JP2001177200A - Flexible printed-wiring board and its manufacturing method - Google Patents

Abstract

PROBLEM TO BE SOLVED: To obtain a flexible printed-wiring board whose heat resistance, break resistance and dimensional stability are superior and whose warping is not generated, by a method wherein a wiring board is coated with a heat-resistant resin solution so as to be dried and to obtain is manufacturing method. SOLUTION: The wiring board in which a conductor circuit is formed on a base material composed of a polyimide, and/or a polyimide film is coated with the heat-resistant resin solution as a polyimide and/or a polyamideimide soluble in an organic solvent and dried. It is wound and heat-treated, and a heat-resistant resin layer is formed.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a method for applying a heat-resistant resin solution onto a wiring board (a base material on which a conductor circuit is formed).
The present invention relates to a flexible printed wiring board which is obtained by drying and at least partially covers a conductive circuit with a heat-resistant resin layer, is excellent in heat resistance, folding resistance, dimensional stability and the like, and has no warp, and a method for producing the same.

[0002]

2. Description of the Related Art A flexible printed wiring board has a circuit surface coated with a coating agent for the purpose of protecting a conductive circuit from dirt, scratches, moisture and the like. As the coating method, two methods have conventionally been used. One method is to bond a heat-resistant film such as polyimide to a wiring board (a base substrate on which a conductive circuit is formed) via an adhesive. This method generally includes: 1) a step of applying and drying an adhesive on a heat-resistant film such as a polyimide; 2) a release paper or a release film on the adhesive side to prevent adhesion of foreign substances such as blocking, dirt, and dust. 3) a step of punching the laminated film into a desired pattern with a mold, 4) removing the release paper or release film, and attaching a heat-resistant film to a predetermined position on the wiring board. There is a problem that productivity is remarkably reduced due to "many manufacturing steps", "loss in punching with a die", and "high die cost". Further, since a non-heat-resistant adhesive is used, the obtained printed wiring board has insufficient heat resistance, and furthermore, it becomes difficult to punch out a fine circuit with a mold.

Another method is to apply a liquid coating material to a wiring board (a base material on which a conductive circuit is formed) by a screen printing method. In this method, since only a screen plate is manufactured in advance, the number of manufacturing steps is small, work efficiency is increased, and productivity is significantly improved. However, since conventional liquid coating materials are mainly composed of epoxy compounds, it is impossible to satisfy both heat resistance and flexibility. In the case of flexible printed wiring boards, either one of them is used at the expense of the other. That is the current situation. In addition, when the film is cured, the flexible printed wiring board is warped due to volume shrinkage and curing shrinkage of the film, which has a serious disadvantage that it cannot be applied to a high-density circuit.

In order to solve these problems, a resin solution containing a polyamic acid, which is a precursor of polyimide, as a main component is placed on a wiring board (a base material on which a conductor circuit is formed).
Techniques for forming a heat-resistant resin layer directly on a circuit by coating and drying have been studied.

For example, JP-A-3-291986 discloses that a polyamic acid-based solution, which is a precursor of polyimide, is applied to a wiring board (a base substrate on which a conductive circuit is formed).
A technique of forming a polyimide resin layer directly on a circuit by drying and then heating and dehydrating and ring-closing has been studied. However, it is difficult to achieve both heat resistance and folding resistance,
In addition, since the dehydration reaction accompanies, the actual situation is that it has various adverse effects. That is, since the ring is dehydrated at a high temperature of 300 ° C. or more, the conductor circuit is oxidized, and the dehydration reaction lowers the adhesion to the conductor circuit. In addition, since the volume shrinks due to dehydration ring closure and solvent drying, there is also a serious problem that the flexible printed wiring board is largely warped.

With respect to the warpage of the flexible printed wiring board, studies have been made to introduce a silicone unit into the polyimide to be coated to lower the elastic modulus, solubilize the solvent and lower the processing temperature. (Japanese Unexamined Patent Publication No. Hei 9-118853
However, in this method, since the glass transition point is lowered, the heat resistance by hand soldering is insufficient, and the elastic modulus is lowered, so that the handling property is deteriorated and the productivity is lowered. There were drawbacks. In addition, since a silicone unit has been introduced, when multi-layering flexible printed wiring boards, the adhesiveness with the adhesive sheet used to bond multiple wiring boards is insufficient. In some cases, some electronic devices cannot be used as wiring boards.

[0007]

SUMMARY OF THE INVENTION An object of the present invention is to solve the above-mentioned problems. That is, by applying and drying a silicone-less heat-resistant resin solution having a relatively high modulus of elasticity on a wiring board (a base substrate on which a conductive circuit is formed), it exhibits sufficient mechanical strength in processing, Another object of the present invention is to manufacture a flexible printed wiring board having excellent heat resistance, folding resistance, dimensional stability and the like without warping efficiently and at low cost.

[0008]

Means for Solving the Problems The inventors of the present invention have conducted intensive studies to achieve the above object, and as a result, have excellent heat resistance and mechanical strength on a wiring board (a base substrate on which a conductive circuit is formed). In producing a flexible printed wiring board by applying and drying a resin solution, it has been found that it can be achieved by applying and drying, winding once, and further performing heat treatment while removing the solvent in a roll form. That is, the present invention provides a flexible printed wiring board excellent in dimensional stability, in which heat resistance and folding resistance are compatible, and the wiring board has a small number of conductor circuits and does not warp even when the substrate or the conductor circuit is thin. Has been found to be inexpensive, and has the following configuration.

A flexible printed wiring board in which a conductive circuit is formed on a base material, and a conductive circuit portion and a non-conductive circuit portion are partially or entirely covered with a heat-resistant resin layer. The flexible printed wiring board, wherein the absolute value of the dimensional change before and after the heat treatment at 150 ° C. for 30 minutes is 0.04% or less, and satisfies the following expression.

