JPH0686534B2 - Flexible printed circuit board manufacturing method - Google Patents

Description

TECHNICAL FIELD The present invention relates to a method for manufacturing a flexible printed circuit board having excellent heat resistance, electrical characteristics, mechanical characteristics and dimensional stability. The present invention relates to a polyimide flexible printed circuit board and a method for producing a metal foil lined polyimide flexible printed circuit board having improved dimensional stability and heat dissipation in one-sided metal foil bonding.

[Conventional technology]

A flexible printed circuit board is a board for manufacturing a flexible printed circuit, and in recent years,
The use of the printed circuit is increasing because the cases that house the printed circuit are made compact. Conventionally, such a flexible printed circuit board is manufactured by laminating a polyimide film on a copper foil with an adhesive. In this substrate, the polyimide film has sufficiently good heat resistance, electrical properties and mechanical properties, but the adhesive property is insufficient, so that the polyimide film properties are not fully utilized.

Therefore, a method of manufacturing a flexible printed circuit board made of a polyimide metal-clad board without using an adhesive layer has been conventionally studied, and as an example, U.S. Pat.
No. 634, JP-A-49-129862, JP-A-58-190091, and JP-A-58-190092. However, a flexible printed circuit board having sufficient heat resistance, adhesiveness, flexibility and dimensional stability has not been obtained.

[Problems to be solved by the invention]

The object of the present invention is to provide further dimensional stability and heat resistance in single-sided and double-sided metal foil-clad polyimide flexible printed circuit boards and single-sided copper foil-clad, which are all excellent in heat resistance, electrical properties, mechanical properties and dimensional stability. It is an object of the present invention to provide a method for manufacturing a polyimide flexible printed circuit board lined with a metal foil having improved radiation.

[Means for solving problems]

The above object is achieved by the following method for manufacturing a flexible printed circuit board. For single-sided copper foil-clad polyimide flexible printed circuit boards, symmetrical aromatic primary amine groups and aromatic tetracarboxylic anhydrides containing symmetrical aromatic meta-substituted primary amine in an equivalent ratio of 100 to 20%. Polyimide produced by reacting with Film (A) (excluding the case) is used as an adhesive for laminating a metal foil and a thermosetting polyimide film.

Symmetric aromatic meta-substituted primary amine in equivalent ratio of 10
A polyimide film produced by reacting a symmetrical aromatic primary amine group containing 0 to 20% with an aromatic tetracarboxylic dianhydride, a film and a metal foil having no adhesiveness with the produced polyimide film. A method for manufacturing a flexible printed circuit board, characterized in that the polyimide film thus produced is directly laminated on a metal foil under pressure and heating.

Further, a polyimide film produced by reacting a symmetric aromatic primary amine group containing a symmetrical aromatic meta-substituted primary amine in an equivalent ratio of 100 to 20% with an aromatic tetracarboxylic dianhydride. Is used as an adhesive and an insulating layer for laminating metal foils to each other, and a method for manufacturing a flexible printed circuit board.

For a polyimide flexible printed circuit board lined with a metal foil for further improving dimensional stability and heat dissipation, a polyimide film (A) is used as a copper foil and a metal foil for improving dimensional stability. Can be used as an adhesive layer and an insulating layer for laminating.

The symmetrical aromatic meta-substituted primary amine (hereinafter abbreviated as m-diamine) used in the present invention can be represented by the following general formula.

[In the above general formula, × is O, SO ₂ , S, CO, CH ₂ , C (C
H ₃ ) ₂ and C (CF ₃ ) ₂ and each x may be the same or different. ] Examples of m-diamine represented by the above general formula are 3,
3'-diaminodiphenyl ether, 3,3'-diaminodiphenyl sulfoxide, 3,3'-diaminodiphenyl sulfoxide, 3,3'-diaminodiphenyl sulfone, 3,3'-diaminobenzophenone, Bis [4- (3-aminophenoxy) phenyl] methane, 2,2-bis [4- (3-aminophenoxy) phenyl] propane, 2,2-bis [4- (3
-Aminophenoxy) phenyl] -1,1,1,3,3,3-hexafluoropropane, 1,3-bis (3-aminophenoxy) benzene, 4,4'-bis (3-aminophenoxy) biphenyl, bis [4 -(3-aminophenoxy) phenyl] ketone, bis [4- (3-aminophenoxy) phenyl] sulfide, bis [4- (3-aminophenoxy) phenyl] sulfoxide, bis [4- (3-aminophenoxy) phenyl] sulfone, bis [4- (3-aminophenoxy) phenyl] ether, 4,4'-bis (3
-Aminophenylsulfonyl) diphenyl ether, 4,
4'-bis (3-aminothiophenoxy) diphenyl sulfone, 1,4-bis [4- (3-aminophenoxy) benzoyl] benzene and the like can be mentioned. These can be used alone or in admixture of two or more. be able to.

