Mulitilayer polyimide film and polyimide metallic laminate

Abstract

Provided is a multilayer polyimide film that is excellent in heat-resistance, low dielectric loss tangent, and dimensional stability. The multilayer polyimide film has: a layer of a heat-resistant polyimide; and a layer of a heat-bondable polyimide laminated on one surface or both surfaces thereof. 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 70-95 mol% of p-phenylenediamine and 5-30 mol% of 2,2'-dimethylbenzidine. The heat-bondable polyimide is obtained from: a tetracarboxylic acid component containing 10-60 mol% of the s-BPDA and 40-90 mol% of the PMDA; and a diamine component containing 50 mol% or more of 2,2-bis[4-(4-aminophenoxy)phenyl]propane.

Description

Multilayer polyimide film and polyimide-metal laminate

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

[0002] Polyimide films have excellent heat resistance and mechanical properties and are widely used as electronic substrate materials for flexible printed circuit boards (hereinafter also referred to as FPCs) and tape automated bonding (hereinafter also referred to as TABs).

[0003] In the manufacture of FPCs and TABs, polyimide metal laminates (e.g., copper-clad laminates) are used, in which a metal foil such as copper foil and a polyimide film are bonded together. While adhesives such as epoxy resins and acrylic resins are known to be used to bond metal foil and polyimide film together, polyimide metal laminates using adhesives have poor heat resistance. Therefore, multilayer polyimide films, in which a heat-resistant polyimide layer and a heat-fusible polyimide layer are laminated together, have been proposed as polyimide films that can be bonded to metal foil such as copper foil without using adhesives (see, for example, Patent Document 1).

[0004] On the other hand, with the recent trend toward the use of high-frequency bands in electronic devices, there is an increasing demand for low transmission loss in polyimides, which are used as electronic circuit board materials. Transmission loss is correlated with the dielectric constant and dielectric loss tangent, and reducing the dielectric loss tangent is particularly effective for reducing transmission loss.

[0005] As a polyimide with a small dielectric loss tangent, Patent Document 2 proposes "a polymer film (claim 1) that includes 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 has an extinction coefficient Df (synonymous with dielectric loss tangent) of 0.005 or less and a specific water absorption coefficient, etc."

[0006] International Publication No. 2016 / 055673 Japanese Patent Application Laid-Open No. 2021-11567

[0007] In FPCs for high-frequency applications, polyimides are required that meet the basic physical properties required for standard FPCs, such as high heat resistance and high dimensional stability, in addition to a low dielectric loss tangent. High dimensional stability not only prevents defects such as circuit misalignment, improving the reliability of circuit boards, but also improving product yield. This problem is generally solved by making the linear thermal expansion coefficient of the polyimide film close to that of the metal foil (copper foil, etc.).

[0008] However, no multilayer polyimide film has been known that has excellent heat resistance, a low dielectric loss tangent, and high dimensional stability even in a highly heated environment. Patent Document 2 describes the use of a polyimide film exhibiting a low dielectric loss tangent as a core layer (heat-resistant polyimide layer) of a multilayer film, but does not describe in detail the heat-sealing layer (thermoplastic layer), and the performance of the multilayer film or metal laminate is unclear.

[0009] An object of the present invention is to provide a multilayer polyimide film that has excellent heat resistance and exhibits both a low dielectric loss tangent and high dimensional stability. Another object of the present invention is to provide a polyimide-metal laminate in which the multilayer polyimide film is laminated with a metal foil such as copper foil.

[0010] The main disclosures of this application can be summarized as follows:

[0011] 1. A multilayer polyimide film having a heat-resistant polyimide layer made of a heat-resistant polyimide (PIc), and a heat-fusible polyimide layer laminated on one or both sides of the heat-resistant polyimide layer and made of a heat-fusible polyimide (PIb); the heat-resistant polyimide (PIc) is obtained by reacting a tetracarboxylic acid component (Ac) containing 75 mol % to 100 mol % of 3,3',4,4'-biphenyltetracarboxylic dianhydride and 0 mol % to 25 mol % of pyromellitic dianhydride with a diamine component (Bc) containing 70 mol % to 95 mol % of p-phenylenediamine and 5 mol % to 30 mol % of 2,2'-dimethylbenzidine; and the heat-fusible polyimide (PIb) is A multilayer polyimide film obtained by reacting a tetracarboxylic acid component (Ab) containing 10 mol % to 60 mol % of 3,3',4,4'-biphenyltetracarboxylic dianhydride and 40 mol % to 90 mol % of pyromellitic dianhydride with a diamine component (Bb) containing 50 mol % or more of 2,2-bis[4-(4-aminophenoxy)phenyl]propane.

[0012] 2. The multilayer polyimide film according to item 1, wherein the heat-resistant polyimide (PIc) is obtained by reacting a tetracarboxylic acid component (Ac) containing 80 mol % or more and less than 100 mol % of 3,3',4,4'-biphenyltetracarboxylic dianhydride and more than 0 mol % and 20 mol % or less of pyromellitic dianhydride with a diamine (Bc) containing 75 mol % or more of p-phenylenediamine and 25 mol % or less of 2,2'-dimethylbenzidine.

