JP2010074190A - Method of manufacturing flexible printed wiring board - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To efficiently and inexpensively manufacture a warpage-free flexible printed wiring board with sufficient mechanical strength for processing, excellent heat resistance, folding resistance and dimensional stability through thermal treatment while removing solvent from a wiring board rolled after application and drying of a resin solution in manufacturing the flexible printed wiring board by applying and drying the resin solution excellent in the heat resistance and mechanical strength on the wiring board (base board on which a conductor circuit is formed). <P>SOLUTION: The method of manufacturing the flexible printed wiring board includes the steps (1)-(3) including: (1) a step of applying and drying a heat-resistant resin solution on a conductor circuit of a base substrate on which the conductor circuit is formed, and on a part or whole of a non-conductor circuit, (2) a step of rolling the base substrate on which the heat-resistant resin solution is applied and dried, and (3) a step of forming a heat-resistant resin layer through thermal treatment of the rolled base substrate. <P>COPYRIGHT: (C)2010,JPO&INPIT

Description

  The present invention provides a heat-resistant resin layer that is at least partially coated with a heat-resistant resin layer by applying and drying a heat-resistant resin solution on a wiring board (base substrate on which a conductor circuit is formed). The present invention relates to a flexible printed wiring board having excellent bending resistance and dimensional stability and having no warpage, and a method for producing the same.

The flexible printed wiring board covers the circuit surface with a coating agent for the purpose of protecting the conductor circuit from dirt, scratches, moisture and the like. As this coating method, two methods have been conventionally used. One is a method in which a heat-resistant film such as polyimide is bonded to a wiring board (base substrate on which a conductor circuit is formed) through an adhesive. This method is generally
1) A process of applying and drying an adhesive on a heat resistant film such as polyimide,
2) A process for obtaining a laminated film by sticking a release paper or a release film on the adhesive side in order to prevent adhesion of foreign matters such as blocking, dust, and dust,
3) A process of punching a laminated film into a target pattern with a mold,
4) The process consists of removing the release paper and release film and attaching the heat-resistant film to the specified position on the wiring board. It consists of “manufacturing processes”, “loss when punching with molds”, “ There is a problem that the productivity is remarkably lowered due to the high die cost. In addition, since a non-heat resistant adhesive is used, the obtained printed wiring board has insufficient heat resistance, and furthermore, when it becomes a fine circuit, it is difficult to punch with a mold.

  Another method is a method in which a liquid coating agent is applied to a wiring board (a base substrate on which a conductor circuit is formed) by a screen printing method. In this method, since only the screen plate is manufactured in advance, the number of manufacturing steps is small, the working efficiency is increased, and the productivity is remarkably improved. However, since conventional liquid coatings 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 is used at the expense of either. This is the current situation. Further, when the film is cured, the flexible printed wiring board is warped due to the volume shrinkage or the curing shrinkage of the film, which has a serious drawback that it cannot be applied to a high-density circuit.

  In order to solve these problems, a resin solution mainly composed of polyamic acid, which is a precursor of polyimide, is applied and dried on a wiring board (base substrate on which a conductor circuit is formed), and then on the circuit. Techniques for directly forming a heat-resistant resin layer have been studied.

  For example, in JP-A-3-291986 (Patent Document 1), a polyamic acid solution, which is a polyimide precursor, is applied and dried on a wiring board (base substrate on which a conductor circuit is formed), and then, A technique for forming a polyimide resin layer directly on a circuit by heating and dehydrating ring closure has been studied. However, it is difficult to achieve both heat resistance and folding resistance, and it is accompanied by a dehydration reaction. In other words, since the dehydration ring is closed at a high temperature of 300 ° C. or higher, there is a drawback that the conductor circuit is oxidized or the adhesion with the conductor circuit is reduced due to the dehydration reaction. Further, since the volume shrinks with dehydration ring closure and solvent drying, there is a serious problem that the flexible printed wiring board is greatly warped.

As for the warpage of the flexible printed wiring board, studies have been made such as introducing a silicone unit into the polyimide to be coated to lower the elastic modulus or solubilize the solvent to lower the processing temperature. (Japanese Patent Laid-Open No. 9-118853, etc., Patent Document 2)
However, this method has the disadvantages that the glass transition point is lowered, so that the soldering heat resistance is insufficient, the elastic modulus is lowered, the handling property is deteriorated, and the productivity is lowered. . In addition, since a silicone unit is introduced, when a flexible printed wiring board is multilayered, it has insufficient adhesion to an adhesive sheet used to bond multiple wiring boards. Some electronic devices cannot be used as wiring boards.

