Multilayer polyimide film and polyimide metal laminate

Abstract

This invention provides a multilayer polyimide film with excellent heat resistance, low dielectric loss tangent, and dimensional stability. The multilayer polyimide film comprises a heat-resistant polyimide layer and a heat-fusion polyimide layer laminated on one or both sides; the heat-resistant polyimide is obtained from a tetracarboxylic acid component containing more than 75 mol% of 3,3',4,4'-biphenyltetracarboxylic dianhydride (s-BPDA) and less than 25 mol% of pyromellitic dianhydride (PMDA), and a diamine component containing 70 mol% to 95 mol% of p-phenylenediamine and 5 mol% to 30 mol% of 2,2'-dimethylbenzidine; the heat-fusion polyimide is obtained from a tetracarboxylic acid component containing 10 mol% to 60 mol% of s-BPDA and 40 mol% to 90 mol% of PMDA, and a diamine component containing more than 50 mol% of 2,2-bis[4-(4-aminophenoxy)phenyl]propane.

Description

Technical Field

[0001] This invention relates to polyimide films and polyimide-metal laminates. Background Technology

[0002] Polyimide films have excellent heat resistance and mechanical properties, and are widely used as materials for electronic substrates such as flexible printed circuit boards (hereinafter also referred to as FPC) and tape auto-bonding (hereinafter also referred to as TAB).

[0003] In the manufacture of FPCs and TABs, polyimide metal laminates (e.g., copper-clad laminates) are used, in which metal foils such as copper foils and polyimide films are laminated together. As a method for laminating metal foils and polyimide films, adhesives such as epoxy resins or acrylic resins are known. However, polyimide metal laminates using adhesives have poor heat resistance. Therefore, as a polyimide film that can be laminated onto metal foils such as copper foils without the use of adhesives, multilayer polyimide films in which heat-resistant polyimide layers and thermally bondable polyimide layers are laminated together have been proposed (e.g., Patent Document 1).

[0004] On the other hand, in recent years, with the use of high-frequency bands in electronic devices, the demand for low transmission loss in polyimide, a material used as a substrate / board for electronic devices, has been increasing. Transmission loss is related to dielectric constant and dielectric loss tangent, and reducing the dielectric loss tangent is particularly effective in reducing transmission loss.

[0005] As a polyimide with a small dielectric loss tangent, Patent Document 2 proposes "a polymer film comprising: one or more dianhydrides selected from the group consisting of crankshaft monomers, flexible monomers, rigid rotating monomers, rigid non-rotating monomers and rotation-inhibiting monomers, and one or more diamines selected from the group consisting of crankshaft monomers, flexible monomers, rigid rotating monomers, rigid non-rotating monomers and rotation-inhibiting monomers, and the polymer film having a dissipation factor Df (synonymous with dielectric loss tangent) of 0.005 or less, and a specific water absorption rate, etc. (see claim 1)".

[0006] Existing technical documents

[0007] Patent documents

[0008] Patent Document 1: WO2016 / 055673

[0009] Patent Document 2: Japanese Patent Application Publication No. 2021-11567 Summary of the Invention

[0010] The technical problem that the invention aims to solve

[0011] In high-frequency applications, FPCs require polyimides that not only possess low dielectric loss tangent but also meet the essential properties required by standard FPCs, including high heat resistance and high dimensional stability. High dimensional stability suppresses defects such as circuit misalignment, which not only increases the reliability of the circuit board but also improves product yield. This is typically addressed by making the linear thermal expansion coefficient of the polyimide film close to that of the metal foil (such as copper foil).

[0012] However, multilayer polyimide films that exhibit excellent heat resistance, low dielectric loss tangent, and high dimensional stability even in high-temperature environments are currently unknown. Patent Document 2 describes the use of a polyimide film exhibiting low dielectric loss tangent as the core layer (heat-resistant polyimide layer) of a multilayer film, but does not describe the thermally bonded layer (thermoplastic layer) in detail, leaving the performance of the multilayer film or metal laminate unclear.

[0013] One object of the present invention is to provide a multilayer polyimide film that has excellent heat resistance and simultaneously exhibits low dielectric loss tangent and high dimensional stability.

[0014] Another object of the present invention is to provide a polyimide metal laminate wherein multiple layers of polyimide film and metal foil such as copper foil are laminated.

[0015] Technical means to solve the problem

[0016] The main disclosures in this application are summarized below.

[0017] 1. A multilayer polyimide film comprising: A heat-resistant polyimide layer composed of heat-resistant polyimide (PIc); and A heat-fusible polyimide layer composed of heat-fusible polyimide (PIb) is laminated on one or both sides of the heat-resistant polyimide layer; The heat-resistant polyimide (PIc) mentioned above is obtained by reacting the following components: The tetracarboxylic acid component (Ac) comprises 75 mol% to 100 mol% of 3,3',4,4'-biphenyltetracarboxylic dianhydride and 0 mol% to 25 mol% of pyromellitic dianhydride, and The diamine component (Bc) comprises 70 mol% to 95 mol% of p-phenylenediamine and 5 mol% to 30 mol% of 2,2'-dimethylbenzidine; and The heat-melting polyimide (PIb) mentioned above is obtained by reacting the following components: The tetracarboxylic acid component (Ab) contains 10 mol% to 60 mol% of 3,3',4,4'-biphenyltetracarboxylic dianhydride and 40 mol% to 90 mol% of pyromellitic dianhydride, and The diamine component (Bb) contains more than 50 mol% of 2,2-bis[4-(4-aminophenoxy)phenyl]propane.

[0018] 2. The multilayer polyimide film as described in Item 1 above, wherein the heat-resistant polyimide (PIc) is obtained by reacting the following components: The tetracarboxylic acid component (Ac) comprises 80 mol% to less than 100 mol% of 3,3',4,4'-biphenyltetracarboxylic dianhydride and 0 mol% to less than 20 mol% of pyromellitic dianhydride. The diamine component (Bc) contains more than 75 mol% of p-phenylenediamine and less than 25 mol% of 2,2'-dimethylbenzidine.

[0019] 3. The multilayer polyimide film as described in item 1 or 2 above, wherein the heat-fusible polyimide (PIb) is obtained by reacting the following components: The tetracarboxylic acid component (Ab) contains more than 15 mol% of 3,3',4,4'-biphenyltetracarboxylic dianhydride and less than 85 mol% of pyromellitic dianhydride, and The diamine component (Bb) contains more than 60 mol% of 2,2-bis[4-(4-aminophenoxy)phenyl]propane.

