JPH01245586A - Flexible printed board - Google Patents

Abstract

PURPOSE:To realize a flexible printed board excellent in workability and valuable for an industrial use by a method wherein the thickness ratio of a resin layer high in thermal expansion to another resin layer low in thermal expansion is specified, where both the layers are polyimide resin layers of an insulator. CONSTITUTION:A flexible printed board composed of, at least, a conductor and an insulator is formed by coating the conductor with a resin layer, where the above insulator is a multilayer structure composed of two or more polyimide resin layers, and the t2/t1 ratio, where t2 denotes the sum of the thicknesses of resin layers low in thermal expansion and t1 represents the sum of the thicknesses of other resin layers high in thermal expansion, is so set as to satisfy an equality, 0.01<t2/t1<20000. The whole thickness (t1+t2) of the insulator is normally 5-100mum, and it is preferable that the linear expansion coefficients of the resin layers high and low in the thermal expansion are 20X10<-6>(1/K) or more and less than 20X10<-6>(1/K) respectively, where the resin layers compose the insulator.

Description

[Detailed Description of the Invention] [Industrial Application Field] The present invention has no curling, twisting, warping, etc. due to temperature changes, and has excellent heat resistance, dimensional stability, adhesiveness, bending resistance, etc. The present invention also relates to a flexible printed circuit board with a low water absorption rate and a method for manufacturing the same.

[Prior Art] Conventionally, flexible printed circuit boards or flat cables (hereinafter referred to as flexible printed circuit boards) are generally manufactured by bonding a conductor and an organic polymer insulator with an adhesive such as epoxy resin or urethane resin. Ta.

However, if a thermal history such as thermocompression bonding is applied at this time, the substrate may curl, twist, warp, etc. when it is cold, making subsequent patterning of the conductor impossible. These problems are caused by the difference in coefficient of linear expansion between conductors and insulators.

In addition, there were other problems such as the flame retardance being lowered due to the adhesive layer, and the polyimide film used being expensive and requiring a great deal of effort to bond together, making the flexible printed circuit board expensive.

In JP-A-56-23-791, etc., a method has been proposed in which a polyamide-imide solution is applied to a metal foil, and after drying, the curl that occurs due to the difference in linear expansion coefficient is alleviated by heat treatment in a subsequent process. However, this method is still unsatisfactory as it requires time and effort to manufacture and curls when reheated in a soldering bath due to different coefficients of linear expansion.

Also, JP-A-60-157,286 and JP-A-60
-243.120 and other publications propose a method of applying a polyimide having a specific structure or a polyimide precursor solution onto a conductor to obtain a resin with low thermal expansion, thereby obtaining a flexible printed circuit board with less curl. The adhesive force may be insufficient, or when the conductor is etched to form a circuit, the film curls significantly with the side that was in contact with the conductor facing inwards, making subsequent work such as protecting the circuit difficult. The problem of becoming one was rare.

In addition, in conventional types using an adhesive layer, the adhesive layer maintains physical properties such as hardness and tear strength that are lacking in polyimide films, but on the other hand, the presence of this adhesive layer makes it difficult to maintain heat resistance, for example. There were problems in various respects such as , hammering workability, etc.

[Problems to be Solved by the Invention] As a result of extensive research in view of this point of view, the present inventor has found that the temperature can be improved by multilayering an insulator with a plurality of polyindo resin layers having different coefficients of linear expansion. The present invention was completed based on the discovery that it is possible to obtain a flexible printed circuit board with excellent reliability in terms of dimensional stability against changes, adhesive strength, flatness after etching, etc.

Therefore, it is an object of the present invention to prevent curling, twisting, warping, etc. even when subjected to heat history, and/or to have sufficient adhesive strength, bending resistance, dimensional stability, etc., and to etch conductors. An object of the present invention is to provide an industrially useful flexible printed circuit board that exhibits little curling and is excellent in workability.

Another objective is to provide a flexible printed circuit board that can easily meet the diversifying demands of consumers.

[Means for Solving the Problems] That is, the present invention provides a flexible printed circuit board that is formed by directly coating a resin layer on a conductor and has at least a conductor and an insulator, in which the insulators are mutually linearly expanded. It is multi-layered consisting of multiple polyindo resin layers with different coefficients, and the thickness of the high thermal expansion resin layer (t1
) and the thickness (t2) of the low thermal expansion resin layer (t2/t
1) is 0.01<t2/t1<20. ooo (However,
The flexible printed circuit board satisfies the condition (tl and t2 are the sum of the thicknesses of the respective resin layers).

