JPH08250860A - Flexible printed board - Google Patents

Abstract

PURPOSE: To provide a flexible printed board which is free from curling, twisting, deflecting, etc., even if heat history is applied, and/or has sufficient adhesion, resistance against bending, size stability, etc., and is excellent in workability and industrially useful with a small curl after a conductor is etched, and a flexible printed board which can easily satisfy diverse needs of demanders. CONSTITUTION: A flexible printed board formed by applying a resin layer directly on a conductor and having at least the conductor and an insulator is of a multilayer structure wherein the insulator comprises a plurality of polyimide resin layers having different linear expansion coefficients from one another. In addition, a resin layer having a higher thermal expansion is in contact with the layer wherein conditions that a ratio (t2 /t1 ) of a thickness (t1 ) of the resin layer having the higher thermal expansion and a thickness (t2 ) of a resin layer having a lower thermal expansion is in a range of 0.01<t2 /t1 <20,000 (where t1 and t2 is a sum of thickness of respective resin layers) are satisfied.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention is free from curling, twisting, warping, etc. with respect to temperature changes, and has heat resistance, dimensional stability,
The present invention relates to a flexible printed circuit board having excellent adhesiveness, bending resistance, etc., and a low water absorption rate, and a method for manufacturing the same.

[0002]

2. Description of the Related Art Conventionally, a flexible printed circuit board or a flat cable (hereinafter, both are referred to as "flexible printed circuit board") is generally formed by bonding a conductor and an organic polymer insulator with an adhesive such as epoxy resin or urethane resin. Was manufactured. However, if a thermal history such as thermocompression bonding is applied at this time, there is a drawback that the substrate is curled, twisted, warped, etc. during cold, making it impossible to perform subsequent conductor patterning or the like. These problems result from the difference in linear expansion coefficient between the conductor and the insulator. Further, there are problems that the flame retardancy is lowered due to the adhesive layer, that the polyimide film used is expensive, and that the flexible printed circuit board becomes expensive due to the large amount of time and effort required for bonding.

JP-A-56-23791 and the like propose a method of applying a polyamideimide solution to a metal foil and, after drying, alleviating curl caused by a difference in linear expansion coefficient by heat treatment in a subsequent step. However, this method is still unsatisfactory since it has not been solved and curled at the time of reheating a solder bath or the like because it takes time to manufacture and the coefficient of linear expansion is different.

Further, in JP-A-60-157286, JP-A-60-243120, etc., a polyimide or a polyimide precursor solution having a specific structure is applied onto a conductor to obtain a resin having a low thermal expansion, Although a method of obtaining a flexible printed circuit board with less curl has been proposed, the film has a film with the surface that was in contact with the conductor when the conductor was etched to form a circuit inside being insufficient due to insufficient adhesion. However, there is a problem in that the post-work such as the circuit protection becomes difficult after that.

Further, in the type using the conventional adhesive layer,
The adhesive layer had hardness, tear strength and other physical properties lacking in the polyimide film, but on the other hand, the presence of this adhesive layer caused problems in various points such as heat resistance and punching processability. there were.

[0006]

DISCLOSURE OF INVENTION Problems to be Solved by the Invention The inventors of the present invention have conducted extensive studies in view of the above-mentioned viewpoint, and as a result, by forming a multilayered insulating material with a plurality of polyimide resin layers having different linear expansion coefficients, The inventors have found that it is possible to obtain a flexible printed circuit board having excellent dimensional stability against changes, adhesive strength, and flatness after etching, and have completed the present invention.

Therefore, an object of the present invention is to prevent curling, twisting, warping, etc. even when heat history is applied, and / or to have sufficient adhesive strength, bending resistance, dimensional stability, etc., and An object of the present invention is to provide an industrially useful flexible printed circuit board which has a small curl after etching a conductor and is excellent in workability. Still another object is to provide a flexible printed circuit board that can easily meet the diversifying demands of customers.

