JPH043492A - Flexible printed circuit board having cover coat and manufacture thereof - Google Patents

Abstract

PURPOSE:To improve the heat resistance of a circuit board particularly by using a high-temperature resin, in which polyimide powder is added to a high- temperature resin having the same composition as a base as a flexibility dative agent, as the cover coat of the board for a flexible printed circuit. CONSTITUTION:Polyimide obtained by heating and curing a polyamic acid mixed solution (C) acquired by mixing and agitating a polyamic acid solution (A), which is obtained by reacting a 3,3',4,4'-biphenyl tetracarboxylic acid bianhydride and paraphenylenediamine, and a polyamic acid solution (S), which is acquired by reacting a pyromellitic acid bianhydride and 4,4'-diaminodiphenyl ether, at the rate of A/B=55/45-75/25 when a tetracarboxylic acid bianhydride component and a diamine component are reacted while acidic component/amine component (a mol ratio) is brought to 0.90-1.00 is used as a high-temperature resin. Polyimide powder acquired by reacting a 3,3',4,4'-biphenyl tetracarboxylic acid bianhydride and diphenylmethane isocyanate is employed as a flexibility dative agent, and added at 1-40wt.%.

Description

DETAILED DESCRIPTION OF THE INVENTION (Technical Field of the Invention) The present invention relates to the method of casting a heat-resistant resin as a cover coat on the circuit-formed surface of a flexible printed circuit board based on a heat-resistant resin. A flexible printed circuit board with a cover coat that is heat-cured and has excellent heat resistance, bending resistance, cold resistance, high frequency electrical properties, mechanical properties, abrasion resistance, chemical resistance, radiation resistance, etc., and its production. It is related to the method.

(Prior art) Conventionally, flexible printed circuit boards are susceptible to moisture, dirt,
In order to protect the conductor surface from damage, it is used to protect the circuit surface using the film coverlay method, in which a film is fused and adhered, or the ink cover coat method, in which a liquid coating agent is applied and cured. ing.

In particular, for flexible printed circuit boards that require heat resistance, flexible printed circuit boards without an adhesive layer are used, which are obtained by directly casting a polyamic acid solution onto metal foil and curing it with heat. There is.

However, the base flexible printed circuit board does not have an adhesive layer (despite its extremely high heat resistance, it has problems with the film coverlay method and ink covercoat method, such as the following). However, the heat resistance, flexibility, and bending durability of the substrate were not good.

In other words, in the film coverlay method, although the polyimide film for coverlay has excellent heat resistance,
Since the heat resistance of the adhesive layer for the coverlay was poor, the heat resistance was significantly inferior to that of the base film for the substrate or the polyimide film.

In addition, the ink used in the ink cover coating method is a normal thermosetting resin or ultraviolet curable resin, and has a different composition from the resin of the base flexible printed circuit board, so it The adhesion to the substrate was extremely poor (and the flexibility, bending durability, and heat resistance were also extremely poor).

(Problems to be Solved by the Invention) As a result of intensive studies to overcome these drawbacks, the present invention has developed a polyamic acid that is made by adding polyimide powder as a flexibility imparting agent to a polyamic acid having the same composition as the base film. The present invention was completed based on the knowledge that a flexible printed circuit board with a cover coat manufactured using the same material has very good heat resistance, is free from curls and wrinkles, and has excellent bending durability and flexibility. This is what led to this.

(Means for Solving the Problems) The present invention provides a method for casting a heat-resistant resin as a cover coat onto the circuit surface of a flexible printed circuit board based on a heat-resistant resin and curing it by heating. A flexible printed circuit board with a cover coat and a method for producing the same are characterized in that a heat-resistant resin having the same composition as the resin and polyimide powder added as a flexibility imparting agent is used.

(Function) The heat-resistant resin used in the present invention has film-forming ability,
It only needs to have good adhesion to the metal foil, but polyimides such as those shown below are most suitable.