The symmetric aromatic primary amine group represents 100% of m-diamine or a mixture of m-diamine and a symmetric aromatic para-substituted primary amine (hereinafter abbreviated as p-diamine). The p-diamine can be represented by the following general formula.

[In the above general formula, × is O, SO ₂ , S, CO, CH ₂ , C (C
H ₃ ) ₂ and C (CF ₃ ) ₂ and each x may be the same or different. ] Examples of p-diamine represented by the above general formula include 4,
4'-diaminodiphenyl ether, 4,4'-diaminodiphenyl sulfoxide, 4,4'-diaminodiphenyl sulfoxide, 4,4'-diaminodiphenyl sulfone, 4,4'-diaminobenzophenone, Bis [4- (4-aminophenoxy) phenyl] methane, 2,2-bis [4- (4-aminophenoxy) phenyl] propane, 2,2-bis [4- (4
-Aminophenoxy) phenyl] -1,1,1,3,3,3-hexafluoropropane, 1,3-bis (4-aminophenoxy) benzene, 4,4'-bis (4-aminophenoxy) biphenyl, bis [4 -(4-Aminophenoxy) phenyl] ketone, bis [4- (4-aminophenoxy) phenyl] sulfide, bis [4- (4-aminophenoxy) phenyl] sulfoxide, bis [4- (4-aminophenoxy) phenyl] sulfone, bis [4- (4-aminophenoxy) phenyl] ether, 4,4'-bis (4
-Aminophenylsulfonyl) diphenyl ether, 4,
4'-bis (4-aminothiophenoxy) diphenyl sulfone, 1,4-bis [4- (3-aminophenoxy) benzoyl] benzene and the like can be mentioned. These can be used alone or in admixture of two or more. be able to.

Aromatic tetracarboxylic acid anhydrides to be reacted with diamines include pyromellitic acid dianhydride, 3,3 ', 4,4'-benzophenone tetracarboxylic acid dianhydride and 2,2', 3,3'-benzophenone. Acid dianhydride, 3,3 ′, 4,4′-biphenyltetracarboxylic dianhydride, 2,2 ′, 3,3′-biphenyltetracarboxylic dianhydride, 2,2-bis (3 , 4-Dicarboxyphenyl) propane dianhydride, 2,2-bis (2,3-dicarboxyphenyl) propane dianhydride, bis (3,4-dicarboxyphenyl) ether dianhydride, bis (3,4-
Dicarboxyphenyl) sulfone dianhydride, 1,1-bis (2,3-dicarboxyphenyl) ethane dianhydride, bis (2,3-dicarboxyphenyl) methane dianhydride, bis (3, 4-dicarboxyphenyl) methane dianhydride, 2,3,
6,7-Naphthalenetetracarboxylic dianhydride, 1,4,5,8-
Naphthalenetetracarboxylic dianhydride, 1,2,5,6-naphthalenetetracarboxylic dianhydride, 1,2,3,4-benzenetetracarboxylic dianhydride, 3,4,9,10-perylenetetra Carboxylic dianhydride, 2,3,6,7-anthracenetetracarboxylic dianhydride, 1,2,7,8-phenanthrenetetracarboxylic dianhydride and the like are used. These may be used alone or in combination of two or more.

Examples of the organic solvent include N-methyl-2-pyrrolidone, N, N-dimethylacetamide, N, N-dimethylformamide, 1,3-dimethyl-2-imidazolidinone, N, N-
Diethylacetamide, N, N-dimethylmethoxyacetamide, dimethylsulfoxide, pyridine, dimethylsulfone, hexmethylphosphoramide, tetramethylurea, N-methylcaprolactam, tetrahydrofuran,
m-dioxane, p-dioxane, 1,2-dimethoxyethane, bis (2-methoxyethyl) ether, 1,2-bis (2-methoxyethoxy) ethane, bis- [2- (2
-Methoxyethoxy) ethyl] ether and the like.