[0008]

That is, the present invention is directed to
It is formed by applying a resin layer directly on the body and at least a conductor
And flexible printed circuit board having an insulator
A plurality of insulators having different linear expansion coefficients from each other.
It has a multi-layered structure consisting of polyindo resin layer and
High thermal expansion resin layer is in contact with the conductor, and high thermal expansion
Thickness of resin layer (t ₁) And the thickness of the low thermal expansion resin layer
(T₂) Ratio (t₂/ T₁) Is 0.01 <t₂/ T₁
<20,000 (however, t₁And t₂Is each resin
Flexible pre-condition that satisfies the condition (which is the sum of layer thicknesses)
It is a printed circuit board.

In the present invention, the flexible printed circuit board formed by direct coating means that the resin solution or its precursor resin solution is directly coated on the conductor, dried, and then cured if necessary to form a conductor. A flexible wiring board for forming a composite material with an insulator or a material thereof.

The polyimide resin referred to in the present invention is a heat resistant resin such as polyimide, polyamideimide, polybenzimidazole, and polyimide ester.

In the present invention, the coefficients of linear expansion differ from each other.
By combining a high thermal expansion resin layer and a low thermal expansion resin layer
A high thermal expansion resin layer that forms an insulator
Thickness (t₁) And the thickness of the low thermal expansion resin layer (t₂) Ratio
Rate (t₂/ T₁) (However, t ₁And t₂Is each tree
Is the sum of the thicknesses of the fat layer), 0.01 to 20,
000, preferably 2 to 100, more preferably 3 to 2
It is necessary to meet the condition of 5. Where high thermal expansion resin
Layer and low thermal expansion resin layer, insulation that forms a multilayer structure
The simple average value of the coefficient of linear thermal expansion of each constituent resin layer of the body
Resin layer having a coefficient of linear expansion higher than that of the standard
Is called a high thermal expansion resin layer and has a lower linear expansion.
The resin layer having a coefficient is referred to as a low thermal expansion resin layer. Of thickness
Ratio (t ₂/ T₁If the value of) is too small,
The linear expansion coefficient of the
The board curls with the insulator inside and
Work becomes difficult, and distortion is released when the conductor is etched
As a result, the dimensions change greatly. On the contrary, the thickness ratio (t
₂/ T₁If the value of) is too large, it is the object of the present invention.
To improve the adhesive strength to the
It becomes difficult to prevent

In the present invention, the total thickness of the insulator (t
₁ + t ₂ ) is usually 5 to 100 μm, preferably 10 to
It is 50 μm. The coefficient of linear expansion of the high thermal expansion resin layer forming this insulator is 20 × 10 ⁻⁶ (1 / K) or more,
It is preferably (30 to 100) × 10 ⁻⁶ (1 / K), and the linear expansion coefficient of the low thermal expansion resin layer is 20 × 10 ⁻⁶ (1
/ K), preferably (0 to 19) × 10 ^-6 (1 /
K), and the linear expansion coefficient between these high thermal expansion resin layer and low thermal expansion resin layer is 5 × 10 ⁻⁶ (1
/ K) or more, preferably 10 × 10 ⁻⁶ (1 / K) or more.

Any polyimide resin may be used as the high thermal expansion resin, but the main component is preferably a polyamideimide resin or polyimide resin having a structural unit represented by the following general formula. .

[0014]

Embedded image (However, in each of the above general formulas, Ar ₁ is a divalent aromatic group having 12 or more carbon atoms, and Ar ₂ is a tetravalent aromatic group.)

Here, the Ar ₁ is, for example,

Embedded image

And the like, and the above Ar ₂
For example,

Embedded image Etc., but from the viewpoint of inexpensiveness and the adhesion with the conductor, preferably

[Chemical 4] Is. As such a polyimide resin having a high thermal expansion property, a compound represented by the following general formula (1) is particularly preferable.

Embedded image (However, Ar ₁ in the formula is a divalent aromatic group having 12 or more carbon atoms.)

The polyimide resin having such a structure usually has a relatively high linear expansion coefficient of 20 × 10 ⁻⁶ (1 / K) or more, but the adhesion with a conductor, flexibility, etc. Demonstrates excellent performance in.

The low thermal expansion resin is not particularly limited as long as it is a polyimide resin having a low linear expansion coefficient, but a polyimide resin having a structural unit represented by the following general formula (2) or (3). Is preferred.