That is, the tetracarboxylic dianhydride component and the diamine component are mixed in an acid component/amine component (molar ratio) of 90 to 1.
．． When reacting as 00, 3.3.4.4'-
A polyamic acid solution obtained by reacting biphenyltetracarboxylic dianhydride and paraphenylenediamine (
A) and a polyamic acid solution (B) obtained by reacting pyromellitic dianhydride and 4,4'-diaminodiphenyl ether, A/B = 55/45 to 75/2.
It is a polyimide obtained by heating and curing a polyamic acid mixed solution (C) obtained by mixing and stirring at a ratio of 5 to 5.

The flexible printed circuit board for pace used in the present invention is obtained by directly casting the above-mentioned polyamic acid solution (C) on metal foil and curing it by heating.

The base flexible printed circuit board is manufactured by a conventional method for manufacturing a two-layer flexible printed circuit board, such as the method disclosed in Japanese Patent Application Laid-Open No. 62-200795.

The polyimide powder used as the flexibility imparting agent in the present invention is generally a polyimide powder obtained by reacting 3.3', 4.4'-biphenyltetracarboxylic dianhydride and diphenylmethane diisocyanate, or 3, 3'
, 4.4'-benzophenone tetracarboxylic dianhydride and diphenylmethane diisocyanate are used.

In the present invention, the polyamic acid solution used as the cover coat is a polyamic acid solution obtained by adding and mixing the above polyimide powder to the above polyamic acid solution (C) so that the solid content weight ratio becomes 40%. The tetracarboxylic dianhydride referred to in the present invention is 3.3'
, 4,4'-biphenyltetracarboxylic dianhydride;
Pyromellitic dianhydride, but other acids such as 2.3.3',4'-biphenyltetracarboxylic dianhydride, 3,3',4.4'-benzophenonetetracarboxylic dianhydride 3.3', 4.4-P-terphenyltetracarboxylic dianhydride, 2,3,6.7-naclentitracarboxylic dianhydride, 3.3',4,4'-
Benzophenone tetracarboxylic dianhydride, 3,3',
4.4'-p-terphenyltetracarboxylic dianhydride, 4.4'-hexafluoroisopropylidene bis (phthalic anhydride), etc. can also be used in combination.

The diamines referred to in the present invention include phenylene diamine and 4,4'-diaminodiphenyl ether, but other amines such as 4,4'-diaminodiphenylmethane,
3,3°-dimethylbenzidine, 4,4'-diamino-
P-terphenylphenyl, 2,8-diaminodiphenylene oxide, etc. can also be used in combination.

The reaction between the tetracarboxylic dianhydride component and the diamine component is preferably carried out at an acid component/amine component (molar ratio) of 0.90 to 1.00; if it is lower than 0.90, the degree of polymerization will not increase and the Poor film properties.

If it is larger than 1.00, gas will be generated during curing, making it impossible to obtain a smooth film.

The reaction to obtain the polyamic acid solution is usually carried out in an organic polar solvent that does not react with the tetracarboxylic dianhydride or diamines. In addition to being inert to the reaction system and being a solvent for the product, this organic polar solvent must be a good solvent for at least one, preferably both, of the reaction components. A typical solvent of this type is N. N-dimethylformamide, N. N-
Examples include dimethylacetamide, dimethylsulfone, dimethylsulfoxide, N-methyl-2-pyrrolidone, and these solvents may be used alone or in combination. In addition, non-polar solvents such as benzene, dioxane, xylene, toluene, and cyclohexane are also used in combination as solvents, as dispersion media for raw materials, reaction regulators, volatilization regulators from products, film smoothing agents, etc. used.

It is generally preferred that the reaction be carried out under anhydrous conditions. This is because the tetracarboxylic dianhydride may be ring-opened by water, inactivated, and the reaction may be stopped. Therefore, it is necessary to remove both the moisture in the raw materials and the moisture in the solvent. However, on the other hand, water is intentionally added in order to adjust the progress of the reaction and control the degree of resin polymerization.