[0013] 3. The multilayer polyimide film according to item 1 or 2, wherein the heat-fusible polyimide (PIb) is obtained by reacting a tetracarboxylic acid component (Ab) containing 15 mol % or more of 3,3',4,4'-biphenyltetracarboxylic dianhydride and 85 mol % or less of pyromellitic dianhydride with a diamine component (Bb) containing 60 mol % or more of 2,2-bis[4-(4-aminophenoxy)phenyl]propane.

[0014] 4. The multilayer polyimide film according to any one of items 1 to 3 above, wherein the multilayer polyimide film has a dielectric dissipation factor of 0.0060 or less, and the polyimide metal laminate has a dimensional change rate (absolute value) of 0.10% or less in the machine direction (MD) and the width direction (TD) (wherein the dimensional change rate is calculated according to the following formula: dimensional change rate (%) = (Y - X) / X × 100), wherein the initial dimension (X) of a polyimide metal laminate produced using the multilayer polyimide film and the dimension (Y) after etching the metal foil and then heat-treating at 250°C for 30 minutes are measured.

[0015] 5. A polyimide metal laminate comprising a metal foil laminated on the heat-fusible polyimide layer side of the multilayer polyimide film according to any one of items 1 to 4 above.

[0016] 6. The polyimide metal laminate according to item 5, wherein the multilayer polyimide film has a heat-sealable polyimide layer on both sides of the heat-resistant polyimide layer, and metal foils are laminated on both sides of the multilayer polyimide film.

[0017] 7. A flexible wiring board manufactured using the polyimide metal laminate according to item 5 above.

[0018] According to the present invention, a multilayer polyimide film can be provided that has a small dielectric loss tangent in the high frequency range, excellent heat resistance, and excellent dimensional stability. Furthermore, according to another aspect of the present invention, a polyimide metal laminate can be provided in which a multilayer polyimide film is laminated with a metal foil such as copper foil. This polyimide metal laminate is suitable for producing high-frequency compatible FPCs.

[0019] The multilayer polyimide film of the present invention has a structure in which a heat-sealable polyimide layer (hereinafter also referred to as a core layer) is laminated on one or both sides of a heat-resistant polyimide layer (hereinafter also referred to as a bondable layer). Hereinafter, the material of the core layer may be represented by the suffix "c" (core), and the material of the bondable layer may be represented by the suffix "b" (bondable).

[0020] <Heat-Resistant Polyimide Layer> The heat-resistant polyimide layer (core layer) contains a heat-resistant polyimide (PIc) obtained by reacting a tetracarboxylic acid component (Ac) with a diamine component (Bc). The tetracarboxylic acid component (Ac) for producing the heat-resistant polyimide contains 3,3',4,4'-biphenyltetracarboxylic dianhydride (s-BPDA) in an amount of 75 mol% to 100 mol%, preferably 80 mol% or more, more preferably 85 mol% or more, preferably less than 100 mol%, and more preferably 95 mol% or less, and pyromellitic dianhydride (PMDA) in an amount of 0 mol% to 25 mol%, preferably more than 0 mol%, more preferably 5 mol% to 5 mol%, preferably 20 mol% to 15 mol%, based on 100 mol% of the total tetracarboxylic acid components.

[0021] As the tetracarboxylic acid component (Ac), 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 preferable that no tetracarboxylic acid dianhydride is contained at all.

[0022] Examples of the tetracarboxylic acid component that can be used in combination include aromatic tetracarboxylic acid dianhydrides and aliphatic (particularly alicyclic) tetracarboxylic acid 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-phenylene, para-ter-phenyl-3,3',4,4'-tetracarboxylic dianhydride, naphthalene-1,4,5,8-tetracarboxylic dianhydride, and 1,2,4,5-cyclohexanetetracarboxylic dianhydride.

[0023] The diamine component (Bc) for producing the heat-resistant polyimide contains p-phenylenediamine (PPD) in an amount 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) in an amount of 5 mol % or more and 30 mol % or less, preferably 7 mol % or more and preferably 25 mol % or less, based on 100 mol % of the total diamine components.

[0024] As the 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 highly preferred that no diamine compound is contained at all.

[0025] Examples of the diamine component that can be used in combination include aromatic diamine compounds and aliphatic (particularly 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'-diaminobenzophenone, 4,4'-diaminobenzophenone, 3,4'-diaminobenzophenone, 3,3'-diaminodiphenylmethane, 4,4'-diaminodiphenylmethane, 3,4'-diaminodiphenylmethane bis(aminophenoxy)benzenes such as benzene, 2,2-di(3-aminophenyl)propane, 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.

