JPH0391290A - Manufacturing method of flexible printed circuit board - Google Patents

Abstract

PURPOSE:To improve heat resistance, low-temperature resistance, electrical characteristics, mechanical characteristics, wear-resistance property, chemical resistance, radioactive ray resistance, etc., and to prevent curling by applying a specific polyamic aid, curing to a semi-cured state, and then pressing continuously using a metal tube for complete curing. CONSTITUTION:A polyamic acid mixed varnish is prepared by mixing a polyamic acid solution (A) which is obtained by enabling 3,3',4,4'- biphenyltetracarbon acid dianhydride and paraphenirange amine to react each other and a polyamic acid solution (B) which is obtained by enabling pyromellitic dianhydride and 4,4'-diaminodiphenyleter to react each other in the ratio of A/B=55/45-75/25 on a metal foil. This varnish is applied, turned into semi-cured state at a temperature above 80 deg.C and below 250 deg.C and then this semi-cured state varnish is wound on the metal foil 1. Further, this roll- shaped printed circuit board 4 is fixed to a metal frame 2 by a metal bolt 3 and is heated to a temperature above 300 deg.C and below 450 deg.C while applying pressure, thus performing press and heating utilizing the difference in linear expansion coefficients between a metal frame 2, a metal bolt 3 and the printed circuit board for complete curing.

Description

Detailed Description of the Invention (Industrial Application Field) The present invention is obtained by directly casting a polyamic acid solution onto a metal foil, bringing it to a semi-cured state, and pressing it onto a metal tube to completely cure it. It relates to circuit boards, and relates to a method for producing curl-free flexible printed circuit boards with excellent heat resistance, cold resistance, electrical properties, mechanical properties, abrasion resistance, chemical resistance, radiation resistance, etc. be.

(Prior Art) Conventionally, flexible printed circuit boards have been manufactured by bonding a polyimide film and metal foil together using an adhesive that can be cured at low temperatures. If the adhesive cures at a high temperature, the thermal history during thermocompression bonding may cause the circuit board to curl or curl when returned to room temperature.
This is because twisting, warping, etc. occur, making subsequent work such as buttering impossible. However, even if a low-temperature curing adhesive is used, the heat resistance of the adhesive is inherently poor, so it has not been possible to utilize the inherent heat resistance of polyimide film, which has good heat resistance, as a circuit board. Therefore, a method of manufacturing flexible printed circuit boards without using adhesives was investigated. For example, a polyamic acid solution obtained by polymerizing a tetracarboxylic acid such as pyromellitic acid and an aromatic primary amine such as 4,4'-diaminodiphenyl ether as shown in U.S. Pat. No. 3,179,634. This is a method for producing a polyimide copper clad board by directly coating copper foil on copper foil and then heating to remove the solvent and generate a polyamide through a condensation reaction of polyamic acid. However, in this method, volume shrinkage occurs because the above-mentioned condensation reaction is a dehydration condensation reaction, but the stress between the copper foil and the imide layer is not relaxed due to expansion, which is thought to be due to rearrangement of molecules before and after the shrinkage. Circuit boards manufactured with conventional general-purpose boria polyscinic acid have weak adhesion and are prone to curling and
Wrinkles, jiggling, etc. occur, and it has been considered practically impossible to manufacture flexible printed circuit boards using this method.

(Problems to be Solved by the Invention) As a result of intensive studies to overcome the above-mentioned drawbacks, the present invention has been developed by coating a specific polyamic acid, curing it to a semi-cured state, and then compressing it using a metal tube. The present invention was completed based on the knowledge that this is a method of manufacturing a flexible printed circuit board by completely curing it, has very good heat resistance, is free from curls and wrinkles, and has excellent adhesion and strength. This is what I came to do.

(Means for Solving the Problems) The present invention provides a semi-cured state by heating from 80°C to 250°C to obtain a flexible printed circuit board by directly casting a heat-resistant resin on metal foil. The heat-resistant resin in
It is cured by heating to below ℃, but at this time, by heating the rolled substrate fixed to a cylindrical metal frame with metal bolts, the difference in linear expansion coefficient between the metal frame and metal bolts and the substrate is utilized. This is a method for manufacturing a flexible printed circuit board, which is characterized by completely curing the printed circuit board by applying pressure and heating.