Moreover, it is preferable that the reaction is carried out in an inert gas atmosphere. This is to prevent oxidation of diamines. Dry nitrogen gas is generally used as the inert gas.

The synthesis reaction of the polyimide resin used in the present invention is carried out in the following manner. That is, 3.3'. A polyamic acid (referred to as A) obtained by reacting 4.4'-biphenyltetracarboxylic dianhydride and paraphenylene diamine, pyromellitic dianhydride, and 4.4'diaminodiphenyl ether is reacted. This is a method of obtaining a polyamic acid (referred to as C) by mixing and stirring the obtained polyamic acid (referred to as B) at a ratio of A/B = 55/45 to 75/25.

When the ratio of A is less than the above-mentioned ratio, curling occurs in the resulting cover-coated flexible printed circuit board, and on the other hand, when it is large, it becomes too rigid and lacks flexibility.

The reaction temperature for synthesizing A and B and mixing them to obtain C is preferably 0 to 100°C. Below 0°C, the reaction rate is slow, and above 100°C, the resulting polyamic This is because the ring-closing reaction and depolymerization reaction of the acid start. Usually, the reaction is carried out at around 20°C.

When using the polyamic acid product produced according to the present invention for producing a flexible printed circuit board, various silane coupling agents, borane coupling agents, titanate coupling agents 1, aluminum coupling agents and other chelate-based Adhesion/adhesion improvers, various solvents, and flow agents may be added (in addition to these, a small amount of a normal acid curing agent, amine curing agent, imidacil, tertiary amine, etc.) may be added. It's okay,
In addition, flexibility agents and viscosity modifiers such as rubber and low-molecular epoxy, or polyamideimide, polyetherimide, polyesterimide, etc. may be blended with talc,
Small amounts of fillers such as mica and quartz powder, colorants such as carbon black and phthalocyanine blue, flame retardants such as tetrabromophenylmethane, and flame retardant aids such as antimony trioxide may be added.

The synthesis reaction of the polyimide powder used as the flexibility imparting agent in the present invention is carried out in the following manner.

That is, 3,3',4,4'-biphenyltetracarboxylic dianhydride or 3,3',4,4-benzophenonetetracarboxylic dianhydride and diphenylmethane diisocyanate were heated at 100°C to 150°C in a solvent. This is a method in which the reaction is carried out at a temperature of °C. If the temperature is lower than the above, the reaction progresses slowly, and the particle size of the particles formed becomes too large, making it unsuitable for the purpose of imparting flexibility. As a sexual enhancement agent, the solid content weight ratio is 1 to 40 in the polyamic acid solution used in the previous stage.
% and mix and stir in the usual manner.

If the amount of polyimide powder added as a flexibility imparting agent is less than 1%, the flexibility will be insufficient, and if it is more than 40%, air bubbles will be drawn in during printing, making it impossible to obtain a smooth cover.

In the method of manufacturing a flexible printed circuit board with a cover coat according to the present invention, first, the copper foil surface of the base flexible printed circuit board is etched by a conventional method to form a circuit. Next, the polyamic acid solution containing the above-mentioned flexibility imparting agent is cast-coated as a cover coat on this circuit surface, and then heated and cured to obtain a cover-coated flexible printed circuit board.

The metal foil used in the present invention is generally copper foil, but aluminum foil, nickel foil, titanium foil, stainless steel foil, etc.
Tungsten foil or the like can also be used. Metal foil is 3
A thickness of ~200 μm is used, and the surface is preferably roughened.

A method for obtaining a base flexible printed circuit board by casting a polyamic acid solution onto a metal foil is to obtain a uniform thickness of 50 to 100μ using known coating means such as a rotary coater, knife coater doctor blade, flow coater, etc. A method of casting is used. Next, the solvent of the polyamic acid is removed by heating and an imide ring is formed. However, if strong heating is applied from the beginning before the polyimide film is formed, the surface will become rough or twitch, so heating is not recommended. It is preferable to gradually increase the temperature from a low temperature. For example, it is heated continuously from 100°C to 350°C over 0.5 hours or more.