General formula (2)

[Chemical 6]

(In the formula, Ar represents a tetravalent aromatic group, and R ₁ and R ₂ represent either a lower alkyl group, a lower alkoxy group or halogen, which may be the same or different from each other. ,, l and m are integers from 0 to 4,
Having at least one lower alkoxy group), preferably the following structural unit

[0021]

[Chemical 7] Polyamide-imide resin containing.

General formula (3)

Embedded image A polyimide resin containing a structural unit represented by.

The synthesis of these polyimide resins is generally performed by N-methylpyrrolidone (NMP), dimethylformamide (DMF), dimethylacetamide (DMA).
c), dimethyl sulfoxide (DMSO), dimethyl sulfate, sulfolane, butyrolactone, cresol, phenol, halogenated phenol, cyclohexanone,
In a solvent such as dioxane, tetrahydrofuran, diglyme, the diamine compound and the acid anhydride compound corresponding to the above general formulas are mixed in a substantially equimolar ratio, and the reaction temperature is 0.
By repeating the reaction in the range of ~ 200 ° C, preferably 0 ~ 100 ° C, a polyimide-based resin precursor solution is obtained, and further, the operation of coating the resin solution on a conductor and drying it is repeated, Alternatively, a multi-layer die or the like may be used to apply multiple layers at the same time and dry to form a multi-layered polyimide-based resin layer or a polyimide-based precursor resin layer on the conductor. As described above, the imidization reaction is performed by heating at 300 ° C. or higher.

In the present invention, the polyimide-based high thermal expansion resin and low thermal expansion resin are subjected to copolymerization using various diamines, tetracarboxylic acid compounds, tricarboxylic acid compounds or their acid anhydrides or separately. The polyimide or the precursor thereof obtained by synthesis and polyamide imide can be blended.

Specific examples include p-phenylenediamine, m-phenylenediamine, 3,4'-diaminodiphenyl ether, 4,4'-diaminodiphenyl ether, 4,4'-diaminodiphenylmethane, 3,
3'-dimethyl-4,4'-diaminodiphenylmethane, 2,2-bis [4- (4-aminophenoxy) phenyl] propane, 1,2-bis (anilino) ethane, diaminodiphenyl sulfone, diaminobenzanilide,
Diaminobenzoate, diaminodiphenyl sulfide, 2,2-bis (p-aminophenyl) propane,
2,2-bis (p-aminophenyl) hexafluoropropane, 1,5-diaminonaphthalene, diaminotoluene, diaminobenzotrifluoride, 1,4-bis (p-aminophenoxy) benzene, 4,4′-bis ( p-aminophenoxy) biphenyl, diaminoanthraquinone, 4,4'-bis (3-aminophenoxyphenyl) diphenyl sulfone, 1,3-bis (anilino)
Hexafluoropropane, 1,4-bis (anilino) octafluorobutane, 1,5-bis (anilino) decafluoropentane, 1,7-bis (anilino) tetradecafluoroheptane, the following general formula

[0026]

[Chemical 9]

(In the formula, R ₄ and R ₆ represent divalent organic groups, R ₃ and R ₅ represent monovalent organic groups, and p and q
Represents an integer greater than 1), 2,2-bis [4- (p-aminophenoxy) phenyl] hexafluoropropane, 2,2-bis [4-
(3-Aminophenoxy) phenyl] hexafluoropropane, 2,2-bis [4- (2-aminophenoxy)]
Phenyl] hexafluoropropane, 2,2-bis [4
-(4-aminophenoxy) -3,5-dimethylphenyl] hexafluoropropane, 2,2-bis [4- (4
-Aminophenoxy) -3,5-ditrifluoromethylphenyl] hexafluoropropane, p-bis (4-amino-2-trifluoromethylphenoxy) benzene,
4,4'-bis (4-amino-2-trifluoromethylphenoxy) biphenyl, 4,4'-bis (4-amino
-3-trifluoromethylphenoxy) biphenyl,
4,4'-bis (4-amino-2-trifluoromethylphenoxy) diphenyl sulfone, 4,4'-bis (3
-Amino-5-trifluoromethylphenoxy) diphenyl sulfone, 2,2-bis [4- (4-amino-3
-Trifluoromethylphenoxy) phenyl] hexafluoropropane, benzidine, 3,3 ', 5,5'-tetramethylbenzidine, octafluorobenzidine,
3,3′-dimethoxybenzidine, o-tolidine, m-
Trizine, 2,2 ', 5,5', 6,6'-hexafluorotolidine, 4,4 "-diaminoterphenyl, 4,
There are diamines such as 4 ′ ″-diaminoquaterphenyl, and diisocyanates obtained by reacting these diamines with phosgene.