[0010]

## EQU2 ## σ = (A ² × E) / 6RS (1-ν) (where σ represents an internal stress, and 0 to 4 kgf / mm)
A is the range of ² , A represents the thickness of the base substrate, 0.0
E is an elastic modulus of the base material, E is in a range of 100 to 1000 kgf / mm ² , and R is a curvature when the heat-resistant resinous resin layer is coated on the base material. Represents a radius, in the range of 30 mm to ∞, S represents the thickness of the heat resistant resin layer, in the range of 0.001 to 0.1 mm, ν represents Poisson's ratio, and 0.1 to 0.6. Range. In one embodiment, the radius of curvature determined from the warpage when a heat-resistant resin layer is coated on a base material that has been subjected to circuit processing on a wiring pattern for folding resistance evaluation conforming to JIS C5016 standard is 30 mm to ∞. There is a feature.

In one embodiment, the heat-resistant resin layer has a glass transition point of 180 ° C. or higher and a hand solder heat resistance of 350 ° C. or higher.

In one embodiment, the elastic modulus of the heat-resistant resin layer is 160 kg / mm ² or more.

In one embodiment, the difference in the coefficient of thermal expansion between the base substrate and the heat-resistant resin layer is 0 to 6.0 × 10 ^-5 , and
The thermal expansion coefficient of the base material on which the heat-resistant resin layer is formed is 6.0 × 10 ⁻⁵ or less.

In one embodiment, the base material coated with a heat-resistant resin layer has an MI of a bending diameter of 2 mm and a load of 500 g.
The number of bending according to the T method is 50,000 or more.

In one embodiment, the base substrate is made of a polyimide and / or polyamideimide film, and a conductor circuit is formed directly on the base substrate.

In one embodiment, the polyamideimide film is characterized by containing the following general formula (1) and / or the following general formula (2) as a structural unit.

[0017]

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(Wherein R ₁ and R ₂ may be the same or different, and each represents hydrogen or C 1-4
Represents an alkyl group. )

[0019]

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The method for producing a flexible printed wiring board of the present invention includes the following steps 1) to 3): 1) On a conductive circuit of a base material on which a conductive circuit is formed, and on a non-conductive circuit. A step of coating and drying a heat-resistant resin solution on a part or the entire surface; 2) a step of winding a base material coated and dried with a heat-resistant resin solution to form a roll; 3) heat-treating the roll to form a heat-resistant resin. Forming a layer;

In one embodiment, the heat treatment is performed under reduced pressure and / or in an inert gas atmosphere.

In one embodiment, at the time of the winding,
The flexible printed wiring board is wound around a long heat-resistant sheet while the coated surface of the heat-resistant resin solution faces outward.

In one embodiment, the heat-resistant resin is polyimide and / or polyamide-imide soluble in an organic solvent.

In one embodiment, the heat-resistant resin contains the following general formula (1) and / or the following general formula (2) as a structural unit.

[0025]

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(Wherein R ₁ and R ₂ may be the same or different, and each represents hydrogen or C 1-4
Represents an alkyl group. )

[0027]

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[0028]

BEST MODE FOR CARRYING OUT THE INVENTION The heat-resistant resin used in the heat-resistant resin solution of the present invention has excellent heat resistance and flame retardancy as a flexible printed wiring board such as hand soldering heat resistance, and has sufficient processing properties. Basically, any resin may be used as long as it forms a film exhibiting mechanical strength.

Preferably, the heat-resistant resin layer formed from the heat-resistant resin solution has an elastic modulus of 160 kg / mm ² or more, a glass transition point of 180 ° C. or more, and a difference in thermal expansion coefficient from the base material of 0%. ６6.0 × 10 ^-5 , the coefficient of thermal expansion of the base material on which the heat resistant resin layer is formed is 0０〜6.00 × 10 ^-5.
The following aromatic polyimides and aromatic polyamideimides having a relatively small amount of silicone or containing substantially no silicone.

The difference between the thermal expansion coefficient of the base material and the thermal expansion coefficient of the base material on which the heat-resistant resin layer is formed is 6.00 ×.
If it is larger than 10 ^-5, the dimensional change rate and warpage of the obtained flexible printed wiring board become large, which is not preferable. Further, the elastic modulus of the heat-resistant resin layer is 160 kg / mm ^2.
When the size is smaller, the loss in various manufacturing processes is increased and the productivity is reduced, and when the glass transition point is smaller than 180 ° C., the solder heat resistance of the heat resistant resin layer, particularly, the hand solder heat resistance becomes insufficient. .

Conversely, in the case of the production method of the present invention, even if the characteristic values of the heat-resistant resin layer such as the thermal expansion coefficient, the elastic modulus, and the glass transition point are in a considerably wide range, regardless of the type of the base material, This means that a flexible printed wiring board free from warpage, that is, free from internal stress, can be molded. As a result, the performance of the flexible printed wiring board can be improved. This is impossible with the conventional processing method.

In the present invention, the thickness of the heat-resistant resin layer is
0.001 to 0.1 mm is preferred. If it is smaller than 0.001 mm, the function as a protective layer of the circuit is insufficient,
If the thickness exceeds 0.1 mm, the bending resistance tends to decrease, and the warpage of the flexible printed wiring board tends to increase.

The aromatic polyimide or aromatic polyamideimide preferably used as the heat-resistant resin can be synthesized by a usual method. For example, the isocyanate method,
An acid chloride method, a low temperature solution polymerization method, a room temperature solution polymerization method, and the like. In particular, in the present invention, the aromatic polyimide or aromatic polyamideimide used as the heat-resistant resin is preferably soluble in an organic solvent in terms of moldability in each manufacturing process, manufacturing cost, and the like. Isocyanate method which can be used directly without purifying the polymerization solution is preferable. The organic solvent soluble in the present invention means N-methyl-2-pyrrolidone, N, N'-dimethylformamide, N, N'-dimethylacetamide, 1,3-dimethyl-2-imidazolidinone, tetramethylurea, Sulfolane, dimethyl sulfoxide, γ-butyrolactone, cyclohexanone, cyclopentanone, etc. alone;
Or a mixed solvent in which a part thereof is replaced with a hydrocarbon-based organic solvent such as toluene and xylene, an ether-based organic solvent such as diglyme, triglyme, and tetrahydrofuran, and a ketone-based organic solvent such as methyl ethyl ketone, methyl isobutyl ketone, and isophorone. That is soluble in 0.1% by weight or more in any of commonly used solvents.