[0026] The heat-resistant polyimide layer is mainly composed of the above-mentioned heat-resistant polyimide, and the resin component excluding additives preferably consists essentially of the above-mentioned heat-resistant polyimide (95% by weight or more, preferably 98% by weight or more), and it is also very preferable that the resin component consists solely of the heat-resistant polyimide (100% by weight).

[0027] The heat-resistant polyimide layer may contain additives as needed in addition to the heat-resistant polyimide. Typical examples include fine inorganic or organic fillers. Examples of inorganic fillers include particulate or flat inorganic fillers. Specific examples include inorganic oxide powders such as fine titanium dioxide powder, silicon dioxide (silica) powder, magnesium oxide powder, aluminum oxide (alumina) powder, and zinc oxide powder; inorganic nitride powders such as fine silicon nitride powder and titanium nitride powder; inorganic carbide powders such as silicon carbide powder; and inorganic salt powders such as fine calcium carbonate powder, calcium sulfate powder, and barium sulfate powder. Examples of organic fillers include polyimide powder, liquid crystal polymer powder, fluororesin 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 depending on the intended use. Furthermore, known methods can be used to uniformly disperse these fillers.

[0028] These inorganic or organic fillers, particularly preferably silica powder, can be contained in the heat-resistant polyimide layer in an amount of preferably 30% by mass or less, more preferably 20% by mass or less, and even more preferably 10% by mass or less (which may be 0% by mass).

[0029] <Heat-Fusible Polyimide Layer> 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). The tetracarboxylic acid component (Ab) for producing the heat-fusible polyimide contains 3,3',4,4'-biphenyltetracarboxylic dianhydride (s-BPDA) in an amount of 10 mol% to 60 mol%, preferably 15 mol% or more, more preferably 20 mol% or more, and preferably 55 mol% or less, and more preferably 50 mol% or less, and pyromellitic dianhydride (PMDA) in an amount of 40 mol% to 90 mol%, preferably 45 mol% or more, more preferably 50 mol% or more, and preferably 85 mol% or less, and more preferably 80 mol% or less, relative to 100 mol% of the total tetracarboxylic acid components.

[0030] 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 preferable that no tetracarboxylic acid dianhydride is contained at all.

[0031] Examples of tetracarboxylic acid components that can be used in combination include aromatic tetracarboxylic acid dianhydrides and aliphatic (particularly alicyclic) tetracarboxylic acid dianhydrides, such as 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.

[0032] The diamine component (Bb) for producing the heat-fusible polyimide contains 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 components, and is also preferably 100 mol %.

[0033] As the diamine component (Bb), a diamine compound other than BAPP may be used, and examples of other diamine components to be 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, and 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.

[0034] The glass transition temperature (Tg) of the heat-fusible polyimide is preferably 250°C to 310°C, more preferably 260°C to 300°C, from the viewpoint of improving the peel strength between the heat-fusible layer and the core layer, and between the heat-fusible layer and the metal foil, and from the viewpoint of solder heat resistance during FPC production.

[0035] The heat-fusible polyimide layer is mainly composed of the above-mentioned heat-fusible polyimide, and the resin composition excluding additives preferably consists essentially of the above-mentioned heat-fusible polyimide (95% by weight or more, preferably 98% by weight or more), and it is also very preferable that the resin composition consists solely of the heat-fusible polyimide (100% by weight).

[0036] The heat-fusible polyimide layer may contain additives in addition to the heat-fusible polyimide, if necessary. Specific additives and amounts thereof may be those described for the heat-resistant polyimide layer.

[0037] <Multilayer Polyimide Film> 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-fusible polyimide layer is preferably 0.5 to 15 μm, more preferably 1 to 12.5 μm. The thickness of the entire multilayer polyimide film is preferably 4 to 100 μm, more preferably 7 to 90 μm.

[0038] 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.

[0039] The dimensional change rate (absolute value) of the multilayer polyimide film is preferably 0.10% or less, preferably less than 0.10%, more preferably 0.09% or less. The dimensional change rate was calculated according to the following formula: Dimensional change rate (%) = (Y - X) / X × 100. For a polyimide metal laminate produced using the multilayer polyimide film, the initial dimension (X) and the dimension (Y) after etching the metal foil, heat-treating at 250°C for 30 minutes, and conditioning the humidity were measured.

[0040] <Method for Producing Multilayer Polyimide Film> The method for producing the multilayer polyimide film of the present invention is not particularly limited, and known methods can be adopted. Representative methods include a coating method and a co-extrusion-casting film-forming method, which will be described below.

[0041] (Production Method by Coating Method) 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 provides a heat-resistant polyimide with a polyimide precursor solution (b) that provides a heat-fusible polyimide, and then heating and drying the obtained multilayer self-supporting film to carry out imidization.

[0042] The polyimide precursor solution (a) that provides a heat-resistant polyimide is obtained by reacting a tetracarboxylic acid component and a diamine component in substantially equimolar amounts or in a slight excess of one component relative to the other in an organic solvent. The structure of the polyimide precursor solution (a) containing multiple tetracarboxylic acid components and diamine components may be a random structure or a block structure, with a random structure being more preferred. A self-supporting film can be obtained by casting the polyimide precursor solution (a) on a support and drying the cast product by heating.

