JP5547874B2 - Polyimide resin - Google Patents

Description

  The present invention relates to a highly adhesive metal-polyimide composite for a flexible printed circuit board, a polyimide resin, and a polyamic acid varnish composition therefor.

  In recent years, the demand for polyimide resins as FPC (Flexible Printed Circuits) substrates has increased dramatically. The structure of a copper clad laminate, FCCL (Flexible Copper Clad Laminate), which is the original fabric of FPC, is mainly classified into three types. That is, 1) A three-layer type in which a polyimide resin layer (polyimide film) and a copper foil are attached using an epoxy adhesive or the like. ) After applying varnish, dry or imidize, or form a copper foil layer on the polyimide film by vapor deposition or sputtering, etc. 2) Adhesive 2 layer type 3) Pseudo 2 layer type using thermoplastic polyimide as adhesive It has been known. In applications where a high degree of dimensional stability is required for the polyimide film, a two-layer FCCL that does not use an adhesive is advantageous.

The polyimide resin as the FPC board is exposed to various thermal cycles in the mounting process and undergoes dimensional changes. In order to suppress this as much as possible, in addition to the glass transition temperature (Tg) of the polyimide resin being higher than the process temperature, it is desirable that the linear thermal expansion coefficient below the glass transition temperature is as low as possible. As will be described later, the control of the linear thermal expansion coefficient of the polyimide resin layer is extremely important from the viewpoint of reducing the residual stress generated during the two-layer FCCL manufacturing process.
Many polyimide resins are insoluble in organic solvents and do not melt above the glass transition temperature, so it is usually not easy to mold the polyimide resin itself. For this reason, polyimide resins generally include an aromatic tetracarboxylic dianhydride such as pyromellitic anhydride (PMDA) and an aromatic diamine such as 4,4′-oxydianiline (ODA) and a non-dimethylacetamide (DMAc) or the like. First, a polyamic acid varnish with a high degree of polymerization is polymerized in an equimolar reaction in a protic polar organic solvent, and this polyamic acid varnish is applied onto a copper foil and heated and dehydrated (imidation) at 250 to 400 ° C. To form a film.

Residual stress is generated in the process of cooling the metal-polyimide composite to room temperature after the imidization reaction at high temperature, and serious problems such as FCCL curling, peeling, and film cracking often occur.
As a measure for reducing thermal stress, it is effective to reduce the linear thermal expansion of the polyimide resin layer itself that is an insulating film. Most polyimide resins have a coefficient of linear thermal expansion in the range of 40-100 ppm / ° C., which is much greater than the linear thermal expansion coefficient of 17 ppm / ° C. of metal foils, such as copper foil, and is close to the value of copper foil, approximately 20 ppm. Research and development of a low linear thermal expansion polyimide resin exhibiting a temperature below / ° C. is being conducted.
Currently, a polyimide resin formed from 3,3 ′, 4,4′-biphenyltetracarboxylic dianhydride and paraphenylenediamine is best known as a material for a polyimide resin having a low coefficient of linear thermal expansion that is practically used. . This polyimide resin layer is known to exhibit a very low linear thermal expansion coefficient of 5 to 10 ppm / ° C., although it depends on the film thickness and production conditions, but does not exhibit a low hygroscopic expansion coefficient (Non-Patent Document). 1).

The dimensional stability of the polyimide resin layer is required not only for thermal cycling but also for moisture absorption. The conventional polyimide resin layer absorbs 2 to 3% by mass. Circuit misalignment due to dimensional changes due to moisture absorption of the polyimide resin layer is a serious problem for high-density wiring and multilayer wiring. A serious problem may be caused by deterioration of electrical characteristics such as corrosion, ion migration, and dielectric breakdown at the polyimide resin layer / conductor interface. Therefore, the polyimide resin layer as an insulating film is required to have as low a hygroscopic expansion coefficient as possible.
As a molecular design for realizing a low hygroscopic expansion coefficient, for example, it is effective to introduce an aromatic ester bond to a polyimide skeleton using an acid anhydride having an ester structure represented by the formula (19) It has been reported (see Patent Document 1).

However, since the adhesiveness with copper foil is low, an adhesive layer using a bisphenol A type epoxy resin or the like is newly required to develop adhesiveness, and as an insulating film (polyimide resin layer + adhesive layer) configured Are concerned about flame retardancy, hygroscopic expansion coefficient, and deterioration of heat resistance, which is a characteristic of polyimide resin.
Studies have also been made to improve the adhesion between a polyimide resin layer and a metal foil obtained by using an additive such as an imidazole compound in a polyamic acid varnish without separately providing an adhesive layer (see Patent Document 2). Similarly, when an additive such as an imidazole compound is used in a polyamic acid varnish containing an ester structure, the adhesion between the polyimide resin layer and the metal foil is lowered, the hygroscopic expansion coefficient is lowered, and the mechanical strength of the resulting polyimide film is lowered. There was a bug that brought

There is a strong demand for an additive for obtaining a polyimide resin having an ester structure that improves adhesion to a metal foil without causing a decrease in glass transition temperature and hygroscopic expansion coefficient.
Macromolecules, 29, 7897 (1996). Japanese Patent Laid-Open No. 10-126091 JP-A-4-85363

  The present invention has been made in view of the above situation, and the polyimide resin layer on the metal foil has excellent adhesion to the metal foil without an adhesive layer, and the linear thermal expansion coefficient is the wire of the metal foil. It aims at providing the polyamic-acid varnish composition which can form the polyimide resin layer equivalent to a thermal expansion coefficient, and the metal-polyimide composite for flexible printed circuit boards using the same.

As a result of intensive studies to solve the above-mentioned problems, the present inventor has found that the above-mentioned object can be achieved, and has made the present invention.
1. A polyamic acid varnish composition comprising a polyamic acid obtained by addition polymerization of an aromatic tetracarboxylic dianhydride and an aromatic diamine, a nitrogen-containing aromatic compound, and a solvent, the aromatic tetracarboxylic dianhydride Has an ester structure represented by the formula (1), and / or the aromatic diamine has an ester structure represented by the formula (2), and the nitrogen-containing aromatic compound is represented by the formulas (3) to (3): oxazole compounds represented by 12), amide compounds, nitrile compounds, and benzofurazan all SANYO that chosen from the group consisting of derivatives, nitrogen-containing aromatic compound, 0.01 to the 100 parts by mass of the polyamic acid A polyamic acid varnish composition characterized by being 20 parts by mass .

