JP2738453B2 - Manufacturing method of copper clad laminate - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION [Industrial Application Field] The present invention is a flexible printed circuit which is free from curling, twisting, warping, etc. after circuit formation, and is excellent in heat resistance, dimensional stability, adhesiveness and bending resistance. The present invention relates to a method for producing a copper-clad laminate for use.

[Prior Art] Conventionally, copper-clad laminates for flexible printed circuits have generally been produced by bonding a conductor and an insulator of an organic polymer with an adhesive such as an epoxy resin or a urethane resin. However, if a heat history such as thermocompression bonding is added at this time, there is a disadvantage that the substrate is curled, twisted, warped, or the like at the time of cooling, so that subsequent conductor patterning or the like becomes impossible. These problems result from the difference in the coefficient of linear expansion between the conductor and the insulator.
Further, there are problems that the flame retardancy is reduced due to the adhesive layer, the polyimide film used is expensive, and the flexible printed circuit board is expensive due to the large labor required for bonding.

Japanese Patent Application Laid-Open No. 56-23,791 proposes a method in which a polyamideimide solution is applied to a metal foil, and curling caused by a difference in linear expansion coefficient after drying is reduced by heat treatment in a post-process. However, this method has yet to be solved and is unsatisfactory in terms of the time required for production and the fact that the curl is caused when the solder bath or the like is reheated due to the difference in linear expansion coefficient.

Also, JP-A-60-157,286 and JP-A-60-243,120
Japanese Patent Application Laid-Open Publication No. H11-163873 proposes a method in which a polyamideimide solution is applied to a metal foil, and after drying, curling caused based on a difference in linear expansion coefficient is relaxed by a heat treatment in a later step. However, such a point and curling upon reheating of a solder bath or the like due to a difference in the coefficient of linear expansion have not been solved yet and have not been satisfactory.

Also, JP-A-60-157,286 and JP-A-60-243,120
In Japanese Patent Application Laid-Open Publication No. H11-157, a method is proposed in which a polyimide having a specific structure or a polyimide precursor solution is applied onto a conductor to obtain a resin having low thermal expansion and a flexible printed board with less curl, but the adhesive strength is low. In addition, there is a problem that the film is largely curled with the surface in contact with the conductor inside when etching the conductor to form a circuit, and the subsequent work such as circuit protection becomes difficult. there were.

Further, in the conventional type using an adhesive layer, the adhesive layer has properties such as hardness and tear strength, which are insufficient for the polyimide film, but on the other hand, because of the presence of the adhesive layer, for example, heat resistance There were problems in various points such as punching workability.

[Problem to be Solved by the Invention] Accordingly, an object of the present invention is to provide a curl,
An industrially useful flexible printed board that is free from twisting, warping, etc., has sufficient adhesive strength, bending resistance, dimensional stability, etc., and has a small curl after conductor etching and excellent workability. Was to provide.

[Means for Solving the Problems] As a result of intensive studies in view of such a viewpoint, the present inventor has found that a plurality of polyimide-based resin layers having different linear expansion coefficients from each other are replaced with a high-thermal-expansion resin layer. Coating on the conductor as the outside, drying and hardening under reduced pressure and / or reducing gas atmosphere, and multilayering to prevent curling of the film after etching the conductor and measure the size against temperature change The present inventors have found that a flexible printed circuit board having excellent reliability in terms of stability, adhesive strength and the like can be obtained, and completed the present invention.

That is, the present invention relates to a method for producing a copper-clad laminate for a flexible printed circuit formed by directly applying a polyimide resin on a conductor, wherein at least two kinds of polyimide resin compositions having different linear expansion coefficients or precursors thereof are used. A copper-clad laminate characterized in that a body composition is coated on a conductor such that a resin layer having a high coefficient of linear expansion is on the outside, and then dried and cured under reduced pressure and / or in a reducing gas atmosphere. This is a method for manufacturing a plate.

In the present invention, a copper-clad laminate for a flexible printed circuit formed by direct coating is directly coated with a resin solution or a precursor resin solution thereof on a conductor, and dried,
A substrate for a flexible wiring body, which is further cured to form a composite material of a conductor and an insulator, or a material thereof.