The raw materials used for the aromatic polyimide include:
The following are mentioned. Examples of the acid component include pyromellitic acid, benzophenone 3,3 ', 4,4'-tetracarboxylic acid, biphenyl 3,3', 4'-tetracarboxylic acid, and diphenylsulfone 3,3 ', 4,4'-tetracarboxylic acid. Carboxylic acid, diphenyl ether-3,3 ', 4,
4'-tetracarboxylic acid, naphthalene-2,3,6,7
-Monoanhydrides, dianhydrides, esterified products such as tetracarboxylic acid, naphthalene-1,2,4,5-tetracarboxylic acid, naphthalene-1,4,5,8-tetracarboxylic acid, alone or in combination of two or more Can be used as a mixture.

As the amine component, p-phenylenediamine, m-phenylenediamine, 3,4'-diaminodiphenyl ether, 4,4'-diaminodiphenyl ether, 4,4'-diaminodiphenyl sulfone,
3,3′-diaminodiphenyl sulfone, 3,4′-diaminobiphenyl, 3,3′-diaminobiphenyl,
3,3′-diaminobenzanilide, 4,4′-diaminobenzanilide, 4,4′-diaminobenzophenone, 3,3′-diaminobenzophenone, 3,4′-diaminobenzophenone, 2,6-tolylenediamine,
2,4-tolylenediamine, 4,4′-diaminodiphenylsulfide, 3,3′-diaminodiphenylsulfide, 4,4′-diaminodiphenylpropane, 3,
3'-diaminodiphenylpropane, 4,4'-diaminodiphenylhexafluoropropane, 3,3'-diaminodiphenylhexafluoropropane, 3,3'-diaminodiphenylmethane, 4,4'-diaminodiphenylmethane, 4,4'- Diaminodiphenylhexafluoroisopropylidene, p-xylenediamine, m-xylenediamine, 1,4-naphthalenediamine, 1,5-
Naphthalenediamine, 2,6-naphthalenediamine,
2,7-naphthalenediamine, O-tolidine, 2,2 ′
-Bis (4-aminophenyl) propane, 2,2'-bis (4-aminophenyl) hexafluoropropane,
1,3-bis (3-aminophenoxy) benzene, 1,
3-bis (4-aminophenoxy) benzene, 1,4-
Bis (4-aminophenoxy) benzene, 2,2-bis [4- (4-aminophenoxy) phenyl] propane,
Bis [4- (4-aminophenoxy) phenyl] sulfone, bis [4- (3-aminophenoxy) phenyl] sulfone, bis [4- (3-aminophenoxy) phenyl] propane, bis [4- (3-amino) Phenoxy) phenyl] hexafluoropropane, 4,4′-bis (4
-Aminophenoxy) biphenyl, 4,4'-bis (3
-Aminophenoxy) biphenyl, 2,2-bis [4-
(4-Aminophenoxy) phenyl] hexafluoropropane, or a corresponding diisocyanate alone or a mixture of two or more thereof can be used.
Further, a resin separately polymerized with a combination of the acid component and the amine component may be used as a mixture.

The raw materials used for the aromatic polyamideimide include trimellitic anhydride, diphenyl ether-3,3 ', 4'-tricarboxylic anhydride and diphenylsulfone-3,3', 4'-tricarboxylic acid as acid components. Tricarboxylic anhydrides such as anhydrides, benzophenone 3,3 ', 4'-tricarboxylic anhydride, and naphthalene-1,2,4-tricarboxylic anhydride alone or as a mixture; ,
Alternatively, a diisocyanate alone or a mixture may be used. Further, a resin separately polymerized with a combination of the acid component and the amine component may be used as a mixture.

From the viewpoints of heat resistance, bending resistance, dimensional change rate, warpage, and moldability and manufacturing cost in each manufacturing process, preferred heat-resistant resins are aromatic polyimides and aromatic polyamides. And more preferably an aromatic polyamideimide containing a structural unit represented by the following general formula (1) or (2).

[0038]

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(In the formula, R ₁ and R ₂ may be the same or different and each represents hydrogen or an alkyl group having 1 to 4 carbon atoms.)

[0040]

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In the present invention, the solvent of the heat-resistant resin used as the heat-resistant resin solution includes N-methyl-2-pyrrolidone, N, N'-dimethylformamide, N, N'-
Examples thereof include dimethylacetamide, 1,3-dimethyl-2-imidazolidinone, tetramethylurea, sulfolane, dimethylsulfoxide, γ-butyrolactone, cyclohexanone, and cyclopentanone, and preferably N-methyl-2-pyrrolidone. In addition, some of these can be replaced with hydrocarbon organic solvents such as toluene and xylene, ether organic solvents such as diglyme, triglyme, and tetrahydrofuran, and ketone organic solvents such as methyl ethyl ketone, methyl isobutyl ketone, and isophorone. It is.

The molecular weight of the heat-resistant resin used as the heat-resistant resin solution is preferably from 0.3 to 3.0 dl / g in logarithmic viscosity at 30 ° C. in N-methyl-2-pyrrolidone. If the logarithmic viscosity is 0.3 dl / g or less, mechanical properties such as folding resistance are insufficient, and 3.0 dl / g.
Above, the solution viscosity becomes high, so that the applicability decreases.

