Multilayer polyimide film and polyimide metal laminate

Abstract

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

Description

Technology Field

[0001] The present invention relates to a polyimide film and a polyimide metal laminate. Background Technology

[0002] Polyimide films have excellent heat resistance and mechanical properties and are widely used as electronic substrate materials such as flexible printed circuit boards (hereinafter also referred to as FPC) and Tape Automated Bonding (hereinafter also referred to as TAB).

[0003] In the manufacture of FPCs or TABs, a polyimide metal laminate (e.g., copper-clad laminate) is used, in which a metal foil, such as copper foil, is bonded to a polyimide film. It is known that adhesives, such as epoxy resin or acrylic resin, are used as a method for bonding the metal foil and the polyimide film. However, since polyimide metal laminates using adhesives have poor heat resistance, a multilayer polyimide film is proposed in which a heat-resistant polyimide layer and a heat-fusible polyimide layer are laminated, as a polyimide film that can be bonded to a metal foil, such as copper foil, without using an adhesive (e.g., Patent Document 1).

[0004] Meanwhile, with the recent use of high-frequency bands in electronic devices, there is an increasing demand for low transmission loss in polyimide, an electronic substrate material. Transmission loss is correlated with dielectric constant and dielectric loss tangent, and lowering the dielectric loss tangent is particularly effective for achieving low transmission loss.

[0005] As a polyimide with a small dielectric loss tangent, Patent Document 2 proposes "a polymer film (Claim 1) comprising one or more dianhydrides selected from the group consisting of crankshaft monomers, flexible monomers, rigid rotational monomers, rigid non-rotational monomers, and rotation-inhibiting monomers, and one or more diamines selected from the group consisting of crankshaft monomers, flexible monomers, rigid rotational monomers, rigid non-rotational monomers, and rotation-inhibiting monomers, and having a divergence coefficient Df (equivalent to the dielectric loss tangent) of 0.005 or less and a specific absorption rate." Prior art literature

[0006] International Publication No. 2016 / 055673 and Japanese Patent Publication No. 2021-11567 The problem to be solved

[0007] For FPCs used in high-frequency applications, polyimides are required that satisfy basic physical properties such as high heat resistance and high water content stability, which are typically demanded of conventional FPCs, in addition to low dielectric loss tangent. High water content stability not only suppresses issues like circuit misalignment and enhances circuit board reliability but also improves product yield. Generally, this is achieved by bringing the linear coefficient of thermal expansion of the polyimide film close to that of the metal foil (such as copper foil).

[0008] However, no multilayer polyimide film has been known that has excellent heat resistance and also achieves high dimensional stability even under high heating environments and low dielectric loss tangent. Patent Document 2 describes using a polyimide film exhibiting a low dielectric loss tangent as the core layer (heat-resistant polyimide layer) of a multilayer film, but it does not provide detailed descriptions regarding the heat-fused layer (thermoplastic layer), so the performance as a multilayer film or metal laminate is unclear.

[0009] The present invention aims to provide a multilayer polyimide film that has excellent heat resistance and achieves both low dielectric loss tangent and high water stability.

[0010] In addition, another aspect of the present invention aims to provide a polyimide metal laminate in which a multilayer polyimide film and a metal foil, such as copper foil, are laminated. means of solving the problem

[0011] The main disclosures of the present application are combined as follows.

[0012] 1. A heat-resistant polyimide layer composed of heat-resistant polyimide (PIc), and

[0013] A heat-fusible polyimide layer composed of heat-fusible polyimide (PIb) laminated on one or both sides of the above-mentioned heat-resistant polyimide layer

[0014] It is a multilayer polyimide film having;

[0015] The above heat-resistant polyimide (PIc) is,

[0016] A tetracarboxylic acid component (Ac) comprising 75 mol% or more and 100 mol% or less of 3,3',4,4'-biphenyltetracarboxylic acid dianhydride, and 0 mol% or more and 25 mol% or less of pyromellitic acid dianhydride, and

[0017] A diamine component (Bc) containing p-phenylenediamine in an amount of 70 mol% or more and 95 mol% or less, and 2,2'-dimethylbenzidine in an amount of 5 mol% or more and 30 mol% or less

[0018] Obtained by reacting;

[0019] The above heat-fusible polyimide (PIb) is,

[0020] A tetracarboxylic acid component (Ab) comprising 3,3',4,4'-biphenyltetracarboxylic acid dianhydride in an amount of 10 mol% or more and 60 mol% or less, and pyromellitic acid dianhydride in an amount of 40 mol% or more and 90 mol% or less, and,

[0021] Diamine component (Bb) containing 50 mol% or more of 2,2-bis[4-(4-aminophenoxy)phenyl]propane

[0022] Obtained by reacting,

[0023] Multilayer polyimide film.

[0024] 2. The above heat-resistant polyimide (PIc) is,

[0025] A tetracarboxylic acid component (Ac) comprising 80 mol% or more and less than 100 mol% of 3,3',4,4'-biphenyltetracarboxylic acid dianhydride, and more than 0 mol% and less than or equal to 20 mol% of pyromellitic acid dianhydride, and

[0026] A diamine (Bc) obtained by reacting at least 75 mol% of p-phenylenediamine and at least 25 mol% of 2,2'-dimethylbenzidine,

[0027] The multilayer polyimide film described in Claim 1 above.

[0028] 3. The above heat-fusible polyimide (PIb) is,

[0029] A tetracarboxylic acid component (Ab) comprising 15 mol% or more of 3,3',4,4'-biphenyltetracarboxylic acid dianhydride and 85 mol% or less of pyromellitic acid dianhydride, and

[0030] A diamine component (Bb) obtained by reacting 2,2-bis[4-(4-aminophenoxy)phenyl]propane in an amount of 60 mol% or more,

[0031] The multilayer polyimide film described in claim 1 or 2 above.

