JPH03291987A - Manufacture of flexible printed circuit board - Google Patents

Abstract

PURPOSE:To obtain excellent adhesive properties and strength without curl and wrinkle and excellent heat resistance by directly coating a metal foil having no roughed surface with specific polyamic acid mixture solution, and curing it. CONSTITUTION:Polyamic acid solution A obtained by reacting 3,3',4,4'- biphenyltetracarboxylic acid dianhydride with paraphenylenediamine and polyamic acid solution B obtained by reacting pyromellitic acid dianhydride with 4,4'-diaminodipheylether are obtained. A metal foil having no roughed surface of 0.3mu or less of surface roughness Ra is coated with varnish of polyamic acid mixture obtained by mixing the A and the B at a ratio of A/B = 55/45-75/25 by rolling, and thermoset to obtain a flexible printed circuit board.

Description

Detailed Description of the Invention (Field of Industrial Application) The present invention improves heat resistance, cold resistance, The present invention relates to a method for manufacturing a curl-free flexible printed circuit board that has excellent properties, mechanical properties, and chemical resistance.

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.

(Prior Art) Conventionally, flexible printed circuit boards have been manufactured by bonding polyimide films and metal foils together using adhesives that can be cured at low temperatures, and processed into circuits. If the adhesive is cured at a high temperature, the heat history during thermocompression bonding will cause the board to curl, twist, or warp when it returns to room temperature, making subsequent work such as buttering impossible. .

However, even if a low-temperature curing adhesive was used, the adhesive originally had poor heat resistance, so it was not possible to utilize the inherent heat resistance of the dariimide film, which has good heat resistance, as a circuit-processed turning board.

Therefore, methods of manufacturing flexible printed circuit boards and processing circuits without using adhesives were investigated. A polyamic acid solution obtained by polymerization with an aromatic primary amine such as 4,4'-diaminodiphenyl ether is applied directly to copper foil, and then heated to remove the solvent and ring-close the polyamic acid to form a polyimide. This is a method for manufacturing copper clad boards.

However, in this method, since the above reaction is a dehydration condensation reaction, volumetric shrinkage occurs, and as a result, the resulting circuit board has curls, wrinkles, wrinkles, etc., and in some cases, the bond between the metal foil and the resin may deteriorate. This method has the disadvantage of causing peeling, which has been a major problem in manufacturing flexible printed circuit boards using this method.

(Problems to be Solved by the Invention) As a result of intensive studies to overcome these drawbacks, the present invention has developed a method in which a specific polyamic acid mixed solution is directly applied onto a metal foil without a roughened surface and cured. The present invention was completed based on the knowledge that the flexible printed circuit board manufactured by the above method is free from curls and wrinkles, has excellent adhesion and strength, and has very good heat resistance.

(Means for Solving the Problems) The present invention has a surface roughness Ra of 0. A polyamic acid solution (A) obtained by reacting 3.3',4.4'-biphenyltetracarboxylic dianhydride and paraphenylene diamine on a metal foil without a roughened surface of 3μ or less. , a polyamic acid solution obtained by reacting pyromellitic dianhydride and 4.4°-diaminodiphenyl ether (B
) in a ratio of A/B = 55/45 to 75/25, a polyamic acid mixture varnish is cast and cured by heating. It is.

(Function) In the present invention, a polyamic acid solution is directly cast and coated at 80°C.
A flexible printed circuit board is obtained by heating or holding heating continuously or stepwise to ~350°C over a period of 0.5 hours or more, and by heating and imidizing the board. A method of obtaining a flexible printed circuit board by spreading is a method of casting to a uniform thickness of 50 to 1000 μm using a known coating method such as a rotary coke, knife coater, doctor blade, or flow coater. .