In the present invention, when the polyamic acid is produced, the equivalent ratio of m-diamine and p-diamine is 100 to 20: m-diamine and p-diamine in an organic solvent in advance.
0-80, preferably 100-30: 0-70, particularly preferably 10
It is important to react with aromatic tetracarboxylic acid anhydride after mixing at 0 to 50: 0 to 50. P in the diamine
-When the equivalent ratio of diamine is 80% or more, the resulting polyimide has poor adhesive properties and the circuit of the flexible printed circuit easily peels off from the polyimide film and cannot be put to practical use.

Further, when producing a polyamic acid, 1,3-bis (3-aminophenoxy) benzene,
3'-diaminobenzophenone and 4,4'-bis (3-aminophenoxy) biphenyl are used alone or in combination, and 1,3-bis (4-aminophenoxy) benzene and 4,4'-diamino are used as p-diamine. Diphenyl ether and 4,4'-bis (4-aminophenoxy) biphenyl are used alone or in combination, and aromatic tetracarboxylic acid anhydrides are pyromellitic dianhydride, 3,3 ', 4,4'.
-The use of benzophenone tetracarboxylic acid dianhydride alone or in combination is particularly preferable, and it is a flexible printed circuit board excellent in mechanical properties such as heat resistance, electrical properties, adhesiveness, flexibility and dimensional stability. Can be manufactured.

In the case of producing a polyimide film from a polyamic acid solution, first, a sheet of steel or the like is coated with a polyamic acid solution having a constant thickness. When coating a sheet with a polyamic acid solution, it is preferable that the solution contains 5 to 40 weight percent of polyamic acid, and the logarithmic viscosity is 0.5 to 6 dl / g (85 ° C., concentration 0.
5 g / ml, a value measured with N, N-dimethylacetamide), and particularly preferably 0.7 to 4.

The operation of coating the polyamic acid solution on the sheet is preferably carried out by cast coating, and specifically, the following method is used. A polyamic acid solution is ejected onto the sheet from the film-forming slit to obtain a uniform thickness (the thickness is generally adjusted to 30 to 300μ).
To form a coating layer. As coating means, roll coater, knife coater, doctor blade,
It is also possible to use other known means such as a flow coater.

The polyamic acid coating layer prepared as described above is then heated to perform solvent removal and dehydration condensation reaction. This operation can be performed under any conditions such as normal pressure, reduced pressure or increased pressure.

Generally, the time required is 80-200 ° C, preferably 100-150
Heat to ° C to remove most of the solvent. When the temperature is 80 ° C or lower, the removal of the solvent is slow and not economical, and when the temperature is 200 ° C or higher, the removal of the solvent is too fast, which may adversely affect the film shape due to film formation, foaming, etc. Adhesion to the sheet starts as the condensation reaction starts, and the film becomes difficult to release from the sheet, which is not preferable.

After removing most of the solvent to form a polyamic acid film, it is peeled off from the sheet and completely removed of the solvent by a pin tenter and dehydration and condensation reaction in water are carried out to form an imidized polyimide film (A). Complete removal of the solvent, dehydration, and condensation reaction should be carried out at 150-350 ° C, preferably 200
Heat to ~ 300 ° C. At 150 ° C or lower, the solvent removal or condensation reaction is not sufficient, so that voids occur in the polyimide film during the laminating step when manufacturing a flexible printed circuit board, resulting in insufficient insulation and adhesion. Further, if the temperature is 350 ° C. or higher, the polyimide is deteriorated, the glass transition point of the polyimide is increased, and it becomes difficult to perform the lamination because the adhesion temperature in the lamination process is required to be high, which is not preferable.

As a metal foil conductor used when manufacturing a flexible printed circuit board using the polyimide film (A) produced as described above, a metal foil such as a copper foil, an aluminum foil, and a nickel foil is generally used. . As the metal foil for backing the substrate for improving the dimensional stability of the substrate, metals such as stainless steel foil, aluminum foil, nickel foil, and copper foil are used.

In order to laminate the polyimide film (A) with a metal foil or the like to form a substrate, it is essential to control the heating temperature and pressure.