[0043] On the other hand, the polyimide precursor solution (b) that gives a heat-fusible polyimide can also be obtained by reacting a tetracarboxylic acid component and a diamine component in substantially equimolar amounts or in a slight excess of one component relative to the other in an organic solvent. The structure of the polyimide precursor solution (b) containing a plurality of tetracarboxylic acid components and diamine components may be a random structure or a block structure, with a random structure being more preferred.

[0044] The monomer compositions for preparing the polyimide precursor solution (a) that provides a heat-resistant polyimide and the polyimide precursor solution (b) that provides a heat-fusible polyimide are the compositions described in <Heat-resistant polyimide layer> and <Heat-fusible polyimide layer>, respectively.

[0045] To prevent gelation, a phosphorus-based stabilizer, such as triphenyl phosphite or triphenyl phosphate, may be added to the polyimide precursor solution (b) and / or the polyimide precursor solution (a) in an amount of 0.01 to 1% by mass relative to the solids (polymer) concentration during polyimide precursor solution polymerization. From the standpoint of film surface condition and productivity, 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 polyimide or polymer. Specific examples of phosphate esters include distearyl phosphate ester and monostearyl phosphate ester. Furthermore, examples of salts of a tertiary amine and a phosphate ester include monostearyl phosphate triethanolamine salt. Regarding the imidization method used in the present invention, either thermal imidization (thermal imidization) or chemical imidization (chemical imidization) can be used. Of these, thermal imidization is preferred.

[0046] A basic organic compound can be added to the polyimide precursor solution (b) and / or the polyimide precursor solution (a) for the purpose of promoting imidization. For example, a lower alkyl-substituted or aromatic-substituted imidazole such as 1,2-dimethylimidazole, N-methylimidazole, N-benzyl-2-methylimidazole, 2-methylimidazole, 2-ethyl-4-methylimidazole, or 2-phenylimidazole, a benzimidazole such as 5-methylbenzimidazole, or a substituted pyridine such as isoquinoline, 3,5-dimethylpyridine, 3,4-dimethylpyridine, 2,5-dimethylpyridine, 2,4-dimethylpyridine, or 4-n-propylpyridine, can be added in a proportion of 0.05 to 10% by mass, more preferably 0.05 to 7% by mass, and 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 the polyimide precursor is promoted at a relatively low temperature to form a polyimide film, and therefore these basic organic compounds can be used to avoid insufficient imidization.

[0047] Examples of organic solvents for producing the polyimide precursor solution 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 may be used alone or in combination.

[0048] The concentration of all monomers in the organic solvent when carrying out the polymerization reaction of the tetracarboxylic acid component and the diamine component can be appropriately selected depending on the purpose of use. For example, the polyimide precursor solutions (a) and (b) preferably have a solids (polymer) concentration of 5 to 40% by mass, more preferably 6 to 35% by mass, and particularly preferably 10 to 30% by mass.

[0049] The production temperature for the polyimide precursor solution (a) and the 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 as not to excessively proceed with the imidization reaction, and the production 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 usually suitably carried out in an inert gas atmosphere, preferably a nitrogen gas atmosphere.

[0050] The solution viscosities of the polyimide precursor solution (a) and the polyimide precursor solution (b) can be appropriately selected depending on the purpose of use (coating, casting, etc.). For example, when the polyimide precursor solution (a) and the polyimide precursor solution (b) are used for casting, from the viewpoint of ease of handling the polyimide precursor solution, the rotational viscosity measured at 30°C is preferably about 100 to 5,000 poise, more preferably 500 to 4,000 poise, and particularly preferably about 1,000 to 3,000 poise. Furthermore, when the polyimide precursor solution (a) and the polyimide precursor solution (b) are used for coating, from the viewpoint of ease of handling 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 desirable to carry out the polymerization reaction to such an extent that the resulting polyimide precursor solution exhibits the above-mentioned viscosity. The viscosity of the solution can also be adjusted by adding the organic solvent described above to the produced polyimide precursor solution.

[0051] A self-supporting film obtained from the polyimide precursor solution (a) that provides a 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 roll, or a metal belt, 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 rays to gradually remove the solvent, and drying the film until it becomes self-supporting (e.g., to the extent that it can be peeled off from the support).

[0052] The self-supporting film that provides the heat-resistant polyimide preferably has a heat loss in the range of 20 to 40% by mass, and an imidization rate in the range of 8 to 40%. When the heat 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 cleanly applied to the upper surface of the self-supporting film, the polyimide film obtained after imidization is less likely to develop bubbles, cracks, crazes, or fissures, and the adhesive strength between the heat-resistant polyimide layer and the heat-fusible polyimide layer is sufficient. The heat loss 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: Heat loss (mass %) = {(W1 - W2) / W1} × 100 The imidization ratio 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 the vibrational band peak areas. Examples of vibrational band peaks that can be utilized include the asymmetric stretching vibration band of the imide carbonyl group and the benzene ring skeleton stretching vibration band. Another method for measuring the imidization ratio is to use a Karl Fischer moisture meter, as described in JP-A-9-316199.