[0020] 4. A multilayer polyimide film as described in any one of items 1 to 3 above, wherein the multilayer polyimide film has a dielectric loss tangent of less than 0.0060, and the dimensional change rate (absolute value) of the polyimide metal laminate in the longitudinal (MD) and transverse (TD) directions is less than 0.10%, wherein the dimensional change rate is determined by measuring the initial dimension (X) of the polyimide metal laminate prepared using the multilayer polyimide film, and the dimension (Y) after heat treatment at 250°C for 30 minutes following etching of the metal foil, and calculating according to the following equation: Dimensional change rate (%) = (YX) / X×100.

[0021] 5. A polyimide metal laminate, wherein a metal foil is laminated on the thermally fusible polyimide layer side of the multilayer polyimide film described in any one of items 1 to 4 above.

[0022] 6. The polyimide metal laminate as described in item 5 above, wherein the multilayer polyimide film has a heat-fusible polyimide layer on both sides of the heat-resistant polyimide layer, and a metal foil is laminated on both sides of the multilayer polyimide film.

[0023] 7. A flexible wiring board manufactured using the polyimide metal laminate described in item 5 above.

[0024] The effects of the invention

[0025] According to the present invention, a multilayer polyimide film exhibiting low dielectric loss tangent, excellent heat resistance, and excellent dimensional stability in the high-frequency range is provided. According to another aspect of the present invention, a polyimide metal laminate is provided, wherein multiple layers of polyimide film and metal foil, such as copper foil, are laminated. This polyimide metal laminate is suitable for manufacturing high-frequency compatible FPCs. Detailed Implementation

[0026] The multilayer polyimide film of the present invention has a structure in which a thermally fusible polyimide layer (hereinafter also referred to as a thermally fusible layer) is laminated on one or both sides of a heat-resistant polyimide layer (hereinafter also referred to as a core layer). In the following, the material of the core layer may be specified by the suffix "c" (…). c The material of the thermal fusion layer can be represented by the suffix "b" (ore), and the material of the thermal fusion layer can be represented by the suffix "b" (ore). b (ondable) indicates.

[0027] <Heat-resistant polyimide layer>

[0028] The heat-resistant polyimide layer (core layer) contains heat-resistant polyimide (PIc) obtained by reacting a tetracarboxylic acid component (Ac) with a diamine component (Bc).

[0029] The tetracarboxylic acid component (Ac) used to prepare heat-resistant polyimide comprises, based on 100 mol% of the total tetracarboxylic acid component, 75 mol% to 100 mol%, preferably 80 mol% or more, more preferably 85 mol% or more, and preferably less than 100 mol%, more preferably less than 95 mol% of 3,3',4,4'-biphenyltetracarboxylic acid dianhydride (s-BPDA), and 0 mol% to 25 mol%, preferably greater than 0 mol%, more preferably more than 5 mol%, and preferably less than 20 mol%, more preferably less than 15 mol% of pyromellitic dianhydride (PMDA).

[0030] As a tetracarboxylic acid component (Ac), tetracarboxylic acid dianhydrides other than s-BPDA and PMDA can be used, but their amount is preferably 10 mol% or less, more preferably 5 mol% or less, more preferably 2 mol% or less, and it is also highly preferred that such other components are not included.

[0031] Examples of tetracarboxylic acid components that can be used in combination include aromatic tetracarboxylic dianhydrides and aliphatic (especially alicyclic) tetracarboxylic dianhydrides. Specific examples include 2,3,3',4'-biphenyltetracarboxylic dianhydride, 3,3',4,4'-benzophenonetetracarboxylic dianhydride, 4,4'-oxydiphthalic dianhydride, 3,3',4,4'-diphenylsulfonetetracarboxylic dianhydride, 2,2-bis(3,4-dicarboxyphenyl)-1,1,1,3,3,3-hexafluoropropane dianhydride, 2,2-bis[(3,4-dicarboxyphenoxy)phenyl]propane dianhydride, bis(1,3-dioxo-1,3-dihydroisobenzofuran-5-carboxylic acid)1,4-epoxyphenyl ester, p-terphenyl-3,3',4,4'-tetracarboxylic dianhydride, naphthalene-1,4,5,8-tetracarboxylic dianhydride, and 1,2,4,5-cyclohexanetetracarboxylic dianhydride.

[0032] The diamine component (Bc) used to prepare heat-resistant polyimide comprises, based on 100 mol% of all diamine components, 70 mol% to 95 mol% (preferably 75 mol% to 93 mol%) of p-phenylenediamine (PPD) and 5 mol% to 30 mol% (preferably 7 mol% to 25 mol%) of 2,2'-dimethylbenzidine (m-TB).

[0033] As a diamine component (Bc), diamine compounds other than PPD and m-TB can be used, but their amount is preferably 10 mol% or less, more preferably 5 mol% or less, more preferably 2 mol% or less, and it is also highly preferred that such other components are not included.

[0034] Examples of diamine components that can be used in combination include aromatic diamine compounds and aliphatic (especially alicyclic) diamine compounds. Specific examples include m-phenylenediamine, 4,4'-diamino-p-terphenyl, 2,4-toluenediamine, 4,4'-diaminodiphenyl ether, 3,4'-diaminodiphenyl ether, 3,3'-diaminodiphenyl sulfide, 3,4'-diaminodiphenyl sulfide, 4,4'-diaminodiphenyl sulfide, 3,3'-diaminodiphenyl sulfone, 3,4'-diaminodiphenyl sulfone, 4,4'-diaminodiphenyl sulfone, 3,3'-diaminodibenzophenone, 4,4'-diaminodibenzophenone, 3,3'-diaminodiphenylmethane, 4,4'-diaminodiphenylmethane, 3,4'-diaminodiphenylmethane, 2,2'-diphenylamine ...3,4'-diaminodiphenylmethane, 2,2'-diphenylamine, 4,4'-diaminodiphenylmethane, 3,4'-diaminodiphenylmethane, 3,4'-diphenylmethane, 3,4'-diaminodiphenylmethane, 3,4'-diphenylmethane, 3,4'-diaminodiphenylmethane, 3,4'-diphenylmethane, 3,4'-diaminodiphenylmethane, 3,4 (3-Aminophenyl)propane, 2,2-bis(4-aminophenyl)propane, 1,3-bis[2-(4-aminophenyl)-2-propyl]benzene, α,α'-bis(4-aminophenyl)-1,4-diisopropylbenzene; bis(aminophenoxy)benzene, such as 1,3-bis(4-aminophenoxy)benzene, 1,4-bis(4-aminophenoxy)benzene, 1,3-bis(3-aminophenoxy)benzene and 1,4-bis(3-aminophenoxy)benzene; 2,2-bis[4-(4-aminophenoxy)phenyl]propane, 4,4'-bis(4-aminophenoxy)biphenyl and 1,4-cyclohexanediamine.

