Polyamic acid, polyimide, multilayer polyimide film and flexible metal foil laminate

Abstract

To provide a laminated polyimide film for a flexible printed circuit board that prevents cracking in the inner walls of vias during the process of forming the vias with laser beams.SOLUTION: The foregoing problem is solved by: a polyamide acid which is an adduct of an acid dianhydride and a diamine, the polyamide acid containing a triamine compound with an isocyanuric acid skeleton in an amount of 1 mol% or more and 20 mol% or less based on the total diamine; a polyimide obtained therefrom; a multilayer polyimide film; and a flexible metal foil laminate.SELECTED DRAWING: None

Description

[Technical Field]

[0001] The present invention relates to polyamic acids, polyimides, multilayer polyimide films and flexible metal foil laminates. [Background technology]

[0002] Among flexible printed circuit boards (FPCs) used in tablets, smartphones, and other devices, two-layer flexible printed circuit boards (2-layer FPCs) made of polyimide film are seeing increasing market demand due to their excellent heat resistance. In the manufacturing of these FPCs, copper foil is laminated to both sides of the polyimide film to form a copper-clad laminate. To form circuits, holes (vias) are drilled in the copper-clad laminate and copper-plated on the inner surfaces of the vias to ensure electrical continuity between the top and bottom of the laminate. The via formation process can be performed using either a through-hole method, in which through-holes are drilled in the copper foil on both sides with a drill or laser, or a blind via hole method, in which only the copper foil on one side is etched and the insulating layer is removed with a laser, leaving the copper foil on the other side. The blind via hole method is frequently used, especially for miniaturized FPCs, to efficiently utilize the surface area.

[0003] Furthermore, after via formation, wet desmearing (cleaning with an alkaline potassium permanganate aqueous solution) is often performed to remove and clean any resin residue adhering to the interior of the via and the surface of the copper foil. However, because residual stress accumulates locally in the laser processing area used to form the via, the desmearing process after via formation can cause defects such as cracks and peeling around the via, which is an issue. Patent Document 1 discloses a method of suppressing the occurrence of defects such as cracks by performing heat treatment after laser processing to reduce residual stress, while Patent Document 2 discloses polyimides with improved resistance to alkaline solutions as a countermeasure against the occurrence of defects, but there is still room for further improvement. [Prior art documents] [Patent documents]

[0004] [Patent Document 1] Japanese Patent Application Laid-Open No. 2012-186377 [Patent Document 2] Japanese Patent Application Laid-Open No. 2017-179148 Summary of the Invention [Problem to be solved by the invention]

[0005] The inventors have found that it is preferable to reduce the molecular orientation of the film in order to alleviate the residual stress inside the film that causes cracks, and have conceived the idea of ​​introducing a branched structure into the polyimide chain for this purpose. The problem to be solved by the present invention is to provide a polyimide laminate film that, by applying a polyimide having such a branched structure, suppresses the occurrence of cracks on the inner walls of vias in the process of forming vias in the polyimide laminate film for flexible printed circuit boards using a laser. [Means for solving the problem]

[0006] As a result of extensive investigations to achieve the above, it was discovered that a polyimide laminate film that suppresses cracking on the inner wall of a via after a via formation process using a laser can be obtained by using a polyimide having a branched structure obtained using a triamine compound.

[0007] [1]. A polyamic acid which is an addition reaction product of an acid dianhydride and a diamine, A polyamic acid characterized by containing a compound represented by chemical formula (1) in an amount of 1 mol % to 20 mol % of all diamines. [ka]

[0008] [2] A polyimide comprising an imidized product of the polyamic acid according to [1].

[0009] [3] A polyimide film, which is a film-like product of the polyimide according to [2].

[0010] [4] A multilayer polyimide film having an adhesive layer laminated on at least one side of the polyimide film according to [3].

[0011] [5] The method for producing a multilayer polyimide film according to [4], wherein the adhesive layer is made of a thermoplastic polyimide.

[0012] A flexible metal foil laminate having a metal layer provided on the adhesive layer of the multilayer polyimide film according to [4] or [5]. [Effects of the Invention]

[0013] The present invention provides a polymer having a branched structure, particularly a polyamic acid or polyimide. Furthermore, the polyimide laminate obtained by the present invention can provide a flexible printed circuit board that suppresses cracks on the inner wall of vias that occur during a via formation process by laser processing, without requiring any special modifications to the film production process. DETAILED DESCRIPTION OF THE INVENTION

[0014] In the present invention, it has been discovered that a polyimide film made of a polyimide having a branched structure polymerized using a triamine compound represented by chemical formula (1) can provide a polyimide laminate film that suppresses the occurrence of cracks on the inner wall of a via after a via formation process using a laser. [ka]

[0015] The present invention is characterized by a polyamic acid which is an addition reaction product of an acid dianhydride and a diamine, and which contains a compound represented by chemical formula (1) in an amount of 1 mol % to 20 mol % of all diamines; a polyimide containing an imidized product of the polyamic acid; and a polyimide film which is a film-like product of the polyimide.

[0016] The compound represented by chemical formula (1) is trifunctional, so it can be a branching point in polymer polymerization. This allows for an increased variety of polymers with various branched structures. Details are explained below.

[0017] <About triamine compounds (chemical formula (1))> The triamine compound (1) can be synthesized by any known method, and the following synthesis scheme is an example. The step of obtaining the trinitro compound (1-2) from isocyanuric acid (1-1) can be synthesized by any known method. For example, (1-1) can be dissolved in an appropriate solvent and reacted with a nitrobenzyl compound in the presence of a base to obtain the diamine precursor (1-2).

[0018] As the nitrobenzyl compound, nitrobenzyl chloride, nitrobenzyl bromide, nitrobenzyl iodide, etc. can be used, and can be used in a ratio of 3.0 to 5.0 equivalents relative to the isocyanurate compound (1-1).

[0019] The solvent is not particularly limited as long as it dissolves the raw material (1-1) and the nitrobenzyl compound and does not inhibit the reaction. For example, aprotic polar solvents such as N,N-dimethylformamide, N,N-dimethylacetamide, N-methylpyrrolidone, and dimethyl sulfoxide, and ether solvents such as tetrahydrofuran and 1,4-dioxane can be used.

[0020] The base is not particularly limited, and examples thereof include triethylamine, diisopropylethylamine, pyridine, quinoline, isoquinoline, lutidine, and picoline. Inorganic bases such as sodium carbonate, potassium carbonate, sodium hydroxide, potassium hydroxide, and sodium hydride can also be used. The base can be used in an amount of 3.0 to 6.0 equivalents relative to the substrate (1-1). The reaction temperature is 20°C to 100°C, preferably 40°C to 90°C. The reaction time can be 1 to 24 hours, preferably 2 to 6 hours.