If the time is less than 0.5 hours, depending on the film thickness, the solvent may be removed insufficiently or the ring closure of the imide may be insufficient and the properties may not be fully exhibited. For example, 30°C at 100°C.
minutes, then 30 minutes at 150℃, 30 minutes at 200℃, 25 minutes.
The temperature may be increased stepwise at 0°C for 30 minutes, at 300°C for 30 minutes, and at 350°C for 20 minutes. Although the heating atmosphere may be in the air in some cases, it is often preferable to conduct the heating under reduced pressure or under non-oxidizing conditions while flowing an inert gas. The polyimide coating layer thus formed typically has a thickness of 10 to 200 microns.

The copper foil surface of the flexible printed circuit board thus obtained is etched by a conventional etching method using, for example, a ferric chloride solution to form a circuit.

Next, a polyamic acid solution containing the above polyimide powder as a flexibility imparting agent is cast as a cover coat onto the circuit forming surface of the flexible printed circuit board on which this circuit is formed.

The polyamic acid solution is applied as a cover coat to the circuit forming surface by casting to a uniform thickness of 20 to 500μ using known coating methods such as screen printing, rotary coater, knife coater, doctor blade, and flow coater. A method is taken to do so.

Next, the solvent of the polyamic acid is removed by heating and an imide ring is formed in the same manner as in the production of the base flexible printed circuit board. The polyimide coating layer thus formed typically has a thickness of 4 to 100 microns.

(Example 1) 108 g of purified anhydrous para-phenylenediamine was placed in a four-separable flask equipped with a thermometer, a stirrer, a reflux condenser, and a dry nitrogen gas inlet, and anhydrous N-methyl-2- A mixed solvent of 90% by weight of pyrrolidone and 10% by weight of toluene was added and dissolved in an amount sufficient to make the solid content ratio in the total raw materials 20% by weight. Dry nitrogen gas was allowed to flow throughout the reaction from the preparatory stage to the product removal. Then purified anhydrous 3
゜294 g of 3',4.4'-biphenyltetracarboxylic dianhydride was added little by little while stirring, but since it was an exothermic reaction, cold water of about 15°C was circulated in an external water tank to cool it. . After addition, set the internal temperature to 20 °C,
After stirring for 5 hours, the reaction was completed and a polyamic acid solution (referred to as A) was obtained. Next, 200 g of anhydrous 4,4'-diaminodiphenyl ether and 218 g of purified anhydrous pyromellitic dianhydride were reacted using the same apparatus and method as described above to obtain a polyamic acid (referred to as B). Next, Ai3 and B were mixed and stirred so that the molar ratio was A/B=60/40 to obtain a polyamic acid solution (C). The obtained product was a transparent yellow and extremely viscous polyamic acid solution, and the intrinsic viscosity of the N-methyl-2-pyro 91290.5% by weight solution was 0.81 (30°C).

Next, using the same apparatus as above, 250 g of diphenylmethane diisocyanate and 294 g of 3,3',4,4'-benzophenonetetracarboxylic dianhydride were reacted at 140°C for 5 hours to obtain polyimide powder.

This polyimide powder was mixed with the above polyamic acid solution (C
) and mixed and stirred to obtain a polyamic acid solution (D) for cover coating.

After casting the above polyamic acid solution (C) on copper foil, it was placed in a dryer and continuously heated from 100°C to 350°C for 2 hours.
The temperature was raised over time.

A circuit was formed by etching the copper foil on the flexible printed circuit board produced in this way, and the polyamic acid solution (D) prepared by the above method was cast as a cover coat on the circuit surface. After that, put it in the dryer for 100 minutes.
The temperature was raised continuously from °C to 350 °C over 2 hours.