In the above aromatic polyimides and aromatic polyamideimides, adipic acid, azelaic acid, sebacic acid, cyclohexane-4 are used as acid components within a range not to impair the object of the present invention such as heat resistance and folding resistance. , 4'-
Dicarboxylic acid, butane-1,2,4-tricarboxylic acid,
Aliphatic or alicyclic dicarboxylic acids such as butane-1,2,3,4-tetracarboxylic acid, cyclopentane-1,2,3,4-tetracarboxylic acid, siloxane dicarboxylic acid and siloxane tetracarboxylic acid; Carboxylic acids, and their monoanhydrides and dianhydrides, esterified products,
As amine components, tetramethylene diamine, hexamethylene diamine, isophorone diamine, 4,4′-dicyclohexyl methane diamine, cyclohexane-1,4
-Aliphatic or alicyclic diamines such as diamines and diaminosiloxanes or diisocyanates corresponding thereto may be used alone or as a mixture of two or more. Further, a resin separately polymerized with a combination of the acid component and the amine component may be used as a mixture.

In the heat-resistant resin solution used in the present invention, for the purpose of improving the coating property on the wiring board (the base substrate on which the circuit is formed) and the properties of the heat-resistant resin layer, the resin solution to be applied is as follows. In addition to the above polymers and solvents, inorganic and / or organic fillers (talc, white carbon, barium sulfate, gypsum alumina white, clay, silica, asbestin, magnesium carbonate, calcium carbonate, titanium oxide, polystyrene copolymer, acrylic Copolymers, fluoropolymer fine particles, sorbitol condensate, etc.), defoamers (silicone compounds, fluorine compounds, acrylic compounds, etc.), leveling agents (silicone compounds, acrylic compounds, etc.), flame retardants (phosphorus compounds, triazine compounds) Compounds, aluminum hydroxide, etc.), crosslinking agents (bisphenol A type epoxy resin, bis Enol F type epoxy resin, phenol novolak type epoxy resin, cresol novolak type epoxy resin, ester type epoxy resin, ether type epoxy resin, urethane modified epoxy resin, alicyclic type epoxy resin, hindatoin type epoxy resin, amino type epoxy resin etc. Epoxy resins, maleimide resins, isocyanate resins, etc.) and their curing agents, coupling agents (titanium coupling agents, silane coupling agents, etc.), and other organic compounds (isocyanate resins, blocked isocyanate resins, acrylic resins, urethane resins, polyesters) Resins, polyamide resins, polyether resins, phenolic resins, etc.), inorganic compounds (titanium oxide, beryllia, magnesia, etc.) etc. within the range which does not impair the object of the present invention (particularly the amount of silicone compounds etc.) If,
Alternatively, it is possible to react. As a compounding method, an ordinary method can be applied, and examples thereof include a ball mill and a three-roll mill.

The viscosity of the heat-resistant resin solution used in the present invention is preferably 10 to 1000 poise, and the degree of thixotropicity is preferably 1.0 to 5.0. The thixotropic degree is one index indicating the thixotropy of a solution and is expressed by the following equation (5). If the viscosity is less than 10 poise, "bleeding" or "repelling" tends to occur in the coating film, and if the viscosity exceeds 1000 poise or the thixotropic degree exceeds 5.0, leveling properties such as pinholes are generated. become worse.

The concentration of the heat-resistant resin solution to be applied is 1 to 5
0% by weight is preferred. Exceeding this range makes it difficult to maintain the desired viscosity value in the above-mentioned appropriate viscosity range when maintaining the desired characteristic value in the present invention in a polymer composition, a molecular weight, or a compounding formulation, resulting in poor coatability.

In the present invention, the wiring board (base substrate on which the conductor circuit is formed) coated with the heat-resistant resin layer may be formed on one or both sides by a conventionally known method such as a subtractive method or an additive method. Having a conductor circuit,
Various structures can be used. In consideration of heat resistance, folding resistance, dimensional stability, warpage of a flexible printed wiring board, etc., a wiring board having a conductive circuit directly formed on one side or both sides of a heat-resistant resin layer such as polyimide or polyamide imide is preferable. .

As the heat-resistant resin used for the insulating material of the base material, the same as the heat-resistant resin used for the heat-resistant resin solution can be used, but preferably, it is formed from the heat-resistant resin. Base material having an elastic modulus of 100 to 10
00Kg / mm ² , the difference in thermal expansion coefficient between the base material and the heat-resistant resin layer is 6.0 × 10 ⁻⁵ or less, and the coefficient of thermal expansion of the base material on which the heat-resistant resin layer is formed is 6.0 × 10 5 ^A resin with excellent heat resistance and flame retardancy of ^-5 or less. Elastic modulus is 100
If it is smaller than Kg / mm ² , sufficient mechanical strength cannot be obtained in processing, and the warpage of the flexible printed wiring board increases. Also, the difference in thermal expansion coefficient from the heat-resistant resin layer is greater than 6.0 × 10 ^−5, or the thermal expansion coefficient of the base material on which the heat-resistant resin layer is formed is greater than 6.0 × 10 ^−5. This increases the warpage and dimensional change rate of the flexible printed wiring board.

From the viewpoints of heat resistance, bending resistance, dimensional change rate, warpage, moldability in each manufacturing process and manufacturing cost of the flexible printed wiring board, preferred heat-resistant resins are aromatic polyimide and aromatic polyimide. A polyamideimide is more preferably an aromatic polyamideimide containing a structural unit represented by the following general formula (1) or (2).

[0050]

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(In the formula, R ₁ and R ₂ may be the same or different and each represents hydrogen or an alkyl group having 1 to 4 carbon atoms.)