[0021] The desired diamine compound (1) can be obtained by reducing compound (1-2). Any known reduction method can be used for the reduction, but catalytic reduction using hydrogen gas and a metal catalyst is the most common.

[0022] Solvents that can be used in this reduction reaction include aprotic polar solvents such as N,N-dimethylformamide, N,N-dimethylacetamide, and dimethyl sulfoxide; ether solvents such as tetrahydrofuran and 1,4-dioxane; and protic solvents such as methanol, ethanol, and 2-isopropanol.

[0023] As the catalyst, for example, a palladium-based catalyst such as palladium carbon or palladium alumina can be used. The catalyst is preferably added in an amount of 0.5 mol % to 10 mol % relative to the substrate. The reaction temperature is 20°C to 150°C, preferably 20°C to 100°C. The reaction time is 3 hours to 48 hours, preferably 6 hours to 24 hours. The hydrogen gas may be at normal pressure or may be pressurized. After the reaction, the catalyst is filtered off, and the filtrate is concentrated to obtain the product. If necessary, a purification procedure such as recrystallization may be performed.

[0024] Other known reduction methods include the use of metal powders such as tin, zinc, or iron in the presence of an acid such as hydrochloric acid, or the use of tin chloride. Alcoholic solvents such as methanol and ethanol are preferred as the solvent, but if the alcoholic solvent is unable to fully dissolve the substrate, a solvent capable of dissolving the substrate may be used in combination. The reaction temperature is 40°C to 100°C, preferably 50°C to 80°C. The reaction time can be 1 hour to 24 hours, preferably 2 hours to 6 hours.

[0025] After the reaction, the product is extracted with an appropriate organic solvent, washed with water, and concentrated. Purification procedures such as recrystallization may be performed as necessary. This compound contains amino groups and can be suitably used in polymers typically polymerized using (di)amine compounds. While the type of polymer is not particularly limited, examples include polyamides, polyamic acids, polyimides, polyamideimides, polymaleimides, polyureas, polyamines, and polymers containing these as part of the repeating units. It can also be used as a curing agent for epoxy resins. [ka]

[0026] (Polyamic acid, polyimide) Polyamic acid is an addition reaction product of acid dianhydride and diamine, and contains the compound represented by chemical formula (1) in an amount of 1 mol % to 20 mol % of the total diamine. [ka]

[0027] The compound represented by chemical formula (1) is a triamine, but is calculated as a type of diamine and comprises 1 mol % to 20 mol % of the total diamines, preferably 1 mol % to 15 mol %, more preferably 3 mol % to 10 mol %, and even more preferably 5 mol % to 10 mol %. If the amount of the compound represented by chemical formula (1) is less than the above range, the effect of suppressing crack generation may be small, and if the amount of the compound represented by chemical formula (1) is more than the above range, the resulting polyamic acid solution may be prone to gelation.

[0028] First, we will explain the polymerization of polyamic acid (polyimide precursor). Any known method can be used to polymerize polyamic acid. Typically, a solution of substantially equimolar amounts of aromatic acid dianhydride and aromatic diamine dissolved in an organic solvent is stirred under controlled temperature conditions until polymerization of the acid dianhydride and diamine is complete, yielding a polyamic acid solution, which is a polyimide precursor. This polyamic acid is then imidized using known imidization techniques to obtain a polyimide. The polyamic acid solution is typically obtained at a concentration of 5 to 35% by weight, preferably 10 to 30% by weight. A concentration within this range ensures appropriate molecular weight and solution viscosity.

[0029] Representative methods for adding monomers in polymerization include: 1) dissolving an aromatic diamine in an organic polar solvent and reacting it with a substantially equimolar amount of aromatic tetracarboxylic dianhydride to polymerize; 2) reacting an aromatic tetracarboxylic dianhydride with a molar excess of an aromatic diamine compound in an organic polar solvent to obtain a prepolymer having acid anhydride groups at both ends, followed by polymerization using an aromatic diamine compound so that the aromatic tetracarboxylic dianhydride and aromatic diamine compound are substantially equimolar throughout all steps; and 3) reacting an aromatic tetracarboxylic dianhydride with a molar excess of an aromatic diamine compound in an organic polar solvent to obtain a prepolymer having amino groups at both ends. Subsequently, an aromatic diamine compound is further added thereto, and then polymerization is carried out using an aromatic tetracarboxylic dianhydride so that the aromatic tetracarboxylic dianhydride and the aromatic diamine compound are substantially equimolar throughout all steps; 4) a method in which an aromatic tetracarboxylic dianhydride is dissolved and / or dispersed in an organic polar solvent, and then polymerization is carried out using an aromatic diamine compound so that the aromatic tetracarboxylic dianhydride and the aromatic diamine compound are substantially equimolar; and 5) a method in which a mixture of substantially equimolar aromatic tetracarboxylic dianhydride and aromatic diamine is reacted in an organic polar solvent to polymerize. These methods may be used alone or in combination.

[0030] The order of addition of the diamine and acid dianhydride raw materials is not particularly limited, and the properties of the resulting polyamic acid and / or polyimide can be controlled not only by controlling the chemical structure of the raw materials but also by controlling the order of addition.

[0031] The order of addition of the triamine compound (1) is not particularly limited, and it can be added at the same timing as the above diamine.

[0032] (diamine) In the present invention, the diamine monomer to be used is not particularly limited, but in particular, as a film material to be used for a polyimide laminate film for a flexible printed circuit board, it is preferable to contain a rigid structure such as a biphenyl structure or a phenyl structure in the polymer molecule from the viewpoint of dimensional stability, etc. Furthermore, a biphenyl structure is less symmetrical than a phenyl structure, and a decrease in the symmetry of the polymer primary structure inhibits molecular packing, resulting in a decrease in the elastic modulus when softened above a certain temperature, making it more preferable from the viewpoint of stress relaxation.

[0033] Specific examples of diamine monomers having a biphenyl structure include 4,4'-diamino-2,2'-dimethylbiphenyl, 4,4'-diaminobiphenyl, 4,4'-diamino-2,2'-dimethylbiphenyl, 4,4'-diamino-3,3'-dimethylbiphenyl, 4,4'-diamino-2,2'-dimethoxybiphenyl, 4,4'-diamino-3,3'-dimethoxybiphenyl, 3,3',5,5'-tetramethylbenzidine, and 4,4'-bis(4-aminophenoxy)biphenyl. However, 4,4'-diaminobiphenyl and 4,4'-diamino-3,3'-dimethylbiphenyl are carcinogenic to humans and therefore are not recommended for practical use. 4,4'-diamino-2,2'-dimethylbiphenyl is particularly preferred for practical use.