In addition, when removing the solvent from a polyamic acid solution by heating, if you apply strong heating from the beginning before the polyimide film is formed, the surface will become rough or twitchy, so it is best to start from a low temperature and gradually increase the heating temperature. For example, 3 is preferable.
0.0 from 100℃ to 350℃. Heat continuously for 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 exhibited. For example, at 100℃ for 30 minutes,
Then, 30 minutes at 150℃, 30 minutes at 200℃, 250
The temperature may be increased stepwise such as 30 minutes at 300°C, 30 minutes at 350°C. Although the heating atmosphere may be in air in some cases, when a metal foil that is easily oxidized such as copper foil is used as the gold RWI, it is 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 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, in reacting the tetracarboxylic dianhydride component and the diamine component, a polyamic acid solution obtained by reacting 3,3',4,4'-biphenyltetracarboxylic dianhydride and paraphenylene diamine. (A)
and a polyamic acid solution (B) obtained by reacting pyromellitic dianhydride and 4.4°-diaminodiphenyl ether, A/B = 55/45 to 75/25.
It is a polyimide obtained by heating and curing a polyamic acid mixed solution obtained by mixing and stirring at a ratio of .

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-naphthalenetetracarboxylic dianhydride, 3.3', 4.4'-
Diphenylsulfone 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 paraphenylene diamine and 4,4°-diaminodiphenyl ether, but other amines such as 4,4°-diaminodiphenylmethane,
3.3゛-dimethylbenzidine, 4.4゛-diamino-
P-terphenyl, 4.4°-diamino-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 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.OO, 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/medium for the product, this organic polar solvent must also 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,
Examples include 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. For this reason, it is necessary to remove water in the raw materials and also water 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' -Polyamic acid obtained by reacting with diaminodiphinyl ether (
This is a method for obtaining a polyamic acid (referred to as C) by mixing and stirring the polyamic acid (referred to as B) and A/B at a ratio of 55,745 to 75/25.

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 is 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 produced according to the present invention, various silane coupling agents, borane coupling agents, titanate coupling agents 1, aluminum coupling agents and other chelate-based adhesion/adhesion improvers can be used. , various solvents, and flow agents may be added, and ductility agents and viscosity modifiers such as rubber and low-molecular-weight epoxy, or polyamideimide, polyetherimide, polyesterimide, etc. may be blended with talc, mica, etc. , fillers such as quartz powder, colorants such as carbon black and phthalocyanine blue, flame retardants such as tetrabromophenylmethane, and flame retardant aids such as antimony trioxide may also be added.

The metal foil used in the present invention has a surface roughness Ra of 0.3μ
The following metal foil without a roughened surface, generally unroughened rolled copper foil without a roughened surface, is used, but other metal foils can also be used as long as they do not have a roughened surface. ,
Aluminum foil, nickel foil, stainless steel foil, tungsten foil, etc. can also be used. The metal foil is roughened,
That is, the surface roughness Ra is 0. If it exceeds 3μ, there will remain areas where solvent evaporation and stress relaxation are insufficient, resulting in uneven distribution of resin hardening and stress relaxation in the thickness direction. Curls and wrinkles occur on the film, while the surface roughness Ra
By using a metal foil that does not have a roughened surface of 0.3μ or less, it is possible to significantly alleviate the unevenness of residual stress that occurs due to shrinkage during heat curing of polyamic acid. Later curls, wrinkles, and dimensional changes can be significantly reduced.

Although the circuit board obtained in this way does not have a roughened surface, the metal foil and film have sufficient adhesive strength. Since it has no surface, it becomes an extremely electrically stable flexible printed circuit board. In addition, since there is no roughened surface, it has excellent circuit workability, and it is easy to make the circuit thinner.

(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'-biphenyltetracarboxylic dianhydride was added little by little with stirring, but since the reaction was exothermic, cold water at 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 to complete the reaction, the polyamic 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 above to obtain a polyamic acid (referred to as B). and B were mixed and stirred so that the molar ratio was A/B = 60/40.The obtained product was a transparent yellow and extremely viscous polyamic acid solution, which was dissolved in N-methyl-2-pyrrolidone. The intrinsic viscosity of a 0.5% by weight solution is 0.81 (30
℃).

After drying this polyamic acid solution on a non-roughened rolled copper foil of 35μ and Ra=0.02u, the film thickness was 25μ.
After applying the coating to the desired temperature, the temperature was continuously raised from 100°C to 200°C over 1 hour in a dryer, and then the temperature was continuously raised from 200°C to 380°C over 1 hour in a dryer. The adhesive strength (JIS C6481) of the flexible printed circuit board manufactured by raising the temperature is 1.1.
Dimensional change rate in Kg/cm (JIS C64811 is 0.
05% (there is no curling at all, and the film after etching the copper foil has no curling at all, the tensile strength (JIS K6760) is 3 L Kg/mm', and the elongation (JIS K676 (1) is excellent at 41%). It was a thing.