In the present invention, a flexible printed circuit board formed by direct coating means that a resin solution or its precursor resin solution is directly applied onto a conductor, dried, and roughened as necessary. This is a single board for a flexible wiring body or a material thereof, which is formed by forming a composite material of an insulator and an insulator.

Moreover, 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, an insulator is formed by combining a high thermal expansion resin layer and a low thermal expansion resin layer with different linear expansion coefficients, and the thickness of the high thermal expansion resin layer (t1
) and the thickness (t2) of the low thermal expansion resin layer (t2/t
1) (However, for tl and [2 is the sum of the thickness of each resin layer), 0°01 furnace 20,000,
It is necessary to satisfy a condition of preferably 2 to 100, more preferably 3 to 25.

Here, the high thermal expansion resin layer and the low thermal expansion resin layer are:
A resin layer having a linear thermal expansion coefficient higher than the simple average value of the linear thermal expansion coefficients of each component resin layer of an insulator forming a multilayer structure is called a high thermal expansion resin layer. A resin layer having a lower coefficient of linear expansion is referred to as a low thermal expansion resin layer.

If the value of the thickness ratio (t2/t1) is too small, the linear expansion coefficient of the insulator as a whole will increase, and the difference in linear expansion coefficient with the conductor will cause the board to curl with the insulator inside, making it difficult to form circuits. When etching the conductor, the distortion may be released and the dimensions may change significantly. On the other hand, if the value of the thickness ratio (t2/tl) is too large, it becomes difficult to improve the adhesive force with the conductor, which is the object of the present invention, and to prevent the film from curling after etching the conductor.

In the present invention, the total thickness (tl+t2) of the insulator is usually 5 to 100 mm, preferably 10 to 50 mm.

In addition, the linear expansion coefficient of the high thermal expansion resin layer constituting this insulator is 20x 10-6 (1/K) or more, preferably (
30 to 100) x 1O-6 (1/K), and the linear expansion coefficient of the low thermal expansion resin layer is 20 x 10-6 (1/K).
), preferably (0 to 19.) x 1O-6(1
/K), there must be a linear expansion coefficient of 5 x 10 between the high thermal expansion resin layer and the low thermal expansion resin layer.
-6(1/K) or more, preferably 10X 1O-6(1
/K) or more is desirable.

The high thermal expansion resin may be any polyimide resin, but preferably one whose main component is a polyamide-imide resin or a polyimide resin having a structural unit represented by the following general formula.

(However, in each of the above general formulas, Ar1 is a divalent aromatic group having 12 or more carbon atoms, and Ar2 is a tetravalent aromatic group.) Here, as the above ^r, for example, ooo, oSO
, oSO2, F3 Go(H)oG, Go-Q-o-Ol-, etc., and the above-mentioned Ar2 is, for example, preferably IQCOC from the point of view of adhesion to the body. .

Polyimide resins with such a structure usually have a relatively high linear expansion coefficient of 20x 10-6 (1/K) or more, but they also have excellent performance in terms of straightness, etc. demonstrate.

In addition, there are no particular restrictions on the low thermal expansion resin as long as it is a polyimide resin with a low coefficient of linear expansion, but polyimide resins having a structural unit represented by the following general formula (II> or (I[I)) may be used. preferable.

General formula (II> (However, in the formula, Ar represents a tetravalent aromatic group, and
represents either a lower alkyl group, a lower alkoxy group or a halogen which may be the same or different from each other; 1, O and m are integers of O to 4, and have at least one lower alkoxy group); A polyamide-imide resin containing the structural units shown, preferably the following structural units.

General formula (III) A polyimide resin containing the structural unit shown below.

The synthesis of these polyimide resins is carried out numerically using N-methylpyrrolidone (NHP), dimethylformamide (DH
F), dimethylacetamide (DHAC), dimethylsulfoxide (D)IsO), dimethyl sulfate, sulfolane, butyrolactone, cresol, phenol,
In a solvent such as halogenated phenol, cyclohexanone, dioxane, tetrahydrofuran, diglyme, etc., diamine compounds and acid anhydride compounds corresponding to each of the above general formulas are mixed in approximately equal molar ratios, and the reaction temperature is O~200'.
C1 Preferably, by reacting in the range of O to 100'C, a precursor solution of polyimide resin is obtained, and further, the operation of coating these resin solutions on the conductor and drying is repeated, or The polyimide resin layer or polyimide precursor resin layer with a multilayer structure is formed on the conductor by simultaneously applying multiple layers using a multilayer die or the like and drying. C or higher,
The imidization reaction is preferably carried out by heat treatment at 300°C or higher.