The tetracarboxylic acids and their derivatives include the following. Although tetracarboxylic acid is exemplified here, it goes without saying that an ester compound, an acid anhydride, or an acid chloride thereof can also be used. Pyromellitic acid, 3,3 ′, 4,4′-biphenyltetracarboxylic acid, 3,3 ′, 4,4′-benzophenonetetracarboxylic acid, 3,3 ′, 4,4′-diphenylsulfonetetracarboxylic acid, 2,3,3 ', 4'-diphenyl ether tetracarboxylic acid, 2,3,3', 4 '
-Benzophenone tetracarboxylic acid, 2,3,6,7-
Naphthalenetetracarboxylic acid, 1,4,5,7-naphthalenetetracarboxylic acid, 1,2,5,6-naphthalenetetracarboxylic acid, 3,3 ′, 4,4′-diphenylmethanetetracarboxylic acid, 2,2- Bis (3,4-dicarboxyphenyl) propane, 2,2-bis (3,4-dicarboxyphenyl) hexafluoropropane, 3,4
9,10-Tetracarboxyperylene, 2,2-bis [4- (3,4-dicarboxyphenoxy) phenyl]
There are propane, 2,2-bis [4- (3,4-dicarboxyphenoxy) phenyl] hexafluoropropane, butanetetracarboxylic acid, cyclopentanetetracarboxylic acid and the like. In addition, trimellitic acid and its derivatives can also be mentioned.

Further, it is possible to introduce a crosslinked structure or a ladder structure by modifying with a compound having a reactive functional group. For example, there are the following methods.

By modifying with a compound represented by the following general formula, a pyrrone ring, an isoindoloquinazolinedione ring or the like is introduced.

[Chemical 10] [Wherein, R ₇ represents a 2 + z-valent (z is 1 or 2) aromatic organic group, and B is a substituent selected from a —NH ₂ group, a —CONH ₂ group, or a —SO ₂ NH ₂ group. Group which is ortho to the amino group]

It is modified with a derivative of an amine, a diamine, a dicarboxylic acid, a tricarboxylic acid or a tetracarboxylic acid having a polymerizable unsaturated bond to form a crosslinked structure at the time of curing. As the unsaturated compound, maleic acid, nadic acid,
Tetrahydrophthalic acid, ethynylaniline and the like can be used.

A network structure is formed by modifying with an aromatic amine having a phenolic hydroxyl group or a carboxylic acid and using a crosslinking agent capable of reacting with the hydroxyl group or the carboxyl group.

The linear thermal expansion coefficient of the low thermal expansion resin of the present invention can be adjusted by modifying it with each of the above components. That is, the polyimide resin having only the structure of the general formula (2) or (3) can form an insulator having a linear expansion coefficient of 1 × 10 ⁻⁵ (K ⁻¹ ) or less in the plane, The linear expansion coefficient can be arbitrarily increased by modifying this using the above-mentioned components. Further, even a polyimide-based resin containing the structural unit represented by the general formula (2) or (3) can be made into a high thermal expansion resin by modifying it using the above-mentioned components. It is also possible to modify it for the purpose of further improving various physical properties such as adhesiveness and bending resistance.