[0052]

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The above-mentioned heat-resistant resin may be added to another resin or an organic compound for the purpose of improving various characteristics of the flexible printed wiring board, for example, mechanical characteristics, electric characteristics, slipperiness, flame retardancy and the like. Inorganic compounds may be mixed or reacted to be used together. For example, lubricants (silica, talc, silicone, etc.), adhesion promoters, flame retardants (phosphorous, triazine, aluminum hydroxide, etc.), stabilizers (antioxidants, ultraviolet absorbers, polymerization inhibitors, etc.), plating activity Agents, organic and inorganic fillers (talc, titanium oxide, fluoropolymer fine particles, pigments, dyes, calcium carbide, etc.),
In addition, silicone compounds, fluorine compounds, isocyanate compounds, blocked isocyanate compounds, acrylic resins, urethane resins, polyester resins, polyamide resins, polyether resins, epoxy resins, resins such as phenolic resins, organic compounds, or curing agents thereof, Inorganic compounds such as silicon oxide, titanium oxide, calcium carbonate, iron oxide and the like can be used in combination as long as the object of the present invention is not impaired, particularly the amount of silicone.

The thickness of the base material is preferably 0.001 to 0.1 mm, similarly to the heat-resistant resin layer. 0.001m
If it is smaller than m, the mechanical properties of the base material will be insufficient, and if it exceeds 0.1 mm, the folding resistance will be poor. From the viewpoint of folding resistance and the like, the thickness is more preferably the same as that of the heat-resistant resin layer.

As the conductor circuit formed on the base material of the present invention, copper, aluminum, steel, nickel and the like can be used. It can also be used for treated metals. Although there is no particular limitation on the thickness of the conductor circuit, for example, 0.003 to 0.05 mm
It is.

In the present invention, a heat-resistant resin solution (coating agent) is applied to a base material, and then the solvent is dried by heating. An internal stress occurs due to a difference in thermal expansion between the layer and the like. If the thickness, elastic modulus, and coefficient of thermal expansion of the heat-resistant resin layer are large, the conventional processing method may warp the flexible printed wiring board depending on the thickness, elastic modulus, coefficient of thermal expansion, and circuit pattern of the base material. Had occurred.

In general, the smaller the circuit pattern, the greater the warpage. However, in the present invention, even in a state where the warp is most likely to occur and there is no circuit (in the case of using only the base substrate), the characteristics of the base substrate depend on the characteristics. (E.g., modulus of elasticity, thermal expansion coefficient, etc.), the generated internal stress is reduced, and a laminate without warpage can be molded.

Specifically, a heat-resistant resin solution is applied to a wiring board (a base substrate on which a conductor circuit is formed), and is initially dried until a tack-free state is obtained, and then wound with the coated surface outside. Then, by heat treatment while removing the solvent in a roll form, even for a heat-resistant resin having a high modulus of elasticity, a glass transition point, a coefficient of thermal expansion, etc., internal stress due to volume shrinkage due to desolvation or curing shrinkage of the resin is reduced. Without warpage, dimensional change,
Alternatively, it is possible to form a flexible printed wiring board having a small dimensional change rate before and after coating.

The dimensional change rate before and after coating refers to the rate of change when the length of this hole interval is measured before and after coating on a wiring board before coating, at the time of before and after coating. The dimensional change rate is an elongation rate or a shrinkage rate before and after heating. The large warp means a case where the maximum height from the flat surface is high when the flexible printed wiring board is placed on a flat surface with the convex surface (the surface opposite to the warp) facing down. It can be determined by measuring the height of the warp (or by finding the radius of curvature) when the entire surface is covered with the heat-resistant resin layer. or,
The internal stress can be obtained by substituting various characteristic values such as a radius of curvature according to Equation 1. The smaller the dimensional change rate and the dimensional change rate before and after coating, the smaller the warpage of the flexible printed wiring board.

In the present invention, the work size of the wiring board (base substrate on which the conductor circuit is formed) to be applied is usually a sheet of about 300 mm × 300 mm.
After drying, a plurality of sheets are stacked and wound, with the coating layer on the outside, and heat-treated in a roll.

As a coating method, a conventionally known method can be applied. For example, printing methods such as screen printing and offset printing, roll coating, knife coating, doctor coating, blade coating, gravure coating, die coating, reverse coating, spin coating, curtain coating,
There is a coating method such as spray coating. The initial drying method is not particularly limited, but the drying temperature is 50 ° C.
~ 180 ° C is preferred. At 180 ° C. or higher, the warpage of the flexible printed wiring board at the time of initial drying becomes large, and the formability (handling property) in the form of a roll afterwards.
Gets worse. On the other hand, when the temperature is lower than 50 ° C., the drying time becomes longer, and the productivity is lowered.

In the present invention, the work size is 300
In order to completely remove the solvent by heat-treating the flexible printed wiring board of about mm x 300 mm with the solvent remaining, and then heat-treating it completely, the coated surface of the heat-resistant resin solution and the non-coated surface are in contact during winding. It is necessary to rewind so that it does not. To avoid contact, the coated surface should be on the outside and a spacer such as tape should be inserted between multiple flexible printed wiring boards, but more sheets of flexible printed wiring boards should be wound together. In order to increase productivity, it is necessary to wind a sheet-like flexible printed circuit board between long sheets while sandwiching the sheet-like flexible printed circuit board such that the covering surface is on the outside. The material of the long sheet is
What is necessary is to select a material that does not deform due to shrinkage, softening, melting, etc. at the heat treatment temperature also serving as a solvent removal, but preferably,
A sheet made of glass, metal, carbon, aramid, cellulose, or the like, such as woven fabric, nonwoven fabric, paper, felt, cloth, and screen. The thickness is preferably 0.01 mm or more, and if it is 0.02 mm or less, the coated surface and the non-coated surface come into contact with each other and the efficiency of solvent removal becomes poor.

In the present invention, the heat treatment must be performed under reduced pressure and / or in an inert gas atmosphere.
When performed in air, the resin layer is degraded or excessively crosslinked, and the dimensional change rate of the flexible printed wiring board and the dimensional change rate before and after coating are increased, and warpage is increased. In addition, the folding resistance also decreases.