JP-A-3-291986 Japanese Patent Laid-Open No. 9-118853

  The object of the present invention has been made to solve the above problems. That is, by applying and drying a silicone-less, heat-resistant resin solution having a relatively high elastic modulus on a wiring board (base substrate on which a conductor circuit is formed), sufficient mechanical strength is shown for processing. In addition, the present invention intends to efficiently and inexpensively produce a flexible printed wiring board having excellent heat resistance, folding resistance, dimensional stability, etc. and having no warpage.

  As a result of diligent research to achieve the above object, the present inventors applied a resin solution having excellent heat resistance and mechanical strength on a wiring board (base substrate on which a conductor circuit is formed) and dried it to be flexible. In producing a printed wiring board, it has been found that it can be achieved by coating and drying, then winding it once, and further heat-treating it while removing the solvent in the form of a scroll. That is, the present invention is a flexible printed wiring board that has both excellent heat resistance and folding resistance, and has excellent dimensional stability that does not cause warping even when the number of conductor circuits of the wiring board is small or the substrate or conductor circuit is thin. It can be manufactured at low cost and has the following configuration.

  A flexible printed wiring board in which a conductor circuit is formed on a base substrate, and a conductor circuit portion and a non-conductor circuit portion are partially or entirely covered with a heat-resistant resin layer. A flexible printed wiring board in which the absolute value of the dimensional change rate before and after the heat treatment for 30 minutes is 0.04% or less and satisfies the following formula.

(Equation 2)
σ = (A ² × E) / 6RS (1−ν)
(However, in the formula, σ represents internal stress, and is in the range of 0 to 4 Kgf / mm ² .
A represents the thickness of the base substrate and is in the range of 0.001 to 0.1 mm.
E represents the elastic modulus of the base substrate and is in the range of 100 to 1000 Kgf / mm ² ;
R represents a radius of curvature when a heat-resistant resin layer is coated on the base substrate, and is in a range of 30 mm to ∞.
S represents the thickness of the heat resistant resin layer, and is in the range of 0.001 to 0.1 mm.
ν represents the Poisson's ratio and is in the range of 0.1 to 0.6. )
In one embodiment, the radius of curvature obtained from the warp when a heat-resistant resin layer is coated on a base substrate that is circuit-processed to a wiring pattern for folding resistance evaluation conforming to JIS C5016 standard is 30 mm to ∞. It is characterized by that.

  In one embodiment, the glass transition point of the heat resistant resin layer is 180 ° C. or higher, and the hand solder heat resistance is 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 thermal expansion coefficient 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 substrate on which the heat-resistant resin layer is formed is 6 0.0 × 10 ⁻⁵ or less.

  In one embodiment, the base substrate coated with the heat-resistant resin layer is characterized in that the number of bending by the MIT method with a bending diameter of 2 mm and a load of 500 g is 50000 times or more.

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

  In one embodiment, the polyamide-imide film includes the following general formula (1) and / or the following general formula (2) as a structural unit.

(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.)

The method for producing a flexible printed wiring board of the present invention includes the following steps 1) to 3):
1) A process of applying and drying a heat-resistant resin solution on a part of or the entire surface of the conductor circuit and non-conductor circuit of the base substrate on which the conductor circuit is formed,
2) A step of winding a base substrate coated and dried with a heat resistant resin solution to form a scroll, and 3) a step of heat-treating the scroll to form a heat resistant resin 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 winding, the flexible printed wiring board is wound around a long heat-resistant sheet with the application surface of the heat-resistant resin solution facing outside.

  In one embodiment, the heat-resistant resin is a polyimide and / or polyamideimide that is 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.

(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.)

  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 there is no warping of the flexible printed wiring board regardless of the base substrate. Since it can be manufactured at low cost, it is industrially useful.

  As the heat-resistant resin used in the heat-resistant resin solution in the present invention, a film having excellent heat resistance and flame resistance as a flexible printed wiring board such as hand solder heat resistance and sufficient mechanical strength in processing. As long as it is formed, basically any resin may be used.

Preferably, the elastic modulus of the heat resistant resin layer formed from the heat resistant resin solution is 160 kg / mm ² or more, the glass transition point is 180 ° C. or more, and the difference in thermal expansion coefficient from the base substrate is 0 to 6. 0 × 10 ⁻⁵ , aromatic base material with a heat resistant resin layer having a coefficient of thermal expansion of 0 to 6.00 × 10 ⁻⁵ or less, a relatively small amount of silicone, or an aromatic substantially free of silicone Polyimide and aromatic polyamideimide.