[0032] 4. A multilayer polyimide film as described in any one of claims 1 to 3, wherein the dielectric loss tangent of the multilayer polyimide film is 0.0060 or less, and the rate of change in dimensions (absolute value) in the length direction (MD) and width direction (TD) of the polyimide metal laminate is 0.10% or less (provided that the rate of change in dimensions is calculated according to the following formula by measuring the initial dimension (X) of the polyimide metal laminate manufactured using the multilayer polyimide film and the dimension (Y) after etching the metal foil and heat treating at 250°C for 30 minutes:

[0033] Dimensional change rate (%) = (YX) / X × 100).

[0034] 5. A polyimide metal laminate having a metal foil laminated on the heat-fusible polyimide layer side of a multilayer polyimide film described in any one of claims 1 to 4 above.

[0035] 6. The polyimide metal laminate described in claim 5, wherein the multilayer polyimide film has heat-sealable polyimide layers on both sides of a heat-resistant polyimide layer, and metal foils are laminated on both sides of the multilayer polyimide film.

[0036] 7. A flexible wiring substrate manufactured using the polyimide metal laminate described in claim 5 above. Effects of the invention

[0037] According to the present invention, a multilayer polyimide film having a small dielectric loss tangent in the high-frequency region, excellent heat resistance, and excellent dimensional stability can be provided. Furthermore, according to another aspect of the present invention, a polyimide metal laminate in which a multilayer polyimide film and a metal foil, such as copper foil, are laminated can be provided. This polyimide metal laminate is suitable for manufacturing high-frequency compatible FPCs. Specific details for implementing the invention

[0038] The multilayer polyimide film of the present invention has a structure in which a heat-fusible polyimide layer (also referred to as a heat-fusible layer) is laminated on one or both sides of a heat-resistant polyimide layer (hereinafter also referred to as a core layer). Hereinafter, the material of the core layer is “c” ( c ore), the material of the heat-fusion layer is 「b」( b There are also cases where it is expressed by adding the suffix of (ondable).

[0039] Heat-resistant polyimide layer

[0040] The heat-resistant polyimide layer (core layer) comprises a heat-resistant polyimide (PIc) obtained by reacting a tetracarboxylic acid component (Ac) with a diamine component (Bc).

[0041] The tetracarboxylic acid component (Ac) for manufacturing the heat-resistant polyimide comprises, with respect to 100 mol% of the total tetracarboxylic acid component, an amount of 3,3',4,4'-biphenyltetracarboxylic acid dianhydride (s-BPDA) of 75 mol% or more and 100 mol% or less, preferably 80 mol% or more, more preferably 85 mol% or more, preferably less than 100 mol%, more preferably 95 mol% or less, and an amount of pyromellitic acid dianhydride (PMDA) of 0 mol% or more and 25 mol% or less, preferably more than 0 mol%, more preferably 5 mol% or more, preferably 20 mol% or less, more preferably 15 mol% or less.

[0042] As the tetracarboxylic acid component (Ac), a tetracarboxylic acid dianhydride other than s-BPDA and PMDA may be used, but the amount is preferably 10 mol% or less, preferably 5 mol% or less, more preferably 2 mol% or less, and it is also very desirable not to include it at all.

[0043] Examples of tetracarboxylic acid components that can be used in combination include aromatic tetracarboxylic acid dianhydrides and aliphatic (especially alicyclic) tetracarboxylic acid dianhydrides. Specifically, 2,3,3',4'-biphenyltetracarboxylic acid dianhydride, 3,3',4,4'-benzophenonetetracarboxylic acid dianhydride, 4,4'-oxydiphthalic acid dianhydride, 3,3',4,4'-diphenylsulfonetetracarboxylic acid 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-phenylene, para-terphenyl-3,3',4,4'-tetracarboxylic acid dianhydride, naphthalene-1,4,5,8-tetracarboxylic acid Examples include dianhydrides and 1,2,4,5-cyclohexane tetracarboxylic acid dianhydrides.

[0044] The diamine component (Bc) for manufacturing the heat-resistant polyimide comprises, with respect to 100 mol% of the total diamine component, an amount of p-phenylenediamine (PPD) of 70 mol% or more and 95 mol% or less, preferably 75 mol% or more and preferably 93 mol% or less, and 2,2'-dimethylbenzidine (m-TB) of 5 mol% or more and 30 mol% or less, preferably 7 mol% or more and preferably 25 mol% or less.

[0045] As a diamine component (Bc), a diamine compound other than PPD and m-TB may be used, but the amount thereof is preferably 10 mol% or less, preferably 5 mol% or less, more preferably 2 mol% or less, and it is also very desirable not to include it at all.

[0046] Examples of diamine components that can be used in combination include aromatic diamine compounds and aliphatic (especially alicyclic) diamine compounds. Specifically, 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'-diaminodiphenylsulfone, 3,4'-diaminodiphenylsulfone, 4,4'-diaminodiphenylsulfone, 3,3'-diaminobenzophenone, 4,4'-diaminobenzophenone, 3,4'-diaminobenzophenone, 3,3'-diaminodiphenylmethane, 4,4'-diaminodiphenylmethane, 3,4'-diaminodiphenylmethane, 2,2-di(3-aminophenyl)propane, Examples include bis(aminophenoxy)benzenes such as 2,2-di(4-aminophenyl)propane, 1,3-bis[2-(4-aminophenyl)-2-propyl]benzene, α,α'-bis(4-aminophenyl)-1,4-diisopropylbenzene, 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.

[0047] The heat-resistant polyimide layer is mainly composed of the heat-resistant polyimide described above, and the resin component excluding additives is preferably substantially composed of the heat-resistant polyimide described above (95 weight% or more, preferably 98 mass% or more), and it is also very desirable that it is composed only of the heat-resistant polyimide (100 mass%).