In the present invention, by providing the high thermal expansion resin layer in contact with the conductor and the low thermal expansion resin layer in contact with it, good adhesive strength, dimensional stability at high temperature, and linear expansion coefficient of the entire insulator can be obtained. It is possible to achieve effects such as reduction. Further, a first high thermal expansion resin layer in contact with the conductor, a low thermal expansion resin layer in contact with the first high thermal expansion resin layer, and a second high thermal expansion resin layer in contact with the low thermal expansion resin layer are provided. Thus, the effects of the above two cases can be achieved at the same time. Further, by further providing a high thermal expansion resin layer in contact with the conductor, a first low thermal expansion resin layer in contact with this and a second low thermal expansion resin layer in contact with this and having a linear expansion coefficient higher than that, The curl of the film can be further reduced. By changing the type and composition of these low thermal expansion resin and high thermal expansion resin, it is possible to control mechanical properties such as elastic modulus and strength of the film, and to meet the needs of various consumers. You can

The flexible printed circuit board of the present invention has at least a conductor and an insulator. As the conductor, copper, aluminum, iron, silver, palladium, nickel, chromium, molybdenum, tungsten, or an alloy thereof is used. Of these, copper is preferred.

These conductors are chemically or siding on the surface with siding, nickel plating, copper-zinc alloy plating, aluminum alcoholate, aluminum chelate, silane coupling agent or the like for the purpose of improving the adhesive strength. Mechanical surface treatment may be applied.

[0037]

BEST MODE FOR CARRYING OUT THE INVENTION A reaction vessel equipped with a thermometer, a calcium chloride tube, a stirrer and a nitrogen inlet is charged with a predetermined diamine component and a solvent under a nitrogen stream and dissolved under stirring. While cooling, a predetermined tetracarboxylic acid dianhydride is added to obtain a polyamic acid (a high thermal expansion polyimide precursor solution and a low thermal expansion polyimide precursor solution).

Next, a highly heat-expandable polyamic acid solution is coated on the rough surface of the conductor foil having a predetermined thickness to a predetermined film thickness and dried at a predetermined temperature to form a first film.
Forming a resin layer, further coating a low thermal expansion polyamic acid solution on the first resin layer to a predetermined film thickness and drying at a predetermined temperature to form a second resin layer. Then, the whole is heated to a predetermined temperature to perform an imidization reaction, and a high thermal expansion resin layer and a low thermal expansion resin layer are sequentially laminated on the conductor, and a flexible printed circuit board having particularly excellent adhesive strength is obtained. obtain.

[0039]

EXAMPLES The present invention will be specifically described below based on Examples and Comparative Examples, but it goes without saying that the present invention is not limited thereto. For the coefficient of linear expansion, a thermomechanical analyzer (T
(MA), the temperature was raised to 250 ° C. and then cooled at 10 ° C./min, and the average linear expansion coefficient from 240 ° C. to 100 ° C. was calculated and calculated. The adhesive strength was determined by using a Tensilon tester, fixing the resin side of a copper-clad product having a width of 10 mm to an aluminum plate with a double-sided tape, and peeling copper in the 180 ° direction at a rate of 5 mm / min. Heat shrinkage rate is 10 mm in width and 200 m in length
The film after etching the conductor of m
Heat treatment was carried out for 30 minutes in a hot air oven at 0 ° C., and the dimensional change rate before and after the heat treatment was used to determine.

The curl of the film after etching is 10c in length after the conductor is entirely etched with an aqueous solution of ferric chloride.
1 x film 10m x 10cm x 25μm thick
After drying at 00 ° C. for 10 minutes, the radius of curvature of the generated curl was calculated and quantified. The strength and elastic modulus of the film after etching are JIS Z-1702, ASTM D-8.
82-67.

The abbreviations in each example are as follows. PMDA: pyromellitic dianhydride BPDA: 3,3 ′, 4,4′-biphenyltetracarboxylic dianhydride BTDA: 3,3 ′, 4,4′-benzophenone tetracarboxylic dianhydride DDE: 4 4′-diaminodiphenyl ether MABA: 2′-methoxy-4,4′-diaminobenzanilide PPD: paraphenylenediamine DDS: 3,3′-diaminodiphenylsulfone BAPP: 2,2-bis [4- (4-aminophenoxy) ) Phenyl] propane DDM: 4,4'-diaminodiphenylmethane DMAc: dimethylacetamide NMP: N-methyl-2-pyrrolidone

Synthesis Example 1 0.1 mol of DDE and 30 while flowing nitrogen at a rate of 200 ml / min into a 500 ml four-neck flask equipped with a thermometer, a calcium chloride tube, a stirrer and a nitrogen inlet.
After 0 ml of DMAc was added and stirred to dissolve it, 0.10 mol of BTDA was gradually added while cooling this solution to 10 ° C. or lower in a water cooling bath. The reaction mixture polymerizes while generating heat and is a viscous polyamic acid (polyimide precursor solution).
was gotten.

