JPH02273984A - Flexible printed circuit board and manufacture thereof - Google Patents

Abstract

PURPOSE:To obtain a flexible printed circuit which is free from curls and wrinkles and is superior in heat-resistance and fire-resistance by combining resin faces of a two layer flexible printed circuit board which is obtained by applying a heat-resistant resin on the face of a metallic foil after directly spreading and extending its heat-resistance resin without using adhesives. CONSTITUTION:A polyamic acid solution is applied on the face of a metallic foil after directly spreading and extending its solution and a resultant resin layer makes its solution to be formed into a film and yet, it does not set completely. Etching of a circuit pattern is performed in accordance with an ordinary process to a circuit board which is obtained by heating it up to a temperature of 150-300 deg.C. After that, a resin is put on top of the other resin face and they are heated at a temperature of 300-450 deg.C and are pressed under a pressure of 1-100kg/cm<2>, The circuit board which is free from curls and wrinkles and is superior in heat-resistance and fire-resistance is thus obtained.

Description

Detailed Description of the Invention (Industrial Application Field) The present invention involves forming a circuit pattern on a flexible printed circuit board in which the V+1 lubricant has not been completely cured, overlapping the circuit patterns, and integrating them by heating and pressing. The present invention relates to a double-sided flexible printed circuit board that has excellent heat resistance, flame resistance, cold resistance, high frequency electrical properties, mechanical properties, abrasion resistance, chemical resistance, radiation resistance, etc., and a method for manufacturing the same.

(Prior art) Conventionally, a flexible printed circuit board having metal foil on both sides is made by pasting metal foil on both sides of an insulating film made of polyimide, polyester, etc. with an adhesive.
The composition was a/adhesive/excellent film/adhesive/metal foil, or metal foil/insulating film/adhesive/extreme film/metal foil.

However, in a circuit board with such a structure, since an adhesive layer exists between the insulating film and the metal foil, the characteristics of the obtained circuit board are influenced by the properties of the adhesive, and the insulating film has high performance. Even when film was used, it had the disadvantage that its properties could not be fully utilized.

As a specific example, when using nylon adhesive,
High water absorption makes it durable as a circuit! ! Relationships get worse. If a rubber adhesive is used, the heat resistance will be poor, and the adhesion between the circuit part and the insulating film will be poor during the soldering process.

On the other hand, as shown in Japanese Patent Application Laid-open No. 55-153393, a double-sided metal-clad flexible printed circuit board is produced by casting W resin varnish on a metal foil and bonding the resin surfaces together with an adhesive. This method is known, but since the product obtained by this method uses common resins and adhesives, it has the following drawbacks. For example, the expansion of the resin when casting on metal foil Because the coefficient does not match the expansion coefficient of the metal foil, the 1-piece N product may curl after casting, making subsequent gluing work difficult, or
For similar reasons, the dimensional stability of the substrate was poor, and the adhesion under harsh conditions such as heat cycle tests was poor.

(Problem H to be Solved by the Invention) As a result of intensive studies to overcome the drawbacks of the present invention, the present invention has revealed that a flexible printed circuit board manufactured using the method specified in the present invention has high heat resistance and flame resistance. The present invention was completed based on the findings that the material has very good properties, is free from curls and wrinkles, and has excellent strength.

(Means for Solving the Problems) The present invention is achieved by bonding the resin surfaces of a flexible printed circuit board, which is obtained by directly casting a heat-resistant resin onto a metal foil, without using an adhesive. The resulting flexible printed circuit board has a metal foil/heat-resistant resin/metal foil structure and a method for manufacturing the same.

(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 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 to 1.
．． When reacting as 00, 3.3', 4.4''
- 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=5f5/45 to 75/2
It is a polyimide obtained by heating and curing a polyamic acid mixed solution obtained by mixing and stirring at a ratio of 5 to 5.

The method for manufacturing a flexible printed circuit board of the present invention includes first casting the above-mentioned polyamic acid solution directly onto a metal foil, causing the resin layer to rebound and not completely curing.
A circuit pattern is formed on the flexible printed circuit board obtained by heating to a temperature of 150 to 300° C. by etching a circuit pattern using a conventional method. After that,
Layer these resin surfaces together at 300-460°C.
Heating at a temperature of 1 to 100 Kg/cwI
By applying pressure at a pressure of 100 mL, a flexible printed circuit board having a metal foil/heat-resistant resin/metal foil structure is obtained.