When the thermal expansion coefficient difference from the base substrate or the thermal expansion coefficient of the base substrate on which the heat-resistant resin layer is formed is larger than 6.00 × 10 ⁻⁵ , the dimensional change rate of the obtained flexible printed wiring board This is not preferable because warpage increases. Further, when the elastic modulus of the heat resistant resin layer is smaller than 160 kg / mm ² , loss in various manufacturing processes is increased and the productivity is lowered. When the glass transition point is smaller than 180 ° C., the solder heat resistance of the heat resistant resin layer is reduced. In particular, the soldering heat resistance and the like are 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, elastic modulus, glass transition point, etc. are in a fairly wide range, warping occurs regardless of the type of base substrate. No, that is, a flexible printed wiring board having no internal stress can be molded. As a result, high performance of the flexible printed wiring board can be achieved. This is impossible with conventional processing methods.

  In the present invention, the thickness of the heat resistant resin layer is preferably 0.001 to 0.1 mm. If it is smaller than 0.001 mm, the function as a protective layer of the circuit is insufficient, and if it exceeds 0.1 mm, the bending resistance is lowered, and the warp 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 an ordinary method. For example, an 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 molding processability and manufacturing cost in each manufacturing process. Is preferably an isocyanate method that can be used directly without purifying the polymerization solution. 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 part of them, hydrocarbon organic solvents such as toluene, xylene, ether organic solvents such as diglyme, triglyme, tetrahydrofuran, methyl ethyl ketone In addition, a solvent that dissolves in an amount of 0.1% by weight or more in any commonly used solvent such as a mixed solvent replaced with a ketone-based organic solvent such as methyl isobutyl ketone or isophorone.

  Examples of raw materials used for the aromatic polyimide include the following. Examples of the acid component include pyromellitic acid, benzophenone 3,3 ′, 4,4′-tetracarboxylic acid, biphenyl 3,3 ′, 4′-tetracarboxylic acid, diphenylsulfone 3,3 ′, 4,4′-tetra Carboxylic acid, diphenyl ether-3,3 ′, 4,4′-tetracarboxylic acid, naphthalene-2,3,6,7-tetracarboxylic acid, naphthalene-1,2,4,5-tetracarboxylic acid, naphthalene-1,4 , 5,8-tetracarboxylic acid and other monoanhydrides, dianhydrides, esterified products and the like can be used alone or as a mixture of two or more.

  Examples of the amine component include 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'-diaminodiphenyl sulfide, 3,3'-diaminodiphenyl sulfide, 4,4'-diaminodiphenylpropane 3,3′-diaminodiphenylpropane, 4, '-Diaminodiphenylhexafluoropropane, 3,3'-diaminodiphenylhexafluoropropane, 3,3'-diaminodiphenylmethane, 4,4'-diaminodiphenylmethane, 4,4'-diaminodiphenylhexafluoroisopropylidene, p-xylene Diamine, 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- ( -Aminophenoxy) phenyl] propane, bis [4- (4-aminophenoxy) phenyl] sulfone, bis [4- (3-aminophenoxy) phenyl] sulfone, bis [4- (3-aminophenoxy) phenyl] propane, Bis [4- (3-aminophenoxy) phenyl] hexafluoropropane, 4,4′-bis (4-aminophenoxy) biphenyl, 4,4′-bis (3-aminophenoxy) biphenyl, 2,2-bis [ 4- (4-Aminophenoxy) phenyl] hexafluoropropane or a diisocyanate corresponding to these may be used alone or in combination of two or more. In addition, a resin separately polymerized by a combination of these acid component and amine component can be mixed and used.

  As raw materials used for aromatic polyamideimide, trimellitic acid anhydride, diphenyl ether-3,3 ′, 4′-tricarboxylic acid anhydride, diphenylsulfone-3,3 ′, 4′-tricarboxylic acid anhydride as an acid component, Tricarboxylic acid anhydrides such as benzophenone 3,3 ′, 4′-tricarboxylic acid anhydride and naphthalene-1,2,4-tricarboxylic acid anhydride are used alone or as a mixture, and the amine component is a diamine or diisocyanate similar to polyimide. These may be used alone or as a mixture. In addition, a resin separately polymerized by a combination of these acid component and amine component can be mixed and used.

  From the viewpoints of heat resistance, folding resistance, dimensional change rate, warpage of the flexible wiring board, molding processability in each manufacturing process, manufacturing cost, and the like, preferred heat resistant resins are aromatic polyimide and aromatic polyamideimide. More preferably, it is an aromatic polyamideimide containing a structural unit represented by the following general formula (1) or (2).

(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.)

  In the present invention, as a solvent of the heat resistant resin used as the heat resistant resin solution, N-methyl-2-pyrrolidone, N, N′-dimethylformamide, N, N′-dimethylacetamide, 1,3-dimethyl-2-imidazo Examples include lydinone, tetramethylurea, sulfolane, dimethylsulfoxide, γ-butyrolactone, cyclohexanone, cyclopentanone, and preferably N-methyl-2-pyrrolidone. 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 N-methyl-2-pyrrolidone having a logarithmic viscosity at 30 ° C. of 0.3 to 3.0 dl / g. When the logarithmic viscosity is 0.3 dl / g or less, the mechanical properties such as folding resistance are insufficient, and when the logarithmic viscosity is 3.0 dl / g or more, the solution viscosity becomes high, so that the coating property is lowered.