The polyamic acid solution was fixed on a stainless steel frame and a commercially available electrolytic copper foil having a thickness of 35 μm (manufactured by Nippon Mining Co., Ltd.) was used on the rough surface so that the film thickness was about 25 μm using an applicator. Coated at 130 ℃
And 150 ° C. in a hot-air oven for 10 minutes to dry in that order, and then the temperature was raised to 360 ° C. over 15 minutes to carry out an imidization reaction. The obtained copper-clad product had the resin largely curled inward. The copper clad product was etched with an aqueous ferric chloride solution, and the linear expansion coefficient of the obtained film was measured and found to be 55 × 10 ⁻⁶ (1 / K).

Synthesis Examples 2 to 6 Similar to Synthesis Example 1, a polymerization reaction was carried out using various diamine compounds and acid anhydrides to prepare a high thermal expansion polyimide precursor solution. Coating on foil gave a film with a thickness of 25 μm. The linear expansion coefficient 7 was measured in the same manner as in Synthesis Example 1. The results are shown in Table 1 together with Synthesis Example 1.

[0045]

[Table 1]

Synthetic Example 7 In the same manner as in Synthetic Example 1, 0.055 mol of MABA and 0.045 mol of DDE were dissolved in 300 ml of DMAc, and 0.10 mol of PMDA was added and reacted to obtain a viscous solution. A new polyamic acid was obtained. The linear expansion coefficient of the polyamide-imide film obtained by using this polyamic acid is 1
It was 3 × 10 ⁻⁶ (1 / K).

Synthesis Example 8 In the same manner as in Synthesis Example 1, 0.090 mol of PPD and 0.010 mol of DDE were dissolved in 300 ml of DMAc, and then 0.10 mol of BPDA was added and reacted to obtain a viscous solution. A new polyamic acid was obtained. The linear expansion coefficient of the polyimide film obtained by using this polyamic acid is 10 × 1.
It was 0 ^-6 (1 / K).

Examples 1 to 6 The resin solutions of Synthesis Examples 1 to 6 were coated on electrolytic copper foil so that the resin layer had a thickness of 2 μm, and then dried at 130 ° C. for 5 minutes. On top of the first resin layer thus obtained, the resin solution of Synthesis Example 7 was further applied to a resin layer having a thickness of 23.
The coating is performed so as to have a thickness of μm, and the coating is left to stand in a hot air oven at 130 ° C. and 150 ° C. for 10 minutes each in order and dried, and then the temperature is raised to 360 ° C. over 15 minutes to carry out an imidization reaction. Was formed into a copper clad product having a total resin layer thickness of 25 μm.

With respect to the obtained copper-clad product, its adhesive strength, film curl, heat shrinkage ratio and thermal expansion coefficient were measured. Table 2 shows the results. As is clear from the results of Table 2, the copper clad products of Examples 1 to 6 are almost flat and have a coefficient of thermal expansion lower than that of each Comparative Example, and the adhesive strength,
It also had excellent performance in curling and heat shrinkage of the film after etching. The film of Example 1 had a strength of 25 kg / mm ² and an elastic modulus of 500 kg / mm ² .

Example 7 A copper clad product was produced in the same manner as in Examples 1 to 6 except that the resin solution of Synthesis Example 8 was used in place of the resin solution of Synthesis Example 7, and its adhesive strength and film Curl, heat shrinkage and thermal expansion coefficient were measured. Table 2 shows the results.

Comparative Examples 1 and 2 The adhesive strength, the curl of the film, the heat shrinkage ratio and the thermal expansion coefficient of the copper clad products obtained by using the resin solutions of Synthesis Examples 7 and 8 were measured. Table 2 shows the results. The strength of the film of Comparative Example 1 obtained from the copper clad product of Synthesis Example 7 is 26 k.
g / mm ² , and the elastic modulus was 600 kg / mm ² .

