JP2910948B2 - Manufacturing method of flexible wiring board with bend - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a flexible wiring board (eg, a flexible wiring member, TAB) in which a conductive material wiring is formed on a large part of the support film (over the entire surface of the support film). Wiring member, etc.), and the flexible wiring board provided with a large number of wirings crossing the slit-shaped opening of the support film at the bent portion, the main wiring area and the slit-shaped opening On one side surface of a large number of wirings crossing the substrate , by polymerizing and imidizing an aromatic tetracarboxylic acid component and a diamine component composed of 50-90 mol% of diaminopolysiloxane and 10-50 mol% of aromatic diamine. A specific coating composition containing the obtained special soluble polyimide siloxane is simultaneously applied by a silk screen printing method to form a coating film. The present invention relates to a method for manufacturing a flexible wiring board with a bent portion, which is dried and each of the wirings is covered with a protective coating film, and the wiring crossing the slit-shaped opening is not easily broken by bending.

[0002]

2. Description of the Related Art Conventionally, conductive wiring is formed on most of a supporting film, a part of the supporting film is opened in a slit shape, and a part of the wiring board is formed in a slit shape. A flexible wiring board (flexible wiring member, wiring member for TAB, etc.) that is easily bent along the opening is finally mounted in a narrow space inside an electric appliance or the like. It is extremely needed for:

However, in such a flexible wiring board with a bent portion, a large number of wirings (bare wires after copper foil is etched) crossing the slit-shaped opening are not supported by a support material or the like. Since the wiring board is extremely thin and has low mechanical strength, if the wiring board is bent as it is along the slit-shaped opening, a large number of wirings crossing the slit-shaped opening may be extremely easily broken and disconnected. There was a need to provide some protection for the wiring.

Further, in the flexible wiring board, it is necessary to apply a heat-resistant insulating protective film on the surface of the wiring area in order to insulate and protect various wirings. Due to the insulating protective film, the wiring board itself is curled, and there is a problem that various processing steps thereafter are extremely difficult and complicated.

[0005] A flexible wiring board and a flexible wiring board which can effectively solve the problem of curling due to the insulating protective film of the wiring board as described above, and can effectively protect the large number of wirings from breaking when bent. Various proposals have been made for the production method, but there are still few simple and industrial means (production methods), and a method for easily producing such a flexible wiring board is required.

[0006]

SUMMARY OF THE INVENTION It is an object of the present invention to provide a flexible wiring board with a bent portion, in which "a large number of wires" crossing a slit-shaped opening in the bent portion are effectively protected against bending. In addition, a flexible wiring board with a bent portion (for example, a flexible wiring board, TA
B wiring board etc.) industrially and easily.

[0007]

According to the present invention, a main wiring of a conductive material is formed on a large part of a support film, and the support film is opened in a slit shape at a bent portion to form a large number of wirings. In the flexible wiring board provided across the slit-shaped opening, a large number of wirings provided across the slit-shaped opening of the support film in the main wiring area and the bent portion of the wiring board. on one surface, and an aromatic tetracarboxylic acid component, 50-90 Mo
% Of a diaminopolysiloxane and 10-50 mol% of a diamine component composed of an aromatic diamine, and a polyimide siloxane or an epoxy resin modified product thereof obtained by polymerizing and imidizing 80% by weight of the resin component. % Of a coating composition mainly containing a resin component containing at least 1% by weight of a coating composition solution uniformly dissolved or dispersed in an organic polar solvent by a silk screen printing method, and And a method for producing a flexible wiring board with a bent portion, characterized in that the coating film is dried at a temperature of 50 to 280 ° C. to form a protective coating film from which volatile components have been substantially removed.

Hereinafter, each invention of the present application will be described in detail with reference to the drawings. FIG. 1 shows an example of a flexible wiring board with a bent portion obtained by the manufacturing method of the present invention (a main wiring region covered with an insulating protective coating made of a solder resist is considerably omitted, and the vicinity of the bent portion is shown). 2 is a cross-sectional view taken along the line AA of the wiring board of FIG. 1, and FIG. 3 is a cross-sectional view of the wiring board of FIG.
FIG. 4 is a cross-sectional view of the wiring board taken along line BB.