As a temperature for molding as a substrate, a glass transition point of the polyimide film (A) to be used is required or more, preferably a glass transition temperature plus 15 to 100 ° C. is suitable, and a pressure for molding as a substrate is Is 1 to 500 kg /
cm ³ is suitable, preferably 5 to 100 kg / cm ³ . The time of heating and pressurizing is 1 to 200 minutes, preferably 5 to 60 minutes.
Minutes. When the surface of the metal foil is exposed to a temperature higher than the temperature at which it is oxidized in the process of molding into the above-mentioned substrate, oxidation of the surface of the metal foil occurs and the mechanical, electrical and adhesive properties of the metal foil deteriorate. When the molding is carried out at a temperature above the temperature at which the surface of the metal foil is oxidized, it is particularly preferable to carry out in an inert gas. The term "inert gas" as used herein means that the surface of the metal foil is in a gas atmosphere that does not undergo an oxidation reaction that adversely affects electrical properties, mechanical properties, adhesive strength, etc. when heated for a predetermined time. Meaning, depending on the heating temperature and time, in many cases it means a gas atmosphere with an oxygen concentration of 2 × 10 ⁻³ mol / l or less,
It can be executed by the following method. The material to be laminated is put in a bag-shaped product made of a heat-resistant film, and first, the air in the bag-shaped product is removed by a vacuum pump. Then, it is molded by a so-called vacuum press (manufactured by Bakium Press, Inc., USA) which is pressurized and heated with an inert gas. When the metal foil is laminated directly on only one side of the polyimide film (A),
The polyimide film (A) is not adhesive and the polyimide film (A) is inserted between the metal foil and the pressure,
It can be carried out by laminating under heating. Examples of the film that does not adhere to the polyimide film (A) under pressure and heating include Teflon (fluorine resin manufactured by Dyupon Co., Ltd.) and Upilex S (polyimide manufactured by Ube Industries, Ltd.).

The flexible printed circuit board made of the polyimide metal-clad sheet produced by the present invention represented by the above-described method does not include an adhesive layer, and the polyimide film (A) serving as an adhesive and an insulating layer is It is excellent in heat resistance, electrical characteristics, mechanical characteristics, and dimensional stability because it is a polyimide that does not substantially contain a solvent and has completed the condensation reaction and has excellent characteristics.

〔Example〕

Next, the present invention and its effects will be specifically described with reference to Examples and Comparative Examples.

The logarithmic viscosity in the examples is a value measured at 35 ° C., 0.5 g / 100 ml, N, N-dimethylacetamide, and the rotational viscosity is a value measured at 25 ° C. using a high viscosity rotor of an E-type viscometer. is there. Various performances as a printed circuit board were measured by the methods described below.

(1) Foil peeling strength It was performed according to the method of IPC-FC-241A.

(2) Surface resistance Measured according to JIS C-6481.

(3) Solder resistance A sample prepared according to JIS C-6481 is placed in a solder bath at 300 ° C.
After soaking for 60 seconds, "blister" and "deformation of polyimide film" were observed.

(4) Folding endurance According to JIS P-8115, the bending radius was 0.8 mm and the static load was 500 g. In the case of a double-sided metal foil-clad substrate, the metal foil on one side was entirely removed by etching, and then the measurement was performed.

(5) Dimensional stability The shrinkage rate was calculated according to the method of IPC-FC-241A.

Example 1 In a container equipped with a stirrer, a reflux condenser and a nitrogen inlet tube,
4'-bis (3-aminophenoxy) biphenyl 73.7g
(0.2 mol) is dissolved in 250 ml of N, N-dimethylacetamide, cooled to around 0 ° C, 43.6 g (0.2 mol) of pyromellitic dianhydride is added under a nitrogen atmosphere, and the mixture is stirred at around 0 ° C for 2 hours. did. Next, the solution was returned to room temperature and stirred under a nitrogen atmosphere for about 20 hours. The polyamic acid solution thus obtained had an inherent viscosity of 1.9 dl / g. The polyamic acid solution was diluted to 12% with N, N-dimethylacetamide and the viscosity was adjusted to 30,000 CPS. This solution was uniformly coated on a smooth glass plate using a doctor blade. The coated glass plate was heated at 135 ° C. for 1 hour to obtain a polyamic acid film. The film was peeled from the glass plate, placed in a pin tenter, and reheated. The heating at that time was gradually performed from 100 ° C to 280 ° C over 2 hours. After that, it was kept at 280 ° C. for 1 hour and then cooled to room temperature to obtain a polyimide film. The film thickness was 15μ and the residual solvent amount was 0.1% or less. This polyimide film is inserted between a rolled copper foil (thickness 35μ) and a Kapton film (polyimide film made by Dyupon Co., thickness 25μ) and laminated to make a Baquium Press (Bakium Press USA).
Molding in nitrogen at 300 ℃, 20kg / cm ³ for 30 minutes,
A Kapton-based single-sided copper-clad flexible printed circuit board was obtained. The characteristics of this substrate are shown in Table 1.