  In addition, in the above aromatic polyimide and aromatic polyamideimide, adipic acid, azelaic acid, sebacic acid, cyclohexane-4,4 ′ are used as acid components within a range that does not impair the object of the present invention such as heat resistance and folding resistance. -Dicarboxylic acid, butane-1,2,4-tricarboxylic acid, butane-1,2,3,4-tetracarboxylic acid, cyclopentane-1,2,3,4-tetracarboxylic acid, siloxane dicarboxylic acid, siloxane tetra Aliphatic and alicyclic dicarboxylic acids such as carboxylic acids, polycarboxylic acids, and their monoanhydrides, dianhydrides, and esterified products, and tetramethylenediamine, hexamethylenediamine, isophoronediamine as amine components 4,4'-dicyclohexylmethanediamine, cyclohexane-1,4-diamine, diaminosiloxa Aliphatic and alicyclic diamines or the corresponding diisocyanates to these or the like may be used alone or in combination of two or more. In addition, a resin separately polymerized by a combination of these acid component and amine component can be mixed and used.

  In the heat-resistant resin solution used in the present invention, the above-mentioned polymer is used as a resin solution to be applied for the purpose of improving the coating property to the wiring board (base substrate on which the circuit is formed) and the characteristics of the heat-resistant resin layer. In addition to solvent and solvent, inorganic and / or organic filler (talc, white carbon, barium sulfate, gypsum alumina white, clay, silica, asbestine, magnesium carbonate, calcium carbonate, titanium oxide, polystyrene copolymer, acrylic copolymer , Fluorine polymer fine particles, sorbitol condensates, etc.), antifoaming agents (silicone compounds, fluorine compounds, acrylic compounds, etc.), leveling agents (silicone compounds, acrylic compounds, etc.), flame retardants (phosphorus compounds, triazine compounds, water) Aluminum oxide, etc.), crosslinking agent (bisphenol A type epoxy resin, bisphenol F) Epoxy resins, phenol novolac type epoxy resins, cresol novolac type epoxy resins, ester type epoxy resins, ether type epoxy resins, urethane modified epoxy resins, alicyclic epoxy resins, hindered-in type epoxy resins, amino type 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, polyester resins, polyamides) Resin, polyether resin, phenol resin, etc.), inorganic compounds (titanium oxide, beryllia, magnesia, etc.), etc. are blended within a range that does not impair the object of the present invention (especially the amount of silicone compound), or It is possible to respond. As a blending method, a normal method can be applied, for example, a ball mill or a three-roll.

  The viscosity of the heat-resistant resin solution used in the present invention is preferably 10 to 1000 poise, and the degree of change is preferably 1.0 to 5.0. The fluctuation degree is one index indicating the thixotropy of the solution, and is expressed by the following formula (5). If the viscosity is less than 10 poise, the film is likely to “bleed” or “repellent”, and if the viscosity exceeds 1000 poise, or if the degree of change exceeds 5.0, leveling properties such as pinholes are generated. Deteriorate.

  The concentration of the heat-resistant resin solution to be applied is preferably 1 to 50% by weight. If this range is exceeded, it becomes difficult to keep the viscosity within the above-mentioned appropriate viscosity range when the polymer composition, molecular weight, or blending prescription is maintained to maintain the target characteristic value in the present invention, and the coating property is deteriorated.

  In the present invention, as a wiring board (base substrate on which a conductor circuit is formed) covered with a heat resistant resin layer, a conductor circuit is formed on one side or both sides by a conventionally known method such as a subtractive method or an additive method. The thing of various structures which have can be used. In consideration of heat resistance, folding resistance, dimensional stability, warping of the flexible printed wiring board, etc., a wiring board in which a conductor circuit is directly formed on one side or both sides of a heat resistant resin layer such as polyimide or polyamideimide is preferable. .

As the heat-resistant resin used for the insulating material of the base substrate, the same heat-resistant resin as that used for the heat-resistant resin solution can be used. Preferably, the base group formed from the heat-resistant resin is used. The elastic modulus of the material is 100 to 1000 kg / mm ² , the difference in thermal expansion coefficient between the base substrate and the heat resistant resin layer is 6.0 × 10 ⁻⁵ or less, and the thermal expansion of the base substrate on which the heat resistant resin layer is formed. It is a resin excellent in heat resistance and flame retardancy with a coefficient of 6.0 × 10 ⁻⁵ or less. When the elastic modulus is smaller than 100 kg / mm ² , sufficient mechanical strength cannot be obtained in processing, and warping of the flexible printed wiring board becomes large. In addition, the difference in thermal expansion coefficient from the heat resistant resin layer is larger than 6.0 × 10 ^−5, or the thermal expansion coefficient of the base substrate on which the heat resistant resin layer is formed is larger than 6.0 × 10 ^−5. As a result, the warp and dimensional change rate of the flexible printed wiring board increase.