[0048] The heat-resistant polyimide layer may include additives as needed in addition to the heat-resistant polyimide. Representative examples include fine inorganic or organic fillers. As for inorganic fillers, examples include particulate or flat inorganic fillers. Specifically, examples include inorganic oxide powders such as finely particulate titanium dioxide powder, silicon dioxide (silica) powder, magnesium oxide powder, aluminum oxide (alumina) powder, and zinc oxide powder; inorganic nitride powders such as finely particulate silicon nitride powder and titanium nitride powder; inorganic carbide powders such as silicon carbide powder; and inorganic salt powders such as finely particulate calcium carbonate powder, calcium sulfate powder, and barium sulfate powder. As for organic fillers, examples include polyimide powder, liquid crystal polymer powder, fluoropolymer powder, and thermosetting resin powder. Two or more of these additives may be used in combination. Regarding the amount and shape (size, aspect ratio) of the fillers, it is desirable to select them according to the intended use. In addition, known means may be applied to uniformly disperse these fillers.

[0049] These inorganic or organic fillers, particularly preferably silica powder, may be included in the heat-resistant polyimide layer in an amount preferably 30 mass% or less, more preferably 20 mass% or less, and even more preferably 10 mass% or less (it may be 0 mass%).

[0050] <Thermofusible polyimide layer>

[0051] The heat-fusible polyimide layer (heat-fusible layer) comprises a heat-fusible polyimide (PIb) obtained by reacting a tetracarboxylic acid component (Ab) with a diamine component (Bb).

[0052] The tetracarboxylic acid component (Ab) for manufacturing the heat-fusible polyimide comprises, with respect to 100 mol% of the total tetracarboxylic acid component, 3,3',4,4'-biphenyltetracarboxylic acid dianhydride (s-BPDA) in an amount of 10 mol% or more and 60 mol% or less, preferably 15 mol% or more, more preferably 20 mol% or more, also preferably 55 mol% or less, more preferably 50 mol% or less, and pyromellitic acid dianhydride (PMDA) in an amount of 40 mol% or more and 90 mol%, preferably 45 mol% or more, more preferably 50 mol% or more, also preferably 85 mol% or less, more preferably 80 mol% or less.

[0053] As the tetracarboxylic acid component (Ab), a tetracarboxylic acid dianhydride other than s-BPDA and PMDA may be used, but the amount thereof is preferably 10 mol% or less, preferably 5 mol% or less, more preferably 2 mol% or less, and it is also very desirable not to include it at all.

[0054] Examples of tetracarboxylic acid components that can be used in combination include aromatic tetracarboxylic acid dianhydrides and aliphatic (especially alicyclic) tetracarboxylic acid dianhydrides. Specific examples include 2,3,3',4'-biphenyltetracarboxylic acid dianhydride, 3,3',4,4'-benzophenonetetracarboxylic acid dianhydride, 4,4'-oxydiphthalic acid dianhydride, 3,3',4,4'-diphenylsulfonetetracarboxylic acid 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 acid dianhydride.

[0055] The diamine component (Bb) for manufacturing the heat-fusible polyimide comprises 2,2-bis[4-(4-aminophenoxy)phenyl]propane (BAPP) in an amount of 50 mol% or more (preferably more than 50 mol%), preferably 60 mol% or more, more preferably 70 mol% or more, even more preferably 80 mol% or more, and even more preferably 90 mol% or more, based on 100 mol% of the total diamine component, and it is also preferable that the amount be 100 mol%.

[0056] As the diamine component (Bb), a diamine compound other than BAPP may be used, and other diamine components used in combination include, for example, 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, Examples include 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.

[0057] The glass transition temperature (Tg) of the heat-fusible polyimide is preferably 250°C to 310°C, and more preferably 260°C to 300°C, in terms of improving the peel strength of the heat-fusible layer and the core layer, and improving the peel strength of the heat-fusible layer and the metal foil, as well as in terms of solder heat resistance during FPC manufacturing.

[0058] The heat-fusible polyimide layer is mainly composed of the heat-fusible polyimide described above, and the resin composition excluding additives is preferably substantially composed of the heat-fusible polyimide described above (95 weight% or more, preferably 98 mass% or more), and it is also very desirable to be composed solely of the heat-fusible polyimide (100 mass%).

[0059] The heat-fusible polyimide layer may include additives as needed in addition to the heat-fusible polyimide. Specific additives and formulation amounts may be those described in the heat-resistant polyimide layer.

[0060] Multilayer Polyimide Film

[0061] 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-sealable polyimide layer is preferably 0.5 to 15 μm, more preferably 1 to 12.5 μm. The total thickness of the multilayer polyimide film is preferably 4 to 100 μm, and more preferably 7 to 90 μm.

[0062] 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.

[0063] The dimensional change rate (absolute value) of the multilayer polyimide film is preferably 0.10% or less, preferably less than 0.10%, and more preferably 0.09% or less.

[0064] The dimensional change rate was calculated according to the following formula by measuring the initial dimension (X) and the dimension (Y) after etching the metal foil, heating at 250°C for 30 minutes, and conditioned for a polyimide metal laminate manufactured using a multilayer polyimide film.

[0065] Dimensional change rate (%) = (YX) / X × 100

[0066] Method for manufacturing multilayer polyimide film

[0067] The method for manufacturing the multilayer polyimide film of the present invention is not particularly limited, and known methods may be employed. As representative methods, the coating method and the co-extrusion-flexible film formation method are described next.

[0068] (Manufacturing method by coating method)

[0069] The multilayer polyimide film of the present invention can be obtained by coating one or both sides of a self-supporting film obtained from a polyimide precursor solution (a) that imparts a heat-fusible polyimide with a polyimide precursor solution (b), and then heating and drying the obtained multilayer self-supporting film to perform imidization.

[0070] A polyimide precursor solution (a) imparting heat-resistant polyimide is obtained by reacting a tetracarboxylic acid component and a diamine component in an organic solvent in substantially equimolar amounts, or with one component in slightly excess relative to the other. The structure of the polyimide precursor solution (a) containing a plurality of tetracarboxylic acid components and a diamine component may exist as a random structure or as a block structure, and it is more preferable for it to exist as a random structure. A self-supporting film can be obtained by applying the polyimide precursor solution (a) onto a support and heating and drying the flexible material.