（Ｍは、式（１）で表される２価の芳香族基より選択され、Ｒ _１ 〜Ｒ _３ は、炭素数１〜４のアルキル基、メトキシ基、または水素原子を表す。）

(M is selected from a divalent aromatic group represented by the formula (1), and R _{1 to} R ₃ represent an alkyl group having 1 to 4 carbon atoms, a methoxy group, or a hydrogen atom.)

(M is selected from a divalent aromatic group represented by the formula (1), and R _{1 to} R ₃ represent an alkyl group having 1 to 4 carbon atoms, a methoxy group, or a hydrogen atom.)

(M = 0 or 1 and R _{4 to} R ₆ represent an alkyl group having 1 to 4 carbon atoms, a methoxy group, or a hydrogen atom.)

(X ₁ and X ₃ are tetravalent aromatic groups represented by the formulas (3), (4), (7) and (8), and X ₂ and X ₄ are the formulas (5) and (9). In the formula, Y _{1 to} Y ₅ are ether, —S—, a saturated, unsaturated alkylene group having 1 to 4 carbon atoms , a carbonyl group, or a sulfonyl group. R _{7 to} R ₁₄ , R _{16 to} R ₂₉ , and R _{31 to} R ₃₃ are each a hydrogen atom, an alkyl group having 1 to 4 carbon atoms, an alkoxy group, a halogenated alkyl group, a halogen group, a nitro group, a cyano group, A hydroxyl group, —SO ₂ H, —OPh, —SCH ₃ , or —SPh, where n = 1 and 2. R ₁₅ , R ₃₀ , and R ₃₄ are a hydrogen atom, an alkyl group having 1 to 4 carbon atoms, an alkoxy group group, halogenated alkyl group, a halogen group, a nitro group, a cyano group, a hydroxyl group, -SO ₂ H, -OP , -SCH _3, is -SPh or a phenyl group.)
2. 2. The polyamic acid varnish composition according to 1, wherein the nitrogen-containing aromatic compound is an oxazole compound represented by any one or more of formulas (13) to (15).

(X ₅ is a tetravalent aromatic group represented by the formula (13), and X ₆ is a divalent aromatic group represented by the formula (14). R _{35 to} R ₃₈ , R ₄₀ is a hydrogen atom, an alkyl group having 1 to 4 carbon atoms, an alkoxy group, a halogenated alkyl group, a halogen group, a nitro group, a cyano group, a hydroxyl group, —SO ₂ H, —OPh, —SCH ₃ , or —SPh. R ₃₉ is a hydrogen atom, an alkyl group having 1 to 4 carbon atoms, an alkoxy group, a halogenated alkyl group, a halogen group, a nitro group, a cyano group, a hydroxyl group, —SO ₂ H, —OPh, —SCH ₃ , —SPh. Or a phenyl group.)
3. 2. The polyamic acid varnish composition according to 1, wherein the nitrogen-containing aromatic compound is an amide compound represented by any one or more of formulas (16) to (18).

(X ₇ is a tetravalent aromatic group represented by the formula (16), and X ₈ is a divalent aromatic group represented by the formula (17). R _{41 to} R ₄₄ , R ₄₆ represents a hydrogen atom, an alkyl group having 1 to 4 carbon atoms, an alkoxy group, a halogenated alkyl group, a halogen group, a nitro group, a cyano group, a hydroxyl group, —SO ₂ H, —OPh, —SCH ₃ , or —SPh. R ₄₅ is a hydrogen atom, an alkyl group having 1 to 4 carbon atoms, an alkoxy group, a halogenated alkyl group, a halogen group, a nitro group, a cyano group, a hydroxyl group, —SO ₂ H, —OPh, —SCH ₃ , —SPh. Or a phenyl group.)
4). 2. The polyamic acid varnish composition according to 1, wherein the nitrogen-containing aromatic compound is an amide compound represented by the formula (16).

(X ₇ is a tetravalent aromatic group represented by the formula (16). R ₄₁ and R ₄₂ are a hydrogen atom, an alkyl group having 1 to 4 carbon atoms, an alkoxy group, a halogenated alkyl group, a halogen atom. Group, nitro group, cyano group, hydroxyl group, —SO ₂ H, —OPh, —SCH ₃ , or —SPh.)
5 . A polyimide resin obtained by imidizing the polyamic acid varnish composition according to 1.
6 . A metal-polyimide composite comprising a polyimide resin obtained by imidizing the polyamic acid varnish composition according to 1, and a metal foil.

  The polyamic acid varnish composition of the present invention can produce a metal-polyimide composite by coating, drying and heating imidization on a metal. The metal-polyimide composite thus obtained has excellent adhesion to the metal foil and has an effect that the linear thermal expansion coefficient is equivalent to the linear thermal expansion coefficient of the metal foil.

Hereinafter, the present invention will be specifically described.
The nitrogen-containing aromatic compound used as an additive is selected from the group consisting of oxazole compounds, amide compounds, nitrile compounds and benzofurazan of general formulas (3) to (12). X ₁ and X ₃ in the formula are tetravalent aromatic groups represented by the general formulas (3), (4), (7) and (8), and X ₂ and X ₄ are the general formula (5). , (9) is a divalent aromatic group. _Wherein, Y 1 to Y ₅ are ethers, -S-, saturated having 1 to 4 carbon atoms, unsaturated alkylene group, a carbonyl group or a sulfonyl group. R _{7 to} R ₁₄ , R _{16 to} R ₂₉ , R _{31 to} R ₃₃ are a hydrogen atom, an alkyl group having 1 to 4 carbon atoms, an alkoxy group, a halogenated alkyl group, a halogen group, a nitro group, a cyano group, a hydroxyl group, _{-SO 2 H, -OPh, -SCH 3} , or a -SPh, a n = 1, 2. R ₁₅ , R ₃₀ and R ₃₄ are hydrogen atoms, alkyl groups having 1 to 4 carbon atoms, alkoxy groups, halogenated alkyl groups, halogen groups, nitro groups, cyano groups, hydroxyl groups, —SO ₂ H, —OPh, —SCH. ₃ , -SPh, or a phenyl group.

Here, from the viewpoint of availability or production cost, the nitrogen-containing aromatic compound is preferably an oxazole compound represented by General Formula (13) to General Formula (15). X ₅ in the formula is a tetravalent aromatic group represented by the general formula (13), and X ₆ is a divalent aromatic group represented by the general formula (14). R _{35 to} R ₃₈ and R ₄₀ are each a hydrogen atom, an alkyl group having 1 to 4 carbon atoms, an alkoxy group, a halogenated alkyl group, a halogen group, a nitro group, a cyano group, a hydroxyl group, —SO ₂ H, —OPh, — SCH _3, or -SPh. R ₃₉ represents a hydrogen atom, an alkyl group having 1 to 4 carbon atoms, an alkoxy group, a halogenated alkyl group, a halogen group, a nitro group, a cyano group, a hydroxyl group, —SO ₂ H, —OPh, —SCH ₃ , —SPh, or It is a phenyl group.