The temperature of the heat treatment depends on the glass transition point of the heat-resistant resin to be used and the kind of the solvent.
３５０350 ° C. If the temperature is higher than 350 ° C., the resin layer is deteriorated or cross-linked, so that the bending resistance of the flexible printed wiring board is reduced, the dimensional change rate or the dimensional change rate before and after coating is increased, and the warpage is increased. If the temperature is lower than 150 ° C., it takes a long time to remove the solvent, so that the productivity is reduced, the internal stress caused by the volume shrinkage of the solvent is not sufficiently relaxed, and the dimensional change rate and warpage of the flexible printed wiring board are increased.

From the viewpoint of the warpage of the flexible printed wiring board, it is advantageous that the thickness of the base material and the conductor layer is larger and the conductor circuit area is larger.
The processing method of the present invention can be applied to base materials having any circuit patterns and thickness configurations.

[0066]

The present invention will be described in more detail with reference to the following examples. The present invention is not particularly limited by the embodiments. The evaluation method of the characteristic value in each embodiment is as follows. The dimensional change before and after coating was measured by the following operation.

1) 226 mm × 3 on which a wiring pattern for folding endurance evaluation according to JIS C 5016 is formed
About 300mm in the MD direction with a drill (diameter 2mm) on a 40mm (longitudinal direction is MD, other is TD) wiring board
Holes were drilled at intervals of about 200 mm in the TD direction.

2) The above wiring board was conditioned at 25 ° C. and 65% for 24 hours, and the distance between the holes was measured in the MD and TD directions.

3) A heat-resistant resin solution was applied, dried, wound up, and heat-treated.

4) The flexible printed wiring board on which the heat-resistant resin layer was formed was conditioned at 25 ° C. and 65% for 24 hours.

5) The length was measured in the MD direction and the TD direction, and the dimensional change rate was calculated by the equation (2).

[0072]

(Equation 3)

Logarithmic Viscosity The polymer was dissolved in N-methyl-2-pyrrolidone so that the polymer concentration became 0.5 g / dl, and the solution viscosity and the solvent viscosity of the solution were measured at 30 ° C. using an Ubbelose type viscosity tube. Was calculated by the following equation.

[0074]

(Equation 4)

Solution viscosity The solution viscosity was measured at a temperature of 25 ° C. at a rate of 10 revolutions / minute using a B-type viscometer.

Twisting degree At a temperature of 25 ° C., 20 revolutions / minute and 2
The solution viscosity was measured under each condition of rotation / minute, and calculated by the following formula.

[0077]

(Equation 5)

Glass Transition Point and Thermal Expansion Coefficient TMA (thermomechanical analysis / manufactured by Rigaku Corporation) was measured by the tensile load method under the following conditions. The sample film is heated to an inflection point once in nitrogen at a heating rate of 10 ° C./min.
Thereafter, the film cooled to room temperature was measured.

Load: 1 g Sample size: 4 (width) × 20 (length) mm Heating rate: 10 ° C./min Atmosphere: nitrogen The sample was prepared as follows. Base substrate: The base material was prepared by directly etching and removing the metal of the used metal laminate. Resin film of heat-resistant resin layer: heat-resistant resin solution is dried on a 0.1 mm PET film to a thickness of 0.1 mm.
It is applied so as to be 02 mm, and heated at 100 ° C. for 10 minutes. Next, after removing the PET film and fixing it to a metal frame,
Further, it was prepared by heating at 200 ° C. for 20 hours in a vacuum.

Residual solvent ratio Calculated from the following equation under the drying conditions of 250 ° C. × 1 hr according to JIS K5400.

[0081]

(Equation 6)

Hand Solder Heat Resistance After humidity control at 40 ° C. and 85% (humidity) for 5 hours, and flux washing, soldering was performed at 350 ° C., and the presence or absence of peeling or swelling was observed with a microscope.

Solder heat resistance (dip method) The humidity was adjusted at 40 ° C. and 85% (humidity) for 5 hours, and after flux washing, the sample was immersed in a jet solder bath at 280 ° C., and the presence or absence of peeling or swelling was observed with a microscope.

Folding resistance According to JIS C5016, bending diameter 2 mm, load 500
g.

Adhesion Cellophane tape was peeled off according to JIS C5016.

The warpage of the flexible printed wiring board was measured by the following operation. 1) The metal laminate used in each Example and Comparative Example was JIS
Circuit processing was performed on a wiring pattern for evaluation of bending resistance conforming to the C5016 standard, or all metals were removed by etching to prepare a base substrate. 2) A heat-resistant resin layer was formed on the obtained base material under the processing conditions shown in each of Examples and Comparative Examples. 3) A flexible printed wiring board in which a heat-resistant resin layer is formed on a wiring pattern for evaluation of folding resistance has a heat-resistant resin layer on a base material in accordance with the wiring and on which all metals have been removed by etching. The formed product was punched out into a 10 cm square using a mold. 4) Punch the sample at 40 ° C and 85% (humidity) for 5 minutes.
hr controlled. 5) After humidity control, the sample was placed on a flat surface with the convex surface facing down, and the maximum height of the warped portion was measured. The radius of curvature was determined from the height.

Measurement of internal stress The internal stress was measured by the following operation. 1) On the base material from which the metal of the metal laminate used in each of the examples and comparative examples was removed by etching, the thickness after drying was 0.1 mm.
A heat-resistant resin solution was applied so as to be 01 mm. 2) Desolvation or stress relaxation was performed under the processing conditions shown in each of the examples and comparative examples. 3) The radius of curvature of the obtained base material was obtained, and the internal stress was obtained by the equation (1).

In the equation (1), the elastic modulus of the base material and the Poisson's ratio of the heat-resistant resin layer were in accordance with the following methods for measuring the “strength, elongation and elastic modulus of the resin film”.

Dimensional change rate A heat-resistant resin layer is formed on the base material from which the metal layer has been removed under various processing conditions.
It measured by the measuring method (150 degreeC x 30 minutes) based on IPC-TM-650 (2.2.4) of 41B specification. The strength, elongation, and elastic modulus of the resin film A film prepared in the same manner as the measurement of the glass transition point was measured by a Tensilon tensile tester under the following conditions.