[0035] The heat-resistant polyimide layer is mainly composed of the aforementioned heat-resistant polyimide, and the resin component without additives is preferably composed of the aforementioned heat-resistant polyimide (95% by mass or more, preferably 98% by mass or more), and it is also very preferred that the resin component is composed of only heat-resistant polyimide (100% by mass).

[0036] In addition to heat-resistant polyimide, the heat-resistant polyimide layer may contain additives as needed. Representative examples include finely milled inorganic or organic fillers. Examples of inorganic fillers include granular or flattened inorganic fillers. Specific examples include inorganic oxide powders, such as finely milled titanium dioxide powder, silica (silica) powder, magnesium oxide powder, alumina (bauxite) powder, and zinc oxide powder; inorganic nitride powders, such as finely milled silicon nitride powder and titanium nitride powder; inorganic carbide powders, such as silicon carbide powder; and inorganic salt powders, such as finely milled calcium carbonate powder, calcium sulfate powder, and barium sulfate powder. Examples of organic fillers include polyimide powder, liquid crystal polymer powder, fluoropolymer powder, and thermosetting resin powder. These additives may be used in combination of two or more. The amount and shape (size, aspect ratio) of the filler are preferably selected according to the intended use. Furthermore, known methods can be used to uniformly disperse these fillers.

[0037] These inorganic or organic fillers, particularly silica powder, are preferably present in a content of less than 30% by mass in the heat-resistant polyimide layer, more preferably less than 20% by mass, and even more preferably less than 10% by mass (or 0% by mass).

[0038] <Thermo-Melt Polyimide Layer>

[0039] The heat-fusible polyimide layer (heat-fusible layer) contains a heat-fusible polyimide (PIb) obtained by reacting a tetracarboxylic acid component (Ab) with a diamine component (Bb).

[0040] The tetracarboxylic acid component (Ab) used to prepare the thermofusible polyimide comprises, based on 100 mol% of the total tetracarboxylic acid component, 10 mol% or more and 60 mol% or less, preferably 15 mol% or more, more preferably 20 mol% or more, even more preferably 55 mol% or less, even more preferably 50 mol% or less of 3,3',4,4'-biphenyltetracarboxylic dianhydride (s-BPDA), and 40 mol% or more and 90 mol% or more, preferably 45 mol% or more, even more preferably 50 mol% or more, even more preferably 85 mol% or less, even more preferably 80 mol% or less of pyromellitic dianhydride (PMDA).

[0041] As a tetracarboxylic acid component (Ab), tetracarboxylic acid dianhydrides other than s-BPDA and PMDA can be used, but their amount is preferably 10 mol% or less, more preferably 5 mol% or less, more preferably 2 mol% or less, and it is also highly preferred that such other components are not included.

[0042] Examples of tetracarboxylic acid components that can be used in combination include aromatic tetracarboxylic dianhydrides and aliphatic (especially alicyclic) tetracarboxylic dianhydrides. Specific examples include 2,3,3',4'-biphenyltetracarboxylic dianhydride, 3,3',4,4'-benzophenone tetracarboxylic dianhydride, 4,4'-oxydiphthalic dianhydride, 3,3',4,4'-diphenylsulfone tetracarboxylic dianhydride, 2,2-bis(3,4-dicarboxyphenyl)-1,1,1,3,3,3-hexafluoropropane dianhydride, 2,2-bis[(3,4-dicarboxyphenoxy)phenyl]propane dianhydride, and 1,2,4,5-cyclohexanetetracarboxylic dianhydride.

[0043] The diamine component (Bb) used to prepare the thermoplastic polyimide contains 2,2-bis[4-(4-aminophenoxy)phenyl]propane (BAPP), and its amount is 50 mol% or more (preferably greater than 50 mol%), more preferably 60 mol% or more, more preferably 70 mol% or more, even more preferably 80 mol% or more, even more preferably 90 mol% or more, and even more preferably 100 mol% based on 100 mol% of the total diamine component.

[0044] As the diamine component (Bb), diamine compounds other than BAPP can be used. Examples of other diamine components used in combination include m-phenylenediamine, 2,2'-dimethylbenzidine, 4,4'-diaminodiphenyl ether, 3,4'-diaminodiphenyl ether, 1,3-bis(4-aminophenoxy)benzene, 1,3-bis(3-aminophenoxy)benzene, 1,4-bis(4-aminophenoxy)benzene, 3,3'-diaminobenzophenone, 4,4'-bis(3-aminophenoxy)biphenyl, 4,4'-bis(4-aminophenoxy)biphenyl, bis[4-(3- [Aminophenoxy)phenyl] sulfone, bis[4-(4-aminophenoxy)phenyl] sulfone, 2,2-bis[4-(3-aminophenoxy)phenyl]propane, 3,3'-diaminodiphenylmethane, 4,4'-diaminodiphenylmethane, 1,3-bis[2-(4-aminophenyl)-2-propyl]benzene, α,α'-bis(4-aminophenyl)-1,4-diisopropylbenzene, bis[4-[4-(4-aminophenoxy)phenoxy]phenyl] ether, and 1,4-cyclohexanediamine.

[0045] From the viewpoints of improving the peel strength between the thermal fusion layer and the core layer, improving the peel strength between the thermal fusion layer and the metal foil, and from the viewpoints of the solder heat resistance during FPC production, the glass transition temperature (Tg) of the thermal fusion polyimide is preferably 250°C to 310°C, and more preferably 260°C to 300°C.

[0046] The thermoplastic polyimide layer is mainly composed of the above-mentioned thermoplastic polyimide, and the resin composition without additives is preferably composed of the above-mentioned thermoplastic polyimide (95% by mass or more, preferably 98% by mass or more), and it is also very preferred that the resin composition is composed of only thermoplastic polyimide (100% by mass).

[0047] In addition to the heat-melt polyimide, the heat-melt polyimide layer may also contain additives as needed. The specific additives and their amounts can be the same as those described for the heat-resistant polyimide layer.