The flexible printed circuit board with a cover coat manufactured in this way has good printability of the cover coat, no bleeding, excellent adhesion of the cover, heat resistance of 400 degrees or more, and folding durability. (MIT method, O, IR
, 0.5kgf) was an extremely excellent flexible printed circuit board that was tested over 10,000 times.

(Example 2) Using the same apparatus and method as in Example 1, a polyamic acid solution (referred to as A) consisting of phenylene diamine and 3.3', 4.4'-biphenyltetracarboxylic dianhydride, and 4 A polyamic acid solution (referred to as B) consisting of 4-diaminodiphenyl ether and pyromellitic dianhydride was synthesized. A and B were mixed and stirred at a molar ratio of 70/30 to obtain a polyamic acid solution (C). The product had an intrinsic viscosity of 0.90. Next, biphenyltetracarboxylic dianhydride and diphenylmethane diisocyanate were reacted to obtain polyimide powder, and 15% by weight of this was added to the above polyamic acid solution (C) to obtain a polyamic acid solution for cover coat (D). .

The above polyamic acid solution (C) was cast onto a copper foil and then placed in a dryer at 100°C for 30 minutes and at 150°C for 30 minutes.
0 minutes, 30 minutes at 200℃, 20 minutes at 250℃, 3
After heating at 00℃ for 10 minutes each, heating from 300℃ to 3
The temperature was continuously raised to 50° C. over 1 hour for annealing.

A circuit was formed by etching the copper foil on the flexible printed circuit board produced in this way, and the polyamic acid solution (D) prepared by the above method was cast as a cover coat on the circuit surface. After that, put it in the dryer for 100 minutes.
The temperature was raised continuously from °C to 350 °C over 2 hours.

The flexible printed circuit board with a cover coat manufactured in this way has good printability of the cover coat (no curls or wrinkles, excellent strength, heat resistance of 400 degrees or more, and a number of folding cycles). It was an extremely excellent flexible printed circuit board that was tested over 8,000 times.

(Comparative Example 1) Using the same apparatus and method as in Example 1, a polyamic acid solution (referred to as A) consisting of paraphenylene diamine and 3.3',4.4'-biphenyltetracarboxylic dianhydride, and 4 .4'-Diamino diphenyl ether and pyromellitic dianhydride polyamic acid solution (referred to as B)
was synthesized. Next, A and B were mixed and stirred so that the molar ratio was 60/40.

A flexible printed circuit board was prepared in the same manner as in Example 1, and the copper foil surface was etched to form a circuit.

Kapton film, which is commonly used as a coverlay, was attached to this circuit surface using an epoxy adhesive. The resulting flexible printed circuit board with a film coverlay had poor adhesion of the coverlay, and the number of folding cycles was only 1.
000 times or less, which was poor. Furthermore, when heated to 350° C., the adhesive layer turned black and carbonized, and the heat resistance was also poor.

(Comparative Example 2) Using the same apparatus and method as in Example 1, a polyamic acid solution (referred to as A) consisting of paraphenylene diamine and 3.3", 4° 4-biphenyltetracarboxylic dianhydride,
A polyamic acid solution (referred to as B) consisting of 4,4-diaminodiphenyl ether and pyromellitic dianhydride was synthesized. Next, A and B were mixed and stirred so that the molar ratio was 60/40.

A flexible circuit board was prepared in the same manner as in Example 1, and the copper foil surface was etched to form a circuit. This circuit surface was coated with an ink containing commonly used melamine or alkyd resin as its main component. However, the obtained flexible printed circuit board with a cover coat had a significantly poor folding resistance of 500 times or less, and furthermore, when heated to 350° C., the cover coat portion carbonized and blackened, resulting in poor heat resistance.