Sample size: width 10 mm, length 100 mm Sample humidity control: 40 ° C., 85% (humidity) Peeling speed: 20 mm / min Distance between chucks: 40 mm

Synthesis Example 1 Synthesis of heat-resistant resin solution A In a reaction vessel, 192 g of trimellitic anhydride, 3,3′-dimethyl-4,4′-biphenyl diisocyanate 211 were added.
g, 2,4-tolylene diisocyanate (35 g), sodium methylate (0.5 g) and N-methyl-2-pyrrolidone (2.5 kg) were added, and the temperature was raised to 140 ° C. for 1 hr.
Further, the reaction was carried out at 140 ° C. for 3 hours. The polymer properties obtained were as follows:

Logarithmic viscosity: 1.5 Glass transition point: 320 ° C. Thermal expansion coefficient: 2.30 × 10 ⁻⁵ Tensile strength: 34 Kg / mm ² Tensile elongation: 43% Tensile modulus: 680 Kg / mm ²

Synthesis Example 2 Synthesis of heat-resistant resin solution B In a reaction vessel, 192 g of trimellitic anhydride, 157 g of 1,5-naphthalenediisocyanate, 31 g of 4,4′-diphenylmethane diisocyanate, 1 g of diazabicycloundecene, and N-methyl 2 kg of -2-pyrrolidone was added, the temperature was raised to 170 ° C for 1 hour, and the reaction was further performed at 170 ° C for 5 hours. The properties of the obtained polymer were as follows.

Logarithmic viscosity: 1.4 Glass transition point: 356 ° C. Thermal expansion coefficient: 2.45 × 10 ⁻⁵ Tensile strength: 41 Kg / mm ² Tensile elongation: 53% Tensile elasticity: 610 Kg / mm ²

Formulation Example 1 Preparation of heat-resistant resin solution C 4 g of a silicone compound (KS603 manufactured by Shin-Etsu Chemical Co., Ltd.) was added to 1 kg of the heat-resistant resin solution A obtained in Synthesis Example 1 (based on the solid content of the heat-resistant resin solution). 1% of an acrylic compound (Floren AC300 manufactured by Kyoeisha Yushi Co., Ltd.)
(1% based on the solid content of the heat-resistant resin solution). Next, the mixture was stirred for 1 hour with a homogenizer, and the solid content was 1%.
An electrothermal resin solution C having 3% and a solution viscosity of 300 poise was obtained. The characteristic values of the film were as follows.

Tg: 308 ° C. Coefficient of thermal expansion: 2.45 × 10 ⁻⁵ Tensile strength: 24 Kg / mm ² Tensile elongation: 46% Elastic modulus: 600 Kg / mm ²

Formulation Example 2 Preparation of Heat-Resistant Resin Solution D To 10.1 g of the heat-resistant resin solution A1 obtained in Synthesis Example 1, 10.3 g of silica (Aerogel # 300 manufactured by Nippon Aerogel Co., Ltd.) and a silicone compound (Shin-Etsu Chemical Co., Ltd.) KS)
603) in an amount of 4 g (3 to the solid content of the heat-resistant resin solution).
%) And 1 g of an acrylic compound (Floren AC300 manufactured by Kyoeisha Yushi Co., Ltd.) (1% based on the solid content of the heat-resistant resin solution). After stirring with a homogenizer for 1 hour, the mixture was dispersed with three rolls, and the solid concentration was 13% and the solution viscosity was 3%.
A heat-resistant resin solution D having a poise of 00 and a thixotropic degree of 1.4 was obtained. The properties of the film were as follows.

Tg: 325 ° C. Coefficient of thermal expansion: 2.29 × 10 ⁻⁵ Tensile strength: 32 kg / mm ² Tensile elongation: 47% Elastic modulus: 689 kg / mm ²

Examples 1-2 The heat-resistant resin solution C or D obtained in the formulation examples was prepared according to Table -1.
"Copper clad laminate" Viroflex T "manufactured by Toyobo Co., Ltd.
M ”(the coefficient of thermal expansion of the base film is 2.2 × 10 ⁻⁵ , the tensile strength is 43 kg / mm ² , the tensile elongation is 60%, and the elastic modulus is 640 kg / mm ² ) in accordance with JIS C5016 standard. A substrate having a thickness of 0.
Printing was performed on the entire surface so as to be 01 mm. Then, at 100 ° C
For 5 minutes.

The same operation was repeated a plurality of times, and the obtained plurality of flexible printed wiring boards were sandwiched between long sheets of stainless steel screen so that the application surface was on the outside, and the flexible printed wiring boards having a diameter of 3 inches were sandwiched. Wound on an aluminum tube.

The wound roll was placed in an inert oven and heat-treated at 150 ° C. for 30 minutes and 280 ° C. for 10 minutes. The solvent in the coating film of the obtained flexible printed wiring board was completely removed, and the properties were as shown in Tables 1 and 2.

Examples 3 and 4 The heat-resistant resin solutions A and B obtained in Synthesis Examples 1 and 2 were applied to the same substrate to be printed as in Example 1 so as to have a thickness of 0.01 mm. Next, it was initially dried at 100 ° C. for 5 minutes.

The same operation was repeated a plurality of times, and the obtained plurality of flexible printed wiring boards were sandwiched between long sheets made of a stainless steel screen such that the coating surface was on the outside, and the flexible printed wiring boards having a diameter of 3 inches were sandwiched. Wound on an aluminum tube.

The wound roll was placed in an inert oven and heat-treated at 150 ° C. for 30 minutes and 280 ° C. for 10 minutes. The solvent in the coating film of the obtained flexible printed wiring board was completely removed, and the properties were as shown in Tables 1 and 2.