From the viewpoint of availability or production cost, the nitrogen-containing aromatic compound is preferably an amide compound represented by the general formula (16) to the general formula (18), and the general formula (16) is further preferable. X ₇ in the formula is a tetravalent aromatic group represented by the general formula (16), and X ₈ is a divalent aromatic group represented by the general formula (17). R _{41 to} R ₄₄ and R ₄₆ are each a hydrogen atom, an alkyl group having 1 to 4 carbon atoms, an alkoxy group, a halogenated alkyl group, a halogen group, a nitro group, a cyano group, a hydroxyl group, —SO ₂ H, —OPh, — SCH _3, or -SPh. R ₄₅ represents a hydrogen atom, an alkyl group having 1 to 4 carbon atoms, an alkoxy group, a halogenated alkyl group, a halogen group, a nitro group, a cyano group, a hydroxyl group, —SO ₂ H, —OPh, —SCH ₃ , —SPh, or It is a phenyl group.

The blending amount of the nitrogen-containing aromatic compound in the ester structure-containing polyamic acid varnish composition is 0.01 to 20 parts by mass with respect to 100 parts by mass of the polyamic acid which is a solid component, from the viewpoint of adhesive strength and heat resistance. Is more preferable, and 0.1 to 10 parts by mass is more preferable.
The polyamic acid varnish composition having an ester structure of the present invention requires that at least one of aromatic tetracarboxylic dianhydride and aromatic diamine, which are raw materials for polyamic acid, has an ester structure.

Examples of the aromatic tetracarboxylic dianhydride having an ester structure include an aromatic tetracarboxylic dianhydride having a repeating unit represented by the general formula (1). M in the formula is selected from an aromatic group represented by the general formula (1), and R _{1 to} R ₃ represent an alkyl group having 1 to 4 carbon atoms, a methoxy group, or a hydrogen atom. Specifically, p-phenylenebis (trimellitic acid monoester acid anhydride), p-methylphenylenebis (trimellitic acid monoester acid anhydride), p-biphenylenebis (trimellitic acid monoester acid anhydride) It is preferable to use an aromatic tetracarboxylic dianhydride containing an ester structure such as Each ester structure-containing aromatic tetracarboxylic dianhydride may be used alone or in combination.

Examples of the aromatic diamine having an ester structure include aromatic diamines represented by the general formula (2). In the formula, m = 0 or 1, and R _{4 to} R ₆ represent an alkyl group having 1 to 4 carbon atoms, a methoxy group, or a hydrogen atom. Specifically, 4-aminophenyl-4′-aminobenzoate, 4-aminophenyl-3′-aminobenzoate, 3-aminophenyl-4′-aminobenzoate, 2-methyl-4-aminophenyl-4′- Ester aromatic diamines such as aminobenzoate, 4-aminophenyl-3′-aminobenzoate, 2-methyl-4-aminophenyl-3′-aminobenzoate, bis (4-aminophenyl) terephthalate, bis (3-methyl- 4-aminophenyl) terephthalate, bis (4-aminophenyl) isophthalate, bis (3-methyl-4-aminophenyl) isophthalate, p-phenylenebis (4-aminobenzoate), m-phenylenebis (4-amino) Benzoate), p-methylphenylenebis (4-aminobenzoate) p- phenylene bis (3-aminobenzoate), p- methyl-phenylene - it is preferable to use a phenylene bis ester structure-containing aromatic diamines such as diester aromatic diamine (3-aminobenzoate). Each ester structure-containing aromatic diamine may be used alone or in combination.

When utilizing aromatic diamine which has ester structure, a conventionally well-known tetracarboxylic dianhydride can be used in the range which does not impair the effect of this invention.
For example, 3,4,3 ′, 4′-biphenyltetracarboxylic acid, 2,3,3 ′, 4′-biphenyltetracarboxylic acid, pyromellitic acid, benzophenonetetracarboxylic acid, oxydiphthalic acid, diphenylsulfonetetracarboxylic acid, And dianhydrides such as 2,3,6,7-naphthalenetetracarboxylic acid. From the viewpoint of improving heat resistance such as linear thermal expansion coefficient and glass transition temperature, 3,4,3 ′, 4′-biphenyltetracarboxylic dianhydride, 2,3,6,7-naphthalenetetracarboxylic dianhydride It is preferable to use a product. Moreover, you may use dianhydrides, such as a non-aromatic tetracarboxylic dianhydride, cyclobutane tetracarboxylic acid, and cyclohexane tetracarboxylic acid, in the range which does not impair the effect of this invention.

Moreover, when utilizing the tetracarboxylic-acid aromatic dianhydride which has ester structure, a conventionally well-known aromatic diamine can be used in the range which does not impair the effect of this invention.
For example, paraphenylenediamine, metaphenylenediamine, 4,4′-diaminodiphenyl ether, 3,4′-diaminodiphenyl ether, 4,4′-diaminobenzanilide, 2,2-dimethyl-4,4-diaminobiphenyl, 1, 3-bis (4-aminophenoxy) benzene, 1,3-bis (3-aminophenoxy) benzene, 2,2-bis (4-aminophenoxyphenyl) propane, 4,4′-bis (4-aminophenoxy) Biphenyl, 4,4′-bis (3-aminophenoxy) biphenyl, bis (4- (4-aminophenoxy) phenyl) sulfone, and bis (4- (3-aminophenoxy) phenyl) sulfone are exemplified. From the viewpoint of improving heat resistance such as linear thermal expansion coefficient and glass transition temperature, paraphenylenediamine, metaphenylenediamine, 4,4′-diaminodiphenyl ether, 3,4′-diaminodiphenyl ether, 4,4′-bis (4 -Aminophenoxy) biphenyl is preferably used.

  The polyamic acid in this invention is obtained by making the said tetracarboxylic dianhydride component and a diamine acid component react. The regularity of the repeating unit constituting the polyamic acid may include a block structure or a random structure. The polyimide resin of this invention is a polyimide resin whose linear thermal expansion coefficient in 50-200 degreeC is 8-25 ppm / degreeC. Moreover, it is more preferable that it is 15-22 ppm / degreeC from the point of matching of a linear thermal expansion coefficient with copper foil.