[0048] <Multilayer polyimide film>

[0049] The thickness of the multilayer polyimide film of the present invention is not particularly limited, but the thickness of the heat-resistant polyimide layer is preferably 3 to 70 μm, more preferably 5 to 65 μm. The thickness of the heat-fusion polyimide layer is preferably 0.5 to 15 μm, more preferably 1 to 12.5 μm. The overall thickness of the multilayer polyimide film is preferably 4 to 100 μm, more preferably 7 to 90 μm.

[0050] The dielectric loss tangent (10 GHz) of the multilayer polyimide film is preferably 0.0060 or less, more preferably less than 0.0060, and even more preferably 0.0055 or less.

[0051] The dimensional change rate (absolute value) of the multilayer polyimide film is preferably 0.10% or less, more preferably 0.10% or less, and even more preferably 0.09% or less.

[0052] The dimensional change rate was determined by measuring the initial size (X) of the polyimide-metal laminate prepared using the multilayer polyimide film, and the size (Y) after etching the metal foil, heat-treating at 250°C for 30 minutes, and humidity control, and calculating it according to the following equation: Dimensional change rate (%) = (YX) / X×100.

[0053] <Manufacturing Method of Multilayer Polyimide Film>

[0054] There are no particular limitations on the method used to manufacture the multilayer polyimide film of the present invention, and any known method may be employed. As representative methods, coating methods and co-extrusion-casting film-forming methods will be described below.

[0055] (Manufacturing method using coating)

[0056] The multilayer polyimide film of the present invention can be obtained by coating one or both sides of a self-supporting film obtained by a polyimide precursor solution (a) that provides a heat-resistant polyimide with a polyimide precursor solution (b) that provides a heat-fusible polyimide, and then heating and drying the resulting multilayer self-supporting film to perform imidization.

[0057] A polyimide precursor solution (a) providing heat-resistant polyimide is obtained by reacting a tetracarboxylic acid component and a diamine component in a substantially equimolar amount or in a slightly excess of one component relative to the other in an organic solvent. The polyimide precursor solution (a) containing multiple tetracarboxylic acid components and diamine components can have a random or block structure, and is preferably random. A self-supporting film can be obtained by casting the polyimide precursor solution (a) on a support and then heating and drying the cast product.

[0058] On the other hand, the polyimide precursor solution (b) providing a thermally fusible polyimide can also be obtained by reacting the tetracarboxylic acid component and the diamine component in an organic solvent in substantially equimolar amounts or in a slight excess of one component relative to the other. The structure of the polyimide precursor solution (b) containing multiple tetracarboxylic acid components and diamine components can be a random structure or a block structure, and is preferably a random structure.

[0059] The monomer compositions used to prepare the polyimide precursor solution (a) providing heat-resistant polyimide and the polyimide precursor solution (b) providing heat-melting polyimide are those described in the <Heat-resistant Polyimide Layer> and <Heat-melting Polyimide Layer>, respectively.

[0060] To suppress gelation, the amount of phosphorus stabilizer (e.g., triphenyl phosphite or triphenyl phosphate) added to the polyimide precursor solution (b) and / or polyimide precursor solution (a) can be from 0.01 to 1 by mass, based on the concentration of solids (polymer) during the polymerization process of the polyimide precursor solution.

[0061] From the viewpoint of membrane surface conditions and productivity, it is preferable to add phosphate esters or salts of tertiary amines and phosphate esters to the polyimide precursor solution. The amount of these additives added is preferably 0.01 to 5 parts by mass relative to 100 parts by mass of polyimide or polymer. Specific examples of phosphate esters include distearate phosphate and monostearate phosphate. Furthermore, examples of salts of tertiary amines and phosphate esters include triethanolamine monostearate phosphate. For the imidization in this invention, either heating imidization (thermal imidization) or chemical imidization (chemical imidization) can be applied. Thermal imidization is preferred.

[0062] To facilitate imidization, a basic organic compound may be added to the polyimide precursor solution (b) and / or the polyimide precursor solution (a). For example, imidazoles substituted with lower alkyl groups or aromatic groups, such as 1,2-dimethylimidazolium, N-methylimidazolium, N-benzyl-2-methylimidazolium, 2-methylimidazolium, 2-ethyl-4-methylimidazolium, and 2-phenylimidazolium; benzimidazoles, such as 5-methylbenzimidazole; and substituted pyridines, such as isoquinoline, 3,5-dimethylpyridine, 3,4-dimethylpyridine, 2,5-dimethylpyridine, 2,4-dimethylpyridine, and 4-n-propylpyridine, may be used at a ratio of 0.05 to 10% by mass, more preferably 0.05 to 7% by mass, or even more preferably 0.1 to 5% by mass, based on the solids (polymer) concentration. When these basic organic compounds are used, the imidization of polyimide precursors is promoted at relatively low temperatures to form polyimide films, thus these basic organic compounds can be used to avoid inadequate imidization.

[0063] Examples of organic solvents used to prepare polyimide precursor solutions include amides, such as N-methyl-2-pyrrolidone, N,N-dimethylacetamide, N,N-diethylacetamide, N,N-dimethylformamide, N,N-diethylformamide, and hexamethylsulfonamide; sulfoxides, such as dimethyl sulfoxide and diethyl sulfoxide; and sulfones, such as dimethyl sulfone and diethyl sulfone. These solvents can be used alone or in combination.

[0064] When the polymerization reaction of the tetracarboxylic acid component and the diamine component is carried out, the concentration of all monomers in the organic solvent can be appropriately selected according to the intended use. For example, the solid content (polymer) concentration of the polyimide precursor solutions (a) and (b) is preferably 5 to 40% by mass, more preferably 6 to 35% by mass, and particularly preferably 10 to 30% by mass.

[0065] The temperature used to prepare the polyimide precursor solution (a) and polyimide precursor solution (b) is not particularly limited, but is preferably 25°C to 100°C, more preferably 25°C to 80°C, and even more preferably 30°C to 70°C, so that the imidization reaction is not over-progressed, and the preparation time is about 1 to 72 hours, more preferably about 2 to 60 hours. The reaction can be carried out in an air atmosphere, but is generally suitable in an inert gas atmosphere, preferably in a nitrogen atmosphere.