  In view of heat resistance, folding resistance, dimensional change rate, warpage of the flexible printed wiring board, molding processability and manufacturing cost in each manufacturing process, preferable heat resistant resins are aromatic polyimide and aromatic polyamideimide. More preferably, it is an aromatic polyamideimide containing a structural unit represented by the following general formula (1) or (2).

(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.)

  In addition, other resins, organic compounds, and inorganic compounds may be added to the above heat-resistant resin for the purpose of improving various characteristics of the flexible printed wiring board, such as mechanical characteristics, electrical characteristics, slipperiness, and flame retardancy. You may make it mix or make it react and use together. For example, lubricant (silica, talc, silicone, etc.), adhesion promoter, flame retardant (phosphorus, triazine, aluminum hydroxide, etc.), stabilizer (antioxidant, UV absorber, polymerization inhibitor, etc.), plating activity Agents, organic and inorganic fillers (talc, titanium oxide, fluoropolymer fine particles, pigments, dyes, calcium carbide, etc.), silicone compounds, fluorine compounds, isocyanate compounds, blocked isocyanate compounds, acrylic resins, urethane resins, Resins and organic compounds such as polyester resins, polyamide resins, polyether resins, epoxy resins and phenol resins, or these curing agents, inorganic compounds such as silicon oxide, titanium oxide, calcium carbonate, iron oxide, especially the amount of silicone It can be used in combination as long as the object of the present invention is not impaired.

  Further, the thickness of the base substrate is preferably 0.001 to 0.1 mm as in the heat resistant resin layer. If it is less than 0.001 mm, the mechanical properties as a base substrate are insufficient, and if it exceeds 0.1 mm, the folding resistance is deteriorated. From the viewpoint of folding resistance and the like, it is more preferably the same thickness as the heat resistant resin layer.

  As the conductor circuit formed on the base substrate of the present invention, copper, aluminum, steel, nickel, and the like can be used, and a composite metal obtained by combining these and a metal treated with another metal such as zinc or a chromium compound. Can also be used. Although there is no limitation in particular about the thickness of a conductor circuit, it is 0.003-0.05 mm, for example.

  In the present invention, a heat-resistant resin solution (coating agent) is applied to the base substrate, and then the solvent is dried by heating. Therefore, volume shrinkage due to solvent removal, or between the base substrate and the heat-resistant resin layer Internal stress is generated due to a difference in thermal expansion. If the thickness, elastic modulus, and thermal expansion coefficient of the heat-resistant resin layer are large, the conventional processing method warps the flexible printed circuit board depending on the thickness, elastic modulus, thermal expansion coefficient, and circuit pattern of the base substrate. Had occurred.

  Normally, the smaller the circuit pattern, the larger the warp. However, in the present invention, the warp is most likely to occur, even in the absence of a circuit (in the case of only the base material), regardless of the characteristics of the base material (elasticity). Rate, thermal expansion coefficient, etc.) and the generated internal stress are alleviated, and it is possible to mold a laminate without warping.

  Specifically, a heat-resistant resin solution is applied to a wiring board (base substrate on which a conductor circuit is formed), and after initial drying until a tack-free state is obtained, the wound surface is wound outward, and then the roll By heat-treating while removing the solvent, the internal stress accompanying volumetric shrinkage and curing shrinkage of the resin is alleviated and warped even with heat-resistant resins with high elastic modulus, glass transition point, thermal expansion coefficient, etc. It is possible to mold a flexible printed wiring board having no dimensional change rate or a small dimensional change rate before and after coating.

  The rate of dimensional change before and after coating refers to the rate of change when the length of the hole interval is measured before and after coating by drilling holes in the wiring board before coating. The dimensional change rate is an elongation rate or shrinkage rate before and after heating. In addition, when the warp is large, the maximum height from the flat surface when the convex surface of the flexible printed wiring board (the surface opposite to the warp) is placed on the flat surface is high. It can be quantified by measuring the height of the warp (or determining the radius of curvature) when the entire surface is covered with the heat resistant resin layer. Further, the internal stress can be obtained by substituting various characteristic values such as a radius of curvature according to the equation (1). The smaller the dimensional change rate and the dimensional change rate before and after coating, the smaller the warp of the flexible printed wiring board.