Further, the polyimide resin in the present invention is a heat-resistant resin such as polyimide, polyamide, 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 having different linear expansion coefficients from each other, and the thickness of the high thermal expansion resin layer (t
Ratio of (1) and thickness (t2) of low thermal expansion resin layer (t2 / t1)
(However, t1 and t2 are the sum of the thicknesses of the respective resin layers), 0.01 to 20,000, preferably 2 to 100,
More preferably, the condition of 3 to 25 must be satisfied. Here, the high thermal expansion resin layer and the low thermal expansion resin layer refer to a linear expansion of a value higher than the simple average value of the linear thermal expansion coefficient of each constituent resin layer of the insulator forming the multilayer structure. The resin layer having a coefficient is called a high thermal expansion resin layer,
A resin layer having a lower linear expansion coefficient is called a low thermal expansion resin layer. If the value of the thickness ratio (t2 / t1) is too small, the coefficient of linear expansion of the insulator as a whole increases, and the substrate curls with the insulator inside, due to the difference in the coefficient of linear expansion with the conductor. It becomes difficult, or the distortion is released when the conductor is etched, and the dimensions change greatly. Conversely,
If the value of the thickness ratio (t2 / t1) is too large, it is difficult to prevent curling of the film after conductor etching, which is the object of the present invention.

In the present invention, the total thickness (t1 + t2) of the insulator is:
It is usually from 5 to 100 μm, preferably from 10 to 50 μm. The high thermal expansion resin layer constituting the insulator has a coefficient of linear expansion of 30 × 10 ⁻⁶ (1 / K) or more, preferably (40 to 100) × 10 6
^-6 (1 / K), and the coefficient of linear expansion of the low thermal expansion resin layer is 30.
Less than × 10 ⁻⁶ (1 / K), preferably (0 to 25) × 10 ⁻⁶ (1 / K)
K), and the coefficient of linear expansion between the high thermal expansion resin layer and the low thermal expansion resin layer is 5 × 10 ⁻⁶ ( ^1/1 ).
It is desirable that there is a difference of not less than K), preferably not less than 10 × 10 ⁻⁶ (1 / K). If it is less than 5 × 10 ⁻⁶ (1 / K), it is difficult to prevent film curl after etching.

In order to prevent film curl, it is necessary to provide a resin layer having high thermal expansion on the outer layer.

In the present manufacturing method, it is necessary to provide at least two polyimide resin layers having such different coefficients of thermal expansion, but for the purpose of further improving the adhesion to the conductor and controlling the physical properties of the film, other resins may be used. Layers may be provided.

As the high thermal expansion resin, any polyimide resin may be used, but preferably a polyamide-imide resin or a polyimide resin having a structural unit represented by the following general formula as a main component from the viewpoint of heat resistance. .

(In 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, as Ar ₁ , for example, And the like, and as Ar ₂ , for example, And the like, but are preferably used because of their low cost and excellent flexibility. It is.

A polyimide resin having such a structure usually has a relatively high coefficient of linear expansion of 30 × 10 ⁻⁶ (1 / K) or more.

In particular, the following general formula (III) The polyimide having the structural unit represented by the formula (1) has thermoplasticity and is suitable for multilayering by thermocompression bonding during circuit processing by being provided in the outermost layer.

The low thermal expansion resin is not particularly limited as long as it is a polyimide resin having a low linear expansion coefficient. However, a polyimide resin having a structural unit represented by the following general formula (I) or (II) is preferable.

General formula (I) (Wherein, Ar represents a tetravalent aromatic group, and R1 and R2 each represent a lower alkyl group, a lower alkoxy group or a halogen which may be the same or different,
l and m are integers of 0 to 4 and have at least one lower alkoxy group), preferably the following structural units And a polyamide-imide resin.

General formula (II) A polyimide resin containing a structural unit represented by

The synthesis of these polyimide resins is generally performed using M-methylpyrrolidone (NMP), dimethylformamide (DM
F), dimethylacetamide (DMAc), dimethylsulfoxide (DMSO), dimethyl sulfate, sulfolane, butyrolactone, cresol, phenol, halogenated phenol, cyclohexanone, dioxane, tetrahydrofuran, diglyme, etc. The diamine compound and the acid anhydride compound corresponding to the above are mixed at a substantially equimolar ratio, and the reaction temperature is 0 to 200 ° C, preferably 0 to 1 ° C.
By reacting at a temperature of 00 ° C., a precursor solution of a polyimide resin is obtained, and further, the operation of applying these resin solutions on a conductor and drying is repeated, or a multilayer die, a knife coat, etc. Simultaneous multi-layer coating, by drying, to form a polyimide-based resin layer or a polyimide-based precursor resin layer of a multilayer structure on the conductor, in the case of the precursor resin layer 200 ° C. or more, preferably 300 ° C
The imidation reaction is performed by the above heat treatment.