[0066] The solutions viscosities of polyimide precursor solution (a) and polyimide precursor solution (b) can be appropriately selected according to their intended use (coating, casting, etc.). For example, when polyimide precursor solution (a) and polyimide precursor solution (b) are used for casting, from the viewpoint of processability of the polyimide precursor solution, the rotational viscosity measured at 30°C is preferably about 100 to 5000 poise, more preferably 500 to 4000 poise, and particularly preferably about 1000 to 3000 poise. Furthermore, when polyimide precursor solution (a) and polyimide precursor solution (b) are used for coating, from the viewpoint of processability of the polyimide precursor solution, the rotational viscosity measured at 30°C is preferably 1 to 100 centipoise, more preferably 3 to 50 centipoise, and particularly preferably 5 to 20 centipoise. Therefore, it is ideal to carry out the above-described polymerization reaction to the extent that the resulting polyimide precursor solution exhibits the above-described viscosity. The viscosity of the solution can also be adjusted by adding the aforementioned organic solvent to the prepared polyimide precursor solution.

[0067] A self-supporting film obtained from a polyimide precursor solution (a) providing heat-resistant polyimide can be obtained, for example, by casting the polyimide precursor solution (a) onto the surface of a suitable support (e.g., a metal, ceramic, or plastic roller, or a metal strip, etc.) to form a film of uniform thickness, and then heating the film to preferably 50 to 210°C, more preferably 60 to 200°C, using a heat source such as hot air or infrared radiation, thereby gradually removing the solvent and drying until the film becomes self-supporting (e.g., until it can be peeled off from the support).

[0068] The self-supporting film providing heat-resistant polyimide preferably has a heating weight loss of 20-40% by mass and an imidization rate of 8-40%. If the heating weight loss and imidization rate are within the above ranges, the mechanical properties of the self-supporting film are sufficient, the polyimide precursor solution (b) can be easily and neatly applied to the upper surface of the self-supporting film, the polyimide film obtained after imidization is unlikely to form bubbles, cracks, fissures, etc., and the adhesive strength between the heat-resistant polyimide layer and the heat-fusion polyimide layer is sufficient.

[0069] The membrane to be tested was dried at 400°C for 30 minutes, and the weight before drying (W1) and the weight after drying (W2) were calculated. The thermal weight loss of the self-supporting membrane was then calculated according to the following equation.

[0070] Loss on heating (mass%) = {(W1-W2) / W1} × 100

[0071] The imidization rate of the self-supporting film can be calculated by measuring the IR spectra of the self-supporting film and its fully cured product (polyimide film) using the ATR method and utilizing the ratio of vibrational band peak areas. Vibrational band peaks can be the asymmetric stretching vibration bands of the imide carbonyl group, the stretching vibration bands of the benzene ring skeleton, etc. Furthermore, methods for measuring the imidization rate using a Karl Fischer moisture meter, such as those described in JP-A-9-316199, also exist.

[0072] Next, the polyimide precursor solution (b) for obtaining a heat-fusible polyimide is coated onto one or both sides of the self-supporting film. The polyimide precursor solution (b) can be coated onto the self-supporting film after it has been peeled off from the support, or it can be coated onto the self-supporting film on the support before it has been peeled off. Preferably, the polyimide precursor solution (b) is uniformly coated onto one or both sides of the self-supporting film. Therefore, it is preferable that the self-supporting film of the polyimide precursor solution (a) has a surface that can be uniformly coated with the polyimide precursor solution (b).

[0073] There are no particular limitations on the method of coating the polyimide precursor solution (b) onto the self-supporting film obtained from the polyimide precursor solution (a), and examples of the method include known coating methods such as gravure coating, spin coating, screen coating, dip coating, spray coating, bar coating, doctor blade coating, roller coating, knife coating and mold coating.

[0074] Next, the self-supporting film of polyimide precursor solution (a) coated with polyimide precursor solution (b) is heated and imidized to obtain a multilayer polyimide film. The maximum heating temperature for the heat treatment of imidization is preferably 330°C to 600°C, more preferably 350°C to 550°C, and even more preferably 370°C to 500°C.

[0075] The heat treatment for imidization is preferably performed stepwise, firstly at a temperature above 200°C and below 300°C for 1 to 60 minutes, then at a temperature above 300°C and below 330°C for 1 to 60 minutes, and then at a maximum heating temperature preferably 330°C to 600°C, more preferably 370°C to 550°C, and even more preferably 370°C to 500°C for 1 to 30 minutes. This heat treatment can be performed using known equipment such as a hot air oven or an infrared heating oven. Furthermore, this heat treatment is preferably performed by fixing a self-supporting film of the polyimide precursor solution (a) coated with the polyimide precursor solution (b) using a pin tenter frame, clamps, or the like.

[0076] (Manufacturing method using co-extrusion-casting film formation)

[0077] The multilayer polyimide film of the present invention can also be prepared by a co-extrusion-casting film formation method (hereinafter also referred to as the "co-extrusion method"), wherein a polyimide precursor solution (hereinafter also referred to as the dope solution) providing a heat-resistant polyimide layer and a dope solution providing a thermally fusible polyimide layer are laminated, dried, and imidized. For such a co-extrusion method, for example, the method described in JP-A-H3-180343 (JP-B-H7-102661) can be used.

[0078] More specifically, in this co-extrusion method, an extruder with a die for extruding two or more layers is first used. Dopant solutions for providing a heat-resistant polyimide layer and dopant solutions for providing a heat-fusion polyimide layer are cast from the die outlet onto a support, thereby forming a laminated film. The film on the support is then dried to form a multilayer self-supporting film. Next, the multilayer self-supporting film is peeled off from the support, and finally, the multilayer self-supporting film is heat-treated. In this method, the dopant solution in contact with the support can be either the dopant solution for providing a heat-resistant polyimide layer or the dopant solution for providing a heat-fusion polyimide layer.

[0079] Both the dopant solutions used to provide the heat-resistant polyimide layer and the dopant solutions used to provide the heat-fusion polyimide layer are prepared as described in (the manufacturing method using a coating method) by reacting a tetracarboxylic acid component with a diamine component to prepare polyimide precursor solutions (a) and (b). When performing multilayer (e.g., two-layer and three-layer, etc.) extrusion as described above, at the temperature of extrusion from the multilayer extrusion die, the dopant solution preferably has a solids (polymer) concentration of 5 to 40% by mass, particularly 10 to 30% by mass, and a "solution viscosity (rotational viscosity)" of about 50 to 10,000 poise, particularly 100 to 6,000 poise.