[0071] Meanwhile, a polyimide precursor solution (b) that imparts a heat-fusible polyimide is also obtained by reacting a tetracarboxylic acid component and a diamine component in an organic solvent in substantially equimolar amounts, or with one component in slightly excess relative to the other. The structure of the polyimide precursor solution (b) containing a plurality of tetracarboxylic acid components and a diamine component may exist as a random structure or as a block structure, and it is more preferable for it to exist as a random structure.

[0072] The monomer composition for preparing the polyimide precursor solution (a) imparting a heat-resistant polyimide and the polyimide precursor solution (b) imparting a heat-fusible polyimide is the composition described in <heat-resistant polyimide layer> and <heat-fusible polyimide layer>, respectively.

[0073] In the polyimide precursor solution (b) and / or the polyimide precursor solution (a), a phosphorus-based stabilizer, such as triphenyl phosphite or triphenyl phosphate, may be added in a range of 0.01 to 1 mass% relative to the solid content (polymer) concentration during polymerization of the polyimide precursor solution for the purpose of limiting gelation.

[0074] In terms of the surface condition and productivity of the film, it is preferable to add a phosphate ester or a salt of a tertiary amine and a phosphate ester to the polyimide precursor solution. The amount of these added is preferably 0.01 to 5 parts by mass per 100 parts by mass of the polyimide or polymer. Specific examples of the phosphate ester include distearyl phosphate esters and monostearyl phosphate esters. In addition, examples of the salts of a tertiary amine and a phosphate ester include monostearyl phosphate ester triethanolamine salts. Regarding the imidation in the present invention, both thermal imidation (thermoimidation) and chemical imidation (chemical imidation) may be applied. Among these, thermal imidation may be suitably applied.

[0075] A basic organic compound may be added to the polyimide precursor solution (b) and / or the polyimide precursor solution (a) to promote imidation. For example, lower alkyl-substituted or aromatic-substituted imidazoles such as 1,2-dimethylimidazole, N-methylimidazole, N-benzyl-2-methylimidazole, 2-methylimidazole, 2-ethyl-4-methylimidazole, 2-phenylimidazole, benzimidazoles such as 5-methylbenzimidazole, isoquinoline, substituted pyridines such as 3,5-dimethylpyridine, 3,4-dimethylpyridine, 2,5-dimethylpyridine, 2,4-dimethylpyridine, 4-n-propylpyridine, etc. may be used in a ratio of 0.05 to 10 mass%, more preferably 0.05 to 7 mass%, and even more preferably 0.1 to 5 mass% with respect to the solid content (polymer) concentration. When these basic organic compounds are used, the imidization of the polyimide precursor is promoted at relatively low temperatures to form a polyimide film; therefore, these basic organic compounds can be used to avoid insufficient imidization.

[0076] Examples of organic solvents for preparing the above polyimide precursor solution include amides such as N-methyl-2-pyrrolidone, N,N-dimethylacetamide, N,N-diethylacetamide, N,N-dimethylformamide, N,N-diethylformamide, and hexamethylsulforamide; sulfoxides such as dimethyl sulfoxide and diethyl sulfoxide; and sulfones such as dimethyl sulfone and diethyl sulfone. These solvents may be used alone or in combination.

[0077] When carrying out the polymerization reaction of the tetracarboxylic acid component and the diamine component, the concentration of the total monomer in the organic solvent can be appropriately selected according to the purpose of use. For example, polyimide precursor solutions (a) and (b) preferably have a solid content (polymer) concentration of 5 to 40 mass%, more preferably 6 to 35 mass%, and particularly preferably 10 to 30 mass%.

[0078] The preparation temperature of the polyimide precursor solution (a) and the polyimide precursor solution (b) is not particularly limited, but is 25°C to 100°C, more preferably 25°C to 80°C, and even more preferably 30°C to 70°C so that the imidation reaction does not proceed too much, and the preparation time is 1 to 72 hours, more preferably 2 to 60 hours. The reaction can be carried out in an air atmosphere, but is typically suitably carried out in an inert gas atmosphere, preferably in a nitrogen gas atmosphere.

[0079] The solution viscosity of the polyimide precursor solution (a) and the polyimide precursor solution (b) can be appropriately selected according to the purpose of use (coating, softening, etc.). For example, when the polyimide precursor solution (a) and the polyimide precursor solution (b) are used for softening, in terms of workability for handling the polyimide precursor solution, it is preferable that the rolling viscosity measured at 30°C is about 100 to 5000 poise, more preferable that it is 500 to 4000 poise, and particularly preferable that it is about 1000 to 3000 poise. In addition, when polyimide precursor solution (a) and polyimide precursor solution (b) are used in a coating, in terms of workability for handling the polyimide precursor solution, it is preferable that the rotational viscosity measured at 30°C is 1 to 100 centipoise, more preferable that it is 3 to 50 centipoise, and particularly preferable that it is 5 to 20 centipoise. Accordingly, it is preferable to carry out the above polymerization reaction until the polyimide precursor solution produced exhibits such viscosity. In addition, the solution viscosity may be adjusted by adding the above organic solvent to the prepared polyimide precursor solution.

[0080] A self-supporting film obtained from a polyimide precursor solution (a) that imparts heat-resistant polyimide can be obtained, for example, by forming the polyimide precursor solution (a) into a film of uniform thickness on the surface of a suitable support (e.g., a metal, ceramic, plastic roll, or metal belt, etc.), then heating it preferably to 50 to 210°C, more preferably to 60 to 200°C using a heat source such as hot air or infrared rays, slowly removing the solvent, and drying it until it becomes self-supporting (e.g., until it can be peeled off from the support).

[0081] The self-supporting film imparting heat-resistant polyimide preferably has a heating loss in the range of 20 to 40 mass% and an imidization rate in the range of 8 to 40%. When the heating loss and imidization rate are within the above ranges, the mechanical properties of the self-supporting film become sufficient, the polyimide precursor solution (b) is easily coated cleanly on the upper surface of the self-supporting film, foaming, cracking, craze, cracks, splitting, etc. are less likely to occur in the polyimide film obtained after imidization, and the adhesion strength between the heat-resistant polyimide layer and the heat-fusible polyimide layer becomes sufficient.