Further, examples of the tetracarboxylic acid and its derivative include the following. Here, tetracarboxylic acid is exemplified, but it is needless to say that these esterified products, acid anhydrides, and acid chlorides 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'-benzophenonetetracarboxylic 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] propane, 2,2-bis [4- (3,4-dicarboxyphenoxy) phenyl] hexafluoropropane,
Butanetetracarboxylic acid, cyclopentanetetracarboxylic acid and the like. Also, trimellitic acid and its derivatives can be mentioned.

Further, it may be modified with a compound having a reactive functional group to introduce a crosslinked structure or a ladder structure. For example, there is the following method.

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

[However, an aromatic organic group R7 is 2 + z value in the formula (z is 1 or 2), B is _a -NH ₂ group, -CONH ₂ group or -SO ₂ N
H ₂ is a substituent selected from the group and is ortho to the amino group.) Amine having a polymerizable unsaturated bond, diamine, dicarboxylic acid, tricarboxylic acid, modified with a derivative of tetracarboxylic acid, at the time of curing Form a bridged structure. As the unsaturated compound, maleic acid, nadic acid, tetrahydrophthalic acid, ethynylaniline and the like can be used.

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

The linear expansion coefficient of the low thermal expansion resin of the present invention can be adjusted by modifying the above-mentioned components. That is, the polyimide resin having only the structure of the general formula (I) or (II) has 1 × 10
^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 the above components. Further, even a polyimide-based resin containing a structural unit of the general formula (I) or (II) can be made into a high thermal expansion resin by modifying using the above-mentioned components.

As the coating method, any coating method for performing multilayer coating is possible, but the following three methods are preferable from the viewpoint of coating accuracy.

Two or more polyimide-based resins or their precursor solutions are simultaneously coated on a conductor by a multilayer die.

After coating by an arbitrary method, further coating is performed on the undried coated surface by knife coating.

After coating and drying by an optional method, the coating is further performed on the dried coating surface by an optional method.

The knife coat method here means a bar, squeegee,
This is a method in which the resin solution is leveled with a knife or the like and applied.

Any method can be used as the drying and curing method.However, in consideration of work efficiency, yield, etc., a polyimide resin is applied and preliminarily dried, then wound into a roll, and further heated at a high temperature. And a batch processing method of drying and curing is preferred. At this time, for the purpose of preventing the conductor from being oxidized, it is preferable to perform the heat treatment at a high temperature (200 ° C. or more) under reduced pressure and / or in a reducing gas atmosphere.

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

In addition, these conductors, on the surface thereof, for the purpose of improving adhesive strength, siding, nickel plating, copper-zinc alloy plating, or aluminum alcoholate,
Chemical or mechanical surface treatment may be performed with an aluminum chelate, a silane coupling agent, or the like.

The insulating layer can also be modified with a coupling agent such as trimethoxysilylaniline or the like for the purpose of improving adhesive strength and the like.

EXAMPLES Hereinafter, the present invention will be specifically described based on Examples and Comparative Examples, but it is needless to say that the present invention is not limited thereto.

The coefficient of linear expansion was determined using a thermomechanical analyzer (TMA) using a sample on which the imidization reaction was sufficiently completed.
After the temperature was raised to 50 ° C., it was cooled at 10 ° C./min., And the average coefficient of linear expansion from 240 ° C. to 100 ° C. was calculated and determined.

After etching the film, the conductor was entirely etched with an aqueous ferric chloride solution, and then a film having a size of 10 cm (length) × 10 cm (width) × 25 μm (thickness) was dried at 100 ° C. for 10 minutes. The radius was calculated and quantified.

The strength and elastic modulus of the film after etching are JIS Z
-1702 and ASTM D-882-67.

 The abbreviations in each example are as follows.

PMDA: pyromellitic dianhydride BPDA: 3,3 ', 4,4'-biphenyltetracarboxylic dianhydride BTDA: 3,3', 4,4'-benzophenonetetracarboxylic dianhydride DDE: 4, 4'-diaminodiphenyl ether MABA: 2'-methyl-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 1 500 ml four-necked flask equipped with thermometer, calcium chloride tube, stirrer and nitrogen inlet While flowing nitrogen at a rate of 200 ml / min, 0.1 mol of DDE and 300 ml of DMAc were added and stirred to dissolve.After cooling the solution to 10 ° C. or lower in a water cooling bath, 0.10 mol of BTDA was gradually added. added. The reaction mixture polymerized while generating heat, and a viscous polyamic acid (polyimide precursor solution) was obtained.

This polyamic acid solution was fixed on a stainless steel frame on a rough surface of a commercially available electrolytic copper foil having a thickness of 35 μm (manufactured by Nippon Mining Co., Ltd.) with a film thickness of about 25 μm using an applicator.
And dried in a hot air oven at 130 ° C. and 150 ° C. sequentially for 10 minutes, and then heated to 360 ° C. over 15 minutes to perform an imidization reaction.