[0034] Furthermore, among the 100% diamine monomer components constituting the multilayer polyimide film (wherein triamine compound (1) is also counted as a type of diamine), the more rigid monomer components there are, the lower the linear expansion coefficient due to the formation of an aggregate structure, and the more effective the film is for excellent dimensional stability. However, if the content is too high, the linear expansion coefficient of the resulting film becomes too low, which is undesirable. The optimum content for a film for flexible printed circuit boards is preferably 10 to 50 mol%, more preferably 15 to 40 mol%, and even more preferably 20 to 35 mol%. Other diamine monomers used are preferably aromatic diamines with high heat resistance. For example, 4,4'-diaminodiphenyl ether, 3,4'-diaminodiphenyl ether, 1,3-bis(4-aminophenoxy)benzene, 1,4-bis(4-aminophenoxy)benzene, 4,4'-diaminodiphenylpropane, 4,4'-diaminodiphenylmethane, benzidine, 3,3'-dichlorobenzidine, 4,4'-diaminodiphenyl sulfide, 3,3'-diaminodiphenyl sulfone, 4,4'-diaminodiphenyl sulfone, 4,4'-diaminodiphenyl ether, 3,3'-diaminodiphenyl ether, 3,4'-diaminodiphenyl ether, 1,5-diaminonaphthalene, 4,4'-diaminodiphenyldiethylsilane, 4,4'-diaminodiphenylsilane, 4,4'-diaminodiphenylethylphosphine oxide, 4,4'-diaminodiphenyl N-methylamine, 4,4'-diaminodiphenyl Examples of the diamine include N-phenylamine, 1,4-diaminobenzene (p-phenylenediamine), 1,3-diaminobenzene, and 1,2-diaminobenzene. The content of the other diamine used is preferably 50 to 90 mol %, more preferably 60 to 85 mol %, and even more preferably 65 to 80 mol %.

[0035] It is preferable to use a combination of 4,4'-diaminodiphenyl ether and paraphenylenediamine, as this allows adjustment of the flexibility of the polymer while maintaining high heat resistance. In this case, the content of 4,4'-diaminodiphenyl ether is preferably 40 to 70 mol%, more preferably 45 to 65 mol%, and even more preferably 50 to 65 mol%, and the content of paraphenylenediamine is preferably 10 to 50 mol%, more preferably 15 to 40 mol%, and even more preferably 15 to 30 mol%.

[0036] (acid dianhydride) In the present invention, any acid dianhydride can be used as a monomer, but as the acid dianhydride monomer used in the polyimide film, an aromatic acid dianhydride is preferred from the viewpoint of heat resistance, etc., and for the same reason as above, it is more preferred that the dianhydride monomer has a certain proportion of a biphenyl structure. For example, pyromellitic dianhydride, 2,3,6,7-naphthalenetetracarboxylic dianhydride, 3,3',4,4'-biphenyltetracarboxylic dianhydride, 1,2,5,6-naphthalenetetracarboxylic dianhydride, 2,2',3,3'-biphenyltetracarboxylic dianhydride, 3,3',4,4'-benzophenonetetracarboxylic dianhydride, 2,2',3,3'-benzophenonetetracarboxylic dianhydride, 4,4'-oxyphthalic dianhydride, 3,4'-oxyphthalic dianhydride, 2,2-bis(3,4-dicarboxyphenyl)propanoic dianhydride, 3,4,9,10-perylenetetracarboxylic dianhydride, bis(3, 4-dicarboxyphenyl)propanoic dianhydride, 1,1-bis(2,3-dicarboxyphenyl)ethanoic dianhydride, 1,1-bis(3,4-dicarboxyphenyl)ethanoic dianhydride, bis(2,3-dicarboxyphenyl)methaneic dianhydride, bis(3,4-dicarboxyphenyl)ethanoic dianhydride, oxydiphthalic dianhydride, bis(3,4-dicarboxyphenyl)sulfonic dianhydride, p-phenylene bis(trimellitic acid monoester acid anhydride), ethylene bis(trimellitic acid monoester acid anhydride), bisphenol A bis(trimellitic acid monoester acid anhydride), and the like.

[0037] Since the multilayer polyimide film of the present invention is required to have high heat resistance, 3,3',4,4'-biphenyltetracarboxylic dianhydride or pyromellitic dianhydride is preferably used, and 3,3',4,4'-biphenyltetracarboxylic dianhydride is more preferred because it contains a biphenyl structure. Of the 100% acid dianhydride monomer components constituting the polyimide film, the 3,3',4,4'-biphenyltetracarboxylic dianhydride content is preferably 20 to 60 mol%, more preferably 25 to 55 mol%, and even more preferably 30 to 50 mol%. When pyromellitic dianhydride is included, of the 100% acid dianhydride monomer components constituting the polyimide film, the content of pyromellitic dianhydride is preferably 40 to 80 mol%, more preferably 35 to 75 mol%, and even more preferably 50 to 70 mol%.

[0038] (Polymerization solvent) The solvent used in polyimide polymerization is not particularly limited, but is required to be one that does not react with diamines or acid dianhydrides and can dissolve polyamic acid. For example, amide-based solvents that have high solubility for polyamic acid, such as 1-methylpyrrolidone, N,N-diethylformamide, N,N-dimethylacetamide, N-methyl-2-pyrrolidone, 1,3-dimethyl-2-imidazolidinone, 3-methoxy-N,N-dimethylpropanamide, and 3-methoxy-N,N-dibutylpropanamide, are preferred. One or more amide-based solvents selected from 1-methylpyrrolidone, N,N-dimethylformamide, and N,N-dimethylacetamide are preferred. These solvents are typically used alone or in combination as needed. From the standpoint of solubility and polymerizability, one or more amide-based solvents selected from 1-methylpyrrolidone, N,N-diethylformamide, and N,N-dimethylacetamide are preferred. Two or more solvents can also be mixed and used as needed. The method for mixing the solvents is not particularly limited.