In the present invention, the polyimide-based high thermal expansion resin and low thermal expansion resin are copolymerized using various diamines, tetracarboxylic acid compounds, tricarphonic acid compounds, or acid anhydrides thereof, or are synthesized separately. The obtained polyimide or its precursor, polyamideimide, etc. can be blended.

Specific examples include 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, diaminodiphenylsulfone, diaminobenzanilide, diaminobenzoate, diaminodiphenylsulfide, 2,2-bis(p-
aminophenyl)propane, 2,2-bis(p-aminophenyl)hexafluoropropane, 1,5-diaminonaphthalene, diaminotoluene, diaminobenzotrifluorite, 1,4-bis(aminophenoxy)benzene, 4, 4′-bis(p-aminophenoxy)biphenyl, diaminoanthraquinone, 4,4′-his(3-
Aminophenoxyphenyl〉diphenyl sulfone, 1,
3-bis(anilino)hex)nafluoropropane, 1,
4-bis(anilino)octa-norreolobutane, 1,
5-bis(anilino)dicafluoropentane, 1,7
-bis(anilino)tetradecafluorohebutane, the following general formula (wherein R4 and R6 represent divalent Ial, and 1
(3 and R5 represent a monovalent Ia group, p and q are 1
2,2-bis[4-(p-aminophenoxy)phenyl]hexafluoropropane, 2,2-bis[4-(3
-aminophenoxy)phenyl]hexafluoropropane, 2,2-bis[4-(2-aminophenoxy)phenyl1hexafluoropropane, 2,2-bis[4-(
4-amitunoenoxy)-3,5-dimethylphenyl]
Hexafluoropropane, 2,2-bis[4-(,ll
-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)diphenylsulfone, 4,4"-bis(3-amino-5-trifluoromethylphenoxy)diphenylsulfone, 2,2-bis[ 4-(4-amino-3-trifluoromethylphenoxy)phenyl]hexafluoropropane, benzidine, 3,3°,5,5°-tetracarboxydine, octafluorobenzidine, 3.3“-
dimethoxybenzidine, o-tolidine, m-tolidine,
2,2°, 5,5°, 6,6°-hexafluorotridine, 4,4°゛-diaminoterphenyl, 4,4111
There are diamines such as -cyamic garter phenyl, and diisocyanates obtained by reacting these diamines with phosgene.

In addition, examples of tetracarboxylic acids and derivatives thereof include the following. Although tetracarboxylic acids are exemplified here, esterified products, acid anhydrides, and acid chlorides thereof can of course also be used. Pyromellitic acid, 3,3°,4,4°-biphenyltetracarboxylic phenonetetracarboxylic acid, 3,3°,4,4°-diphenylsulfonetetracarbonyl ethertetracarboxylic 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)ph[nyl]
Examples include propane, 2,2-bis[4-(3,4-dicarboxyphenoxy)phenyl]hexylfluoropropane, butanetetracarboxylic acid, cyclopentanetetracarboxylic acid, and the like. Also mentioned are trimellitic acid and its derivatives.

Furthermore, it is also possible to introduce a crosslinked structure or ladder structure by modifying with a compound having a reactive functional group.

For example, there are the following methods.

(2) By modifying with a compound represented by the following general formula, a pyrrolone ring, isoindoquinazolinedione ring, etc. are introduced.

[However, in the formula, 1<7 is 2+z value (l is 1 or 2)
represents an aromatic organic group, 8 is a -Nl'12 group, -co
A substituent selected from su2 group or -302N2 group, which is ortho to the amine group] ■ A derivative of amine, diamine, dicarboxylic acid, tricarboxylic acid, or tetracarboxylic acid having a polymerizable unsaturated bond It is modified to form a cross-linked structure upon curing. As the unsaturated compound, maleic acid, nadic acid, tetrahydrophthalic acid, ethynylaniline, etc. can be used.

(2) Modification with an aromatic amine having a phenolic hydroxyl group or carboxylic acid, and forming a network structure using a crosslinking agent that can react with the hydroxyl group or carboxylic acid group.