[0053] Next, a polyimide precursor solution (b) that provides a heat-fusible polyimide is applied to one or both sides of the self-supporting film. The polyimide precursor solution (b) may be applied to the self-supporting film after it has been peeled from the support, or may be applied to the self-supporting film on the support before it is peeled from the support. It is preferable that the polyimide precursor solution (b) is applied uniformly to 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 allows the polyimide precursor solution (b) to be uniformly applied.

[0054] The method for applying the polyimide precursor solution (b) to the self-supporting film obtained from the polyimide precursor solution (a) is not particularly limited, and examples thereof include known application methods such as gravure coating, spin coating, silk screening, dip coating, spray coating, bar coating, knife coating, roll coating, blade coating, and die coating.

[0055] 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 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.

[0056] The heat treatment for imidization is preferably carried out in stages, with a primary heat treatment being carried out at a temperature of 200°C or higher but lower than 300°C for 1 minute to 60 minutes, followed by a secondary heat treatment at a temperature of 300°C or higher but lower than 330°C for 1 minute to 60 minutes, and then a tertiary heat treatment being carried out at a maximum heating temperature of preferably 330°C to 600°C, more preferably 370 to 550°C, and even more preferably 370 to 500°C for 1 minute to 30 minutes. This heat treatment can be carried out using known equipment such as a hot air oven or an infrared heating oven. Furthermore, this heat treatment is preferably carried out by fixing the self-supporting film of polyimide precursor solution (a) coated with polyimide precursor solution (b) using a pin tenter, clips, or the like.

[0057] (Production Method by Co-extrusion-Casting Film Forming Method) The multilayer polyimide film of the present invention can also be produced by a co-extrusion-casting film forming method (hereinafter also referred to as "co-extrusion method"), in which a polyimide precursor solution (hereinafter also referred to as "dope solution") that provides a heat-resistant polyimide layer and a dope solution that provides a heat-fusible polyimide layer are laminated, dried, and imidized. As this co-extrusion method, for example, the method described in JP-A-3-180343 (JP-B-7-102661) can be used.

[0058] More specifically, in this co-extrusion method, an extruder having a die for extrusion molding two or more layers is first used. A dope liquid for providing a heat-resistant polyimide layer and a dope liquid for providing a heat-fusible polyimide layer are cast onto a support from the outlet of the die, thereby forming a laminated thin film. The thin film on the support is then dried to form a multilayer self-supporting film. The multilayer self-supporting film is then peeled from the support, and finally, the multilayer self-supporting film is heat-treated. In this process, the dope liquid in contact with the support may be either the dope liquid for providing a heat-resistant polyimide layer or the dope liquid for providing a heat-fusible polyimide layer.

[0059] Both the dope solution for forming the heat-resistant polyimide layer and the dope solution for forming the heat-fusible polyimide layer are prepared by reacting a tetracarboxylic acid component with a diamine component, as explained in the (production method by coating method), to produce polyimide precursor solutions (a) and (b). The dope solution preferably has a solids (polymer) concentration of 5 to 40% by weight, particularly 10 to 30% by weight, and a "solution viscosity (rotational viscosity)" of about 50 to 10,000 poise, particularly 100 to 6,000 poise at the temperature at which it is extruded from the multilayer extrusion die during the multilayer extrusion molding of two layers, three layers, or the like.

[0060] Examples of bilayer extrusion dies include those with dope supply ports, each with a dope passage extending from the port to each manifold. The manifolds have bottom channels that converge at a confluence point, and the resulting dope passage (lip) communicates with a slit-shaped outlet, from which the dope is discharged in the form of a thin film onto a support (multi-manifold bilayer die). The lip adjustment bolts adjust the spacing between the lips. The bottoms of the manifolds (near the confluence points) have choke bars that adjust the spacing of the gaps in the channels. Preferably, each manifold has a hanger-coat shape. The bilayer extrusion die has dope supply ports on the left and right sides of the upper part of the die, and the dope passages converge immediately at a confluence point equipped with a partition plate. The dope flow path from the junction to a manifold, and the dope flow path (lip portion) at the bottom of the manifold is connected to a slit-shaped discharge port, from which the dope is discharged onto a support in the form of a groove film (a feedblock-type two-layer die or a single-manifold-type two-layer die).

[0061] In addition to the two-layer extrusion described above, a multi-layer extruded polyimide film can also be produced using a die for extrusion molding three or more layers in the same manner as two-layer extrusion molding. That is, a three-layer polyimide film can be produced by using a composition of a first dope liquid for forming a heat-fusible polyimide layer, a dope liquid for forming a heat-resistant polyimide layer, and a second dope liquid for forming a heat-fusible polyimide layer. The first and second dope liquids for forming the heat-fusible polyimide layer may be the same or different.