  The polyimide resin of the present invention can be obtained by imidizing the polyamic acid varnish composition of the present invention. Usually, the molecular weight and terminal structure of the polyimide resin to be produced can be adjusted by adjusting the charging ratio of the tetracarboxylic dianhydride and the diamine compound used in the production. The preferred molar ratio of total tetracarboxylic dianhydride to total diamine is 0.90 to 1.10.

The terminal structure of the resulting polyimide becomes an amine or acid anhydride structure depending on the molar charge ratio of all tetracarboxylic dianhydrides and all diamines at the time of production. When the terminal structure is an amine, it may be end-capped with a carboxylic acid anhydride. Examples of these include phthalic anhydride, 4-phenylphthalic anhydride, 4-phenoxyphthalic anhydride, 4-phenylcarbonylphthalic anhydride, 4-phenylsulfonylphthalic anhydride, and the like. This is not a limitation. You may use these carboxylic anhydrides individually or in mixture of 2 or more types.
In addition, when the terminal structure is an acid anhydride, the terminal structure may be capped with a monoamine. Specific examples include aniline, toluidine, aminophenol, aminobiphenyl, aminobenzophenone, naphthylamine and the like. You may use these monoamines individually or in mixture of 2 or more types.

As a solvent in the polyamic acid varnish composition of the present invention, any solvent can be used as long as it is mixed with the above polyamic acid. Examples thereof include γ-butyrolactone, γ-valerolactone, N-methyl-2-pyrrolidone, N, N- Examples include dimethylformamide, N, N-dimethylacetamide, dimethyl sulfoxide, 1,3-dioxane, 1,4-dioxane, cyclopentanone, cyclohexanone, diethylene glycol dimethyl ether, and tetramethylurea. Preferred solvents for use in the present invention are γ-butyrolactone, N, N-dimethylacetamide and N-methyl-2-pyrrolidone. These can be used alone or in admixture of two or more.
Moreover, as long as the physical properties are not impaired, fillers such as silica and surface modifiers such as silane coupling agents and titanate coupling agents may be added as additives.
There is no restriction | limiting in particular in the usage-amount of these solvents, According to the viscosity etc. of a polyamic-acid varnish composition, it can utilize.

The polyamic acid varnish composition of the present invention is selected from polyamic acid varnish obtained by addition polymerization of aromatic tetracarboxylic dianhydride and aromatic diamine in a solvent, an oxazole compound, an amide compound, a nitrile compound, and benzofurazan. It is obtained by mixing and dissolving the nitrogen-containing aromatic compound. Here, the nitrogen-containing aromatic compound may be added to the system in which the addition polymerization of the polyamic acid is proceeding, either before or after the polyamic acid polymerization.
There is no restriction | limiting in particular in solid content concentration in a solvent. The solid content concentration is a percentage of the mass of the wholly aromatic tetracarboxylic dianhydride and the aromatic diamine with respect to the total mass of the wholly aromatic tetracarboxylic dianhydride and the aromatic diamine including the solvent. A preferable solid content concentration is 5-35 mass%, More preferably, it is 10-25 mass%.

About addition polymerization conditions, it can carry out according to the addition polymerization conditions of the polyamic acid currently performed conventionally. Specifically, first, an aromatic diamine is dissolved in a solvent at 0 ° C. to 80 ° C. under an inert atmosphere such as nitrogen, helium, or argon at atmospheric pressure. The addition polymerization is carried out for 4 to 8 hours while the anhydride is rapidly added. Thereby, a polyamic acid varnish is obtained. About the viscosity of the polyamic acid varnish obtained, it is preferable to adjust the solid content concentration so as to be 1 poise to 2500 poise.
Further, from the viewpoint of the toughness of the polyimide film and the handling of the polyamic acid varnish, the intrinsic viscosity of the polyamic acid varnish is preferably in the range of 0.1 to 25.0 dL / g, preferably 0.3 to 20 dL / g. Is more preferably in the range of 0.5 to 15.0 dL / g.

  The metal-polyimide composite of the present invention is one in which a polyimide resin layer is provided on a metal foil. A composite with a polyimide resin layer obtained by imidizing the polyamic acid varnish composition of the present invention on a metal foil, or a polyimide obtained by drying the polyamic acid varnish composition of the present invention on a metal foil at a high temperature It is a composite with a resin layer. Although the thickness of a polyimide resin layer is not specifically limited, Preferably it is 50 micrometers or less, More preferably, it is 1-25 micrometers.

Various metal foils can be used as the metal foil, but aluminum foil, copper foil, stainless steel foil and the like are preferably used for the flexible printed circuit board. These metal foils may be subjected to surface treatment such as mat treatment, plating treatment, chromate treatment, aluminum alcoholate treatment, aluminum chelate treatment, silane coupling agent treatment, and the like.
Although the thickness of metal foil is not specifically limited, Preferably it is 35 micrometers or less, More preferably, it is 18 micrometers or less.

  The metal-polyimide composite obtained from the polyamic acid varnish composition of the present invention can be produced as follows. First, the polyamic acid varnish composition of the present invention is coated on a metal foil using a blade coater, a lip coater, a gravure coater, etc., and then dried to form a polyamic acid varnish composition layer (polyamide) as a polyimide precursor layer. Acid film). The coating thickness is affected by the solid content concentration of the polyamic acid varnish composition. A polyimide resin layer can be formed by thermally imidizing the polyamic acid varnish composition layer at 200 to 400 ° C. in an inert atmosphere such as nitrogen, helium, and argon.

  The metal-polyimide laminate of the present invention using the polyimide film described above is obtained by stacking a metal foil on one side or both sides of the polyimide film, and the polyimide film and the metal foil by a known method involving heating and / or pressurization. Can be obtained by laminating As a lamination method, a known method such as batch processing by a single plate press, hot roll lamination, or continuous processing by a double belt press (DBP) can be used.

The heating method in the laminating method is not particularly limited, and for example, a heating means employing a conventionally known method capable of heating at a predetermined temperature such as a heat circulation method, a hot air heating method, an induction heating method, or the like is used. it can. Similarly, the pressurization method in the laminating method is not particularly limited, and for example, a pressurization employing a conventionally known method that can apply a predetermined pressure, such as a hydraulic method, a pneumatic method, a gap pressure method, or the like. Means can be used.
The metal-polyimide composite thus obtained has good adhesion between a metal foil, particularly a copper foil and a polyimide resin layer.

EXAMPLES The present invention will be specifically described below with reference to examples, but the present invention is not limited to these examples.
In the following Examples, the properties of the polyamic acid varnish composition and the physical properties of the polyimide resin and copper-polyimide composite after imidization were measured as follows.
(1) Intrinsic viscosity (η)
A 0.5 mass% polyamic acid varnish composition was measured at 30 ° C. using an Ostwald viscometer.