  In the present invention, the work size of the applied wiring board (base substrate on which the conductor circuit is formed) is usually a sheet of about 300 mm × 300 mm, and after coating and drying, a plurality of sheets are coated with the coating layer outside. Then, it is rolled up and heat-treated in the form of a scroll.

As a coating method, a conventionally known method can be applied. For example, there are printing methods such as screen printing and offset printing, coating methods such as roll coating, knife coating, doctor coating, blade coating, gravure coating, die coating, reverse coating, spin coating, curtain coating, and spray coating. Although there is no limitation in particular, 50 to 180 degreeC is preferable for drying temperature. If it is 180 ° C. or higher, the warp of the flexible printed wiring board at the time of initial drying becomes large, and the molding processability (handling property) in the form of a later roll worsens. Moreover, at 50 degrees C or less, drying time becomes long and productivity falls.

  In the present invention, a plurality of flexible printed wiring boards having a work size of about 300 mm × 300 mm are wound up in a state where the solvent remains, and then heat-treated to remove the solvent completely. It is necessary to wind up the coated surface and the non-coated surface so as not to contact each other. To avoid contact, it is sufficient to place the coated surface on the outside and insert a spacer such as tape between multiple flexible printed wiring boards. However, more sheet-like flexible printed wiring boards can be wound together. In order to increase productivity, it is necessary to wind the sheet-like flexible printed wiring board between the long sheets so that the covering surface is on the outside. The material of the long sheet may be selected from a material that does not deform due to shrinkage, softening, melting, etc. at a heat treatment temperature that also serves as a solvent removal, preferably made from glass, metal, carbon, aramid, cellulose, etc. Sheets of woven fabric, nonwoven fabric, paper, felt, cloth, screen and the like. 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 are in contact with each other, or the efficiency of solvent removal is deteriorated.

  In the present invention, the atmosphere during the heat treatment needs to be performed under reduced pressure and / or in an inert gas atmosphere. When carried out in the air, the resin layer is deteriorated or excessively cross-linked, and the dimensional change rate of the flexible printed wiring board and the dimensional change rate before and after coating increase, resulting in a large warp. In addition, folding resistance also decreases.

  Although the temperature of heat processing is dependent on the glass transition point of the heat resistant resin to be used and the kind of solvent, it is about 150 to 350 degreeC. Above 350 ° C., the bending resistance of the flexible printed wiring board decreases due to deterioration or crosslinking of the resin layer, the dimensional change rate and the dimensional change rate before and after coating increase, and warpage increases. When the temperature is 150 ° C. or lower, solvent removal takes a long time, so that productivity is reduced, internal stress due to volumetric shrinkage of the solvent is insufficient, and the dimensional change rate and warpage of the flexible printed wiring board are increased.

  From the viewpoint of warping of the flexible printed wiring board, it is advantageous that the thickness of the base substrate and the conductor layer is thicker, and that the conductor circuit area is larger. However, in the processing method of the present invention, all circuit patterns and thickness configurations can be obtained. Applicable to base substrate.

Hereinafter, the present invention will be described in more detail with reference to examples. The present invention is not particularly limited by the examples. Moreover, the evaluation method of the characteristic value in each Example is as follows.
Dimensional change rate before and after coating Measured by the following operation.

    1) A wiring board of 226 mm x 340 mm (longitudinal direction is MD, and the other is TD) on which a circuit pattern for folding resistance evaluation according to JIS C 5016 is formed, is drilled (diameter 2 mm) in the MD direction. Holes were drilled at intervals of about 200 mm in the TD direction at 300 mm.

2) The wiring board was conditioned at 25 ° C. and 65% for 24 hours, and then the hole interval was measured in the MD direction and the TD direction.

3) A heat resistant resin solution was applied, dried, wound 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 obtained by the equation (2).

Logarithmic viscosity Dissolved in N-methyl-2-pyrrolidone so that the polymer concentration is 0.5 g / dl. The solution viscosity and solvent viscosity of the solution were measured at 30 ° C. using an Ubellose type viscosity tube. Calculated with the formula.

Solution viscosity Measured with a B-type viscometer at a temperature of 25 ° C. under conditions of 10 revolutions / minute.

Thickness of change The solution viscosity was measured with a B-type viscometer at a temperature of 25 ° C. under the conditions of 20 revolutions / minute and 2 revolutions / minute, and calculated according to the following formula.

Glass transition point and coefficient of thermal expansion Measurement was carried out under the following conditions by TMA (Thermomechanical Analysis / manufactured by Rigaku Corporation) tensile load method. The sample film was measured for a film that was once heated to the inflection point in nitrogen at a heating rate of 10 ° C./min and then cooled to room temperature.