[0039] (imidization) Generally, polyimides are obtained by a dehydration conversion reaction (dehydration ring-closing reaction) from a polyimide precursor, i.e., polyamic acid. The two most widely known methods for this conversion reaction are a thermal curing method using only heat and a chemical curing method using a chemical curing agent. Of these, the chemical curing method using a chemical curing agent improves productivity and ensures the mechanical strength of the film. Either method may be used in the present invention. However, the chemical curing method is particularly preferred for achieving rapid drying. In this case, a dehydration agent and an imidization catalyst are added to the polyimide precursor solution immediately before film formation.

[0040] Here, the chemical curing agent includes a dehydrating agent and an imidization catalyst. The dehydrating agent is a dehydrating ring-closing agent for polyamic acid, and aliphatic acid anhydrides, aromatic acid anhydrides, N,N'-dialkylcarbodiimides, lower aliphatic halides, halogenated lower aliphatic acid anhydrides, arylsulfonic acid dihalides, thionyl halides, or mixtures of two or more thereof are preferably used. Among these, aliphatic acid anhydrides and aromatic acid anhydrides work better. Acetic anhydride is particularly preferred. The suitable amount of dehydrating agent to be introduced is 0.5 to 4.0 mol, preferably 0.7 to 4.0 mol, and particularly preferably 1.0 to 4.0 mol per mol of amic acid units in the polyamic acid contained in the solution. If the amount exceeds this range, the conductor may corrode. If the amount is below this range, the curing rate may be insufficient, and the effects of the present invention may not be achieved.

[0041] The imidization catalyst is a component that promotes the dehydration ring-closure reaction of the curing agent with the polyamic acid. Examples of suitable catalysts include aliphatic tertiary amines, aromatic tertiary amines, and heterocyclic tertiary amines. Among these, nitrogen-containing heterocyclic compounds such as pyridine, imidazole, benzimidazole, isoquinoline, quinoline, and pyridine compounds substituted with alkyl groups at the β- and / or γ-positions are preferred. Pyridine, isoquinoline, and pyridine compounds substituted with alkyl groups at the β- and / or γ-positions are particularly preferred. The suitable amount of imidization catalyst is 0.05 to 2.0 mol, preferably 0.1 to 2.0 mol, and particularly preferably 0.2 to 2.0 mol, per mol of amic acid units in the polyamic acid contained in the solution containing the imidization catalyst. If the amount exceeds this range, the imidization catalyst may remain in the polyimide layer, resulting in poor long-term heat resistance. If the amount is below this range, the curing rate may be insufficient, and the effects of the present invention may not be achieved.

[0042] Furthermore, an organic polar solvent may be appropriately added to the chemical curing agent solution containing the dehydration agent and the imidization catalyst. The type and amount of this organic polar solvent are not particularly limited, but it is necessary that the polyamic acid not precipitate when mixed with the chemical curing agent solution. Therefore, for example, N,N-dimethylformamide, N,N-dimethylacetamide, N-methyl-2-pyrrolidone, 1,3-dimethyl-2-imidazolidinone, 3-methoxy-N,N-dimethylpropanamide, and 3-methoxy-N,N-dibutylpropanamide, which dissolve polyamic acid well, are preferably used. 1-Methylpyrrolidone, N,N-dimethylformamide, and N,N-dimethylacetamide are preferred.

[0043] (Method of manufacturing (multilayer) polyimide film) The (multilayer) polyimide film of the present invention can be obtained by the following steps: i) reacting a diamine and an acid dianhydride in an organic solvent to obtain a polyamic acid solution, ii) casting a film-forming dope containing the polyamic acid solution onto a support, iii) heating the film on the support and then peeling the gel film from the support, and iv) further heating to imidize the remaining polyamic acid and drying to produce a non-thermoplastic polyimide film, which is then used as a non-thermoplastic polyimide layer and provided with an adhesive layer by coating or the like on at least one side of the non-thermoplastic polyimide film. Alternatively, in step ii), a co-extrusion die having multiple flow channels may be used to cast and coat a solution containing a polyimide resin precursor for forming the non-thermoplastic polyimide layer and a solution containing a polyimide resin precursor for forming the adhesive layer onto a support, thereby simultaneously forming multiple resin layers (co-extrusion casting and coating method).

[0044] (Adhesive layer) The polyamic acid solution, which is a precursor of polyimide, used in the adhesive layer of the present invention can be produced by the same method as described for (Polyamic Acid). In addition to polyamic acid and polyimide resin, the adhesive layer may contain thermosetting resins such as epoxy resins and phenoxy resins, and thermoplastic resins such as polyether ketones and polyether ether ketones, as long as the dielectric properties and adhesive properties are not impaired. However, thermoplastic polyimides are preferred.

[0045] The diamine and tetracarboxylic dianhydride components used in the polyamic acid, which is the precursor of the thermoplastic polyimide suitable for use in the adhesive layer, include the same diamine and tetracarboxylic dianhydride components as those exemplified for the polyimide layer. However, to obtain a thermoplastic polyimide film, it is preferable to react a flexible diamine with an acid dianhydride. Examples of flexible diamines include 4,4'-diaminodiphenyl ether, 4,4'-bis(4-aminophenoxy)biphenyl, 4,4'-bis(3-aminophenoxy)biphenyl, 1,3-bis(3-aminophenoxy)benzene, 1,3-bis(4-aminophenoxy)benzene, and 2,2-bis(4-aminophenoxyphenyl)propane. Examples of acid dianhydrides that can be suitably combined with these diamines include pyromellitic dianhydride, 3,3',4,4'-benzophenonetetracarboxylic dianhydride, 3,3',4,4'-biphenyltetracarboxylic dianhydride, 4,4'-oxydiphthalic dianhydride, and pyromellitic dianhydride.

[0046] The polyamic acid, which is the precursor of the polyimide contained in the adhesive layer, is obtained by mixing and reacting at least one diamine and at least one acid dianhydride in an organic solvent in a substantially equimolar ratio. To impart softening properties sufficient to function as an adhesive layer, it is possible to adjust the thickness by using a diamine or acid dianhydride with a flexible structure. It is more preferable to use a single polyimide resin in the adhesive layer rather than a mixture of two or more polyimide resins. The thickness of the multilayer polyimide film of the present invention is preferably 12.5 μm or more. There is no particular upper limit to the thickness of the multilayer polyimide film, but considering the ease of production and productivity of the multilayer polyimide film, it is preferably 50 μm or less.

[0047] (flexible metal foil laminate) The multilayer polyimide film obtained as described above can be made into a flexible metal foil laminate by providing a metal foil on at least one side of the multilayer polyimide film. Examples of means for forming a metal foil on a multilayer polyimide film include the following a) and b). a) After obtaining a multilayer polyimide film as described above, a metal foil is laminated onto the multilayer polyimide film by heating and pressing to obtain a flexible metal foil laminate. b) A method of casting an organic solvent solution containing polyamic acid onto a metal foil, removing the solvent by heating, and carrying out imidization to obtain a flexible metal foil laminate.