[0080] An example of a bilayer extrusion die is a die with a structure (multi-manifold bilayer die) having a supply port for the dopant, wherein channels for the dopant are formed from each supply port toward each manifold, the flow paths at the bottom of the manifolds are connected at a junction, and the channels for the dopant (lips) communicate with a slit-shaped discharge port after the connection, and the dopant is discharged from the discharge port in the form of a thin film onto a support. The lips are designed such that the gap between the lips can be adjusted by lip adjusting bolts.

[0081] Additionally, the gap in the flow path at the bottom (near the connection point) of each manifold is adjusted by respective baffles. Each manifold is preferably shaped like a hanging jacket. The double-layer extrusion die has dopant supply ports on the left and right sides of the upper part of the die, and the channels for the dopant are directly connected at the connection point equipped with baffles. The flow path for the dopant communicates from the connection point to the manifold, and the channel (lip) for the dopant at the bottom of the manifold communicates with a slit-shaped discharge port. The die can be structured such that the dopant is discharged from the discharge port onto the support in the form of a concave film (feed block type double-layer die or single-manifold type double-layer die).

[0082] In addition to the two-layer extrusion described above, multilayer extruded polyimide films can be prepared using the same forming method as two-layer extrusion, by using a die for three or more layers. That is, a three-layer polyimide film can be obtained by using a composition of "a first dopant for providing a heat-bonding polyimide layer / a dopant for providing a heat-resistant polyimide layer / a second dopant for providing a heat-bonding polyimide layer". The first and second dopants used to provide the heat-bonding polyimide layer can be the same or different.

[0083] For the implementation of drying conditions and heating conditions after the continuous extrusion onto the support in the co-extrusion-cast film forming method, the contents described in the above-mentioned "Manufacturing method using coating method" can be directly applied.

[0084] In coating or co-extrusion methods, when heating the self-supporting membrane to prepare a polyimide membrane, a stretching operation may be performed if necessary.

[0085] Through the above operations, long strips of polyimide film can be continuously manufactured.

[0086] When a thick, multilayered polyimide film is required, it can be prepared by laminating the multilayered polyimide film prepared by the above method. The lamination operation can also be performed continuously.

[0087] <Polyimide Metal Laminate>

[0088] Polyimide metal laminates can be prepared by laminating multiple polyimide films (or layers) and metal foils (or layers) using the polyimide precursor solution or multilayer polyimide film of the present invention. The polyimide metal laminate has a structure in which metal foils (or layers) are laminated on one or both sides of the multilayer polyimide film. Examples of methods for preparing polyimide metal laminates include the following methods.

[0089] (i) A method of directly bonding a multilayer polyimide film and a metal foil without the use of an adhesive, and laminating the film by applying pressure or by heating and pressing.

[0090] (ii) A method of applying a polyimide precursor solution onto a metal foil and drying and imidizing it.

[0091] (iii) A method for directly forming a metal layer on a multilayer polyimide film by means of dry methods (metal application, such as vacuum deposition and sputtering) and / or wet methods (coating).

[0092] Various metal foils, such as copper, aluminum, gold, or alloys thereof, can be used as the metal foils mentioned in (i) and (ii) above. Copper foil is preferred. Those using copper foil as the metal foil are also referred to as "copper-clad laminates". When metal layers are deposited on both sides of a multilayer polyimide film, the same or different metals can be used. Specific examples of copper foil include rolled copper foil and electrolytic copper foil. While not particularly limited, the thickness of the copper foil is preferably 2 to 35 μm, particularly preferably 5 to 18 μm; regarding Ra and Rz, which indicate surface roughness, Ra is preferably 0.01 μm to 0.4 μm, and Rz is preferably 0.2 μm to 2.0 μm.

[0093] The multilayer polyimide film and copper foil are preferably continuously hot-pressed under heating using at least one pair of pressure members. The temperature of the pressure members is at least 50°C higher than the glass transition temperature of the hot-melted polyimide, more preferably at least 60°C higher, and even more preferably at least 70°C higher. Such a heating temperature provides the advantageous effect of firmly laminating the multilayer polyimide film and copper foil. In addition, from the viewpoint of preventing thermal degradation of the multilayer polyimide film and copper foil, the heating temperature is preferably 420°C or lower. As mentioned above, the glass transition temperature of the hot-melted polyimide is preferably 250°C or higher; therefore, specifically, hot-pressing bonding is preferably performed in a temperature range of 300°C or higher and 420°C or lower, more preferably in a temperature range of 310°C or higher and 410°C or lower, and even more preferably in a temperature range of 320°C or higher and 400°C or lower.

[0094] For thermoforming equipment, known equipment can be used, such as a dual-belt press or a roll laminator with pressure metal rollers. For example, rolled-up multilayer polyimide film and copper foil can be continuously supplied to the thermoforming equipment, and copper foil laminates (polyimide metal laminates) can be manufactured in a rolled-up state.

[0095] As the dry method (metal coating method) used in (iii) above, known methods such as vacuum deposition, sputtering, ion plating, and electron beam can be used. The metal used in the metal coating method can be metals such as copper, nickel, chromium, manganese, aluminum, iron, molybdenum, cobalt, tungsten, vanadium, titanium, tantalum, or alloys thereof, or oxides of these metals, carbides of these metals, etc., but is not particularly limited to these materials. The thickness of the formed metal layer is, for example, from 1 nm to 500 nm, and metal platings such as copper and tin can be provided on the surface with a thickness of, for example, from 1 μm to 40 μm by electrolytic plating or electroless plating.

[0096] As the wet plating method used in (iii) above, known plating methods can be used, and examples of plating methods include electrolytic plating and electroless plating, and these methods can be used in combination. There are no restrictions on the metals used in the wet plating method, as long as they can be wet-plated.

[0097] The thickness of the metal layer formed by the wet plating method can be appropriately selected according to the intended use, and is preferably 0.1 μm to 50 μm, more preferably 1 μm to 30 μm, for practical applications. The number of metal layers formed by the wet plating method can be appropriately selected according to the intended use, and can be one, two, or three or more layers.

[0098] Examples of wet plating methods include the conventionally known Elfseed method available from Ebara-Udylite Co., Ltd., and the Catalyst Bond method (a surface treatment method) available from JX Nippon Mining & Metals Co., Ltd., followed by electroless copper plating.

[0099] The polyimide metal laminate of the present invention has good formability and can be directly drilled, bent, stretched, and used to form metal wiring. Furthermore, the multilayer polyimide film of the present invention can be used to thermo-press electronic circuits onto wiring.