FIG. 4 is a sectional view showing a state in which a flexible wiring board with a bent portion obtained by the method of the present invention is bent at the bent portion. FIG. 5 partially shows an example of a flexible wiring board used for manufacturing the flexible wiring board with a bent portion of the present invention.
7 is a cross-sectional view of the CC line of the wiring board of FIG. 5, and FIG.
FIG. 6 is a sectional view taken along line DD of the wiring board of FIG. 5.

As shown in FIGS. 5, 6, and 7, a flexible wiring board with a bent portion used in the manufacturing method of the present invention has an etching process in which a main wiring is mostly formed on a support film 1 by a metal foil. The flexible film 2 may be a flexible wiring board in which the support film 1 is opened in a slit shape at the bent portion 3 and a large number of wirings 5 are provided across the slit opening 4.

Examples of the support film include a heat-resistant polymer film, for example, an aromatic polyimide film, an aromatic polyamide film, an aromatic polyester film, an inorganic film, and the like.
As the conductive wiring, a fine wiring (line width: 10 to 500) formed by etching or the like from a metal foil (thickness: 10 to 200 μm) such as a copper foil or an aluminum foil.
μm, especially 30 to 300 μm, and line spacing: 10 to 5
00 μm, especially 30 to 400 μm).

In the present invention, as the support film, a long heat-resistant film having a pair of sprockets (holes) arranged at both ends and particularly used for a wiring board for TAB is preferable. .

In the method for manufacturing a flexible wiring board with a bent portion according to the present invention, the "main wiring area" and the "crossing the slit-shaped opening 4 of the support film 1 at the bent portion 3" in the aforementioned flexible wiring board are roughly described. A specific coating composition in which a coating composition containing polyimidesiloxane or its modified epoxy resin is uniformly dissolved or dispersed in an organic polar solvent on one surface of a large number of wirings 5 "provided. Solution is simultaneously applied by a silk screen printing method, and the applied film is sufficiently dried at a temperature of 50 to 260 ° C., and as shown in FIG. 1, FIG. 2, and FIG. A flexible insulating protective film from which volatile matter was substantially removed was formed on one surface of the "region", and volatile matter was substantially removed on one surface of "the wiring 5 crossing the slit opening 4". Flexible It is to form a coating film 6.

The polyimide siloxane compounded in the coating composition is (A) 2,3,3 ', 4'- or 3,3', 4,4'-biphenyltetracarboxylic acid or acid dianhydride. Or an aromatic tetracarboxylic acid component (containing 60 mol% or more, particularly 70 to 100 mol%) containing biphenyltetracarboxylic acids as main components, such as acid derivatives thereof, and (B) (a) A

(Equation 1) [Wherein, R ₁ is a divalent hydrocarbon residue, particularly 2 to 6 carbon atoms.
Wherein R ₂ each independently represents 1 carbon atom
Represents an alkyl group or a phenyl group, and n represents 3 to 3
It represents an integer of 0, especially 5 to 20. 50-90 mol%, especially 55-85 mol% of the diaminopolysiloxane represented by the formula: and (b) 10-50 mol% of the aromatic diamine, especially 15-4 mol
It is preferably a soluble polyimide siloxane obtained by polymerizing and imidizing a diamine component comprising 5 mol% in an organic polar solvent.

In the above-mentioned aromatic tetracarboxylic acid component, "other aromatic tetracarboxylic acids" which can be used together with biphenyltetracarboxylic acids include:
3,3 ′, 4,4′-benzophenonetetracarboxylic acid, 3,3 ′, 4,4′-biphenylethertetracarboxylic acid, pyromellitic acid or a dianhydride of those acids,
Alternatively, esters of these acids can be mentioned.

The diaminopolysiloxane represented by the general formula A is a divalent hydrocarbon residue in which R _{1 in the} general formula A is a “multiple methylene group” having 2 to 6 carbon atoms or a phenylene group. , R ₂ are each independently a methyl group,
It is preferably an alkyl group having 1 to 3 carbon atoms such as an ethyl group or a propyl group, or a phenyl group.
n is preferably about 5 to 20.

The aromatic diamine is preferably an aromatic diamine compound having a plurality of benzene rings, for example, 4,4'-diaminodiphenyl ether,
Aromatic diamine compounds having two benzene rings such as 4'-diaminodiphenylmethane, 4,4'-diaminodiphenylsulfone, o-tolidine, o-dianisidine,
1,4-bis (4-aminophenoxy) benzene, 1,
An aromatic diamine compound having three benzene rings such as 4-bis (4-aminophenyl) benzene, and bis [4- (4-aminophenoxy) phenyl] sulfone;
Aromatic diamine compounds having four benzene rings, such as 2,2-bis [4- (4-aminophenoxy) phenyl] propane, are preferred.