(2) Glass transition temperature (Tg) and coefficient of linear thermal expansion (CTE)
The obtained copper-polyimide composite was cut into a length of 50 mm, a width of 3 mm, and a thickness of 25 μm, immersed in a ferric chloride aqueous solution (manufactured by Tsurumi Soda), and the copper foil layer was etched and washed with water. After drying the obtained polyimide film at 105 ° C. with a hot air dryer, using a thermal analyzer (TMA-50, manufactured by Shimadzu Corporation), a tensile mode, a 5 g load, a sample length of 15 mm, and a heating rate. Measurement was performed at 10 ° C./min in an N ₂ atmosphere, Tg was determined from the intersection of tangents, and the linear thermal expansion coefficient from 50 ° C. to 200 ° C. was calculated.

(3) Adhesive strength In the same manner as described above, a copper-polyimide composite was cut into a length of 150 mm, a width of 10 mm, and a thickness of 25 μm. It was immersed in an aqueous solution (manufactured by Tsurumi Soda), and the copper foil was etched and washed with water. Then, after removing the vinyl tape and drying the obtained flexible substrate with a hot air dryer at 105 ° C., a 3 mm wide copper foil was peeled off from the polyimide resin, and the stress was measured. The peeling angle was 90 ° and the peeling speed was 50 mm / min.

(4) Solder heat resistance A 3 cm long x 6 cm wide copper-polyimide composite was cut out, and 2.5 cm x 2.5 cm in the center was masked with vinyl tape and immersed in a ferric chloride aqueous solution (manufactured by Tsurumi Soda). Then, the copper foil was etched and washed with water. Thereafter, the vinyl tape was removed, and the obtained copper-polyimide composite was dried at 105 ° C. with a hot air dryer, and then the sample was placed in the solder bath set at 300 ° C. with the copper foil glossy side facing the solder bath. Evaluation was performed by changing the appearance when left for 1 min so as to come into contact with.

(5) Boiling solder heat resistance In the same manner as described above, a copper-polyimide composite having a length of 3 cm and a width of 6 cm was cut out, and a central portion of 2.5 cm × 2.5 cm was masked with a vinyl tape, and a ferric chloride aqueous solution ( It was immersed in Tsurumi Soda) and the copper foil was etched and washed with water. Thereafter, the vinyl tape was removed, and the obtained sample was immersed in boiling water for 2 hours, then immersed in water at room temperature, taken out, wiped off water adhering to the surface, and immediately left at 280 ° C. for 1 min. Evaluation was performed by changing the appearance.

(6) Hygroscopic expansion coefficient: CHE
A film having a width of 3 mm, a length of 20 mm (length between chucks of 15 mm), and a thickness of 20 to 25 μm was formed using a thermal mechanical analyzer (TM-9400) and a humidity atmosphere adjustment device (HC-1) manufactured by ULVAC-RIKO Inc. The hygroscopic expansion coefficient of the polyimide film was determined as an average value in 30% RH to 70% RH from the elongation of the test piece when the humidity was changed from 30% RH to 70% RH at 23 ° C. and a load of 5 g.

(7) Elastic modulus, elongation at break (Synthesis Example 1) Synthesis 1 of a nitrogen-containing aromatic compound
In a 2 L Separa flask, 1000 g of polyphosphoric acid and 200 mmol of 3,3′-dihydroxy-4,4′-diaminobiphenyl (manufactured by Wakayama Seika Kogyo Co., Ltd.) are placed and stirred at 150 ° C. for 2 hours in a nitrogen atmosphere. It was. Thereafter, 400 mmol of benzoic acid (manufactured by Wako Pure Chemical Industries, Ltd.) was added and reacted at 200 ° C. for 5 hours. The reaction solution was allowed to reach room temperature, then dropped into purified water, and the resulting yellow-green precipitate was collected by filtration and then vacuum dried at 125 ° C. to obtain crude crystals. Thereafter, the crude crystals were dissolved in N-methylpyrrolidone at around 100 ° C., the solution allowed to cool to room temperature was filtered, insoluble components were removed, and then 3% by mass of sodium carbonate aqueous solution was dropped into the obtained filtrate. A solid was precipitated. The precipitated solid was collected by filtration, washed 2 to 3 times with purified water, then vacuum dried at 125 ° C., and a nitrogen-containing aromatic compound containing an oxazole structure represented by the following formula (20) (below) , Referred to as OXAN).

Synthesis Example 2 Synthesis of nitrogen-containing aromatic compound 2
In a 2 L Separa flask, 1200 ml of N, N′-dimethylformamide solution, 200 mmol of 3,3′-dihydroxybiphenyl (manufactured by Wakayama Seika Kogyo Co., Ltd.) and 400 mmol of triethylamine were dissolved and cooled to 0 ° C. in a nitrogen atmosphere. . Thereafter, a solution obtained by dissolving 400 mmol of p-nitrobenzoyl chloride in 100 ml of an N, N′-dimethylformamide solution was added dropwise over 2 hours so as to be 10 ° C. or less, and then stirred for 6 hours.
Next, the precipitate is filtered, washed with N, N′-dimethylformamide, further washed with water, dried, and 3,3′-dihydroxy-4,4′- represented by the formula (21). Yellowish white crystals of dinitrobiphenylanilide were obtained.

[Example 1]
<Evaluation of polyamic acid varnish composition, imidization and polyimide film characteristics>
10 mmol of 4-aminophenyl-4′-aminobenzoate (hereinafter referred to as APAB) containing an ester group in the monomer skeleton in a well-closed sealed reaction vessel equipped with a stirrer, 10 mmol, 4,4′-diaminodiphenyl ether (hereinafter referred to as ODA) , N-methyl-2-pyrrolidone 191 mL (dehydrated) (manufactured by Wako Pure Chemical Industries, Ltd.) (hereinafter referred to as NMP), p-biphenylenebis (tri) containing an ester group in the monomer skeleton was added to this solution. 50 mmol of merit acid monoester anhydride (hereinafter referred to as TABP) powder was gradually added. After 30 minutes, the solution viscosity increased rapidly. Furthermore, it stirred at 80 degreeC for 4 hours, and obtained the polyamic-acid varnish which has a transparent, uniform and viscous ester group. In this polyamic-acid varnish, the nitrogen-containing aromatic compound (OXAN) obtained by the synthesis example 1 was added so that it might become 6 mass parts with respect to resin solid content, and it was made to melt | dissolve, and the polyamic-acid varnish composition was obtained. The obtained polyamic acid varnish composition did not precipitate or gel at all even when allowed to stand at room temperature and −20 ° C. for one month, and showed high solution storage stability. The intrinsic viscosity of the polyamic acid varnish composition measured with an Ostwald viscometer in NMP at a concentration of 0.5% by mass at 30 ° C. was 0.72 dL / g. This polyamic acid varnish composition is allowed to stand on a metal coating table with a 12 μm thick copper foil (F2-WS foil, F2-WS foil) mat surface side as the surface. The surface temperature of the coating table is set to 90 ° C., and the polyamic acid varnish composition is applied to the copper foil mat surface with a doctor blade. Then, after leaving still on a coating stand for 30 minutes, and also leaving still at 100 degreeC for 30 minutes in a dryer, the polyamic-acid film (45 micrometers in thickness) without tackiness was obtained. Then, a polyamic acid film is attached to a metal plate made of SUS, and heated in a hot air drier in a nitrogen atmosphere at a heating rate of 5 ° C./min, 150 ° C. for 30 min, 200 ° C. for 1 h, and 400 ° C. for 1 h. Imidization was performed. A polyimide film with a copper foil having a thickness of 25 μm and no curling was obtained.