(Comparative Example 3) Using the same apparatus and method as in Example 1, a polyamic acid solution (referred to as A) consisting of paraphenylene diamine and 3,3',4,4-biphenyltetracarboxylic dianhydride,
A polyamic acid solution (referred to as B) consisting of 4.4'-diaminodiphenyl ether and pyromellitic dianhydride was synthesized. Next, A and B were mixed and stirred so that the molar ratio was 60,740.

A flexible circuit board was prepared in the same manner as in Example 1, and the copper foil surface was etched to form a circuit. The polyamic acid solution prepared by the above method was cast onto the circuit surface as a cover coat, and then placed in a drying oven at 100° C. and heated continuously to 350° C. over 2 hours.

The flexible printed circuit board with a cover coat manufactured in this manner had a durability of about 5,000 folds, but the printability of the cover coat was poor and bleeding and stringiness were observed.

(Comparative Example 4) Using the same apparatus and method as in Example 1, a polyamic acid solution (referred to as A) consisting of paraphenylene diamine and 3,3',4,4-biphenyltetracarboxylic dianhydride,
A polyamic acid solution (referred to as B) consisting of 4,4'-diaminodiphenyl ether and pyromellitic dianhydride was synthesized. Next, A and B were mixed and stirred so that the molar ratio was 80/20.

A flexible circuit board was prepared in the same manner as in Example 1, and the copper foil surface was etched to form a circuit. The polyamic acid solution prepared by the above method was cast onto the circuit surface as a cover coat, and then placed in a dryer at 100° C. and heated continuously to 350° C. over 2 hours.

The cover coated flexible printed circuit board manufactured in this way had poor printability with the cover coat, smearing and stringiness were observed, was rigid and inflexible, and had poor folding durability of about 600 times. Ta.

(Effects of the Invention) The method of the present invention makes it possible to manufacture a flexible printed circuit board with a coverlay based on a flexible printed circuit board without an adhesive layer, which was previously impossible. The flexible printed circuit board has excellent heat resistance because it does not have an adhesive layer, has good workability because it does not curl, and has excellent adhesion, bending durability, and flexibility.

The flexible printed circuit board with a cover coat obtained by the present invention is used not only for wiring boards for various electrical and electronic devices, but also for flat motors, tape carriers, floppy disk heads, high frequency anti-electromagnetic shielding boards, etc.

Claims (4)

[Claims] (1) When polyimide is cast as a cover coat on the circuit surface of a polyimide-based flexible printed circuit board and cured by heating, polyimide powder is added to a heat-resistant resin with the same composition as the base polyimide. A flexible printed circuit board with a cover coat, characterized in that a heat-resistant resin to which 1 to 40% by weight is added as a coating agent is used. (2) The polyimide contains the tetracarboxylic dianhydride component and the diamine component, and the acid component/amine component (molar ratio) is 0.
．． When reacting as 90 to 1.00, 3,3'
, 4,4'-biphenyltetracarboxylic dianhydride and paraphenylenediamine, and a polyamic acid solution (A) obtained by reacting pyromellitic dianhydride and 4,4'-biphenyltetracarboxylic dianhydride.
A/B=55/45~
The flexible printed circuit board with a cover coat according to claim 1, which is a polyimide obtained by heating and curing a polyamic acid mixed solution obtained by mixing and stirring at a ratio of 75/25. (3) The polyimide powder added as a flexibility imparting agent is
Polyimide powder obtained by reacting 3,3',4,4'-biphenyltetracarboxylic dianhydride and diphenylmethane diisocyanate, or 3,3',4,4'
- The flexible printed circuit board with a cover coat according to claim 1, which is a polyimide powder obtained by reacting benzophenone tetracarboxylic dianhydride and diphenylmethane diisocyanate. (4) A circuit is formed by etching on the copper foil surface of a flexible printed circuit board obtained by directly casting the polyamic acid solution according to the above patent claim 2 on a metal foil and curing it by heating. 2. The method for manufacturing a flexible printed circuit board with a cover coat according to claim 1, wherein the polyamic acid solution is cast as a cover coat and cured by heating.