As the aromatic diamine, an aromatic diamine compound having one or more benzene rings is used together with an aromatic diamine compound having two or more benzene rings in a proportion of 60 mol% or less based on the total aromatic diamine component. The aromatic diamine compound having one benzene ring may be, for example, paraphenylenediamine, metaphenylenediamine, 2,4-diaminotoluene, 3,5-
Diaminobenzoic acid, 2,6-diaminobenzoic acid, 3,5
-Diaminobenzyl acrylate and the like.

In the above polyimide siloxane,
When the content ratio of the `` main chain unit based on diaminopolysiloxane '' relative to all diamine components decreases, the solubility of such polyimide siloxane may decrease,
On the other hand, when the content ratio of the "main chain unit based on diaminopolysiloxane" is increased, the heat resistance, mechanical properties, adhesiveness to wiring, etc. of the polymer may be considerably reduced, which is not preferable.

The polyimide siloxane has a concentration of 0.
High molecular weight polymer having a logarithmic viscosity (indicating the degree of polymerization of the polymer) measured at a measurement temperature of 30 ° C. with a polymer solution of 5 g / 100 ml (N-methyl-2-pyrrolidone) is about 0.05 to 3 Is preferable, and
The imidation ratio of polyimide siloxane (ratio of “imide bond” by infrared absorption spectroscopy) is about 9
It is preferably from 0% to 100%, and the absorption peak of "amide-acid bond" is not substantially found in the IR chart.

The above-mentioned polyimide siloxane is partially modified with an appropriate room temperature or thermosetting resin, for example, an epoxy resin such as a phenol-based epoxy resin, a novolak-type epoxy resin, and a bisphenol-based epoxy resin. A protective coating containing such a modified epoxy resin of polyimide siloxane is preferable because of its excellent chemical resistance and heat resistance (such as solder heat resistance).

The polyimide siloxane is, for example,
(A) an aromatic tetracarboxylic acid component mainly containing 2,3,3 ′, 4′-biphenyltetracarboxylic acids, (B) (a) a diaminopolysiloxane represented by the general formula A, and (b) an aromatic It can be produced by heating a diamine component comprising an aromatic diamine in a substantially equimolar organic polar solvent to a high temperature of 120 ° C. or higher, and polymerizing and imidizing in one step. In addition, the polyimide siloxane, the two components of the acid component and the diamine component, approximately equimolar, in an organic polar solvent, polymerized at a low temperature of 80 ℃ or less to generate a polyamic acid, the polyamic acid suitable Means (imidation method using chemical imidizing agent, or
Imidization by high-temperature heating).

Examples of the organic polar solvent used in the method for producing the polyimide siloxane include sulfoxide-based solvents, formamide-based solvents, acetamide-based solvents, pyrrolidone-based solvents, glyme-based solvents such as methyldiglyme, methyltridiclime and the like. Examples include methylene phosphoramide, γ-butyrolactone, cyclohexanone, and the like, and phenol solvents.

The coating composition solution described above is low in inorganic fillers such as wollastonite, silica, and talc, polymer fillers, curable resins such as inorganic or organic dyes, epoxy resins, and curatives. It may be blended in a ratio.

When a film is formed from the coating composition (solution) by a solution casting method, the film has an initial elastic modulus of 1 to 70 kg / mm ² and is flexible.
Suitable mechanical strength (strength at break at 25 ° C .: about 0.5 to 2)
0 kg / mm ² , elongation percentage: about 30 to 500%), maintaining a sufficient level of electrical insulation, and heat resistance (the thermal decomposition onset temperature is about 250 to 500 ° C., 200
(Eg, exhibiting solder heat resistance of at least 1 ° C. for 1 minute or more).

The coating composition solution is prepared by adding the above-mentioned polyimide siloxane together with other coating components such as a curable resin (epoxy resin) and a filler to a boiling point of 100 ° C. to 250 ° C.
It can be prepared by dissolving or dispersing in an organic polar solvent that is at
It is preferably about 2 to 60% by weight, particularly about 5 to 50% by weight, and its rotational viscosity (at 25 ° C.) is a solution viscosity of about 500 to 60,000 centipoise, especially 1,000 to 50,000 centipoise.