Comparative Examples 1-2 The heat-resistant resin solution C or D obtained in Formulation Examples 1 and 2 was
It was applied to the same substrate to be printed as in Example 1 via a stainless screen plate so that the thickness became 0.01 mm. Next, after drying at 100 ° C. for 5 minutes, the mixture is left in a state close to a flat surface without being rolled, and is left at 150 ° C. for 30 minutes.
For 10 minutes at 280 ° C. The solvent in the coating film of the obtained flexible printed wiring board was completely removed, and the properties were as shown in Tables 1 and 2.

Comparative Example 3 A flexible copper-clad laminate obtained by laminating a polyimide film with an adhesive (Nikaflex F, manufactured by Nickan Industry Co., Ltd.)
-30VC112RC11 / 2), the same wiring circuit as in the example was subjected to circuit processing under the same processing conditions to obtain a base material.

In addition to this, a cover with a polyimide adhesive
Film (CISV-1215 manufactured by Nikkan Industry Co., Ltd.)
Cut into a predetermined shape, press pressure 50Kg /
cm ^TwoHot press at 150 ° C for 30 minutes
Was.

When the solder heat resistance and the manual solder heat resistance of the flexible printed wiring board thus obtained were evaluated,
Swelling and peeling were observed.

[0109]

[Table 1]

[0110]

[Table 2]

[0111]

As described above, the flexible printed wiring board of the present invention is excellent in heat resistance, folding resistance, dimensional stability, mechanical strength, etc., and is flexible regardless of the base material. It is industrially useful because it can be manufactured at low cost without any warpage.

 ──────────────────────────────────────────────────続 き Continued on the front page F term (reference) 4J043 PA02 PC016 QB15 QB21 QB24 QB26 QB32 RA05 RA34 SA06 SB01 TA11 TA13 TA21 TA71 TB01 UA122 UA131 UA261 UB011 UB051 UB121 UB151 UB152 UB221 UB281 UB301 VA011 VA061 VA061 VA061 VA0122 VA0121 VA082 VA091 VA092 XA14 XA16 XA18 ZA24 ZA31 ZA41 ZB50 5E314 AA24 AA36 BB02 CC01 CC02 CC07 FF06 GG08 GG19

Claims (13)

[Claims] 1. A flexible printed wiring board in which a conductive circuit is formed on a base material, and a conductive circuit portion and a non-conductive circuit portion are partially or entirely covered with a heat-resistant resin layer. A flexible printed wiring board having an absolute value of a dimensional change rate of a conductor circuit portion before and after heat treatment at 150 ° C. for 30 minutes of 0.04% or less and satisfying the following expression. ## EQU1 ## σ = (A ² × E) / 6RS (1-ν) (where σ represents an internal stress and 0 to 4 kgf / mm)
A is the range of ² , A represents the thickness of the base substrate, 0.001 to 0.1 mm
E represents the modulus of elasticity of the base material, and is 100 to 1000 kg.
f / mm ² , R represents the radius of curvature of the base material coated with the heat-resistant resin layer, and ranges from 30 mm to ∞; S represents the thickness of the heat-resistant resin layer; 0.1m
m, and ν represents Poisson's ratio, which is in the range of 0.1 to 0.6. ) 2. A radius of curvature determined from warpage when a heat-resistant resin layer is coated on a base material processed into a wiring pattern for evaluation of folding resistance conforming to JIS C5016 standard is 30 mm to ∞. The flexible printed wiring board according to claim 1, wherein: 3. The heat-resistant resin layer has a glass transition point of 18
The flexible printed wiring board according to claim 1, wherein the hand solder heat resistance is 350 ° C. or higher at 0 ° C. or higher. 4. The heat-resistant resin layer has an elastic modulus of 160 kg.
/ Mm ² or more, the flexible printed wiring board according to any one of claims 1 to 3, wherein 5. The thermal expansion coefficient difference between the base material and the heat-resistant resin layer is 0 to 6.0 × 10 ^-5 , and the thermal expansion coefficient of the base material on which the heat-resistant resin layer is formed. Is 6.0 × 1
Characterized in that at 0 ^-5, flexible printed wiring board according to any one of claims 1 to 4. 6. The base material coated with the heat-resistant resin layer, wherein the number of bending by the MIT method with a bending diameter of 2 mm and a load of 500 g is 50,000 or more,
The flexible printed wiring board according to claim 1. 7. The flexible according to claim 1, wherein the base material is made of a polyimide and / or polyamideimide film, and a conductor circuit is formed directly on the base material. Printed wiring board. 8. The flexible printed wiring board according to claim 7, wherein the polyamide-imide film contains the following general formula (1) and / or the following general formula (2) as a constituent unit. Embedded image (In the formula, R ₁ and R ₂ may be the same or different and each represents hydrogen or an alkyl group having 1 to 4 carbon atoms.) 9. A method of manufacturing a flexible printed wiring board including the following steps (1) to (3): (1) a part on a conductor circuit of a base material on which a conductor circuit is formed and a part on a non-conductor circuit, or A step of applying and drying a heat-resistant resin solution over the entire surface, (2) a step of winding the base material coated and dried with the heat-resistant resin solution to form a roll, and (3) heat-treating the roll with heat-resistant resin. Forming a layer; 10. The method for manufacturing a flexible printed wiring board according to claim 9, wherein the heat treatment is performed under reduced pressure and / or in an inert gas atmosphere. 11. The method according to claim 1, wherein, at the time of the winding, the base material coated and dried with the heat resistant resin solution is wound around a long heat resistant sheet while the coated surface of the heat resistant resin solution is outside. The method for manufacturing a flexible printed wiring board according to claim 9 or claim 10. 12. The method according to claim 9, wherein the heat-resistant resin is polyimide and / or polyamideimide soluble in an organic solvent. 13. The flexible print according to claim 9, wherein the heat-resistant resin contains the following general formula (1) and / or the following general formula (2) as a constitutional unit. Manufacturing method of wiring board. Embedded image (In the formula, R ₁ and R ₂ may be the same or different and each represents hydrogen or an alkyl group having 1 to 4 carbon atoms.)