[0048] Details of a) and b) are explained below. In the method a), a metal foil is laminated to the obtained multilayer polyimide film by heating and pressing (laminating), thereby obtaining the flexible metal foil laminate of the present invention. The means and conditions for laminating the metal foil may be appropriately selected from those known in the art.

[0049] In the method (b), the means for casting the organic solvent solution containing the polyamic acid onto the metal foil is not particularly limited, and conventionally known means such as a die coater, a comma coater (registered trademark), a reverse coater, or a knife coater can be used. To produce the flexible metal-clad laminate of the present invention, a solution containing a polyimide resin precursor for forming the adhesive layer is cast onto the metal foil, heated and dried to remove the solvent, and then a solution containing a polyimide resin precursor for forming the non-thermoplastic polyimide layer is cast onto the metal foil, heated and dried to remove the solvent. After forming the multilayer polyamic acid layer in this manner, the multilayer polyamic acid layer is heated and imidized to produce a flexible metal-clad laminate. The above-described process is repeated depending on the number of layers, such as by providing additional adhesive layers, to form a multilayer polyamic acid layer, which is then heated and imidized to obtain a flexible metal-clad laminate. Conventional heating means for solvent removal and imidization can also be used, such as a hot air oven or a far-infrared oven.

[0050] When metal foil layers are provided on both sides of the resin layer, the metal foil-free surfaces of two single-sided flexible metal-clad laminates may be bonded together by applying heat and pressure, preferably via a thermoplastic polyimide layer.

[0051] The metal foil that can be used is not particularly limited, but when the flexible metal-clad laminate of the present invention is used for electronic or electrical equipment applications, examples include foils made of copper or copper alloys, stainless steel or its alloys, nickel or nickel alloys (including 42 alloy), and aluminum or aluminum alloys. Copper foils such as rolled copper foils and electrolytic copper foils are commonly used in general flexible laminates, and they can also be preferably used in the present invention. The surface of these metal foils may be coated with an anti-corrosion layer, a heat-resistant layer, or an adhesive layer. The thickness of the metal foil is not particularly limited, as long as it is thick enough to perform its functions appropriately depending on the application. A flexible printed circuit board can be obtained by etching the metal layer of the flexible metal-clad laminate obtained in this manner using a known method.

[0052] (Via formation process using laser processing) In flexible PCB manufacturing, vias can be formed in copper-clad laminates by laser processing. Irradiating the processed area with a laser penetrates the substrate, forming through-holes (THs) or blind via holes (BVHs), removing only the top copper foil and polyimide resin. Known laser types can be used. Short-wavelength lasers such as UV-YAG lasers and excimer lasers are preferred because they exhibit high absorption rates for both resin and copper, enabling processing. Direct drilling of through-holes is also widely used for THs. Meanwhile, desmearing is performed to remove resin debris generated during processing. A typical wet desmear process involves a swelling step using an alkaline aqueous solution or a solution containing an organic solvent, a roughening step using an alkaline aqueous solution such as sodium permanganate or potassium permanganate, and a neutralization step. Cracks on the inner wall of holes that occur during processing of copper-clad laminates using polyimide laminate films often occur on the inner wall of the holes after desmearing. Longer swelling and roughening times during desmearing increase the likelihood of cracks. Furthermore, metal plating of the inside of the holes after desmearing creates vias. There are no particular limitations as long as it is a general metal plating, but a plating layer of the desired thickness may be formed by electroless copper plating alone, or a thin electroless copper plating layer may be formed first, followed by electrolytic copper plating to form a plating layer of the desired thickness.

[0053] (Hole crack test: crack evaluation method) Cracks that occur on the inner walls of vias during FPC manufacturing are usually detected by visual inspection or other methods after FPC manufacturing. The inventors discovered that the occurrence of cracks on the inner walls of vias during the FPC manufacturing process can be easily evaluated by cutting test pieces from the long flexible metal-clad laminate used as the raw material and performing a hole crack test to evaluate cracks that occur on the inner walls of holes during the via formation process, from laser processing to desmearing. This evaluation method involves etching the copper foil of the test piece after desmearing, and observing the test piece with a polarized microscope under crossed Nicols to confirm the presence or absence of cracks on the inner walls of the vias. By combining this with polarized microscope observation, it was confirmed that cracks on the inner walls of the vias are detected as light leakage. [Example]

[0054] The present invention will be specifically described below with reference to examples, but is not limited to these examples.

[0055] (Hole crack test) A 12 μm thick electrolytic copper foil (3EC-M3S-HTE, manufactured by Mitsui Metals) was placed on each side of the polyimide film laminate obtained in the following Examples and Comparative Examples. Protective films (Apical 125NPI, manufactured by Kaneka, thickness 125 μm) were then placed on both sides of the copper foil, and thermal lamination was performed under conditions of a lamination temperature of 360°C, a lamination pressure of 265 N / cm (27 kgf / cm), and a lamination speed of 1.0 m / min to produce a flexible metal-clad laminate.

[0056] Next, the flexible metal-clad laminate was cut into a square measuring 5.0 cm x 20.0 cm, and blind via holes with a diameter of 100 μm were laser processed using a UV-YAG laser according to the process in Table 1. For each condition, a pattern of 10 holes in each row was formed at 1 mm intervals (100 holes each). After laser processing, a desmearing process was carried out according to the process in Table 2.

[0057] After removing the copper foil by etching, the specimens were observed under a polarizing microscope at a magnification of 200x under crossed Nicols. Any holes through which light leaked were considered to be cracks. After observing 100 specimens, the percentage of specimens that had cracks was calculated. [Table 1] [Table 2]

[0058] (Synthesis Example of Triamine Compound (1)) Under a nitrogen atmosphere, g (0.20 mol) of isocyanuric acid, g (0.66 mol) of 4-nitrobenzyl chloride, and 500 mL of tetrahydrofuran were placed in a 2 L flask equipped with a thermometer and a propeller, and the reaction solution was heated to 70°C. The reaction solution was thoroughly stirred, and 66.8 g (0.66 mol) of triethylamine was slowly added dropwise thereto while taking care to avoid a sudden rise in temperature. After completion of the addition, the mixture was stirred at 70°C for 3 hours.