The organic polar solvent used in the coating composition solution is an organic polar solvent having a boiling point of 100 ° C. to 250 ° C., and is preferably capable of easily dissolving the above-mentioned polyimide siloxane. The organic polar solvents used in the production of the above-mentioned polyimide siloxane can also be used, and phenol solvents, amide solvents (pyrrolidone solvents, formamide solvents, acetamide solvents, etc.), oxane solvents (dioxane, trioxane) And the like, and a glyme-based solvent (methyl diglyme, methyl triglyme, etc.) are particularly preferred, and xylene, ethyl cellosolve and the like may be partially incorporated.

The organic polar solvent includes a boiling point of 120.
A glyme-based solvent having a temperature of ~ 240 ° C is particularly preferred, and a triglyme-based solvent is most preferred.
The coating composition solution prepared by dissolving polyimide siloxane or the like in a triglyme solvent does not increase the viscosity of the coating composition solution due to rapid evaporation of the solvent.
In addition, it has excellent storage stability, and it is easy to prepare (e.g., roll kneading) a coating composition solution (printing ink) for forming the protective coating, and use the printing ink. Thus, there is an advantage that a coating operation such as silk screen printing can be suitably performed without any trouble.

The coating composition solution is applied to the main wiring region of the above-mentioned flexible wiring board and one surface of the wiring at the bent portion of the flexible wiring board having a bent portion at room temperature or under heating at a silk screen printing machine. , And then the coating film is heated to 50 to 280 ° C., preferably 60 to 260 ° C.
More preferably, at a temperature of 100 to 250 ° C., 0.1 to 10
Drying time, especially 0.2 to 5 hours, and in the case of containing a curable resin, by heat treatment for further curing, the above-mentioned insulating protective coating film (thickness) from which volatile components have been substantially removed. Is about 0.5 to 200 μm, especially about 1 to 100 μm).

As the coating composition solution, a polyimidesiloxane polymerization solution obtained by one-step polymerization and imidization of an aromatic tetracarboxylic acid component and a diamine component in an organic polar solvent can be used as it is. Alternatively, the polymerization solution may be diluted with an organic solvent similar to the polymerization solvent to an appropriate concentration before use. In addition, the coating composition solution is prepared by isolating the polyimide siloxane powder once by precipitating it from the above-described polymerization solution, and uniformly dissolving the isolated polyimide siloxane powder in the organic polar solvent. Can also.

As shown in FIG. 1, a flexible wiring board with a bent portion obtained by the method of the present invention has a wiring of a conductive material on a surface of a support film (base material) 1 made of metal foil. Flexible wiring board formed by etching process (for example, flexible wiring board, TAB wiring, etc.)
2, a flexible insulating protective coating film 7 (also referred to as a solder resist film) made of a coating composition containing a specific polyimidesiloxane is applied on the surface of most (region) of the main wiring. In the flexible wiring board 2, the support film 1 has a slit-shaped opening at the bent portion 3, and a large number of wirings 5 are provided across the slit-shaped opening 4. In addition, one surface of a large number of wirings 5 provided across the slit-shaped openings 4 of the support film 1 is covered with a flexible protective coating film 6 made of a coating composition containing a specific polyimide siloxane. Is what is being done.

As shown in FIG. 1, the flexible wiring board 2
The protective coating 6 covering one surface of a large number of wirings 5 traversing the slit-shaped opening 4 of the bent portion 3 and the insulating protective coating 7 covering the main wiring area, The protective coating is formed from the specific coating composition containing the above-mentioned polyimide siloxane or its epoxy modified product, has a low initial elasticity and is flexible, and the thickness of the protective coating 6 is a slit. The thickness is preferably 0.2 to 5 times the thickness of a large number of wirings 5 crossing the opening 4, and particularly preferably about 0.5 to 200 μm.

In the flexible wiring board with a bent portion obtained by the manufacturing method of the present invention, the large number of wires 5 crossing the slit-shaped opening 1 of the bent portion 3 have low initial elasticity and are flexible. The protective coating 6 covers one surface thereof, and as shown in FIG.
Are provided at the slit opening 4 of the support film 1 up to 180 °, the large number of wirings 5 made of metal foil are not broken at the bent portions. It is.

In the flexible wiring board with a bent portion obtained by the method of the present invention, the main wiring region is covered with a flexible insulating protective coating made of polyimide siloxane or an epoxy-modified product thereof. Therefore, the protective coating does not substantially curl.