The linear expansion coefficient of the low thermal expansion resin of the present invention can be adjusted by modifying it using each of the above-mentioned components. That is, a polyimide resin consisting only of the structure of general formula (n) or (I) has I
Although it is possible to form an insulator having a coefficient of linear expansion of -5 (K-1) or less, the coefficient of linear expansion can be arbitrarily increased by modifying the insulator using each of the above-mentioned components. Further, even a polyimide resin containing the structural unit of general formula (II) or (1) can be made into a high thermal expansion resin by modifying it using each of the above-mentioned components.

Further, it is also possible to modify it for the purpose of roughly improving various physical properties such as adhesiveness and bending resistance.

In the present invention, an insulator is formed by combining at least one polyimide-based high thermal expansion resin layer and at least one polyimide-based low thermal expansion resin layer.
The arrangement of the layers is arbitrary.

In other words, by providing a high thermal expansion resin layer in contact with the conductor and a low thermal expansion resin layer in contact with it, effects such as good adhesive strength, dimensional stability at high temperatures, and a reduction in the coefficient of linear expansion of the insulator as a whole are achieved. can do. Furthermore, by providing a low thermal expansion resin layer in contact with the conductor and a high thermal expansion resin layer in contact with it, curling of the film after etching the conductor can be reduced. 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. Accordingly, the effects of the above two cases can be achieved simultaneously. Furthermore, by 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 higher coefficient of linear expansion, Curling of the film can be further reduced. By changing the type and composition of these low thermal expansion resins and high thermal expansion resins, the mechanical properties such as the elastic modulus and strength of the film can be controlled arbitrarily to meet the needs of various customers. Can be done.

The flexible printed circuit board of the present invention has at least a conductor and an insulator, and examples of the conductor include copper, aluminum, iron, silver, palladium, nickel, chromium,
Examples include molybdenum, tungsten, and alloys thereof, and copper is preferable.

In addition, the surface of these conductors is coated with zaiding, nickel plating, and copper-plating to improve adhesion.
Chemical or mechanical surface treatment may be performed using zinc alloy plating, aluminum alcoholade, aluminum chelate, silane coupling agent, or the like.

[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.

The coefficient of linear expansion is determined using a 1-nerm mechanical analyzer (t8) using a sample that has undergone a sufficient imidization reaction.
After heating to 250°C, cool at 10'C/min for 24 hours.
The average coefficient of linear expansion from 0'C to 100'C was calculated.

The adhesive strength was determined by fixing the resin side of a 10 mm wide copper-clad product to an aluminum plate with double-sided tape and peeling off the copper in a 180° direction at a rate of 5 mm/min using a Tensilon tester.

The heat shrinkage rate was determined from the dimensional change rate before and after heat treatment using a film after etching a conductor with a width of 10 mm and a length of 200 mm in a hot air oven at 250'C for 30 minutes.

The curl of the film after etching is determined by etching the entire surface of the conductor with a ferric chloride aqueous solution.
After drying a film having a size of m x thickness of 25 IJR at 100'C for 10 minutes, the radius of curvature of the curls generated was determined and quantified.

The strength and elastic modulus of the film after etching are JIS
7-1702 and ASrHD-882-67.

The abbreviations in each example are as follows.

1) HD8: Pyromellitic dianhydride BPDA: 3,3',4,4'-biphenyltetracarboxylic anhydride BT D^: 3,3',4,4''-benzophenonetetracarboxylic dianhydride DDE: 4,4°-diaminodiphenyl ether H
BA: 2"-methyl-4,4"-diaminobenzanilide PPD: paraphenylenediamine I) I) S: 3,3'-diaminodiphenylsulfon 88 PP: 2,2-bi's [4-(4-aminophenoxy)phenyl]propane DDH: 4.4'-diaminodiphenylmethane DH
Ac Nidimethylacetamide N) IP: N-Methyl-2-pyrrolidone Synthesis Example 1 While flowing nitrogen at a speed of 200 m/min into a 500 m fourth flask equipped with a thermometer, calcium chloride tube, stirrer, and nitrogen inlet. , 0.1 mol of DI)E and 3
D) lAc of 00d was added and dissolved by stirring, and then 0.10 mol of BTDA was gradually added while cooling the solution to below 10'C in a water cooling bath. The reaction mixture was polymerized while generating heat, and a viscous polyamic acid (polyimide precursor solution) was obtained.