[0100] The multilayer polyimide film and polyimide metal laminate of the present invention can be suitably used as electronic substrate materials such as FPC and TAB, cover layers, and adhesive sheets that require reliability at high temperatures.

[0101] Example

[0102] The present invention will be described in more detail below with reference to embodiments and comparative examples, but the present invention is not limited to these embodiments.

[0103] The following abbreviations will be used in the following text: Tetracarboxylic Acid s-BPDA: 3,3',4,4'-Biphenyltetracarboxylic acid dianhydride PMDA: Pyromellitic dianhydride <Diamine> PPD: p-phenylenediamine m-TB: 2,2'-Dimethylbenzidine BAPP: 2,2-bis[4-(4-aminophenoxy)phenyl]propane TPE-R: 1,3-Bis(4-aminophenoxy)benzene Bisaniline P: α,α'-bis(4-aminophenyl)-1,4-diisopropylbenzene <Other> DMAc: N,N-dimethylacetamide Evaluation of (Multilayer) Polyimide Films [Coefficient of linear thermal expansion (CTE)] Using an EXSTAR6100 manufactured by SII, measurements were taken in tensile mode of polyimide films with a length of 15 mm and a width of 3 mm under a load of 4 gf and a heating rate of 20 °C / min. The first heating was performed at 300 °C to eliminate thermal shrinkage during film formation. Afterward, the samples were cooled to room temperature, and measurements were taken during a second heating process at 20 °C / min to 300 °C. The coefficient of linear expansion was calculated from the TMA curves from 50 °C to 200 °C.

[0104] [Measurement of dielectric loss tangent]

[0105] A 10 GHz split cylindrical resonator CR-710 (manufactured by EM Lab) was used as the measurement device, and the dielectric loss tangent of the polyimide film was measured under the following conditions.

[0106] Measurement frequency: 10 GHz

[0107] Measurement conditions: Temperature 25±2℃, Humidity 50±3% RH

[0108] Measurement sample: Use the sample that has been left to stand for 24 hours under the above measurement conditions.

[0109] [MIT Flexibility Test]

[0110] Cut test pieces for MIT flexural strength testing with a width of 15 mm across the entire width. According to ASTM D2176, measure the number of bends until the polyimide film breaks under the conditions of a radius of curvature of 0.38 mm, a load of 9.8 N, a bending speed of 175 cycles / min, and a left and right bending angle of 135 degrees.

[0111] Evaluation of Polyimide Metal Laminates (Copper-Clad Laminates)

[0112] (Manufacturing of copper-clad laminates)

[0113] A copper foil is stacked on both sides of a multilayer polyimide film using a roller laminator and then hot-pressed to prepare a copper foil laminate, wherein the copper foil is stacked on both sides of the multilayer polyimide film.

[0114] [Rate of Dimensional Change]

[0115] The copper foil laminate was stamped using a stamping machine, and the initial dimensions (X) were measured. The copper foil was then removed by etching on both sides, followed by heating at 250°C for 30 minutes. After heating, the sample was humidified at 25°C and 60% RH for 24 hours, and the dimensions (Y) were measured. The dimensional change rate (%) was calculated according to the following equation.

[0116] Dimensional change rate (%) = (YX) / X×100

[0117] [Appearance Evaluation]

[0118] Etching was performed on both sides of the copper-clad laminate to remove the copper foil. The film surface was observed using an optical microscope and evaluated as follows.

[0119] ○: No surface defects (foaming)

[0120] ×: Surface defects (foaming)

[0121] <Example 1>

[0122] [Preparation of polyimide precursor solution]

[0123] (Polyimide precursor solution for the core layer)

[0124] DMAc was added to a reaction vessel equipped with a stirrer and a nitrogen inlet pipe, followed by PPD and m-TB as diamine components. Next, s-BPDA and PMDA as tetracarboxylic dianhydrides were added in equimolar amounts to the diamine components, and the mixture was reacted to obtain a polyimide precursor solution with a monomer concentration of 18% by mass and a solution viscosity of 2000 poise at 30°C. The molar ratio of PPD to m-TB was 80:20, and the molar ratio of s-BPDA to PMDA was 90:10.

[0125] (Polyimide precursor solution for thermal fusion layer)

[0126] DMAc was added to a reaction vessel equipped with a stirrer and a nitrogen inlet pipe, followed by BAPP as the diamine component. Next, s-BPDA and PMDA, as tetracarboxylic dianhydrides, were added in equimolar amounts to the diamine components, and the mixture was reacted to obtain a polyimide precursor solution B with a monomer concentration of 18% by mass and a solution viscosity of 800 poise at 30°C. The molar ratio of s-BPDA to PMDA was 30:70.

[0127] [Preparation of a monolayer core polyimide film]

[0128] Polyimide precursor solution A was cast as a thin film onto a glass plate, heated in an oven at 120°C for 12 minutes, and then peeled off from the glass plate to obtain a self-supporting film. The four edges of the self-supporting film were fixed using a pin tenter frame, and then gradually heated in a furnace from 150°C to 400°C to remove the solvent and imidize the film, thereby obtaining a single-layer polyimide film with a thickness of 25 μm.

[0129] [Manufacturing method of multilayer polyimide film]

[0130] Polyimide precursor solution A and polyimide precursor solution B are continuously extruded from a three-layer extrusion die and cast onto the upper surface of a smooth metal support, forming a thin film of polyimide precursor solution B (thermal fusion layer) / polyimide precursor solution A (core layer) / polyimide precursor solution B (thermal fusion layer). This thin-film cast product is continuously dried with hot air at 140°C to form a self-supporting film. After peeling the self-supporting film from the support, it is conveyed by a stretching device while maintaining both ends in the width direction, and gradually heated in a furnace from 200°C to 490°C to remove the solvent and imidize, thereby obtaining a strip-shaped multilayer film with a thickness of 50 μm. The thickness of each of the two thermal fusion layers is 5 μm, and the thickness of the core layer is 40 μm. Furthermore, for the resulting multilayer polyimide film, MD (machine direction) represents the longitudinal direction (conveyance direction), and TD (transverse direction) represents the width direction.

[0131] The obtained polyimide film was subjected to linear thermal expansion coefficient (CTE), dielectric loss tangent, and mitral displacement (MIT) tests. The results are shown in Table 1.