[0035]

The present invention will be described in more detail with reference to the following Examples and Comparative Examples.

Example 1 [Production of polyimide siloxane] 2,3,3 ', 4'-biphenyltetracarboxylic dianhydride (a-BPDA) 14 was placed in a 2-liter glass separable flask.
A-BPDA was charged with 7.2 g (500 mmol) and 1274 g of N-methyl-2-pyrrolidone (NMP).
And, while stirring the solution at room temperature,
Diaminopolysiloxane (DAPS) [X-22-161AS, manufactured by Shin-Etsu Silicon Co., Ltd., R:-(CH ₂ ) _{3
-, R 2: -CH 3,} n = 9 ] 304.9g (346.
5 mmol) and 530 g of diglyme in 3
The polymerization and imidization reaction was carried out for 3 hours while adding nitrogen gas at a polymerization temperature of 190 ° C. and passing nitrogen gas at a polymerization temperature of reflux while removing water by refluxing methyl diglyme. Then, the reaction solution was once returned to room temperature. While stirring, 62.19 g of 2,2-bis [4- (4-aminophenoxy) phenyl] propane (BAPP) was added to the cooled reaction solution.
(51.5 mmol) and 500 g of NMP were added dropwise over 30 minutes, and reacted at a reaction temperature of 200 to 210 ° C. for 6 hours to produce a polyimidesiloxane.

After the reaction solution was cooled, it was added to 20 liters of methanol, and 30
The polymer powder was isolated by filtration and the polymer powder was isolated, and the polymer powder was subjected to “10 minutes washing with a disperser in 10 liters of methanol” twice, and further at 60 ° C. for 8 minutes. After vacuum drying for 42 hours, 428.9 g of a polyimidesiloxane powder was obtained.
The polyimide siloxane obtained as described above had a logarithmic viscosity (30 ° C.) of 0.24 and an imidization ratio of substantially 100%.

As for the above-mentioned polyimide siloxane, 0.2 g of the polyimide siloxane powder was added to 0.8 g of methyl diglyme at 20 ° C. and allowed to stand. did. The polyimidesiloxane has a thermal decomposition onset temperature of about 360 ° C. as measured by a DuPont 951 thermogravimeter.

[Preparation of Coating Composition Solution] 3.5 g of the polyimide siloxane prepared as described above was dissolved in 6.5 g of methyl diglyme at room temperature, and the polyimide siloxane was dissolved in methyl diglyme at a polymer concentration of 35 g. weight%
* A coating composition solution uniformly dissolved in was prepared. The coating composition solution had a solution viscosity (rotational viscosity; 25 ° C.) of 3500 centipoise.

A 200 μm spacer was arranged as a frame on a glass plate, and the coating composition solution was cast on the glass plate to form a thin film.
Drying at 150 ° C. for 30 minutes, and drying at 200 ° C. for 30 minutes to form a film having a thickness of about 40 to 60 μm. The film is subjected to a universal tensile tester (Tensilon UTM manufactured by Orientec Co., Ltd.). -11-2
0), the breaking strength, the elongation and the initial elasticity were measured. As a result, the breaking strength was 2.0 kg / mm ² and the elongation was 509.
%, And initial elastic modulus: 25 kg / mm ² .

The above film was subjected to a heat and durability test in which the film was left in a furnace at 150 ° C. for 2000 hours to have a tensile strength of 1.6 kg / mm ² , an elongation of 80%, and an initial elastic modulus of 23 kg / mm ^2. And had extremely excellent heat resistance and durability.

[Coating Composition Solution Operation: Formation of Protective Coating] As shown in FIG. 5, FIG. 6 and FIG.
m, a flexible wiring board (copper foil wiring width: about 300 μm, wiring density: 6) based on an aromatic polyimide film (UPILEX S-75, manufactured by Ube Industries, Ltd.)
0%, size of slit opening: 8 mm x 20 mm)
A screen for screen printing is arranged on one surface of the above, and the above-mentioned coating composition solution is applied using a screen printing machine to form a coating film. 30 minutes at 150 ° C., 30 minutes at 150 ° C., 18
Drying and heat treatment (baking) at 0 ° C. for 30 minutes to form an insulating protective coating and a protective coating (average thickness: about 30 μm), as shown in FIGS. 1, 2 and 3 A flexible wiring board with a bent portion was manufactured.