[0082] The heating weight of the self-supporting film is calculated by drying the film to be measured at 400°C for 30 minutes, and then calculating the weight before drying (W1) and the weight after drying (W2) according to the following formula.

[0083] Heat loss (mass%) = {(W1-W2) / W1}×100

[0084] The imidation rate of a self-supporting film can be calculated by measuring the IR spectra of the self-supporting film and its full-cured product (polyimide film) separately using the ATR method and utilizing the ratio of the vibration band peak areas. As vibration band peaks, the asymmetric stretching vibration band of the imide carbonyl group or the benzene ring framework stretching vibration band can be used. Additionally, regarding the measurement of the imidation rate, there is also a method using the Karl Fischer moisture meter described in Japanese Patent Publication No. Hei 9-316199.

[0085] Next, a polyimide precursor solution (b) that imparts a heat-sealable polyimide is coated on one or both sides of the self-supporting film. The polyimide precursor solution (b) may be coated on the self-supporting film peeled from the support, or may be coated on the self-supporting film on the support before peeling from the support. It is preferable to apply the polyimide precursor solution (b) uniformly on one or both sides of the self-supporting film. Accordingly, the self-supporting film of the polyimide precursor solution (a) preferably has a surface capable of homogeneously coating the polyimide precursor solution (b).

[0086] As a method for coating a self-supporting film obtained from a polyimide precursor solution (a) with a polyimide precursor solution (b), there are no particular limitations, but examples include known coating methods such as gravure coating, spin coating, silkscreen, dip coating, spray coating, bar coating, knife coating, roll coating, blade coating, and die coating.

[0087] Next, a self-supporting film of the polyimide precursor solution (a) coated with the polyimide precursor solution (b) is heated and imidized to obtain a multilayer polyimide film. The maximum heating temperature for heat treatment for imidization is preferably 330°C to 600°C, more preferably 350°C to 550°C, and even more preferably 370°C to 500°C.

[0088] It is preferable to perform the heat treatment for imidization in stages. First, a first heat treatment is performed at a temperature of 200°C or higher and less than 300°C for 1 minute to 60 minutes, followed by a second heat treatment at a temperature of 300°C or higher and less than 330°C for 1 minute to 60 minutes, and then a third heat treatment is performed at a maximum heating temperature of preferably 330°C to 600°C, more preferably 370°C to 550°C, and even more preferably 370°C to 500°C for 1 minute to 30 minutes. This heat treatment can be performed using known devices, such as a hot air furnace or an infrared furnace. Additionally, this heat treatment is preferably performed by fixing the self-supporting film of the polyimide precursor solution (a), coated with the polyimide precursor solution (b), using a pin tenter, a clip, etc.

[0089] (Manufacturing method by co-extrusion-flexible film formation method)

[0090] The multilayer polyimide film of the present invention may be manufactured by a method of laminating, drying, and imidizing a polyimide precursor solution (hereinafter also referred to as a dope solution) that imparts a heat-resistant polyimide layer and a dope solution that imparts a heat-fusible polyimide layer by a co-extrusion-flexible film-forming method (hereinafter also simply referred to as the "co-extrusion method"). For example, the method described in Japanese Patent Publication No. Hei 3-180343 (Japanese Patent Publication No. Hei 7-102661) may be used for this co-extrusion method.

[0091] To explain in more detail, in this co-extrusion method, first, an extrusion molding machine having two or more extrusion molding dies is used. From the discharge port of the die, a dope liquid that imparts a heat-resistant polyimide layer and a dope liquid that imparts a heat-fusible polyimide layer are applied onto a support, thereby forming a laminated thin film. Then, the thin film on the support is dried to form a multilayer self-supporting film. Subsequently, the multilayer self-supporting film is peeled off from the support, and finally, the multilayer self-supporting film is heat-treated. In this process, the dope liquid in contact with the support can be either the dope liquid that imparts a heat-resistant polyimide layer or the dope liquid that imparts a heat-fusible polyimide layer.

[0092] For both the dope solution for imparting a heat-resistant polyimide layer and the dope solution for imparting a heat-fusible polyimide layer, polyimide precursor solutions (a) and (b) are prepared by reacting a tetracarboxylic acid component with a diamine component as described in the (manufacturing method by coating method). As for the dope solution, it is preferable that the solid content (polymer) concentration be 5 to 40 weight%, particularly 10 to 30 weight%, and that the "solution viscosity (rolling viscosity)" at the discharge temperature from the multilayer extrusion die during the multilayer extrusion molding of the above-described 2-layer, 3-layer, etc. is about 50 to 10,000 poise, particularly 100 to 6,000 poise.

[0093] As for a two-layer extrusion die, for example, it may be structured such that it has a dope liquid supply port, and a dope liquid passage is formed from each supply port toward each manifold, and the lower flow paths of the manifolds merge at a junction point, and the dope liquid passage (lip portion) after the junction is connected to a slit-shaped discharge port, so that the dope liquid is discharged as a thin film onto a support from this discharge port (multi-manifold type two-layer die). The gap of the lip portion can be adjusted by a lip adjustment bolt.

[0094] In addition, the gap of the air passage at the bottom of each manifold (at a location close to the confluence point) is controlled by each choke bar. It is preferable that each of the above-mentioned manifolds have a hanger coat type shape. Furthermore, as a die for two-layer extrusion molding, each dope liquid supply port is provided on the left and right sides of the upper part of the die, and the dope liquid passages are configured to immediately merge at a confluence point equipped with a partition plate. A dope liquid passage is connected from the confluence point to the manifold, and a dope liquid passage (lip part) at the bottom of the manifold is connected to a slit-shaped discharge port. It may be structured so that the dope liquid is discharged from this discharge port onto a support in the form of a grooved film (feed block type two-layer die or single manifold type two-layer die).

[0095] In addition to the above two-layer extrusion, a multilayer extruded polyimide film can be manufactured using a molding method similar to that of two-layer extrusion molding by using a die for three or more layers. That is, a three-layer polyimide film can be obtained by using a first dope solution that imparts a heat-fusible polyimide layer, a dope solution that imparts a heat-resistant polyimide layer, and a second dope solution that imparts a heat-fusible polyimide layer. The first dope solution and the second dope solution that impart a heat-fusible polyimide layer may be the same or different.