Load: 1g
Sample size: 4 (width) x 20 (length) mm
Temperature increase rate: 10 ° C / min
Atmosphere: Nitrogen Samples were prepared as follows.
Base substrate: prepared by etching away the metal of the metal laminate used.
Resin film of heat-resistant resin layer: A heat-resistant resin solution is applied to a 0.1 mm PET film so that the thickness after drying is 0.02 mm, and heated at 100 ° C. for 10 minutes. Next, the PET film was removed, fixed to a metal frame, and then heated at 200 ° C. for 20 hours in a vacuum.

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

Manual soldering heat resistance was adjusted for 5 hours at 40 ° C. and 85% (humidity), washed with flux, soldered at 350 ° C., and observed for peeling or swelling with a microscope.

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

Folding resistance Measured according to JIS C5016 with a bending diameter of 2 mm and a load of 500 g.

Adhesion Cellotape (registered trademark) was peeled off according to JIS C5016.

Warpage of flexible printed wiring board Measurement was performed by the following operation.
1) The metal laminate used in each example and comparative example was subjected to circuit processing into a wiring pattern for folding resistance evaluation conforming to JIS C5016 standard, or all metal was removed by etching to prepare a base substrate.
2) On the obtained base substrate, a heat resistant resin layer was formed 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 the base substrate in accordance with the wiring and from which all metals have been removed by etching. What was formed was punched into a 10 cm square using a mold.
4) The punched sample was conditioned at 40 ° C. and 85% (humidity) for 5 hours.
5) After humidity control, the sample was placed on a flat surface with the convex surface down, and the maximum height of the warped portion was measured.
Also, the radius of curvature was determined from this height.

Measurement of internal stress The internal stress was measured by the following operation.
1) A heat resistant resin solution was applied on the base substrate from which the metal of the metal laminate used in each Example and Comparative Example was removed by etching so that the thickness after drying was 0.01 mm. 2) Solvent removal or stress relaxation was performed under the processing conditions shown in each Example and Comparative Example.
3) The curvature radius of the obtained base substrate was determined, and the internal stress was determined by the equation (1).

  In Equation 1, the elastic modulus of the base substrate and the Poisson's ratio of the heat-resistant resin layer were in accordance with the measurement method of “strength, elongation, elastic modulus of resin film” in the next section.

Dimensional change rate On the base substrate from which the metal layer has been removed, a heat-resistant resin layer is formed under each processing condition, and the base substrate is formed according to IPC-FC241B standard IPC-TM-650 (2.2.4). Was measured by a measurement method (150 ° C. × 30 minutes) based on the above.
Strength, elongation, and elastic modulus of resin film A film prepared in the same manner as the measurement of the glass transition point was measured with a Tensilon tensile tester under the following conditions.

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

Synthesis Example 1 Synthesis of Heat Resistant Resin Solution A In a reaction vessel, 192 g of trimellitic anhydride, 211 g of 3,3′-dimethyl-4,4′-biphenyl diisocyanate, 35 g of 2,4-tolylene diisocyanate, 0.5 g of sodium methylate , And 2.5 kg of N-methyl-2-pyrrolidone were added, the temperature was raised to 140 ° C. over 1 hour, and the reaction was further continued 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-naphthalene diisocyanate, 31 g of 4,4′-diphenylmethane diisocyanate, 1 g of diazabicycloundecene, and N-methyl-2- 2 kg of pyrrolidone was added, the temperature was raised to 170 ° C. over 1 hour, and further reacted at 170 ° C. for 5 hours. The characteristics 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 modulus: 610 Kg / mm ²

Formulation Example 1 Preparation of Heat Resistant Resin Solution C To 1 heat-resistant resin solution A1Kg obtained in Synthesis Example 1, 4 g of silicone compound (KS603 manufactured by Shin-Etsu Chemical Co., Ltd.) (3% of solid content of heat-resistant resin solution) ), 1 g (1% with respect to the solid content of the heat-resistant resin solution) of acrylic compound (Kyoeisha Yushi Co., Ltd., Floren AC300) was added. Subsequently, it stirred with the homogenizer for 1 hour, and the thermophilic resin solution C with a solid content concentration of 13% and a solution viscosity of 300 poise was obtained. The characteristic values of the film were as follows.

Tg: 308 ° C
Thermal expansion coefficient: 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 heat-resistant resin solution A1Kg obtained in Synthesis Example 1, 10.3 g of silica (Aerogel # 300 manufactured by Nippon Aerogel Co., Ltd.) and silicone compound (manufactured by Shin-Etsu Chemical Co., Ltd.) 4 g of KS603) (3% relative to the solid content of the heat-resistant resin solution) and 1 g of acrylic compound (Floren AC300 manufactured by Kyoeisha Yushi Co., Ltd.) were added (1% relative to the solid content of the heat-resistant resin solution). After stirring for 1 hour with a homogenizer, the mixture was dispersed with three rolls to obtain a heat resistant resin solution D having a solid content concentration of 13%, a solution viscosity of 300 poise, and a degree of change of 1.4. The characteristics of the film were as follows.