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. A polyamic acid solution (referred to as B) consisting of 4°-diaminodiphenyl ether and pyromellitic dianhydride was synthesized. Next, A and B were mixed and stirred so that the molar ratio was 70/30.

The product had an intrinsic viscosity of 0.90.

This polyamic acid solution was cast onto the same metal foil as in Example 1 so that the film thickness after drying was 25μ, then placed in a dryer and heated at 100°C for 30 minutes at 150°C.
After heating at ℃ for 30 minutes and 200℃ for 30 minutes, put in a dryer and heat at 200℃ for 30 minutes and 250℃ 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 1.2 kg/cm, a dimensional change rate of 0°07%, and has no curls at all, and the film after etching the copper foil has no curls at all and is heat resistant. is 500℃
The tensile strength was excellent, 30 Kg/mm', and the elongation was 40%.

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. 35μ, Ra=1.0
This polyamic acid solution was cast onto a general rolled copper foil with a roughened surface of μ so that the film thickness after drying was 25μ, and then placed in a dryer and continuously heated from 100℃ to 380℃ for 2 hours. The temperature was raised over time.

The flexible printed circuit board manufactured in this way had a roughened surface, so the residual stress was not sufficiently alleviated, and the film after copper foil etching had severe curls and wrinkles, making it unsuitable for use as a circuit board. .

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 (referred to as A), and 4.4゛-Polyamic acid solution consisting of 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 80/20.

A flexible circuit board was created using the same 35μ non-roughened rolled copper foil as in Example 1, but the flexible printed circuit board manufactured in this way had an adhesive strength of 0. 5Kg
/cm, 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 polyamic acid solution (referred to as A) consisting of paraphenylene diamine and 3.3', 4.4°-biphenyltetracarboxylic dianhydride (referred to as A), and 4.4 - A polyamic acid solution (referred to as B) consisting of diaminodiphenyl ether and pyromellitic dianhydride 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 the same 35μ non-roughened rolled copper foil as in Example 1, but it curled significantly and was unsuitable for use as a circuit board.

(Effect of the invention) By using a metal foil without a roughened surface as in the present invention, it is possible to significantly alleviate the non-uniformity of residual stress that occurs due to shrinkage during heat curing of polyamic acid. Also, curls, wrinkles, and dimensional changes after metal foil etching can be significantly reduced. In addition, the metal foil and film have sufficient adhesion strength even though they do not have a roughened surface, and since there is no roughened surface on the metal foil that deteriorates high frequency conductive properties, it is an extremely electrically stable flexible print. You can get a circuit board. For example, it has been confirmed that while the effective conductivity of a flexible printed circuit board normally drops to about 30% of the DC value in the 10 GHz frequency range, it is possible to increase it to over 80% by using this metal foil. It is being Furthermore, since there is no roughened surface, it has excellent circuit workability, and it is easy to make the circuit thinner. It is now possible to produce a flexible printed circuit board without an adhesive layer that does not curl at all, which was previously difficult, and the flexible printed circuit board thus obtained has excellent heat resistance and no curling due to the absence of an adhesive layer. The substrate had good processability because it was free of oxidation, and also had excellent properties as a film.

Claims (1)

[Claims] (1) Surface roughness Ra (JIS B0601) is 0.3μ
3.3', 4.4' on metal foil without roughened surface which is below.
- A polyamic acid solution (A) obtained by reacting biphenyltetracarboxylic dianhydride and paraphenylene diamine, and a polyamic acid solution obtained by reacting pyromellitic dianhydride and 4,4'-diaminodiphenyl ether. acid solution (B), A/B=55/45 to 75/25
1. A method for producing a flexible printed circuit board, which comprises casting a varnish of a polyamic acid mixture obtained by mixing the mixture in a ratio of 1 to 1, and heating and curing the varnish.