[0096] In addition, regarding the form of drying conditions or heating conditions following the operation of continuous extrusion onto a support in the co-extrusion-flexible film-forming method, the contents described in the above "manufacturing method by coating method" may be applied as is.

[0097] In either the coating method or the co-extrusion method, when manufacturing a polyimide film by heating a self-supporting film, a stretching operation may be performed as needed.

[0098] By the above operations, it is possible to manufacture a polyimide film of a long shape continuously.

[0099] If a thick multilayer polyimide film is required, it may be manufactured by bonding multilayer polyimide films produced by the above manufacturing method. The bonding operation can also be performed continuously.

[0100] Polyimide Metal Laminate

[0101] A polyimide metal laminate can be manufactured by using the polyimide precursor solution or the multilayer polyimide film of the present invention and laminating a multilayer polyimide film (or layer) and a metal foil (or layer). The polyimide metal laminate has a structure in which a metal foil (or layer) is laminated on one or both sides of a multilayer polyimide film. As a method for manufacturing a polyimide metal laminate, the following methods may be used.

[0102] (i) A method in which a multilayer polyimide film and a metal foil are directly bonded without an adhesive and laminated by pressure or heat pressure.

[0103] (ii) A method of applying a polyimide precursor solution onto a metal foil and drying and imidizing it.

[0104] (iii) A method of directly forming a metal layer on a multilayer polyimide film by a dry method (metallizing such as vacuum deposition, sputtering, etc.) and / or a wet method (plating).

[0105] As the metal foil of (i) and (ii) above, various metal foils such as copper, aluminum, gold, or alloys thereof may be used. Among these, copper foil is preferably used. A copper foil used as the metal foil is also called a "copper-clad laminate." In addition, when metal layers are laminated on both sides of a multilayer polyimide film, the same or different metals may be used. Specific examples of copper foil include rolled copper foil or electrolytic copper foil. Although there are no particular limitations, the thickness of the copper foil is preferably 2 to 35 μm, and particularly preferably 5 to 18 μm. Regarding Ra and Rz, which indicate surface roughness, it is preferable that Ra be 0.01 μm to 0.4 μm and Rz be 0.2 μm to 2.0 μm.

[0106] It is preferable that the multilayer polyimide film and the copper foil be continuously heat-pressed under heating by at least one pair of pressing members. The temperature of the pressing members is preferably 50°C or higher than the glass transition temperature of the heat-fusible polyimide, more preferably 60°C or higher, and even more preferably 70°C or higher. By adopting such a heating temperature, the advantageous effect of the multilayer polyimide film and the copper foil being rigidly laminated is achieved. In addition, it is preferable that the heating temperature be 420°C or lower in order to prevent thermal degradation of the multilayer polyimide film and the copper foil. As described above, since the glass transition temperature of the heat-fusible polyimide is preferably 250°C or higher, specifically, it is preferable to heat press in a temperature range of 300°C or higher and 420°C or lower, more preferable to heat press in a temperature range of 310°C or higher and 410°C or lower, and more preferable to heat press in a temperature range of 320°C or higher and 400°C or lower.

[0107] The thermal compression device may use known devices such as a double belt press or a roll laminate using a compression metal roll, and, for example, a multilayer polyimide film wound on a roll and a copper foil are each continuously supplied to the thermal compression device to manufacture a copper-clad laminate (polyimide metal laminate) in a rolled state.

[0108] As the dry method (metallizing method) used in (iii) above, known methods such as vacuum deposition, sputtering, ion plating, and electron beam may be used. As the metal used in the metallizing method, metals such as copper, nickel, chromium, manganese, aluminum, iron, molybdenum, cobalt, tungsten, vanadium, titanium, and tantalum, or alloys thereof, or oxides of these metals, or carbides of these metals, may be used, but are not particularly limited to these materials. The thickness of the metal layer formed is, for example, 1 nm to 500 nm, and on this surface, a metal plating layer such as copper or tin may be provided with a thickness of, for example, 1 μm to 40 μm by electroplating or electroless plating.

[0109] As for the wet method (plating method) used in (iii) above, known plating methods may be used, and examples include electroplating and electroless plating, and combinations thereof may be used. As for the metal used in the wet plating method, there are no restrictions at all as long as it is a metal that can be wet-plated.

[0110] The thickness of the metal layer formed by the wet plating method can be appropriately selected according to the purpose of use, and preferably, a range of 0.1 μm to 50 μm, more preferably 1 μm to 30 μm, is preferred because it is suitable for practical use. The number of metal layers formed by the wet plating method can be appropriately selected according to the purpose of use, and may be one layer, two layers, or three or more layers.

[0111] As a wet plating method, conventionally known methods such as the Elf Seed process of Ebara Yujirite Co., Ltd. or the Catalyst Bond process, a surface treatment process of Nikko Kinzoku Co., Ltd., followed by electroless copper plating can be cited.

[0112] The polyimide metal laminate of the present invention has good moldability, so it can be punched, bent, drawn, or metal wiring formed as is. In addition, the multilayer polyimide film of the present invention can be used for thermal compression of electronic circuits over wiring.

[0113] 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 requiring reliability under high temperatures.

[0114] [Example]

[0115] The present invention will be explained in more detail below based on examples. However, the present invention is not limited by the examples.

[0116] The following abbreviations are used below.