  This polyimide film with copper foil was etched with a ferric chloride solution to obtain a light brown polyimide film with a thickness of 25 μm. This polyimide film did not break even in the 180 ° bending test and showed flexibility. Moreover, it did not show any solubility in organic solvents. This polyimide film showed a linear thermal expansion coefficient (average value between 50 ° C. and 200 ° C.) of 18 ppm / ° C. as low as that of the copper foil by TMA measurement. Further, when the hygroscopic expansion coefficient was measured, it was 5.5 ppm /% RH (an average value between 30% RH and 70% RH) and an extremely low hygroscopic expansion coefficient. Further, when the 90 ° copper foil adhesive strength was measured, it showed a high adhesive strength of 1.1 kg / cm.

Similarly, this polyamic acid varnish composition was spin-coated on a 6-inch silicon wafer with a spin coater (manufactured by MS-250 Mikasa Co., Ltd.) and allowed to stand at 100 ° C. for 30 minutes in a dryer. A polyamic acid film (thickness 17 μm) having no tackiness was obtained. Thereafter, the silicon wafer was imidized in a hot air drier in a nitrogen atmosphere at a rate of temperature increase of 5 ° C./min at 150 ° C. for 30 min, 200 ° C. for 1 h, and 400 ° C. for 1 h. Thereafter, it was peeled from the silicon wafer with hydrofluoric acid to obtain a polyimide film having a thickness of 10 μm.
The obtained polyimide film was subjected to a tensile test to obtain an elastic modulus of 6.9 GPa and an elongation at break of 53%.

[Example 2] to [Example 7]
Instead of OXAN, the nitrogen-containing aromatic compound represented by the general formula (21) and any of the following formulas (22) to (26) is added so as to be 3 or 6 parts by mass with respect to the solid content of the resin. Then, the same operation as in Example 1 was repeated to obtain a polyamic acid varnish composition, a polyimide resin, and a copper-polyimide composite.
In addition, the nitrogen-containing aromatic compound used in Example 2 except for the general formula (21) obtained in the synthesis of Synthesis Example 2, the following formula (22) to the following formula (26) (used in Examples 3 to 7 in order) ) Was made by Tokyo Chemical Industry Co., Ltd.

[Example 8]
4-aminophenyl-4′-aminobenzoate (hereinafter referred to as APAB) 45 mmol, 4,4′-diaminodiphenyl ether (hereinafter referred to as ODA) containing an ester group in the monomer skeleton in a well-dried sealed reaction vessel with a stirrer After being dissolved in 5 mmol, 191 mL of N-methyl-2-pyrrolidone (dehydrated) (manufactured by Wako Pure Chemical Industries, Ltd.) (hereinafter referred to as NMP), this solution contains p-methylphenylenebis containing an ester group in the monomer skeleton. (Trimellitic acid monoester anhydride (hereinafter referred to as MTAHQ) powder 50 mmol was gradually added. After 30 minutes, the viscosity of the solution increased rapidly. Further, the mixture was stirred at 80 ° C. for 4 hours to be transparent, uniform and viscous. A polyamic acid varnish having an ester group was obtained, and a nitrogen-containing aromatic compound (O AN) was added to the resin solid content so as to be 6 parts by mass and dissolved to obtain a polyamic acid varnish composition, which was allowed to stand at room temperature and −20 ° C. for one month. However, precipitation and gelation did not occur at all, and high solution storage stability was exhibited.Intrinsic viscosity of the polyamic acid varnish composition measured with an Ostwald viscometer in NMP at a concentration of 0.5% by mass was 30 ° C. The polyamic acid varnish composition was statically placed on a metal coating table with a 12 μm thick copper foil (F2-WS foil, Furukawa Circuit Foil Co., Ltd.) matte side. Set the surface temperature of the coating table to 90 ° C., and apply it to the copper foil mat surface with a doctor blade using the polyamic acid varnish composition. 3 at 100 ° C in After standing for 0 min, a polyamic acid film (thickness: 45 μm) having no tackiness was obtained, and then the polyamic acid film was attached to a metal plate made of SUS, and the heating rate was 5 ° C. in a hot air drier in a nitrogen atmosphere. / Min, imidization was performed at 150 ° C. for 30 min, 200 ° C. for 1 h, and 400 ° C. for 1 h, and a 25 μm thick polyimide film with a copper foil without curling was obtained.

  This polyimide film with copper foil was etched with a ferric chloride solution to obtain a light brown polyimide film with a thickness of 25 μm. This polyimide film did not break even in the 180 ° bending test and showed flexibility. Moreover, it did not show any solubility in organic solvents. This polyimide film exhibited a linear thermal expansion coefficient (average value between 50 ° C. and 200 ° C.) of 20 ppm / ° C. as low as that of the copper foil by TMA measurement. Further, when the hygroscopic expansion coefficient was measured, it was 4.7 ppm /% RH (an average value between 30% RH and 70% RH) and an extremely low hygroscopic expansion coefficient. Further, when the 90 ° copper foil adhesive strength was measured, it showed a high adhesive strength of 1.0 kg / cm.

Similarly, this polyamic acid varnish composition was spin-coated on a 6-inch silicon wafer with a spin coater (manufactured by MS-250 Mikasa Co., Ltd.) and allowed to stand at 100 ° C. for 30 minutes in a dryer. A polyamic acid film (thickness 17 μm) having no tackiness was obtained. Thereafter, the silicon wafer was imidized in a hot air drier in a nitrogen atmosphere at a rate of temperature increase of 5 ° C./min at 150 ° C. for 30 min, 200 ° C. for 1 h, and 400 ° C. for 1 h. Thereafter, it was peeled from the silicon wafer with hydrofluoric acid to obtain a polyimide film having a thickness of 10 μm.
By repeating the same operation as in Example 1, a polyimide resin and a copper-polyimide composite were obtained.