[0059] After cooling, the mixture was concentrated to dryness under reduced pressure. 1 L of water was added to the concentrated solid and washed. This washing procedure was repeated two more times to obtain a solid. Recrystallization was performed using a mixed solvent of ethyl acetate and hexane to obtain 1,3,5-tris[(4-nitrophenyl)methyl]isocyanurate. Next, 14.5 g of the 1,3,5-tris[(4-nitrophenyl)methyl]isocyanurate synthesized above, 86 g of tin chloride dihydrate, and 400 mL of ethanol were added to a 2 L flask equipped with a thermometer and a propeller, and the reaction was carried out with stirring at 70 °C for 1 hour. After completion of the reaction, the mixture was neutralized with saturated aqueous sodium bicarbonate, and ethyl acetate was added and stirred. The reaction solution was filtered to remove precipitated tin salts. The organic layer was washed with water, and the concentrated solid was recrystallized from ethanol to obtain 1,3,5-tris[(4-aminophenyl)methyl]isocyanurate (triamine compound (1)).

[0060] (Synthesis of non-thermoplastic polyamic acid (polyimide precursor)) (Synthesis Example 1) A 2000 ml glass flask was charged with 334.13 g of N,N-dimethylformamide (DMF) and 17.70 g of 4,4'-diaminodiphenyl ether (ODA). Under a nitrogen atmosphere, 18.01 g of 3,3',4,4'-biphenyltetracarboxylic dianhydride (BPDA) was gradually added with stirring at room temperature. After visually confirming that the BPDA had dissolved, 7.79 g of pyromellitic dianhydride (PMDA) was gradually added. After visually confirming that the PMDA had dissolved, the mixture was stirred for 30 minutes. The mixture was then cooled on ice and 5.78 g of 4'-diamino-2,2'-dimethylbiphenyl (m-TB), 6.52 g of p-phenylenediamine (PDA), 2.42 g of triamine (1), and 11.85 g of PMDA were added. The mixture was then stirred for 30 minutes. Finally, 0.46 g of PMDA was added to a DMF solution to a solids concentration of 7.2%. The solution was gradually added to the reaction solution. When the viscosity at 23°C reached 2500 poise, the addition was stopped to obtain non-thermoplastic polyimide precursor A (containing 3 mol % of the compound represented by formula (1) in total diamines).

[0061] (Synthesis Example 2) A 2000 ml glass flask was charged with 334.13 g of DMF and 17.70 g of ODA. Under a nitrogen atmosphere, 18.01 g of BPDA was gradually added with stirring at room temperature. After visually confirming that the BPDA had dissolved, 7.79 g of pyromellitic dianhydride (PMDA) was gradually added. After visually confirming that the PMDA had dissolved, the mixture was stirred for 30 minutes. The mixture was then cooled on ice and 5.78 g of m-TB, 6.12 g of PDA, 4.30 g of triamine (1), and 11.85 g of PMDA were added, followed by stirring for 30 minutes. Finally, 0.46 g of PMDA was added to the DMF solution to a solids concentration of 7.2%. The addition was stopped when the viscosity at 23°C reached 2000 poise, yielding non-thermoplastic polyimide precursor B (containing 5 mol% of the compound represented by formula (1) relative to the total diamine content).

[0062] (Synthesis Example 3) A 2000 ml glass flask was charged with 334.13 g of DMF and 17.70 g of ODA. Under a nitrogen atmosphere, 18.01 g of BPDA was gradually added with stirring at room temperature. After visually confirming that the BPDA had dissolved, 7.79 g of PMDA was gradually added. After visually confirming that the PMDA had dissolved, the mixture was stirred for 30 minutes. The mixture was then cooled on ice and 5.78 g of m-TB, 5.74 g of PDA, and 5.64 g (12.7 mmol) of triamine (1) were added, followed by 11.85 g of PMDA. The mixture was then stirred for 30 minutes. Finally, 0.46 g of PMDA was added to a DMF solution adjusted to a solids concentration of 7.2%. The addition was stopped when the viscosity at 23 °C reached 2500 poise, yielding non-thermoplastic polyimide precursor C (containing 7 mol% of the compound represented by formula (1) relative to the total diamine content).

[0063] (Synthesis Example 4) A 2000 ml glass flask was charged with 334.13 g of DMF and 17.70 g of ODA. Under a nitrogen atmosphere, 18.01 g of BPDA was gradually added with stirring at room temperature. After visually confirming that the BPDA had dissolved, 7.79 g of PMDA was gradually added. After visually confirming that the PMDA had dissolved, the mixture was stirred for 30 minutes. The mixture was then cooled on ice and 5.78 g of m-TB, 5.15 g of PDA, 8.06 g (18.1 mmol) of triamine (1), and 11.85 g of PMDA were added. The mixture was then stirred for 30 minutes. Finally, 0.46 g of PMDA was added to the DMF solution to a solids concentration of 7.2%. The addition was stopped when the viscosity at 23 °C reached 2500 poise, yielding non-thermoplastic polyimide precursor D (containing 10 mol% of the compound represented by formula (1) relative to the total diamine content).

[0064] (Synthesis Example 5) A 2000 ml glass flask was charged with 334.13 g of DMF, 2.42 g of triamine (1), and 17.70 g of ODA. Under a nitrogen atmosphere, 18.01 g of BPDA was gradually added with stirring at room temperature. After visually confirming that the BPDA had dissolved, 7.79 g of PMDA was gradually added. After visually confirming that the PMDA had dissolved, the mixture was stirred for 30 minutes. The mixture was then cooled on ice and 5.78 g of m-TB was added, followed by 6.52 g of PDA, followed by 11.85 g of PMDA, and stirred for 30 minutes. Finally, 0.46 g of PMDA was added to the DMF solution to a solids concentration of 7.2%. The addition was stopped when the viscosity at 23°C reached 2500 poise, yielding non-thermoplastic polyimide precursor E (containing 3 mol% of the compound represented by formula (1) relative to the total diamine content).

[0065] (Synthesis Example 6) A 2000 ml glass flask was charged with 334.13 g of DMF and 17.70 g of ODA. Under a nitrogen atmosphere, 18.01 g of BPDA was gradually added while stirring at room temperature. After visually confirming that the BPDA had dissolved, 7.79 g of PMDA was gradually added. After visually confirming that the PMDA had dissolved, the mixture was stirred for 30 minutes. The mixture was then cooled on ice and 5.78 g of m-TB was added, followed by 7.11 g of PDA, followed by 11.85 g of PMDA, and stirred for 30 minutes. Finally, 0.46 g of PMDA was added to a DMF solution adjusted to a solids concentration of 7.2%. The addition was stopped when the viscosity at 23 °C reached 2500 poise, yielding non-thermoplastic polyimide precursor F.