This polyamic acid solution was applied using an applicator onto the rough surface of a commercially available 35 μm thick electrolytic copper foil (manufactured by Nippon Mining Co., Ltd.) fixed on a stainless steel frame to a film thickness of approximately 255 μm.
m, coated at 130'C and 150
The mixture was left to dry in a hot air oven at 360°C for 10 minutes, and then the temperature was raised to 360°C over 15 minutes to perform an imidization reaction.

The resulting copper-clad product is made by curling the resin inward.

When this copper-clad product was etched with an aqueous ferric chloride solution and the linear expansion coefficient of the obtained film was measured, it was found to be 55x.
I got it at 10-6 (1/K).

Synthesis Examples 2 to 6 In the same manner as in 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 was performed to obtain a film with a thickness of 25 μm. The linear expansion coefficient was measured in the same manner as in Synthesis Example 1. The results are shown in Table 1.

Synthesis Example 7 In the same manner as in Synthesis Example 1, 0.055 mol of HABA and 0.045 mol of DDE were dissolved in 300 mol of DHAc, and then 0.10 mol of PMDA was added and reacted to form a viscous polyamic. Obtained acid.

The linear expansion coefficient of the polyamideimide film obtained using this polyamic acid was 13×10 −6 (1/K).

Synthesis Example 8 In the same manner as in Synthesis Example 1, 0.090 mol of PPD and 0
．． After dissolving 0.10 mol of DDE in 300 ml of DHAc, 0.10 mol of BPOA was added and reacted to obtain a viscous polyamic acid.

The linear expansion coefficient of the polyimide film obtained using this polyamic acid was 10×10 −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 2IIf&, and then heated at 130°C for 5
Dry for a minute. On the thus obtained first resin layer, the resin solution of Synthesis Example 7 was further applied so that the thickness of the resin layer was 23IJR, and 130'C and 150
'C' hot air oven for 10 minutes at a time to dry, then raise the temperature to 360°C over 15 minutes to perform an imidization reaction and form a second resin layer. A copper-clad product with a thickness of 25 μm was produced.

The adhesive strength, film curl, heat shrinkage rate, and thermal expansion coefficient of the obtained copper-clad crystal were measured. Second result
Shown in the table.

As is clear from the results in Table 2, the copper cladding of each of Examples 1 to 6 is almost flat, and the coefficient of thermal expansion is necessarily lower than that of each comparative example, and the adhesive strength and etching The resulting film also had excellent performance in terms of curl and heat shrinkage.

In addition, the strength of the film of Example 1 is 25 kg/mm.
2, and the elastic modulus was 500 Kg/mm2.

Example 7 The resin solution of Synthesis Example 8 was used in place of the resin solution of Synthesis Example 7, and the copper tension was prepared in the same manner as in Examples 1 to 6 above, and the adhesive strength, film curl, and heating were evaluated. The shrinkage rate and thermal expansion coefficient were measured. The results are shown in Table 2.

Comparative Examples 1 and 2 The adhesive strength, film curl, heat shrinkage rate, and thermal expansion coefficient of the copper tensions obtained in Synthesis Examples 7 and 8 were measured. The results are shown in Table 2.

The strength of the film of Comparative Example 1 obtained from the copper cladding amount of Synthesis Example 7 was 26'J/mm2, and the elastic modulus was 600'J/mm2.
/mm2.

Examples 8 to 11 The resin solutions of Synthesis Examples 1 to 4 were coated on the resin layer with the copper cladding obtained in Synthesis Example 7 so that the thickness of the resin layer was 2IJR, and the mixture was heated at 130'C for 5 minutes. After drying, apply for 15 minutes 3
The temperature was raised to 60'C to carry out an imidization reaction, and a resin layer having a copper cladding thickness of 27 μm was obtained.

Regarding the obtained copper tension, its adhesive strength, film curl, heat shrinkage rate, and thermal expansion coefficient were measured. Second result
Shown in the table.

As is clear from the results in Table 2, each of these Examples 8-
The curl of No. 11 film is significantly improved.

Examples 12 to 15 The resin solutions of Synthesis Examples 1 to 4 were coated on the resin layer with the copper cladding obtained in Example 1 so that the thickness of the resin layer was 2 μs, and the mixture was heated at 130'C for 5 minutes. After drying, 36 minutes for 15 minutes.
The temperature was raised to 0'C to perform an imidization reaction to form a third resin layer, and the copper cladding amount of the resin layer was 27 IU thick.