[0062] In the co-extrusion-casting film-forming method, the drying conditions and heating conditions after the operation of continuously extruding onto the support can be applied as is to the above-mentioned "Production method by coating method."

[0063] In both the coating method and the co-extrusion method, a stretching operation may be carried out if necessary when the self-supporting film is heated to produce a polyimide film. By the above-described operations, a long polyimide film can be continuously produced. When a thick multilayer polyimide film is required, it can also be produced by laminating multilayer polyimide films produced by the above-described production methods. The lamination operation can also be carried out continuously.

[0064] <Polyimide-metal laminate> A polyimide-metal laminate can be produced by laminating a multilayer polyimide film (or layer) and a metal foil (or layer) using the polyimide precursor solution or multilayer polyimide film of the present invention. 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. Examples of methods for producing a polyimide-metal laminate include the following: (i) a method in which a multilayer polyimide film and a metal foil are directly bonded together without an adhesive, and lamination is performed by applying pressure or heat and pressure; (ii) a method in which a polyimide precursor solution is applied to a metal foil, followed by drying and imidization; and (iii) a method in which a metal layer is directly formed on a multilayer polyimide film by a dry method (metallizing such as vacuum deposition or sputtering) and / or a wet method (plating).

[0065] As the metal foil (i) or (ii) above, various metal foils can be used, such as copper, aluminum, gold, or alloy foils thereof. Among these, copper foil is preferred. Those using copper foil as the metal foil are also called "copper-clad laminates." Furthermore, when metal layers are laminated 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, more preferably 5 to 18 μm, and with respect to Ra and Rz, which indicate surface roughness, it is preferred that Ra be 0.01 μm to 0.4 μm and Rz be 0.2 μm to 2.0 μm.

[0066] The multilayer polyimide film and the copper foil are preferably continuously thermocompression bonded under heating by at least one pair of pressure members. The temperature of the pressure members is preferably at least 50°C higher than the glass transition temperature of the heat-fusible polyimide, more preferably at least 60°C higher, and even more preferably at least 70°C higher. By adopting such a heating temperature, the multilayer polyimide film and the copper foil are advantageously laminated together firmly. Furthermore, a heating temperature of 420°C or lower is preferred from the viewpoint of preventing thermal degradation of the multilayer polyimide film and the copper foil. As described above, the glass transition temperature of the heat-fusible polyimide is preferably 250°C or higher. Therefore, specifically, thermocompression bonding is preferably performed at a temperature range of 300°C to 420°C, more preferably at a temperature range of 310°C to 410°C, and even more preferably at a temperature range of 320°C to 400°C.

[0067] The thermocompression bonding device can be a known device such as a double belt press or a roll laminator using a pressure-bonding metal roll. For example, a rolled multilayer polyimide film and a copper foil can be continuously fed to the thermocompression bonding device, and a copper-clad laminate (polyimide-metal laminate) can be produced in a rolled state.

[0068] The dry method (metallizing method) used in (iii) above can be a known method such as vacuum deposition, sputtering, ion plating, or electron beam. Metals used in the metallizing method include, but are not limited to, metals such as copper, nickel, chromium, manganese, aluminum, iron, molybdenum, cobalt, tungsten, vanadium, titanium, and tantalum, as well as alloys thereof, oxides of these metals, and carbides of these metals. The metal layer formed has a thickness of, for example, 1 nm to 500 nm, and a metal plating layer of copper, tin, or the like can be formed on this surface by electroplating or electroless plating to a thickness of, for example, 1 μm to 40 μm.

[0069] The wet method (plating method) used in (iii) above can be a known plating method, such as electrolytic plating or electroless plating, or a combination of these. The metal used in the wet plating method is not particularly limited as long as it can be wet-plated.

[0070] The thickness of the metal layer formed by wet plating can be appropriately selected depending on the purpose of use, and is preferably in the range of 0.1 μm to 50 μm, more preferably 1 μm to 30 μm for practical use. The number of layers of the metal layer formed by wet plating can be appropriately selected depending on the purpose of use, and may be one layer, two layers, or three or more layers.

[0071] Examples of wet plating methods include conventionally known methods such as the Elfseed process manufactured by Ebara-Udylite Co., Ltd., or the Catalyst Bond process, a surface treatment process manufactured by Nippon Mining & Metals Co., Ltd., followed by electroless copper plating.

[0072] The polyimide metal laminate of the present invention has good moldability and can be directly subjected to drilling, bending, drawing, metal wiring formation, etc. Furthermore, the multilayer polyimide film of the present invention can be used for thermocompression bonding of electronic circuits onto wiring.

[0073] 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, coverlays, and adhesive sheets that require reliability at high temperatures.

[0074] The present invention will be described in more detail below based on examples, but the present invention is not limited to these examples.