[0066] (Synthesis Example 7) A 2000 ml glass flask was charged with 334.13 g of DMF and 17.70 g of ODA. Under a nitrogen atmosphere, 18.01 g of BPDA was gradually added with stirring at room temperature. After visually confirming that the BPDA had dissolved, 7.79 g of PMDA was gradually added. After visually confirming that the PMDA had dissolved, the mixture was stirred for 30 minutes. The mixture was then cooled on ice and 5.78 g of m-TB, 6.12 g of PDA, and 1.14 g of melamine were added, followed by 11.85 g of PMDA, followed by stirring for 30 minutes. Finally, 0.46 g of PMDA was added to a DMF solution adjusted to a solids concentration of 7.2%. This was gradually added to the reaction solution. The addition was stopped when the viscosity at 23 °C reached 2000 poise, yielding non-thermoplastic polyimide precursor G.

[0067] (Synthesis Example 8) A 2000 ml glass flask was charged with 334.13 g of DMF and 17.70 g of ODA. Under a nitrogen atmosphere, 18.01 g of BPDA was gradually added with stirring at room temperature. After visually confirming that the BPDA had dissolved, 7.79 g of PMDA was gradually added. After visually confirming that the PMDA had dissolved, the mixture was stirred for 30 minutes. The mixture was then cooled on ice and 5.78 g of m-TB, 5.15 g of PDA, 2.28 g of melamine, and 11.85 g of PMDA were added. The mixture was then stirred for 30 minutes. Finally, 0.46 g of PMDA was added to a DMF solution adjusted to a solids concentration of 7.2%. The DMF solution was gradually added to the reaction solution. The addition was stopped when the viscosity at 23 °C reached 2500 poise, yielding non-thermoplastic polyimide precursor H.

[0068] (Synthesis of thermoplastic polyamic acid (polyimide precursor) that constitutes the adhesive layer) (Synthesis Example 9) A 2000 ml glass flask was charged with 673.24 g of DMF and 71.83 g of 2,2-bis[4-(4-aminophenoxy)phenyl]propane (BAPP). Under a nitrogen atmosphere, 7.72 g of BPDA was gradually added with stirring at room temperature. After visually confirming that the BPDA had dissolved, 31.30 g of PMDA was added and the mixture was stirred for 30 minutes. Finally, 1.15 g of PMDA was dissolved in DMF to prepare a 7.2% solids solution. This solution was gradually added to the reaction mixture, stopping the addition when the viscosity at 23 °C reached 200 poise, yielding Thermoplastic Polyimide Precursor I.

[0069] Example 1 In a 500 mL separable flask, 65 g of the non-thermoplastic polyimide precursor A obtained in Synthesis Example 1 was added with 32.5 g of a curing agent consisting of acetic anhydride / isoquinoline / DMF (weight ratio 11.48 / 3.40 / 18.18). The mixture was stirred and degassed at temperatures below 0°C and then coated onto aluminum foil using a comma coater. The resulting resin film was heated at 115°C for 100 seconds, after which the self-supporting gel film was peeled off the aluminum foil and fixed to a metal frame. The film was then imidized at 250°C for 15 seconds and 350°C for 79 seconds to obtain a 17 μm-thick polyimide film. This film was also fixed to a metal frame and heated at 450°C for 2 minutes, retaining its shape, confirming its non-thermoplasticity.

[0070] Next, a solution of the thermoplastic polyimide precursor I obtained in Synthesis Example 9 diluted with DMF to a solids concentration of 8 wt% was applied to both sides of the non-thermoplastic polyimide film obtained above so that the final thickness per side was 4 μm. The film was then heated at 120°C for 2 minutes. This was followed by heating and imidization at 350°C for 15 seconds to obtain a polyimide laminate film.

[0071] Example 2 In a 500 mL separable flask, 65 g of the non-thermoplastic polyimide precursor B obtained in Synthesis Example 2 was added with 32.5 g of a curing agent consisting of acetic anhydride / isoquinoline / DMF (weight ratio 11.48 / 3.40 / 18.18). The mixture was stirred and degassed at temperatures below 0°C and then coated onto aluminum foil using a comma coater. The resulting resin film was heated at 115°C for 100 seconds, after which the self-supporting gel film was peeled off the aluminum foil and fixed to a metal frame. The film was then imidized at 250°C for 15 seconds and 350°C for 79 seconds to obtain a 17 μm-thick polyimide film. This film retained its shape after being fixed to a metal frame and heated at 450°C for 2 minutes, confirming its non-thermoplasticity.

[0072] Next, a solution of the thermoplastic polyimide precursor I obtained in Synthesis Example 9 diluted with DMF to a solids concentration of 8 wt% was applied to both sides of the non-thermoplastic polyimide film obtained above so that the final thickness per side was 4 μm. The film was then heated at 120°C for 2 minutes. This was followed by heating and imidization at 350°C for 15 seconds to obtain a polyimide laminate film.

[0073] Example 3 In a 500 mL separable flask, 65 g of the non-thermoplastic polyimide precursor C obtained in Synthesis Example 3 was added with 32.5 g of a curing agent consisting of acetic anhydride / isoquinoline / DMF (weight ratio 11.48 / 3.40 / 18.18). The mixture was stirred and degassed at temperatures below 0°C and then coated onto aluminum foil using a comma coater. The resulting resin film was heated at 115°C for 100 seconds, after which the self-supporting gel film was peeled off the aluminum foil and fixed to a metal frame. The film was then imidized at 250°C for 15 seconds and 350°C for 79 seconds to obtain a 17 μm-thick polyimide film. This film retained its shape after being fixed to a metal frame and heated at 450°C for 2 minutes, confirming its non-thermoplasticity.

[0074] Next, a solution of the thermoplastic polyimide precursor I obtained in Synthesis Example 9 diluted with DMF to a solids concentration of 8 wt% was applied to both sides of the non-thermoplastic polyimide film obtained above so that the final thickness per side was 4 μm. The film was then heated at 120°C for 2 minutes. This was followed by heating and imidization at 350°C for 15 seconds to obtain a polyimide laminate film.

[0075] Example 4 In a 500 mL separable flask, 65 g of the non-thermoplastic polyimide precursor D obtained in Synthesis Example 4 was added with 32.5 g of a curing agent consisting of acetic anhydride / isoquinoline / DMF (weight ratio 11.48 / 3.40 / 18.18). The mixture was stirred and degassed at temperatures below 0°C and then coated onto aluminum foil using a comma coater. The resulting resin film was heated at 115°C for 100 seconds, after which the self-supporting gel film was peeled off the aluminum foil and fixed to a metal frame. The film was then imidized at 250°C for 15 seconds and 350°C for 79 seconds to obtain a 17 μm-thick polyimide film. This film retained its shape after being fixed to a metal frame and heated at 450°C for 2 minutes, confirming its non-thermoplasticity.