[Example 9]
By adding the nitrogen-containing aromatic compound represented by the general formula (21) synthesized in Synthesis Example 2 so as to be 6 parts by mass with respect to the solid content of the resin, the same operation as in Example 8 is repeated to obtain polyamic acid. A varnish, a polyimide resin and a copper-polyimide composite were obtained.

[Comparative Example 1]
In a well-dried sealed reaction vessel equipped with a stirrer, 40 mmol of APAB containing ester groups in the monomer skeleton, 10 mmol of ODA, and 191 mL of NMP (dehydrated) were dissolved, and 50 mmol of TABP powder containing ester groups in the monomer skeleton was gradually added to this solution. Added to. After 30 minutes, the solution viscosity increased rapidly. Furthermore, it stirred at 80 degreeC for 4 hours, and obtained the polyamic-acid varnish which has a transparent, uniform and viscous ester group. The obtained polyamic acid varnish did not precipitate or gel at all even when it was allowed to stand at room temperature and −20 ° C. for one month, and showed high solution storage stability. The intrinsic viscosity of the polyamic acid measured with an Ostwald viscometer at a concentration of 0.5% by mass in NMP at 30 ° C. was 0.72 dL / g. In the same manner as in Example 1, this polyamic acid varnish is allowed to stand on a metal coating stand so that the mat surface side of the 12 μm-thick copper foil (F2-WS foil, F2-WS foil) is the surface. The surface temperature of the coating table is set to 90 ° C., and it is applied to the copper foil mat surface with a doctor blade using a polyamic acid varnish. Then, after leaving still on a coating stand for 30 minutes, and also leaving still at 100 degreeC for 30 minutes in a dryer, the polyamic-acid film (45 micrometers in thickness) without tackiness was obtained. Then, a polyamic acid film is attached to a metal plate made of SUS, and heated in a hot air drier in a nitrogen atmosphere at a heating rate of 5 ° C./min, 150 ° C. for 30 min, 200 ° C. for 1 h, and 400 ° C. for 1 h. Imidization was performed. A polyimide film with a copper foil having a thickness of 25 μm and no curling was obtained.

This polyimide film with copper foil was etched with a ferric chloride solution to obtain a light brown polyimide film with a thickness of 25 μm. This polyimide film did not break even in the 180 ° bending test and showed flexibility. Moreover, it did not show any solubility in organic solvents.
Similarly, this polyamic acid varnish is spin-coated on a 6-inch silicon wafer with a spin coater (MS-250 Mikasa Co., Ltd.), left standing at 100 ° C. for 30 minutes in a dryer, and then tacky. A polyamic acid film (thickness: 17 μm) with no film was obtained. Thereafter, the silicon wafer was imidized in a hot air drier in a nitrogen atmosphere at a rate of temperature increase of 5 ° C./min at 150 ° C. for 30 min, 200 ° C. for 1 h, and 400 ° C. for 1 h. Thereafter, it was peeled from the silicon wafer with hydrofluoric acid to obtain a polyimide film having a thickness of 10 μm.

  Glass transition temperature (Tg) and linear thermal expansion coefficient (CTE), hygroscopic expansion coefficient (CHE), elastic modulus, elongation at break, adhesive strength of copper-polyimide composite, solder heat resistance and moisture absorption solder heat resistance of the obtained polyimide resin The sex results are shown in Table 1.

[Comparative Example 2]
Polyamic acid varnish obtained by adding 2-ethyl-4-methyl-imidazole (product name 2E4MZ, manufactured by Shikoku Kasei Co., Ltd.) to the polyamic acid varnish obtained in Comparative Example 1 so as to be 6 parts by mass with respect to the resin solid content. A composition was obtained. By repeating the same operation as in Comparative Example 1, a polyimide resin and a copper-polyimide composite were obtained.
Glass transition temperature (Tg) and linear thermal expansion coefficient (CTE), hygroscopic expansion coefficient (CHE), elastic modulus, elongation at break, adhesive strength of copper-polyimide composite, solder heat resistance and moisture absorption solder heat resistance of the obtained polyimide resin The sex results are shown in Table 1.

[Comparative Example 3]
4-aminophenyl-4′-aminobenzoate (hereinafter referred to as APAB) 45 mmol, 4,4′-diaminodiphenyl ether (hereinafter referred to as ODA) containing an ester group in the monomer skeleton in a well-dried sealed reaction vessel with a stirrer After being dissolved in 5 mmol, 191 mL of N-methyl-2-pyrrolidone (dehydrated) (manufactured by Wako Pure Chemical Industries, Ltd.) (hereinafter referred to as NMP), this solution contains p-methylphenylenebis containing an ester group in the monomer skeleton. (Trimellitic acid monoester anhydride (hereinafter referred to as MTAHQ) powder 50 mmol was gradually added. After 30 minutes, the viscosity of the solution increased rapidly. Further, the mixture was stirred at 80 ° C. for 4 hours to be transparent, uniform and viscous. A polyamic acid varnish having an ester group was obtained, which was obtained at room temperature and at -20 ° C. No precipitation or gelation occurred even after standing for a month, showing high solution storage stability.Intrinsic viscosity of the polyamic acid measured with an Ostwald viscometer in NMP at a concentration of 0.5% by mass was 30 ° C. The polyamic acid varnish was placed on a metal coating table so that the mat surface side of the copper foil (F2-WS foil, Furukawa Circuit Foil Co., Ltd.) having a thickness of 12 μm was the surface. The surface temperature of the coating table is set to 90 ° C., and it is applied to the copper foil mat surface with a doctor blade using a polyamic acid varnish, then left still for 30 minutes on the coating table, and further 100 ° C. in a dryer. After standing for 30 min, a polyamic acid film (thickness: 45 μm) having no tackiness was obtained, and then the polyamic acid film was attached to a SUS metal plate, and the heating rate was 5 in a hot air drier in a nitrogen atmosphere. ℃ min at, 30min, 200 ° C. in 1h, was imidized at 1h at 400 ° C.. copper foil polyimide film curl without 25μm thickness was obtained at 0.99 ° C..