[0075] The following abbreviations are used hereinafter: <Tetracarboxylic acids> s-BPDA: 3,3',4,4'-biphenyltetracarboxylic dianhydride PMDA: pyromellitic dianhydride <Diamines> 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 <Others> DMAc: N,N-dimethylacetamide

[0076] <Evaluation of (Multilayer) Polyimide Film> [Coefficient of Linear Thermal Expansion (CTE)] Using an EXSTAR6100 manufactured by SII Corporation, a polyimide film sampled to a length of 15 mm and a width of 3 mm was subjected to measurement in tensile mode under a load of 4 gf and at a heating rate of 20°C / min, followed by primary heating to 300°C to remove thermal shrinkage during film formation. After cooling to room temperature, secondary heating was performed at 20°C / min to 300°C, and the coefficient of linear expansion was calculated from the TMA curve from 50°C to 200°C.

[0077] <Measurement of Dielectric Loss Tangent> A split cylinder resonator 10 GHz CR-710 (manufactured by EM Lab) was used as the measuring device to measure the dielectric loss tangent of the polyimide film under the following conditions: Measurement frequency: 10 GHz Measurement conditions: Temperature 25±2°C, humidity 50±3% RH Measurement sample: A sample that had been left to stand for 24 hours under the above measurement conditions was used.

[0078] [MIT Folding Endurance Test] A test piece having a width of 15 mm across the entire width was cut out for the MIT folding endurance test. In accordance with ASTM D2176, the number of times until the polyimide film broke was measured under the following conditions: radius of curvature 0.38 mm, load 9.8 N, folding speed 175 times / min, and left-right folding angle 135°.

[0079] [Evaluation of Polyimide Metal Laminate (Copper Clad Laminate)] (Production of Copper Clad Laminate) Using a roll laminator, copper foil was superimposed on both sides of a multilayer polyimide film and thermocompression bonded to produce a copper clad laminate in which copper foil was laminated on both sides of the multilayer polyimide film.

[0080] [Dimensional Change Rate] A copper clad laminate was punched using a press puncher, and the initial dimension (X) was measured. Subsequently, the copper foil was removed by etching on both sides, and the laminate was then heat-treated at 250°C for 30 minutes. After heating, the laminate was conditioned at 25°C and 60% RH for 24 hours, and then the dimension (Y) was measured. The dimensional change rate (%) was calculated according to the following formula: Dimensional change rate (%) = (Y - X) / X x 100

[0081] [Appearance Evaluation] After etching 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: ∘: No defects (foaming) on ​​the surface ×: Defects (foaming) on ​​the surface

[0082] Example 1 Preparation of Polyimide Precursor Solution Polyimide Precursor Solution for Core Layer DMAc was added to a reaction vessel equipped with a stirrer and a nitrogen inlet tube, followed by the addition of PPD and m-TB as diamine components. Subsequently, s-BPDA and PMDA as tetracarboxylic dianhydride components were added in equimolar amounts to the diamine components, and the mixture was allowed to react to obtain a polyimide precursor solution A having a monomer concentration of 18% by mass and a solution viscosity of 2,000 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.

[0083] (Polyimide precursor solution for heat-sealable layer) DMAc was added to a reaction vessel equipped with a stirrer and a nitrogen inlet tube, and BAPP was further added as a diamine component. Subsequently, s-BPDA and PMDA were added as tetracarboxylic dianhydride components in equimolar amounts to the diamine component, and the mixture was allowed to react to obtain a polyimide precursor solution B having 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.

[0084] [Production of Core Single-Layer Polyimide Film] Polyimide precursor solution A was cast onto a glass plate in the form of a thin film, heated in an oven at 120°C for 12 minutes, and peeled off from the glass plate to obtain a self-supporting film. The four sides of this self-supporting film were fixed with pin tenters and gradually heated in a heating 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.

[0085] [Production of Multilayer Polyimide Film] Polyimide precursor solution A and polyimide precursor solution B were continuously extruded and cast onto the upper surface of a smooth metal support from a three-layer extrusion die so as to form a thin film in the following order: polyimide precursor solution B (thermal adhesive layer) - polyimide precursor solution A (core layer) - polyimide precursor solution B (thermal adhesive layer). The thin-film cast was continuously dried with hot air at 140°C to form a self-supporting film. After peeling the self-supporting film from the support, it was conveyed while gripping both ends of the self-supporting film in the width direction using a tenter device and gradually heated from 200°C to 490°C in a heating furnace to remove the solvent and imidize, resulting in a long multilayer film with a thickness of 50 μm. The thicknesses of the two thermal adhesive layers were each 5 μm, and the thickness of the core layer was 40 μm. Note that with respect to the resulting multilayer polyimide film, MD (machine direction) refers to the longitudinal direction (conveyance direction), and TD (transverse direction) refers to the width direction.