[0117] Tetracarboxylic acids

[0118] s-BPDA: 3,3',4,4'-biphenyltetracarboxylic acid dianhydride

[0119] PMDA: Pyromylic acid dianhydride

[0120] Diamines

[0121] PPD: p-phenylenediamine

[0122] m-TB: 2,2'-dimethylbenzidine

[0123] BAPP: 2,2-Bis[4-(4-aminophenoxy)phenyl]propane

[0124] TPE-R: 1,3-Bis(4-aminophenoxy)benzene

[0125] Bis-aniline P: α,α'-bis(4-aminophenyl)-1,4-diisopropylbenzene

[0126] Others

[0127] DMAc: N,N-dimethylacetamide

[0128] Evaluation of (Multilayer) Polyimide Films

[0129] [Coefficient of Thermal Expansion (CTE)]

[0130] Using SII EXSTAR6100, a polyimide film sampled with a length of 15 mm and a width of 3 mm was measured in tensile mode with a load of 4 gf and a heating rate of 20 ℃ / min, and the thermal shrinkage during film formation was obtained by performing a first heating to 300 ℃. Afterward, the film was cooled to room temperature, and then a second heating was performed to 300 ℃ at 20 ℃ / min, and the coefficient of linear expansion was calculated from the TMA curve from 50 ℃ to 200 ℃.

[0131] Measurement of the genetic dropout

[0132] As a measuring device, a 10GHz split cylinder resonator CR-710 (manufactured by EM Lab) was used, and the dielectric loss tangent of the polyimide film was measured under the following conditions.

[0133] Measurement frequency: 10GHz

[0134] Measurement conditions: Temperature 25±2℃, Humidity 50±3%RH

[0135] Measurement sample: Under the above measurement conditions, a sample left for 24 hours was used.

[0136] [MIT Internal Exam]

[0137] A 15 mm wide specimen for the MIT fracture test was cut across the entire width. According to ASTM D2176, the number of times the polyimide film was fractured was measured with a radius of curvature of 0.38 mm, a load of 9.8 N, a bending speed of 175 times / min, and a left-right bending angle of 135 degrees.

[0138] [Evaluation of Polyimide Metal Laminate (Copper Laminate)]

[0139] (Manufacture of copper laminates)

[0140] A copper-clad laminate having copper foil laminated on both sides of a multilayer polyimide film was manufactured by using a roll laminating device and heat-pressing while overlapping copper foil on both sides of the multilayer polyimide film.

[0141] [Dimensional Change Rate] A copper laminate was punched using a press punching machine, and the initial dimension (X) was measured. Subsequently, the copper foil was removed by double-sided etching, and then heat-treated at 250°C for 30 minutes. After heating, the dimensions (Y) were measured after humidification at 25°C under 60% RH for 24 hours. The dimensional change rate (%) was calculated according to the following formula.

[0142] Dimensional change rate (%) = (YX) / X × 100

[0143] [Appearance Evaluation]

[0144] After removing the copper foil by double-sided etching of the copper laminate, the film surface was observed using an optical microscope and evaluated as follows.

[0145] ○: No defects (foaming) on ​​the surface

[0146] ×: Surface defect (foaming)

[0147] <Example 1>

[0148] [Preparation of Polyimide Precursor Solution]

[0149] (Polyimide precursor solution for core layer)

[0150] DMAc was added to a reaction vessel equipped with a stirrer and a nitrogen inlet tube, and PPD and m-TB were added as diamine components. Subsequently, s-BPDA and PMDA were added as tetracarboxylic acid dianhydride components in an equimolar manner with respect to the diamine components and reacted to obtain polyimide precursor solution A, which had a monomer concentration of 18 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.

[0151] (Polyimide precursor solution for heat-sealable layers)

[0152] DMAc was added to a reaction vessel equipped with a stirrer and a nitrogen inlet tube, and BAPP was added as a diamine component. Subsequently, s-BPDA and PMDA were added as tetracarboxylic acid dianhydride components in an equimolar manner with respect to the diamine component and reacted to obtain polyimide precursor solution B, having a monomer concentration of 18 mass% and a solution viscosity of 800 poise at 30°C. The molar ratio of s-BPDA to PMDA was 30:70.

[0153] [Manufacturing of Core Single-Layer Polyimide Film]

[0154] Polyimide precursor solution A was cast as a thin film onto a glass plate, heated at 120°C for 12 minutes using an oven, and peeled off from the glass plate to obtain a self-supporting film. The four sides of this self-supporting film were fixed with a pin tenter, and the film was gradually heated in a furnace from 150°C to 400°C to remove the solvent and perform imidization, thereby obtaining a single-layer polyimide film with a thickness of 25 μm.

[0155] [Manufacture of Multilayer Polyimide Film]

[0156] Polyimide precursor solution A and polyimide precursor solution B were continuously extruded from a three-layer extrusion die onto the upper surface of a smooth metal support in the order of polyimide precursor solution B (thermal fusion layer) - polyimide precursor solution A (core layer) - polyimide precursor solution B (thermal fusion layer) to form a flexible, thin film. The flexible thin film was continuously dried with hot air at 140°C to form a self-supporting film. After peeling the self-supporting film from the support, the film was conveyed by a tenter device while gripping both ends in the width direction, and gradually heated in a furnace from 200°C to 490°C to remove the solvent and perform imidization, thereby obtaining an elongated multilayer film with a thickness of 50 μm. The thickness of each of the two thermal fusion layers was 5 μm, and the thickness of the core layer was 40 μm. In addition, regarding the obtained multilayer polyimide film, MD (Machine Direction) indicates the length direction (transport direction), and TD (Transverse Direction) indicates the width direction.

[0157] For the obtained polyimide film, the coefficient of thermal expansion (CTE), dielectric loss tangent, and MIT cutoff test were performed. The results are shown in Table 1.

[0158] [Polyimide Metal Laminate (Copper Laminate)]

[0159] A copper-clad laminate having copper foil laminated on both sides of a multilayer polyimide film was manufactured by using a roll laminating device to overlap copper foil (JX Metal Co., Ltd., BHM-C102F-HA-V2, thickness 12 μm) on both sides of a multilayer polyimide film, and then heat-pressing at a laminating temperature of 360°C, a laminating pressure of 1.5 MPa, and a laminating speed of 0.5 m / min.

[0160] The obtained copper laminate was etched, and the rate of dimensional change and appearance were evaluated.