(Function) The method for manufacturing the flexible printed circuit board used in the present invention involves first directly casting the above-mentioned polyamic acid solution onto a metal foil, and then continuously or stepwise applying the polyamic acid solution to a temperature of 80°C to 250°C. The temperature is raised or maintained for 5 hours or more to dry the film surface, wound onto a metal tube, and M1
This is a method of manufacturing a flexible printed circuit board by fixing it on a metal frame as shown in the figure and heating and imidizing it while applying pressure to 350 to 450°C.

A method for obtaining a base flexible printed circuit board by casting a polyamic acid solution onto a metal foil is to apply a uniform thickness of 50 to 1000μ using known coating means such as a rotary coater, knife coater, doctor blade, or flow coater. A method of casting is used.

Next, the solvent of boria pink acid is removed by heating.
If strong heating is applied from the beginning before the polyibide film is formed, the surface will become rough or twitchy, so it is preferable to heat the film gradually from a low temperature. For example, from 100°C to 250°C, 0. Heat continuously for 5 hours or more. 0. If the time is less than 5 hours, depending on the film thickness, solvent removal may be insufficient and the film surface may not be completely dry. For example, at 100℃ for 30 minutes, then at 50℃ for 30 minutes, at 200℃ for 30 minutes, and at 250℃ for 3 minutes.
The temperature may be raised stepwise such as 0 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 polyibide coating layer thus formed typically has a thickness of 10 to 200 microns. This substrate is wound in a roll onto a metal tube.

This metal-7 roll-shaped substrate is fixed to a cylindrical metal frame as shown in Figure 11, and the solvent is removed by heating while applying pressure from 300°C to 45°C. By heating while fixed with metal bolts,
Utilizing the difference in linear expansion coefficient between the metal ♂f and metal porcelain φ substrates, the material is heated under pressure to be completely cured.

If strong heating is applied from the beginning before the polyimide film is formed, the surface will become rough or twitchy, so it is preferable to gradually increase the heating temperature. For example, 20
Continuously heat from 0°C to 350°C over 0°5 hours. If the time is less than 0.5 hours, imidization may not be sufficiently carried out, although it depends on the film thickness. For example,
30 minutes at 200℃, then 30 minutes at 250℃, then 300℃
The temperature may be increased stepwise, such as at 350° C. for 30 minutes and at 350° C. for 30 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 polyamide film layer formed in this manner generally has a thickness of 10 to 20
It is 0μ.

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 the polyimide shown below is most suitable for the purpose.

That is, the tetracarboxylic dianhydride component and the diamine component are mixed at an acid component/amine component (molar ratio) of 0.90-1.
．． When reacting as 00, 3.3', 4.4'
- A boria chestnut acid solution (A) obtained by reacting biphenyltetracarboxylic dianhydride and paraphenylenediamine, and a solution obtained by reacting pyromellitic dianhydride with 4,4'-diaminodiphenyl ether. and the polyamic acid solution (B), A/B=55/45 to 75/
This is a polyamide obtained by heating and curing a polyamic acid mixed solution obtained by mixing and stirring at a ratio of 25%.

The tetracarboxylic dianhydride referred to in the present invention is 3.3'
, 4,4ξbiphenyltetracarboxylic dianhydride, and pyromellitic dianhydride, but other acids such as 2
, 3.3', 4'-biphenyltetracarboxylic dianhydride, 3.3', 4.4'-benzophenonetetracarboxylic dianhydride, 3.3', 4.4'-P-terphenyl Tetracarboxylic dianhydride, 2,3,6.7-naphthalenetetracarboxylic 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 para-phenylene diamine and 4,4'-diaminodiphenyl ether, but other diamines such as 4,4'-diaminodiphenylmethane,
3,3'-dimethylbenzidine, 4,42-diamino-
P-terphenyl, 4,4'-cyano-P-quarterphenyl, 2,8-diaminodiphenylene oxide, etc. can also be used in combination.