[0076] Next, a solution of the thermoplastic polyimide precursor I obtained in Synthesis Example 9 diluted with DMF to a solids concentration of 8 wt% was applied to both sides of the non-thermoplastic polyimide film obtained above so that the final thickness per side was 4 μm. The film was then heated at 120°C for 2 minutes. This was followed by heating and imidization at 350°C for 15 seconds to obtain a polyimide laminate film.

[0077] Example 5 In a 500 mL separable flask, 65 g of the non-thermoplastic polyimide precursor E obtained in Synthesis Example 5 was added with 32.5 g of a curing agent consisting of acetic anhydride / isoquinoline / DMF (weight ratio 11.48 / 3.40 / 18.18). The mixture was stirred and degassed at temperatures below 0°C and then coated onto aluminum foil using a comma coater. The resulting resin film was heated at 115°C for 100 seconds, after which the self-supporting gel film was peeled off the aluminum foil and fixed to a metal frame. The film was then imidized at 250°C for 15 seconds and 350°C for 79 seconds to obtain a 17 μm-thick polyimide film. This film was also fixed to a metal frame and heated at 450°C for 2 minutes, retaining its shape, confirming its non-thermoplasticity.

[0078] Next, a solution of the thermoplastic polyimide precursor I obtained in Synthesis Example 9 diluted with DMF to a solids concentration of 8 wt% was applied to both sides of the non-thermoplastic polyimide film obtained above so that the final thickness per side was 4 μm. The film was then heated at 120°C for 2 minutes. This was followed by heating and imidization at 350°C for 15 seconds to obtain a polyimide laminate film.

[0079] (Comparative Example 1) In a 500 mL separable flask, 65 g of the non-thermoplastic polyimide precursor F obtained in Synthesis Example 6 was added with 32.5 g of a curing agent consisting of acetic anhydride / isoquinoline / DMF (weight ratio 11.48 / 3.40 / 18.18). The mixture was stirred and degassed at temperatures below 0°C and then coated onto aluminum foil using a comma coater. The resulting resin film was heated at 115°C for 100 seconds, after which the self-supporting gel film was peeled off the aluminum foil and fixed to a metal frame. The film was then imidized at 250°C for 15 seconds and 350°C for 79 seconds to obtain a 17 μm-thick polyimide film. This film retained its shape after being fixed to a metal frame and heated at 450°C for 2 minutes, confirming its non-thermoplasticity.

[0080] Next, a solution of the thermoplastic polyimide precursor I obtained in Synthesis Example 9 diluted with DMF to a solids concentration of 8 wt% was applied to both sides of the non-thermoplastic polyimide film obtained above so that the final thickness per side was 4 μm. The film was then heated at 120°C for 2 minutes. This was followed by heating and imidization at 350°C for 15 seconds to obtain a polyimide laminate film.

[0081] (Comparative Example 2) In a 500 mL separable flask, 65 g of the non-thermoplastic polyimide precursor G obtained in Synthesis Example 7 was added with 32.5 g of a curing agent consisting of acetic anhydride / isoquinoline / DMF (weight ratio 11.48 / 3.40 / 18.18). The mixture was stirred and degassed at temperatures below 0°C and then coated onto aluminum foil using a comma coater. The resulting resin film was heated at 115°C for 100 seconds, after which the self-supporting gel film was peeled off the aluminum foil and fixed to a metal frame. The film was then imidized at 250°C for 15 seconds and 350°C for 79 seconds to obtain a 17 μm-thick polyimide film. This film was also fixed to a metal frame and heated at 450°C for 2 minutes, retaining its shape, confirming its non-thermoplasticity.

[0082] Next, a solution of the thermoplastic polyimide precursor I obtained in Synthesis Example 9 diluted with DMF to a solids concentration of 8 wt% was applied to both sides of the non-thermoplastic polyimide film obtained above so that the final thickness per side was 4 μm. The film was then heated at 120°C for 2 minutes. This was followed by heating and imidization at 350°C for 15 seconds to obtain a polyimide laminate film.

[0083] (Comparative Example 3) In a 500 mL separable flask, 65 g of the non-thermoplastic polyimide precursor H obtained in Synthesis Example 8 was added with 32.5 g of a curing agent consisting of acetic anhydride / isoquinoline / DMF (weight ratio 11.48 / 3.40 / 18.18). The mixture was stirred and degassed at temperatures below 0°C and then coated onto aluminum foil using a comma coater. The resulting resin film was heated at 115°C for 100 seconds, after which the self-supporting gel film was peeled off the aluminum foil and fixed to a metal frame. The film was then imidized at 250°C for 15 seconds and 350°C for 79 seconds to obtain a 17 μm-thick polyimide film. This film was also fixed to a metal frame and heated at 450°C for 2 minutes, retaining its shape, confirming its non-thermoplasticity.

[0084] Next, a solution of the thermoplastic polyimide precursor I obtained in Synthesis Example 9 diluted with DMF to a solids concentration of 8 wt% was applied to both sides of the non-thermoplastic polyimide film obtained above so that the final thickness per side was 4 μm. The film was then heated at 120°C for 2 minutes. This was followed by heating and imidization at 350°C for 15 seconds to obtain a polyimide laminate film.

[0085] (Evaluation results) The polyimide laminated films obtained in Examples 1 to 5 and Comparative Examples 1 to 3 were subjected to the hole crack test by the above method. The results are shown in Table 3. [Table 3]

Claims

1. A polyamic acid which is an addition reaction product of an acid dianhydride and a diamine, A polyamic acid comprising a compound represented by chemical formula (1) in an amount of 1 mol % to 20 mol % of all diamines. 【Chemistry 1】

2. A polyimide comprising the imidized product of the polyamic acid according to claim 1.

3. A polyimide film which is a film-like product of the polyimide according to claim 2.

4. A multilayer polyimide film comprising the polyimide film according to claim 3 and an adhesive layer laminated on at least one surface of the polyimide film.

5. 5. The method for producing a multilayer polyimide film according to claim 4, wherein the adhesive layer is made of a thermoplastic polyimide.

6. A flexible metal foil laminate comprising a metal layer provided on the adhesive layer of the multilayer polyimide film according to claim 4 or 5.

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