Example 2 A polyimide film having a thickness of 25 μm (residual solvent content: 0.1% or less) prepared in the same manner as in Example 1 was rolled into a copper foil (thickness: 35).
μ) and Iupilex S film (25μ), and stack them.
Molding was carried out at 20 ° C. and 20 kg / cm ³ for 40 minutes. After cooling to room temperature,
The Upilex S film was peeled from the laminated sheet to obtain a single-sided copper-clad flexible printed circuit board without using an adhesive layer. The characteristics of this substrate are shown in Table 1.

Example 3 In a container equipped with a stirrer, a reflux condenser and a nitrogen introducing tube,
4'-bis (3-aminophenoxy) biphenyl 51.6g
(0.14 mol) and 1,3-bis (3-aminophenoxy) benzene 17.5 g (0.06 mol) were dissolved in 250 ml of N, N-dimethylacetamide, cooled to around 0 ° C., and pyromellitic acid was added under a nitrogen atmosphere. 43.6 g (0.2 mol) of dianhydride was added, and the mixture was stirred at around 0 ° C for 2 hours. Next, the solution was returned to room temperature and stirred under a nitrogen atmosphere for about 20 hours. The polyamic acid solution thus obtained had an inherent viscosity of 1.6 dl / g. The polyamic acid solution was diluted to 15% with N, N-dimethylacetamide and the viscosity was adjusted to 25,000 CPS.
This solution was uniformly coated on a smooth glass plate using a doctor blade. 135 this coated glass plate
The film was heated at ° C for 1 hour to obtain a polyamic acid film. The film was peeled from the glass plate, placed in a pin tenter, and reheated. The heating at that time is 100 ℃ to 250 ℃
It took about 2 hours until it was done gradually. After that, it was kept at 250 ° C. for 1 hour and then cooled to room temperature to obtain a polyimide film. The film thickness was 25μ, and the amount of residual solvent was not detected. This polyimide was inserted between two electrolytic copper foils (18μ thick) and laminated, and molded by hot pressing at 250 ° C and 40kg / cm ³ for 20 minutes. Polyamide was the adhesive and insulating layer. A double-sided copper clad flexible printed circuit board was obtained. The characteristics of this substrate are shown in Table 1.

Example 4 1,3 in a container equipped with a stirrer, a reflux condenser and a nitrogen inlet tube
-Bis (3-aminophenoxy) benzene 14.6 g (0.05
Mol) and 4,4'-diaminodiphenyl ether 10.0 g (0.
(05 mol) and N, N-dimethylacetamide (200 ml) and dissolved in a nitrogen atmosphere at room temperature to give 3,3 ', 4,4'-
32.2 g (0.1 mol) of benzophenone tetracarboxylic acid dianhydride was added, and the mixture was stirred under a nitrogen atmosphere for about 22 hours.
The polyamic acid solution thus obtained was used to prepare a polyimide film in the same manner as in Example 3 (final drying temperature: 250 ° C.). The thickness of this polyimide film is 25μ,
The residual solvent was 0.2%. This film is an electrolytic copper foil (3
5μ) and Iupilex S film (25μ) are inserted and laminated, using a Bakiyumu press in nitrogen at 280
Molding was carried out at 20 ° C. and 20 kg / cm ³ for 30 minutes. After cooling to room temperature, the Upilex S film was peeled off from the laminated sheet to obtain a single-sided copper-clad flexible printed circuit board without using an adhesive layer. The characteristics of this substrate are shown in Table 1.