The reaction between the tetracarboxylic dianhydride component and the diamine component is carried out at an acid component/amine component (molar ratio) of 0.90 to 1. It is preferable to use OO, and if it is lower than 0.90, the degree of polymerization will not increase and the properties of the film after curing will be poor.

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

The reaction 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. Typical solvents of this type include N,N-dimethylformamide, N,N-dimethylacetamide, dimethylsulfone, dimethylsulfoxide, and N-methyl-2
-pyrrolidone, etc., 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, a polyamic acid (referred to as A) obtained by reacting 3,3'',4,4'-biphenyltetracarboxylic dianhydride and paraphenylenediamine, pyromellitic dianhydride, and 4,4 '-Diamino diphenyl ether obtained by reacting polyamic l(B
By mixing and stirring A/B=55/45 to 75/25, polyamitsutaic acid (referred to as C) is obtained.
This is the way to obtain.

When the ratio of A is less than the above-mentioned ratio, curling occurs, and on the other hand, when it is larger than the above ratio, the material becomes too rigid and loses flexibility.

The reaction temperature for synthesizing A and B and mixing them to obtain C is preferably 0 to 100°C.

This is because if the temperature is below 0°C, the reaction rate will be slow, and if it is above 100°C, the ring-closing reaction and depolymerization reaction of the produced polyamic acid will start. Usually, the reaction is carried out at around 20°C.

When using the polyamic acid product 11- produced according to the present invention, various silane coupling agents,
Borane coupling agent, titanate coupling agent 1
, aluminum-based coupling agents, chelate-based adhesion/adhesion improvers, various solvents, and flow agents may be added. A small amount of a curing accelerator such as A-based resin may be added, or a flexibility agent or viscosity modifier such as rubber or low-molecular epoxy, or a blend of polyamideimide, polyetherimide, polyesterimide, etc. Fillers such as talc, mica, and quartz powder,
Colorants such as carbon black and phthalocyanine blue,
Small amounts of flame retardants such as tetrabromophenylmethane and flame retardant aids such as antimony dioxide may also be added.

The metal foil used in the present invention is generally copper foil, but aluminum foil, nickel foil, stainless steel foil, tungsten foil, etc. can also be used.

The metal foil used has a thickness of 3 to 200 microns, and preferably has a roughened surface.

12- The metal frame and metal bolt used in the present invention are generally made of iron, but metals such as stainless steel and titanium, which have excellent mechanical strength and a relatively small coefficient of linear expansion, can also be used. .

(Example) Example 1 108 g of purified anhydrous para-phenylenediamine was placed in a four-piece variable flask equipped with a thermometer, a stirrer, a reflux condenser, and a dry nitrogen gas inlet, and anhydrous N-methyl- A mixed solvent of 90% by weight of 2-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'-t' phenyltetracarboxylic dianhydride was added little by little while stirring, but since it was an exothermic reaction, cold water at about 15°C was circulated in an external water tank. Cooled. After the addition, the internal temperature was set at 20°C and stirred for 5 hours to complete the reaction, and the boriapinic acid solution (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, A and B were mixed and stirred so that the molar ratio was A/B = 60/40. The product obtained is a transparent yellow, extremely viscous polyamic acid solution with an intrinsic viscosity of 0.81 as a 0.5% by weight solution in N-methyl-2-pyrrolidone (at 30 °C
)Met.

After this polyamic acid solution was cast onto rolled copper foil, it was placed in a dryer and the temperature was raised continuously from 100°C to 200°C over 1 hour, and then wound onto a metal tube to form the iron shown in Figure 1. It was fixed with a frame and placed in a dryer, and the temperature was raised continuously from 200°C to 380°C over 1 hour.

The flexible printed circuit board manufactured in this manner has an adhesive strength of 1.2 Kg/am and a dimensional change rate of 0. 1%
There is no curling at all, and the heat resistance of the film alone after etching the copper foil is 500℃, and the tensile strength is 21
Kg/mm2 and elongation were excellent at 31%.