This polyimide film with copper foil was etched with a ferric chloride solution to obtain a light brown polyimide film with a thickness of 25 μm. This polyimide film did not break even in the 180 ° bending test and showed flexibility. Moreover, it did not show any solubility in organic solvents.
Similarly, this polyamic acid varnish is spin-coated on a 6-inch silicon wafer with a spin coater (MS-250 Mikasa Co., Ltd.), left standing at 100 ° C. for 30 minutes in a dryer, and then tacky. A polyamic acid film (thickness: 17 μm) with no film was obtained. Thereafter, the silicon wafer was imidized in a hot air drier in a nitrogen atmosphere at a rate of temperature increase of 5 ° C./min at 150 ° C. for 30 min, 200 ° C. for 1 h, and 400 ° C. for 1 h. Thereafter, it was peeled from the silicon wafer with hydrofluoric acid to obtain a polyimide film having a thickness of 10 μm.
Glass transition temperature (Tg) and linear thermal expansion coefficient (CTE), hygroscopic expansion coefficient (CHE), elastic modulus, elongation at break, adhesive strength of copper-polyimide composite, solder heat resistance and moisture absorption solder heat resistance of the obtained polyimide resin The sex results are shown in Table 1.

[Comparative Example 4]
Polyamic acid varnish obtained by adding 2-ethyl-4-methyl-imidazole (product name 2E4MZ, manufactured by Shikoku Kasei Co., Ltd.) to the polyamic acid varnish obtained in Comparative Example 3 so as to be 6 parts by mass with respect to the resin solid content. A composition was obtained. By repeating the same operation as in Comparative Example 1, a polyimide resin and a copper-polyimide composite were obtained.
Glass transition temperature (Tg) and linear thermal expansion coefficient (CTE), hygroscopic expansion coefficient (CHE), elastic modulus, elongation at break, adhesive strength of copper-polyimide composite, solder heat resistance and moisture absorption solder heat resistance of the obtained polyimide resin The sex results are shown in Table 1.

  The polyamic acid varnish composition of the present invention can be suitably used for wiring substrates such as flexible printed boards and IC package boards that require high-density wiring and high reliability.

Claims (6)

A polyamic acid varnish composition comprising a polyamic acid obtained by addition polymerization of an aromatic tetracarboxylic dianhydride and an aromatic diamine, a nitrogen-containing aromatic compound, and a solvent, the aromatic tetracarboxylic dianhydride Has an ester structure represented by the formula (1), and / or the aromatic diamine has an ester structure represented by the formula (2), and the nitrogen-containing aromatic compound is represented by the formulas (3) to (3): 12) selected from the group consisting of an oxazole compound, an amide compound, a nitrile compound, and a benzofurazan derivative, wherein the nitrogen-containing aromatic compound is 0.01 to 20 with respect to 100 parts by mass of the polyamic acid. A polyamic acid varnish composition characterized by being part by mass.

(M is selected from a divalent aromatic group represented by the formula (1), and R _{1 to} R ₃ represent an alkyl group having 1 to 4 carbon atoms, a methoxy group, or a hydrogen atom.)

(M = 0 or 1 and R _{4 to} R ₆ represent an alkyl group having 1 to 4 carbon atoms, a methoxy group, or a hydrogen atom.)

(X ₁ and X ₃ are tetravalent aromatic groups represented by the formulas (3), (4), (7) and (8), and X ₂ and X ₄ are the formulas (5) and (9). In the formula, Y _{1 to} Y ₅ are ether, —S—, a saturated, unsaturated alkylene group having 1 to 4 carbon atoms , a carbonyl group, or a sulfonyl group. R _{7 to} R ₁₄ , R _{16 to} R ₂₉ , and R _{31 to} R ₃₃ are each a hydrogen atom, an alkyl group having 1 to 4 carbon atoms, an alkoxy group, a halogenated alkyl group, a halogen group, a nitro group, a cyano group, A hydroxyl group, —SO ₂ H, —OPh, —SCH ₃ , or —SPh, where n = 1 and 2. R ₁₅ , R ₃₀ , and R ₃₄ are a hydrogen atom, an alkyl group having 1 to 4 carbon atoms, an alkoxy group group, halogenated alkyl group, a halogen group, a nitro group, a cyano group, a hydroxyl group, -SO ₂ H, -OPh, -SCH _3, it is -SPh or a phenyl group.) The polyamic acid varnish composition according to claim 1, wherein the nitrogen-containing aromatic compound is an oxazole compound represented by any one or more of formulas (13) to (15).

(X ₅ is a tetravalent aromatic group represented by the formula (13), and X ₆ is a divalent aromatic group represented by the formula (14). R _{35 to} R ₃₈ , R ₄₀ is a hydrogen atom, an alkyl group having 1 to 4 carbon atoms, an alkoxy group, a halogenated alkyl group, a halogen group, a nitro group, a cyano group, a hydroxyl _{group, -SO 2 H, -OPh, -SCH} 3, or -SPh R ₃₉ is a hydrogen atom, an alkyl group having 1 to 4 carbon atoms, an alkoxy group, a halogenated alkyl group, a halogen group, a nitro group, a cyano group, a hydroxyl group, —SO ₂ H, —OPh, —SCH ₃ , —SPh. Or a phenyl group.) The polyamic acid varnish composition according to claim 1, wherein the nitrogen-containing aromatic compound is an amide compound represented by any one or more of formulas (16) to (18).

(X ₇ is a tetravalent aromatic group represented by the formula (16), and X ₈ is a divalent aromatic group represented by the formula (17). R _{41 to} R ₄₄ , R ₄₆ is a hydrogen atom, an alkyl group having 1 to 4 carbon atoms, an alkoxy group, a halogenated alkyl group, a halogen group, a nitro group, a cyano group, a hydroxyl group, —SO ₂ H, —OPh, —SCH ₃ , or —SPh. R ₄₅ is a hydrogen atom, an alkyl group having 1 to 4 carbon atoms, an alkoxy group, a halogenated alkyl group, a halogen group, a nitro group, a cyano group, a hydroxyl group, —SO ₂ H, —OPh, —SCH ₃ , —SPh. Or a phenyl group.) The polyamic acid varnish composition according to claim 1, wherein the nitrogen-containing aromatic compound is an amide compound represented by the formula (16).

(X ₇ is a tetravalent aromatic group represented by the formula (16). R ₄₁ and R ₄₂ are a hydrogen atom, an alkyl group having 1 to 4 carbon atoms, an alkoxy group, a halogenated alkyl group, a halogen atom. Group, nitro group, cyano group, hydroxyl group, —SO ₂ H, —OPh, —SCH ₃ , or —SPh.)   A polyimide resin obtained by imidizing the polyamic acid varnish composition according to claim 1.   A metal-polyimide composite comprising a polyimide resin obtained by imidizing the polyamic acid varnish composition according to claim 1 and a metal foil.