In the flexible wiring board with a bent portion manufactured as described above, the portion where the insulating protective coating is formed in the main wiring area is cut out as a 3 × 5 cm test piece, and the test piece is cut out. As a result of measuring the height of the test piece from the horizontal plane at the end in the longitudinal direction, the test piece was left standing on a table on a horizontal plane, and the result was 1 m.
m or less, and substantially no curl. Further, the flexible wiring board with the bent portion is set so that the bent portion has a state (180 ° bent) as shown in FIG.
The wire was repeatedly bent zero or more times, but none of the wires 5 of the slit-shaped opening was broken.

Further, in the flexible wiring board with the bent portion, the insulating protective coating (main wiring area) and the protective coating (on the wiring crossing the slit-shaped opening) have an adhesive property. As a result of performing a test method according to a cross cut test method (peeling off with an adhesive tape), there was substantially no peeled portion with the adhesive tape.

The heat resistance of the insulating protective coating and the protective coating was determined by immersing the protective coating in a solder bath at 200 ° C. for 30 seconds and observing the change in the state of the protective coating after immersion. There was no trouble at all.

[0046]

According to the present invention, a flexible wiring board (for example, a flexible wiring member, a wiring for TAB) in which conductive wiring is formed on a large part of the supporting film (a part over the entire surface of the supporting film). A flexible wiring board provided with a large number of wirings crossing the slit-shaped opening of the support film at the bent portion. A specific coating composition containing a special soluble polyimide siloxane,
Simultaneously apply simultaneously by silk screen printing method and dry their coating film, each wiring is covered with a protective coating etc., and the wiring crossing the slit-shaped opening is easily broken by bending This is a novel method that can easily and industrially produce a flexible wiring board with a bent portion that does not have any curl and that is not substantially curled.

[Brief description of the drawings]

FIG. 1 is a plan view partially showing an example of a flexible wiring board with a bent portion obtained by a manufacturing method of the present invention.

2 is an AA of the flexible wiring board with a bent portion of the present invention shown in FIG. 1;
It is sectional drawing of a line.

FIG. 3 is a BB view of the flexible wiring board with a bent portion of the present invention shown in FIG. 1;
It is sectional drawing of a line.

FIG. 4 is a cross-sectional view showing a state in which a flexible wiring board with a bent portion obtained by the manufacturing method of the present invention is bent at a bent portion of a slit opening.

FIG. 5 is a plan view partially showing an example of a flexible wiring board used for manufacturing a flexible wiring board with a bent portion of the present invention.

6 is a cross-sectional view of the flexible wiring board of FIG. 5 taken along line CC.

FIG. 7 is a cross-sectional view taken along the line DD of the flexible wiring board of FIG. 5;

[Explanation of symbols]

 REFERENCE SIGNS LIST 1 support film 2 flexible wiring board with bent portion 3 bent portion 4 slit-shaped opening 5 wiring (wiring across slit-shaped opening 5) 6 protective coating 7 insulating protective coating

──────────────────────────────────────────────────続 き Continuation of the front page (56) References JP-A-56-169390 (JP, A) JP-A-1-121325 (JP, A) JP-A-2-88677 (JP, A) 64248 (JP, U) Japanese Utility Model Showa 54-103558 (JP, U) (58) Fields investigated (Int. Cl. ⁶ , DB name) H05K 3/28

Claims (1)

(57) [Claims] 1. A main wiring of a conductive material is formed on a large part of a support film, and the support film has a slit-like opening at a bent portion, and a large number of wirings pass through the slit-like opening. In a flexible wiring board provided transversely, an aromatic tetrahedral is provided on one surface of a large number of wirings provided across a slit-shaped opening of a support film in a main wiring area and a bent portion of the wiring board. Polyimide siloxane obtained by polymerizing and imidizing a carboxylic acid component and a diamine component composed of 50-90 mol% of diaminopolysiloxane and 10-50 mol% of aromatic diamine, or an epoxy resin modified product thereof is a resin. The coating composition mainly containing the resin component containing at least 80% by weight of the component is uniformly dissolved or dispersed in the organic polar solvent. The sprayed coating composition solution is simultaneously applied by a silk screen printing method, and the applied film is dried at a temperature of 50 to 280 ° C. to form a protective coating film from which volatile components have been substantially removed. A method for producing a flexible wiring board with a bent portion, characterized by being formed.