Reference Examples 1 to 4 On the resin layer of the copper clad product obtained by using the resin solution of Synthetic Example 7, the resin solutions of Synthetic Examples 1 to 4 are 2 μm thick.
And then dried at 130 ° C for 5 minutes.
The temperature was raised to 360 ° C over 5 minutes to carry out the imidization reaction,
A copper clad product having a resin layer thickness of 27 μm was obtained. With respect to the obtained copper-clad product, its adhesive strength, film curl, heat shrinkage ratio and thermal expansion coefficient were measured. Table 2 shows the results. As is clear from the results in Table 2, the curl of the films of each of Reference Examples 1 to 4 is significantly improved.

Examples 8 to 11 The resin solutions of Synthesis Examples 1 to 4 were coated on the resin layer of the copper clad product obtained in Example 1 so that the thickness of the resin layer was 2 μm, and the temperature was 130 ° C. After drying for 5 minutes, 360 minutes over 15 minutes
The temperature was raised to ° C to carry out an imidization reaction to form a third resin layer, and a copper clad product having a resin layer thickness of 27 µm was obtained. With respect to the obtained copper-clad product, its adhesive strength, film curl, heat shrinkage ratio and thermal expansion coefficient were measured. Table 2 shows the results. As is clear from the results in Table 2, each of these Examples 8
The adhesion and curl of the ~ 11 films are significantly improved.

Example 12 The copper-clad article obtained in Example 7 was coated with the resin solution of Synthesis Example 1 so that the resin layer had a thickness of 2 μm, and the temperature was 130 ° C.
After drying for 5 minutes, the temperature was raised to 360 ° C. over 15 minutes to carry out an imidization reaction to obtain a copper clad product having a resin layer thickness of 27 μm. With respect to the obtained copper-clad product, its adhesive strength, film curl, heat shrinkage ratio and thermal expansion coefficient were measured. Table 2 shows the results.

Comparative Examples 3 and 4 In the same manner as in Comparative Example 1 or 2, copper-clad products with a single resin layer having a thickness of 27 μm were produced. With respect to the obtained copper-clad product, its adhesive strength, film curl, heat shrinkage ratio and thermal expansion coefficient were measured. Table 2 shows the results.

Comparative Example 5 A copper-clad product obtained by using the resin solution of Synthesis Example 1 was
The adhesive force, the curl of the film, the heat shrinkage ratio and the thermal expansion coefficient were measured. Table 2 shows the results. The strength of this film is 18 kg / mm ² , and the elastic modulus is 250 k.
g / mm ² .

[0057]

[Table 2]

[0058]

The flexible printed circuit board of the present invention is
Dimensional stability against temperature changes, adhesive strength, excellent reliability in flatness after etching, etc., excellent workability such as protection of circuits made by etching,
It is extremely useful industrially.

Claims (4)

[Claims] 1. A resin layer is formed by directly coating a resin layer on a conductor.
A flexible probe having at least a conductor and an insulator.
In a lint board, the insulators are
Multilayer structure consisting of multiple polyimide resin layers with different numbers
And the high thermal expansion resin layer is in contact with the conductor,
The thickness of the high thermal expansion resin layer (t₁) And low thermal expansion tree
Thickness of fat layer (t₂) Ratio (t₂/ T₁) Is 0.01 <
t₂/ T ₁<20,000 (however, t₁And t₂Is it
(Which is the sum of the thickness of each resin layer)
Characteristic flexible printed circuit board. 2. The high thermal expansion resin layer has a linear expansion coefficient of 20 ×.
The flexible printed circuit board according to claim 1, wherein the flexible printed board has a coefficient of linear expansion of less than 20 × 10 ^-6 (1 / K), and the coefficient of linear expansion of the low thermal expansion resin layer is 10 ^-6 (1 / K) or more. 3. The flexible printed board according to claim 1, wherein the insulator comprises two layers, a high thermal expansion resin layer in contact with the conductor and a low thermal expansion resin layer in contact with the conductor. 4. A first high thermal expansion resin layer in which an insulator contacts the conductor, a low thermal expansion resin layer in contact with the first high thermal expansion resin layer, and a second high thermal expansion resin layer in contact with the low thermal expansion resin layer. The flexible printed circuit board according to claim 1, which has a three-layer structure including a high thermal expansion resin layer.