[0132] [Polyimide metal laminate (copper-clad laminate)]

[0133] A copper foil (manufactured by JX Metals Corporation, BHM-C102F-HA-V2, 12 μm thick) was deposited on both sides of a multilayer polyimide film using a roller laminator. The copper foil was then hot-pressed and bonded at a lamination temperature of 360°C, a lamination pressure of 1.5 MPa, and a lamination speed of 0.5 m / min to prepare a copper foil laminate, wherein the copper foil is deposited on both sides of the multilayer polyimide film.

[0134] The resulting copper-clad laminate was etched, and the rate of dimensional change and appearance were evaluated.

[0135] <Examples 2 to 7, Comparative Examples 1 to 10>

[0136] Polyimide precursor solutions for the core layer and for the thermally bonded layer were prepared in the same manner as in Example 1. The compositions are shown in Tables 1 to 3. Core monolayer polyimide films, multilayer polyimide films, and copper-clad laminates were prepared and evaluated in the same manner as in Example 1. The results are shown in Table 1 (Examples), Table 2 (Comparative Examples, multilayer film thickness 50 μm), and Table 3 (Comparative Examples, multilayer film thickness 75 μm).

[0137] In the multilayer polyimide film with a thickness of 75 μm (Examples 6 and 7, Comparative Examples 7 to 10), the thickness of each of the two thermally bonded layers is 7 μm, and the thickness of the core layer is 61 μm.

[0138] Table 1

[0139] Table 2

[0140] Table 3

[0141] As shown in Tables 1 to 3, the multilayer polyimide films of all embodiments exhibit low dielectric loss tangents below 0.0060. The multilayer polyimide films of Comparative Examples 3, 5, and 9 exhibit low dielectric loss tangents, but have large dimensional change rates, which poses a problem in practical applications. The other comparative examples all have large dielectric loss tangents.

[0142] Regarding the rate of dimensional change, all examples showed smaller values, while all comparative examples showed larger values. In Comparative Examples 7 and 10, attempts were made to prepare copper-clad laminates using 75 μm multilayer films, but evaluation was not possible due to foaming.

[0143] Furthermore, this experiment demonstrates that the dimensional change rate depends not only strongly on the CTE of the multilayer film but also strongly on the combination of the core layer and the thermally bonded layer. The CTE of a 50 μm thick multilayer polyimide film was investigated; the CTE (MD and TD) of the multilayer polyimide film in Comparative Example 6 was equal to the CTE of the copper foil, at 18 ppm / K, while the CTEs of the multilayer polyimide films in Examples 1 to 5 and Comparative Example 1 were also approximately close to the CTE of the copper foil. However, when comparing the dimensional change rate, the multilayer polyimide films of the examples showed extremely small dimensional change rates, while Comparative Examples 6 and 1 showed larger dimensional change rates. Similarly, the 75 μm thick multilayer film was investigated; the multilayer polyimide film of Example 6 and the multilayer polyimide film of Comparative Example 9 had the same CTE, but Comparative Example 9 showed a larger dimensional change rate.

[0144] The reason is believed to be the optimization of the heat-resistant polyimide layer (core layer), which has a significant impact on the dielectric loss tangent, and the optimization of the thermally fused polyimide layer (thermal fusion layer) that matches the core layer. This result could not be predicted by conventional CTE-based methods.

[0145] Industrial availability

[0146] The polyimide film prepared from the polyimide precursor solution of the present invention is suitable for high-frequency compatible FPC applications.

Claims

1. A multilayer polyimide film comprising: A heat-resistant polyimide layer composed of heat-resistant polyimide (PIc); and A heat-fusible polyimide layer composed of heat-fusible polyimide (PIb) is laminated on one or both sides of the heat-resistant polyimide layer; The heat-resistant polyimide (PIc) mentioned above is obtained by reacting the following components: The tetracarboxylic acid component (Ac) comprises 75 mol% to 100 mol% of 3,3',4,4'-biphenyltetracarboxylic dianhydride and 0 mol% to 25 mol% of pyromellitic dianhydride, and The diamine component (Bc) comprises 70 mol% to 95 mol% of p-phenylenediamine and 5 mol% to 30 mol% of 2,2'-dimethylbenzidine; and The heat-melting polyimide (PIb) mentioned above is obtained by reacting the following components: The tetracarboxylic acid component (Ab) contains 10 mol% to 60 mol% of 3,3',4,4'-biphenyltetracarboxylic dianhydride and 40 mol% to 90 mol% of pyromellitic dianhydride, and The diamine component (Bb) contains more than 50 mol% of 2,2-bis[4-(4-aminophenoxy)phenyl]propane.

2. The multilayer polyimide film of claim 1, wherein the heat-resistant polyimide (PIc) is obtained by reacting the following components: The tetracarboxylic acid component (Ac) comprises 80 mol% to less than 100 mol% of 3,3',4,4'-biphenyltetracarboxylic dianhydride and 0 mol% to less than 20 mol% of pyromellitic dianhydride. The diamine component (Bc) contains more than 75 mol% of p-phenylenediamine and less than 25 mol% of 2,2'-dimethylbenzidine.

3. The multilayer polyimide film of claim 1, wherein the heat-fusible polyimide (PIb) is obtained by reacting the following components: The tetracarboxylic acid component (Ab) contains more than 15 mol% of 3,3',4,4'-biphenyltetracarboxylic dianhydride and less than 85 mol% of pyromellitic dianhydride, and The diamine component (Bb) contains more than 60 mol% of 2,2-bis[4-(4-aminophenoxy)phenyl]propane.

4. The multilayer polyimide film of claim 1, wherein the multilayer polyimide film has a dielectric loss tangent of less than 0.0060, and the dimensional change rate (absolute value) of the polyimide metal laminate in the longitudinal (MD) and transverse (TD) directions is less than 0.10%, wherein the dimensional change rate is determined by measuring the initial dimension (X) of the polyimide metal laminate prepared using the multilayer polyimide film, and the dimension (Y) after heat treatment at 250°C for 30 minutes following etching of the metal foil, and calculating according to the following equation: Dimensional change rate (%) = (YX) / X×100.

5. A polyimide metal laminate, wherein a metal foil is laminated on the thermally fusible polyimide layer side of the multilayer polyimide film of claim 1.

6. The polyimide metal laminate of claim 5, wherein the multilayer polyimide film has a thermally fusible polyimide layer on both sides of the heat-resistant polyimide layer, and the metal foil is laminated on both sides of the multilayer polyimide film.

7. A flexible wiring board manufactured using the polyimide metal laminate of claim 5.

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