 The obtained copper-clad product largely curled the resin inside.

The copper-clad product was etched with an aqueous ferric chloride solution, and the coefficient of linear expansion of the obtained film was measured.
^-6 (1 / K).

Synthesis Examples 2 to 6 A polymerization reaction was performed using various diamine compounds and acid anhydrides in the same manner as in Synthesis Example 1 to prepare a high thermal expansion polyimide precursor solution. Coating was performed to obtain a film having a thickness of 25 μm. The coefficient of linear expansion 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 MABA and 0.045 mol of DDE were dissolved in 300 ml of DMAc, and 0.10 mol of PMDA was added to react to obtain a viscous polyamic acid.

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

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 0.10 mol of BPDA was added to react 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). Also,
The curl was noticeable.

Examples 1 to 6 The thickness of the resin solution obtained in Synthesis Example 7 fixed to a metal frame
After coating on a 35 μm electrolytic copper foil with a bar so that the film thickness becomes 23 μm and drying at 130 ° C. for 5 minutes, Synthesis Example 1
The final film thickness of the resin solution obtained in ~ 6 is 25 μm
After drying at 130 ° C. for 10 minutes, the temperature was raised to 360 ° C. over 15 minutes to perform an imidization reaction.

The obtained copper-clad product was almost flat, and the film obtained by etching copper with an aqueous ferric chloride solution was also flat.

Examples 7 to 12 In the same manner as in Examples 1 to 6, copper-clad products were obtained using the resin solution of Synthesis Example 8 and the resin solutions of Synthesis Examples 1 to 6. There was no curling of the copper-clad product and the film, and it was sufficiently usable.

Comparative Examples 1 to 6 Copper-clad products were obtained in the same manner as in Examples 1 to 6, using only the resin solutions obtained in Synthesis Examples 1 to 6.

The copper-clad product had a large curl, and the film after copper etching had a large curl, exhibiting a radius of curvature of about 20 mm, and was unusable.

Comparative Examples 7 and 8 Copper-clad products were obtained in the same manner as in Examples 7 and 8, using only the resin solutions obtained in Synthesis Examples 7 and 8.

Although there was no curling of the copper-clad product, the resulting film exhibited a radius of curvature of 10 mm and was unusable.

Example 13 In the same manner as in Example 1, the resin solution of Synthesis Example 7 was applied, and then the resin solution of Synthesis Example 1 was applied on an undried coated surface with a bar, and the same heat treatment was performed.

 The copper-clad product and the film were good without curling.

Example 14 In a coating apparatus having a dryer unit with a line length of 7 m, using a multilayer die, the resin solution of Synthesis Example 1 and Synthesis Example 7 were used.
Simultaneously extrude the resin solution into a curtain shape, coated on the copper foil surface so that the final resin thickness is 23μm, 2μm respectively,
Heat treatment was performed by continuously raising the temperature from 130 ° C. to 360 ° C. at a line speed of 0.2 m / min.

The obtained copper-clad product had no curl, the film after etching was flat, and it was sufficiently usable.

Example 15 In the same manner as in Example 1, the resin solutions of Synthesis Examples 7 and 1 were applied, dried at 130 ° C., and further dried in a vacuum dryer.
In a torr atmosphere, the temperature was gradually increased from 130 ° C., and heat treatment was performed to 360 ° C. over 10 hours. The copper-clad product obtained after cooling had no oxidation of the copper foil and no curling of the copper-clad product and the film.

Example 16 In the same manner as in Example 15, an uncured copper-clad product was heat-treated to 360 ° C in an inert oven in a nitrogen gas atmosphere.

The obtained copper-clad product was useful, as in Example 15, without copper foil oxidation, copper-clad product curl, and film curl.

[Effect of the Invention] The production method of the present invention is extremely useful for producing an industrially useful copper-clad laminate for a flexible printed circuit.

Claims (2)

(57) [Claims] 1. A method for producing a copper-clad laminate for a flexible printed circuit formed by directly applying a polyimide resin on a conductor, wherein at least two kinds of polyimide resin compositions having different linear expansion coefficients or precursors thereof are provided. A copper-clad laminate characterized in that the composition is coated on a conductor such that a resin layer having a high linear expansion coefficient is on the outside, and then dried and cured under reduced pressure and / or in a reducing gas atmosphere. Manufacturing method. 2. The method for producing a copper-clad laminate according to claim 1, wherein at least two polyimide layers having a difference in linear expansion coefficient of 5 × 10 ⁻⁶ (1 / K) or more are formed.