[0086] The obtained polyimide film was subjected to measurement of the coefficient of linear thermal expansion (CTE), the dielectric loss tangent, and the MIT folding endurance test. The results are shown in Table 1.

[0087] [Polyimide Metal Laminate (Copper-Clad Laminate)] Using a roll laminator, copper foil (manufactured by JX Nippon Mining Corporation, BHM-C102F-HA-V2, thickness 12 μm) was superimposed on both sides of a multilayer polyimide film, and thermocompression 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 produce a copper-clad laminate in which copper foil was laminated on both sides of the multilayer polyimide film.

[0088] The copper-clad laminate thus obtained was subjected to etching, and the dimensional change rate and appearance were evaluated.

[0089] Examples 2 to 7, Comparative Examples 1 to 10 Polyimide precursor solutions for the core layer and the heat-sealing layer were prepared in the same manner as in Example 1. The compositions are shown in Tables 1 to 3. Furthermore, core single-layer polyimide films, multilayer polyimide films, and copper-clad laminates were produced 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). In the 75 μm-thick multilayer polyimide films (Examples 6 and 7, Comparative Examples 7 to 10), the thicknesses of the two heat-sealing layers were each 7 μm, and the thickness of the core layer was 61 μm.

[0090]

[0091]

[0092]

[0093] As shown in Tables 1 to 3, the multilayer polyimide films of all Examples exhibited low dielectric dissipation factors of 0.0060 or less. The multilayer polyimide films of Comparative Examples 3, 5, and 9 exhibited low dielectric dissipation factors, but their dimensional change rates were large, posing practical problems. The other Comparative Examples all had large dielectric dissipation factors. Regarding dimensional change rates, all Examples exhibited low values, while the Comparative Examples all exhibited large values. In Comparative Examples 7 and 10, attempts were made to fabricate copper-clad laminates using 75 μm multilayer films, but foaming occurred, making evaluation impossible. Furthermore, this experiment revealed that the dimensional change rate is strongly dependent 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 a 50 μm-thick multilayer polyimide film, the CTE (MD and TD) of the multilayer polyimide film of Comparative Example 6 was found to be consistent with the CTE of copper foil, 18 ppm / K, and the multilayer polyimide films of Examples 1 to 5 and Comparative Example 1 also had CTEs roughly similar to that of copper foil. However, when the dimensional change rates were compared, the multilayer polyimide films of the Examples showed an extremely small dimensional change rate, whereas the dimensional change rates were large in Comparative Examples 6 and 1. Similarly, when a 75 μm-thick multilayer film was examined, the multilayer polyimide film of Example 6 and the multilayer polyimide film of Comparative Example 9 had the same CTE, but the dimensional change rate of Comparative Example 9 was large. This is thought to be due to the optimization of the heat-resistant polyimide layer (core layer), which has a large effect on the dielectric loss tangent, and the optimization of the heat-fusible polyimide layer (heat-fusible layer) to match the core layer, and is a result that could not be predicted from a conventional CTE-based approach.

[0094] The polyimide film produced from the polyimide precursor solution of the present invention can be suitably used for high frequency compatible FPC applications.

Claims

1. A multilayer polyimide film having a heat-resistant polyimide layer made of a heat-resistant polyimide (PIc), and a heat-fusible polyimide layer made of a heat-fusible polyimide (PIb) laminated on one or both sides of the heat-resistant polyimide layer; the heat-resistant polyimide (PIc) is obtained by reacting a tetracarboxylic acid component (Ac) containing 75 mol % to 100 mol % of 3,3',4,4'-biphenyltetracarboxylic dianhydride and 0 mol % to 25 mol % of pyromellitic dianhydride with a diamine component (Bc) containing 70 mol % to 95 mol % of p-phenylenediamine and 5 mol % to 30 mol % of 2,2'-dimethylbenzidine; the heat-fusible polyimide (PIb) is A multi-layer polyimide film obtained by reacting a tetracarboxylic acid component (Ab) containing 10 mol % or more and 60 mol % or less of 3,3',4,4'-biphenyltetracarboxylic dianhydride and 40 mol % or more and 90 mol % or less of pyromellitic dianhydride with a diamine component (Bb) containing 50 mol % or more of 2,2-bis[4-(4-aminophenoxy)phenyl]propane.

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

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

4. The multilayer polyimide film according to claim 1, wherein the multilayer polyimide film has a dielectric loss tangent of 0.0060 or less, and the polyimide metal laminate has a dimensional change rate (absolute value) of 0.10% or less in the longitudinal direction (MD) and transverse direction (TD) (wherein the dimensional change rate is calculated by measuring the initial dimension (X) of a polyimide metal laminate produced using the multilayer polyimide film and the dimension (Y) after etching the metal foil and then heating the laminate at 250°C for 30 minutes, according to the following formula: Dimensional change rate (%) = (Y - X) / X x 100).

5. A polyimide metal laminate comprising a metal foil laminated on the heat-fusible polyimide layer side of the multilayer polyimide film according to claim 1.

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

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

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