Example 2 Using the same apparatus and method as in Example 1, a polyamic acid solution (referred to as A) consisting of paraphenylenediamine and 3.3',4.4'-biphenyltetracarboxylic dianhydride, 4, Polyamine chloride solution consisting of 4'-diaminodiphenyl ether and pyromellitic dianhydride (referred to as B)
was synthesized. Next, A and B were mixed and stirred so that the molar ratio was 70/3.0.

The product had an intrinsic viscosity of 0.90.

After casting this boria-based succinic acid solution onto electrolytic copper foil heated to 180°C, it was placed in a dryer and heated at 100°C for 30 minutes, 150°C for 30 minutes, and 200°C for 30 minutes. It was rolled up onto a metal tube, fixed with the iron frame shown in Figure 1, and placed in a dryer at 200°C for 30 minutes and then at 250°C for 30 minutes.
0 minutes, 30 minutes at 300°C, and 20 minutes at 380°C.

The flexible printed circuit board manufactured in this way has an adhesive strength of 1.3 kg/cm, a dimensional change rate of 0.1%, and no curling at all, and the heat resistance of the film alone after etching the copper foil is At 500°C, the tensile strength was 20 kg/mm2 and the elongation was 30%, which were excellent.

Comparative Example 1 A polyamic acid solution similar to that of Example 1 was prepared using the same apparatus and method as that of Example 1, and this polyamic acid solution was cast onto a rolled copper foil, and then placed in a dryer and heated from 100°C. The temperature was raised continuously to 380°C over 2 hours.

The adhesive strength of the flexible printed circuit board manufactured in this way was Q, probably because it was fixed to the metal frame and no pressure was applied.
The weight was 4 kg/cm, making it unsuitable for use as a circuit board.

Comparative Example 2 Using the same apparatus and method as in Example 1, a polyamine chloride solution (referred to as A) consisting of rose phenylene thiamine and 3.3',4.4'-biphenyltetracarboxylic dianhydride, A boria polysuccinic acid 16-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 printed circuit board was produced using rolled foil in the same manner as in Example 1, but the flexible printed circuit board produced in this way had an adhesive strength of 0°5 Kg/c.
It was rigid, inflexible, and had poor folding durability, making it unsuitable for use as a circuit board.

Comparative Example 3 Using the same apparatus and method as in Example 1, a polyamine chloride solution (referred to as A) consisting of paraphenylenediamine and 3.3',4.4'-biphenyltetracarboxylic dianhydride, and 4, Polyamine chloride solution consisting of 4'-diaminodiphenyl ether and pyromellitic dianhydride (referred to as B)
was synthesized. Next, A and B were mixed and stirred so that the molar ratio was 40/60.

A flexible circuit board was made using electrolytic foil in the same manner as in Example 1, but it curled significantly and was unsuitable as a circuit board.

(Effects of the Invention) The method of the present invention makes it possible to manufacture a flexible printed circuit board without an adhesive layer, which was previously considered impossible, and the flexible printed circuit board thus obtained has no adhesive layer. Therefore, the circuit board had excellent heat resistance, was easy to process due to no curling, and had excellent properties as a film.

The flexible printed circuit board obtained by the present invention can be used not only for wiring boards for various electrical and electronic devices, but also for flat motors,
It is also used in tape carriers, floppy disk heads, high frequency antennas, electromagnetic shielding plates, etc.

4. Brief explanation of the figure When used, it is wrapped in a roll on a metal tube, sandwiched within an iron frame, and tightened with bolts for good balance.

Claims (1)

[Claims] (1) A polyamic acid solution (A) obtained by reacting 3,3',4,4'-biphenyltetracarboxylic dianhydride and paraphenylenediamine on a metal foil, and pyromellitic dianhydride. A polyamic acid mixed varnish obtained by mixing a polyamic acid solution (B) obtained by reacting a substance with 4,4'-diaminodiphenyl ether in a ratio of A/B = 55/45 to 75/25. Cast coating, 80
It was semi-hardened at a temperature of ℃ or higher and 250℃ or lower, and then the semi-hardened product was wound onto a metal tube, which was further pressed with a cylindrical metal frame, and this metal frame was fixed with metal bolts. A method for producing a flexible printed circuit board, which comprises heating the substrate to a temperature of 300° C. or higher and 450° C. or lower to completely cure the board.