Example 5 1,3 in a container equipped with a stirrer, a reflux condenser and a nitrogen inlet tube
29.2 g (0.1 mol) of bis (3-aminophenoxy) benzene was dissolved in 200 ml of N, N-dimethylacetamide, and 3,3 ′, 4,4′-benzophenonetetracarboxylic acid dicarboxylic acid was dissolved at room temperature in a nitrogen atmosphere. Anhydrous 32.2 g (0.1 mol) was added, and the mixture was stirred under a nitrogen atmosphere for about 20 hours. The polyamic acid solution thus obtained had an inherent viscosity of 1.72 dl / g. This polyamic acid solution was diluted with N, N-dimethylacetamide 14
% And diluted to a viscosity of 31,000 CPS. This solution was uniformly coated on a smooth glass plate using a doctor blade. The coated glass plate was heated at 135 ° C. for 1 hour to obtain a polyamic acid film. The film was peeled from the glass plate, placed in a pin tenter, and reheated. The heating at that time was gradually performed from 100 ° C to 240 ° C over 90 minutes. After that, it was kept at 220 ° C. for 1 hour and then cooled to room temperature to obtain a polyimide film. The film thickness was 25μ, and the amount of residual solvent was not detected. The polyimide film was laminated by inserting between the electrolytic copper foil (35micro) and aluminum foil (50.mu.), 230 ° C. at hot press performs molding 40 kg / cm ³ 30 minutes, aluminum foil dimensional stability Used as a backing material for improvement. A single-sided copper-clad flexible printed circuit board was obtained. The characteristics of this substrate are shown in Table 1.

Comparative Example 1 A container equipped with a stirrer, a reflux condenser and a nitrogen inlet tube was used to
4'-diaminodiphenyl ether 20.0 g (0.1 mol)
Dissolve in 200 ml of N, N-dimethylacetamide, add 21.8 g (0.1 mol) of pyromellitic dianhydride at 5 ° C. in a nitrogen atmosphere at room temperature and stir for about 2 hours, then return to room temperature and further Stirred for 20 hours. The polyamic acid solution thus obtained had an inherent viscosity of 1.6 dl / g. This polyamic acid solution was diluted to 15% with N, N-dimethylacetamide and the viscosity was adjusted to 28,000 CPS. 223g of this solution
Then, 88 g of the diluted solution obtained in Example-5 was thoroughly mixed under a nitrogen atmosphere to obtain a polyamic acid solution of m-diamine: p-diamine = 0.2: 0.8 (equivalent ratio). This solution was used in Example 1
A polyimide film was prepared by the same method as above (final drying temperature 280 ° C.). The film thickness of this polyimide film is 25μ
And the residual solvent amount was 0.1%. Using this film, a single-sided copper-clad flexible printed circuit board was obtained in the same manner as in Example 2. The characteristics of this substrate are shown in Table 1.

Comparative Example-2 In Example 2, molding was carried out at 280 ° C. and 40 kg / cm ³ for 40 minutes using a normal hot press in place of the vacuum press. After cooling to room temperature, the Upilex S film was peeled from the laminated sheet to obtain a single-sided copper-clad flexible printed circuit board without using an adhesive layer. The characteristics of this board are shown in Table-1.
It was on the street.

[Effect of the Invention] According to the present invention, as described in the above embodiment, by using a polyimide film having an adhesive property and excellent in insulating property, the polyimide film can be directly laminated on the metal foil. , Heat resistance, electrical characteristics and adhesiveness,
It has become possible to manufacture single-sided and double-sided metal foil-clad polyimide flexible printed circuit boards which are excellent in mechanical properties such as flexibility and dimensional stability.

Claims (5)

[Claims] 1. A symmetric aromatic meta-substituted primary amine is produced by reacting a group of symmetric aromatic primary amines containing 100 to 20% in an equivalent ratio with an aromatic tetracarboxylic dianhydride. Polyimide (However, polyimide The method for producing a flexible printed circuit board is characterized in that the film (1) is used as an adhesive for laminating a metal foil and a thermosetting polyimide film. 2. A reaction product of a symmetric aromatic primary amine group containing 100 to 20% of a symmetrical aromatic meta-substituted primary amine in an equivalent ratio, and an aromatic tetracarboxylic dianhydride. The laminated polyimide film is inserted between the film and the metal foil which are not adhesive to the generated polyimide film and laminated, and the laminated polyimide film is laminated directly on the metal foil under pressure and heating. And a method for manufacturing a flexible printed circuit board. 3. A symmetric aromatic meta-substituted primary amine is produced by reacting a group of symmetric aromatic primary amines containing 100 to 20% by weight of an equivalent amount with an aromatic tetracarboxylic dianhydride. A method for manufacturing a flexible printed circuit board, characterized in that the above-mentioned polyimide film is used as an adhesive and insulating layer for laminating metal foils. 4. The method according to claim 3, wherein at least one of the two metal foils is a copper foil. 5. The method according to any one of claims 1 to 4, wherein the laminating step is performed by heating and pressurizing in an inert gas.