Tg: 325 ° C
Thermal expansion coefficient: 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 blending example was obtained from Toyobo Co., Ltd., copper-clad laminate “Viroflex ™” (the thermal expansion coefficient of the base film was 2.2 × 10 ^−5). A tensile strength of 43 Kg / mm ² , a tensile elongation of 60%, and an elastic modulus of 640 Kg / mm ² ) in accordance with JIS C5016 standard and printed on a printed circuit board that is circuit-processed into a wiring pattern for folding resistance evaluation. It printed on the whole surface through the board so that thickness might be set to 0.01 mm. Subsequently, it dried at 100 degreeC for 5 minute (s).

  The same operation is repeated several times, and the obtained flexible printed wiring board is sandwiched between a long sheet made of stainless steel screen and the coated surface is on the outside. Winded up.

  The wound roll was put into 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 characteristics were as shown in Table-1 and Table-2.

Examples 3-4
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 that the thickness was 0.01 mm. Subsequently, initial drying was performed at 100 ° C. for 5 minutes.

  The same operation is repeated several times, and the obtained flexible printed wiring board is sandwiched between a long sheet made of stainless steel screen and the coated surface is on the outside. Winded up.

  The wound roll was put into 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 characteristics were as shown in Table-1 and Table-2.

Comparative Examples 1-2
The heat resistant resin solution C or D obtained in Formulation Examples 1 and 2 was applied to the same substrate to be printed as in Example 1 through a stainless screen plate so that the thickness was 0.01 mm. Next, after drying at 100 ° C. for 5 minutes, it was left in a state close to a flat surface without being wound, 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 characteristics were as shown in Table-1 and Table-2.

Comparative Example 3
A flexible copper-clad laminate (Nikaflex F-30VC112RC11 / 2, manufactured by Nikkan Kogyo Co., Ltd.) with a polyimide film bonded together with an adhesive is circuit-processed under the same processing conditions as the base circuit. I got the material.

A cover film with a polyimide adhesive film (Niskan Kogyo Co., Ltd., CISV-1215) was cut into a predetermined shape, and heat-pressed as it was under the conditions of a pressing pressure of 50 kg / cm ² , a temperature of 150 ° C., and a time of 30 minutes. .

  When the solder heat resistance and the hand solder heat resistance of the flexible printed wiring board obtained as described above were evaluated, swelling and peeling were observed.

Claims (6)

Manufacturing method of flexible printed wiring board including the following steps (1) to (3):
(1) A step of applying and drying a heat-resistant resin solution on a part of or the entire surface of the conductor circuit and non-conductor circuit of the base substrate on which the conductor circuit is formed,
(2) A step of winding the base substrate coated with the heat-resistant resin solution and drying it into a roll,
(3) A step of heat-treating the scroll to form a heat-resistant resin layer. The method for manufacturing a flexible printed wiring board according to claim 1, wherein the heat treatment is performed under reduced pressure and / or in an inert gas atmosphere. The base substrate coated with the heat-resistant resin solution and dried at the time of winding is wound around a long heat-resistant sheet with the application surface of the heat-resistant resin solution facing outward. The manufacturing method of the flexible printed wiring board of Claim 2. The method for producing a flexible printed wiring board according to any one of claims 1 to 3, wherein the heat-resistant resin is polyimide and / or polyamideimide soluble in an organic solvent. The said heat resistant resin contains the following general formula (1) and / or the following general formula (2) as a structural unit, The manufacturing method of the flexible printed wiring board in any one of Claims 1-4 characterized by the above-mentioned. .

(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.)

A manufacturing method of a flexible printed wiring board including the following steps (1) to (3),
  The heat-resistant resin in step (1) is a polyimide and / or polyamideimide soluble in an organic solvent,
  At the time of winding in the step (2), the base substrate on which the heat-resistant resin solution is applied and dried is wound around a long heat-resistant sheet with the application surface of the heat-resistant resin solution facing outside.
  The method for producing a flexible printed wiring board, wherein the heat treatment in the step (3) is performed at a heat treatment temperature of 150 to 350 ° C. under reduced pressure and / or in an inert gas atmosphere:
(1) A step of applying and drying a heat-resistant resin solution on a part of or the entire surface of the conductor circuit and non-conductor circuit of the base substrate on which the conductor circuit is formed,
(2) A step of winding the base substrate coated with the heat-resistant resin solution and drying it into a roll,
(3) A step of heat-treating the scroll to form a heat-resistant resin layer.