Regarding the obtained copper tension, its adhesive strength, film curl, heat shrinkage rate, and thermal expansion coefficient were measured. Second result
Shown in the table.

As is clear from the results in Table 2, each of these Example 12
The adhesion and curl of the ~15 films are significantly improved.

Example 16 The resin solution of Synthesis Example 1 was applied to the copper-clad suspension obtained in Example 7 so that the resin layer had a thickness of 2 mm, dried at 130°C for 5 minutes, and then dried for 15 minutes. The temperature was raised to 360'C to carry out an imidization reaction, and a resin layer having a copper cladding thickness of 27 μm was obtained.

Regarding the obtained copper tension, its adhesive strength, film curl, heat shrinkage rate, and thermal expansion coefficient were measured. Second result
Shown in the table.

Comparative Examples 3 and 4 In the same manner as in Synthesis Example 7 or 8, a copper-clad single resin layer having a thickness of 27 mm was produced.

Regarding the obtained copper cladding, its adhesive horn, film curl, heat shrinkage rate, and thermal expansion coefficient were measured. The results are shown in Table 2.

Comparative Example 5 Regarding the copper cladding obtained in Synthesis Example 1, its adhesive strength, film curl, heat shrinkage rate, and thermal expansion coefficient were measured.

The results are shown in Table 2.

Further, the strength of this film was 18 Kg/mm2, and the elastic modulus was 250 Kg/mm2.

[Effects of the Invention] The flexible printed circuit board of the present invention has excellent reliability in terms of dimensional stability against temperature changes, adhesive strength, flatness after etching, etc., and is useful for protecting circuits fabricated by etching. It has excellent workability and is extremely useful industrially.

Patent applicant: Nippon Steel Chemical Co., Ltd.

Claims (8)

[Claims] (1) In a flexible printed circuit board formed by directly coating a resin layer on a conductor and having at least a conductor and an insulator, the insulator is a multilayer consisting of a plurality of polyimide resin layers having different coefficients of linear expansion. structure, and the ratio (t2/t1) of the thickness (t1) of the high thermal expansion resin layer and the thickness (t2) of the low thermal expansion resin layer is 0.01.
A flexible printed circuit board that satisfies the following condition: <t2/t1<20,000 (where t1 and t2 are the sum of the thicknesses of the respective resin layers). (2) The linear expansion coefficient of the high thermal expansion resin layer is 20×10^-
The flexible printed circuit board according to claim 1, wherein the linear expansion coefficient of the low thermal expansion resin layer is less than 20 x 10^-^6 (1/K). (3) Claim 1 or 2 consisting of two layers: a high thermal expansion resin layer in contact with the insulator or the conductor and a low thermal expansion resin layer in contact with it.
The flexible printed circuit board described. (4) Claim 1 or 2 in which the insulator consists of two layers: a low thermal expansion resin layer in contact with the conductor and a high thermal expansion resin layer in contact with it.
The flexible printed circuit board described. (5) A first high thermal expansion resin layer in which the insulator is 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. 2. The flexible printed circuit board according to claim 1, which has a three-layer structure composed of flexible resin layers. (6) The high thermal expansion resin layer has the following general formula (I)▲mathematical formula,
There are chemical formulas, tables, etc. ▼ (I) Claim 1 characterized in that it is a polyimide resin containing a structural unit represented by (wherein Ar_1 in the formula is a divalent aromatic group having 12 or more carbon atoms). 6. The flexible printed circuit board according to any one of 5 to 5. (7) The low thermal expansion resin layer has the following general formula (II) ▲ There are mathematical formulas, chemical formulas, tables, etc. ▼ (II) (However, in the formula, Ar represents a tetravalent aromatic group, and R1 and R
2 represents either a lower alkyl group, a lower alkoxy group, or a halogen, which may be the same or different from each other, l and m are integers of 0 to 4, and have at least one lower alkoxy group) The flexible printed circuit board according to any one of claims 1 to 6, which is a polyamideimide resin containing the structural units shown. (8) The low thermal expansion resin layer has the following general formula (III)▲mathematical formula,
7. The flexible printed circuit board according to claim 1, which is a polyimide resin containing a structural unit represented by the chemical formula, table, etc. ▼(III).