[0161] <Examples 2 to 7, Comparative Examples 1 to 10>

[0162] In the same manner as in Example 1, a polyimide precursor solution for the core layer and a polyimide precursor solution for the heat-sealable layer were prepared. The compositions are as shown in Tables 1 to 3. In addition, a core single-layer polyimide film, a multilayer polyimide film, and a copper-clad laminate were manufactured and evaluated in the same manner as in Example 1. The results are shown in Table 1 (Example), Table 2 (Comparative Example, multilayer film thickness 50 μm), and Table 3 (Comparative Example, multilayer film thickness 75 μm).

[0163] In addition, in the multilayer polyimide film with a thickness of 75 μm (Examples 6, 7, Comparative Examples 7 to 10), the thickness of the two heat-fused layers was 7 μm each, and the thickness of the core layer was 61 μm.

[0164]

[0165]

[0166]

[0167] As shown in Tables 1 to 3, the multilayer polyimide films of all examples exhibited a low dielectric loss tangent of 0.0060 or less. The multilayer polyimide films of Comparative Examples 3, 5, and 9 exhibited a low dielectric loss tangent, but had a large rate of dimensional change, which posed a practical problem. In all other Comparative Examples, the dielectric loss tangent was large.

[0168] Regarding the rate of dimensional change, all examples showed small values, whereas all comparative examples showed large values. In Comparative Examples 7 and 10, an attempt was made to fabricate copper-clad laminates using a 75 μm multilayer film, but it could not be evaluated because foaming occurred.

[0169] Furthermore, this experiment revealed that the rate of dimensional change strongly depends not only on the CTE of the multilayer film but also on the combination of the core layer and the heat-sealable layer. When examining this with respect to a multilayer polyimide film with a thickness of 50 μm, the multilayer polyimide film of Comparative Example 6 had a CTE (MD and TD) value consistent with the copper foil's CTE of 18 ppm / K, and the multilayer polyimide films of Examples 1 to 5 and Comparative Example 1 also had a CTE approximately close to that of the copper foil. However, when comparing the rates of dimensional change, the multilayer polyimide film of the Examples showed an extremely small rate of dimensional change, whereas Comparative Examples 6 and 1 showed a large rate of dimensional change. Similarly, when examining a multilayer film with a thickness of 75 μm, the multilayer polyimide film of Example 6 and the multilayer polyimide film of Comparative Example 9 had the same CTE, but regarding the rate of dimensional change, Comparative Example 9 showed a large value.

[0170] This is believed to be due to the optimization of the heat-resistant polyimide layer (core layer), which has a significant influence on the dielectric loss tangent, and the optimization of the heat-fusible polyimide layer (heat-fusible layer) to match the core layer; this is a result that could not have been predicted from a conventional CTE-based approach. Industrial applicability

[0171] The polyimide film prepared from the polyimide precursor solution of the present invention can be suitably used for high-frequency compatible FPC applications.

Claims

Claim 1 A multilayer polyimide film having a heat-resistant polyimide layer composed of a heat-resistant polyimide (PIc), and a heat-fusible polyimide layer composed of a heat-fusible polyimide (PIb) laminated on one or both sides of the heat-resistant polyimide layer; wherein the heat-resistant polyimide (PIc) is obtained by reacting a tetracarboxylic acid component (Ac) containing 3,3',4,4'-biphenyltetracarboxylic acid dianhydride in an amount of 75 mol% or more and 100 mol% or less, and pyromellitic acid dianhydride in an amount of 0 mol% or more and 25 mol% or less, with a diamine component (Bc) containing p-phenylenediamine in an amount of 70 mol% or more and 95 mol% or less, and 2,2'-dimethylbenzidine in an amount of 5 mol% or more and 30 mol% or less; and wherein the heat-fusible Polyimide (PIb) is a multilayer polyimide film obtained by reacting a tetracarboxylic acid component (Ab) containing 3,3',4,4'-biphenyltetracarboxylic acid dianhydride in an amount of 10 mol% or more and 60 mol% or less, and pyromellitic acid dianhydride in an amount of 40 mol% or more and 90 mol% or less, with a diamine component (Bb) containing 2,2-bis[4-(4-aminophenoxy)phenyl]propane in an amount of 50 mol% or more. Claim 2 A multilayer polyimide film according to claim 1, wherein the heat-resistant polyimide (PIc) is obtained by reacting a tetracarboxylic acid component (Ac) containing 3,3',4,4'-biphenyltetracarboxylic acid dianhydride in an amount of 80 mol% or more and less than 100 mol% and pyromellitic acid dianhydride in an amount greater than 0 mol% and less than 20 mol%, with a diamine component (Bc) containing 75 mol% or more of p-phenylenediamine and less than 2,2'-dimethylbenzidine in an amount of 25 mol% or less. Claim 3 A multilayer polyimide film according to claim 1, wherein the heat-fusible polyimide (PIb) is obtained by reacting a tetracarboxylic acid component (Ab) containing 3,3',4,4'-biphenyltetracarboxylic acid dianhydride in an amount of 15 mol% or more and pyromellitic acid dianhydride in an amount of 85 mol% or less with a diamine component (Bb) containing 2,2-bis[4-(4-aminophenoxy)phenyl]propane in an amount of 60 mol% or more. Claim 4 In claim 1, a multilayer polyimide film having a dielectric loss tangent of 0.0060 or less and a dimensional change rate (absolute value) in the length direction (MD) and width direction (TD) of a polyimide metal laminate of 0.10% or less (wherein the dimensional change rate is calculated by measuring the initial dimension (X) of a polyimide metal laminate manufactured using the multilayer polyimide film and the dimension (Y) after etching the metal foil and heat treating at 250°C for 30 minutes, and according to the following formula: dimensional change rate (%) = (YX) / X × 100). Claim 5 A polyimide metal laminate having a metal foil laminated on the heat-fusible polyimide layer side of the multilayer polyimide film described in claim 1. Claim 6 In claim 5, the polyimide metal laminate is formed such that the multilayer polyimide film has heat-sealable polyimide layers on both sides of a heat-resistant polyimide layer, and metal foils are laminated on both sides of the multilayer polyimide film. Claim 7 A flexible wiring substrate manufactured using the polyimide metal laminate described in paragraph 5.

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