single panel and a double panel, but none of them are in the outermost layer and the inner layer. A cover sheet is formed on the circuit surface.

Further, the present technology can also be applied to an inner layer cover sheet structure of a so-called soft and hard composite board in which a flexible circuit board and a rigid circuit board are combined.

A plurality of flexible circuit boards according to the above embodiments may be stacked and electrically connected between wirings of two adjacent flexible circuit boards. The conduction method may be, for example, a method of forming a wiring on the insulating film. The through hole embeds the conductive material in the through hole and causes the conductive material to protrude toward the side opposite to the surface on which the wiring is disposed on the insulating film, and allows the protruding portion to come into contact with the wiring of the other flexible circuit board. But not limited to this method.

10‧‧‧ Covering film
12‧‧‧Protective film
14, 15‧‧‧Adhesive
20‧‧‧Wiring forming film
22‧‧‧Insulation film
30, 30a‧‧‧ wiring
31‧‧‧Wiring
32, 32a‧‧‧ wiring
33‧‧‧ wiring
34‧‧‧Wiring
39‧‧‧ upper surface
50, 52‧‧‧ conductive layer

Figure 1 is a schematic cross-sectional view showing a preparation process. Figure 2 is a schematic cross-sectional view showing the bonding process. Figure 3 is a schematic cross-sectional view showing the adhesive exposure process. 4 is a schematic cross-sectional view showing a wiring exposure process. Fig. 5 is a schematic cross-sectional view showing a flexible circuit board according to another embodiment. Fig. 6 is a schematic cross-sectional view showing a flexible circuit board according to another embodiment.

12‧‧‧Protective film

15‧‧‧Adhesive

22‧‧‧Insulation film

32‧‧‧Wiring

30‧‧‧Wiring

39‧‧‧ upper surface

Claims (10)

A flexible circuit board comprising an insulating film, a wiring formed on the insulating film, and an insulating protective film disposed on the insulating film and a portion of the wiring, the protective film being adhered to the In the insulating film and the wiring, an upper surface of a portion of the wiring in which the protective film is not disposed is exposed and the adhesive is adhered to the side or the periphery. The flexible circuit board according to claim 1, wherein the protective film is composed of one of a polyimide resin and a polyester resin. A flexible circuit board comprising an insulating film, a wiring formed on the insulating film, and an insulating protective film disposed on the insulating film and a portion of the wiring, the protective film being adhered to the In the insulating film and the wiring, in the portion where the protective film is not disposed, the adhesive is adhered to the side or the periphery of the wiring, and the insulating film is not provided on the insulating film where the wiring is not formed. The adhesive is described, and a surface of the adhesive and an upper surface of the wiring are covered with a conductive layer made of a conductive material. The flexible circuit board of claim 3, wherein the conductive layer is a plating layer. A method for manufacturing a flexible circuit board, comprising: a process for preparing a wiring for forming a film, wherein the wiring forming film is a film having a wiring formed on the insulating film; and a bonding process, wherein an adhesive is formed on one surface of the insulating protective film a cover sheet on which the cover sheet is placed on the wiring forming film in such a manner that the adhesive is applied to the wiring; the adhesive exposing process, removing a part of the protective film to allow the A part of the adhesive is exposed; and a wiring exposure process is performed to remove an upper portion of the portion of the adhesive exposed to expose an upper surface of the wiring. The method of manufacturing a flexible circuit board according to claim 5, wherein the protective film is composed of one of a polyimide resin and a polyester resin, and the adhesive exposure process is performed by etching. The method of manufacturing a flexible circuit board according to claim 5, wherein the wiring exposure process is performed by etching, and the permanganate-containing solution is used for the etching. The method of manufacturing a flexible circuit board according to claim 7, wherein the wiring is exposed to the solution used in the process, and further contains sodium hydroxide. The method of manufacturing a flexible circuit board according to claim 7 or 8, wherein the solution used in the wiring exposure process satisfies one of the following conditions: a 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; or The concentration of potassium acid 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. 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 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. . The method of manufacturing a flexible circuit board according to claim 7 or 8, wherein the solution used in the wiring exposure process satisfies one of the following conditions: a 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; or 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, manganese The concentration of sodium 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 sodium permanganate is 0.1% by mass or more and less than 0.5% by mass. The concentration of sodium hydroxide is 1.5% by mass or more and less than 18% by mass.