The tetracarboxylic dianhydride used in the present invention is 3.3
',4,4'-biphenyltetracarboxylic 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-terphenyltetracarboxylic dianhydride, 2,3. G.? -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 used in the present invention include phenylene diamine and 4,4'-diaminodiphenyl ether, but other amines such as 4,41-diaminodiphenylmethane, 3.3ξdimethylbenzidine, 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! , OO, gas is generated during curing and a smooth film cannot be obtained.

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 The 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 are 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, and volatilization regulators from products.
Used as a film smoothing agent, etc.

It is generally preferable to carry out the reaction under anhydrous conditions, since water may cause the tetracarboxylic dianhydride to undergo ring closure, inactivation, and termination of the reaction. 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.

Further, the reaction is preferably carried out in an inert gas atmosphere in order to prevent oxidation of the 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 phenylenediamine, pyromellitic dianhydride, and 4.4' -Polyamic acid B obtained by reacting with diaminodiphenyl ether
Polyamic acid (referred to as C) is mixed and stirred with A/B = 55/45 to 75/25.
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.

If the temperature is below 0°C, the reaction rate will be slow, and if the temperature 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 used, the polyamic acid product produced according to the present invention improves the adhesion and adhesion of various silane coupling agents, borane coupling agents, titanate coupling agents, aluminum coupling agents, and chelate systems. In addition to these, small amounts of ordinary acid curing agents, amine curing agents, imidazole, tertiary amines and other curing accelerators may be added. Flexibility agents and viscosity modifiers such as molecular epoxy, or polyamideimide, polyetherimide, polyesterimide, etc. may be blended with fillers such as talc, mica, and quartz powder, and colorants such as carbon black and phthalocyanine blue. Small amounts of additives, flame retardants such as tetrabromophenylmethane, and flame retardant aids such as antimony trioxide may also be added.

For the flexible printed circuit board used in the present invention, the above-mentioned polyamic acid solution is directly cast-coated onto metal foil, and the resin layer forms a film but does not completely cure.
Those heated to a temperature of ~300°C are used.

The flexible printed circuit board is manufactured by a conventional method for manufacturing a two-layer flexible printed circuit board, such as the method described in Japanese Patent Application Laid-Open No. 62-200795, at a heating temperature of 150° C. Finish at a leap temperature of ~300°C.

At temperatures below 150° C., the evaporation of the solvent is insufficient, resulting in curling and large dimensional changes during etching of the circuit pattern, and poor adhesion due to the generation of steam during the subsequent pressurization and heating. At a temperature of 300° C. or higher, curing progresses more than necessary, and even if the next pressurization and heating is performed, sufficient adhesion will not occur.

The metal foil used in the present invention is generally steel 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.

Next, the resin surfaces are overlapped and heated at a temperature of 300 to 450°C and pressed at a pressure of 1 to 100K11 cm using a normal electric press.300
If the temperature is below 450°C, the resin layer will not be sufficiently cured and the adhesion between the resin layers will be poor, and if it is above 450°C, the resin layer will begin to thermally decompose, resulting in deterioration of the performance of the substrate. Also, I Kg/
Adhesion is not sufficient if the pressure is more than cm2, and the pressure of 100 g
A pressure greater than 1/cm" is not good because the circuit pattern will be deformed.

(Example 1) 108 g of purified anhydrous bulk phenylenediamine was placed in a four-piece rose para 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 biolidone 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 purified anhydrous pyromellitic acid were added using the same apparatus and method as above. 218 g of dianhydride was reacted to obtain polyamine nic acid (referred to as B). A and B were mixed and stirred so that the molar ratio was A/B = 60/40. The product obtained is a yellow transparent and extremely viscous polyamic acid S solution, with a concentration of 0.0% in H.methyl-2-pyrrolidone. The intrinsic viscosity of a 5% by weight solution is 0.81 (at 30°C
) This polyamic acid solution was cast onto a copper foil, then placed in a dryer at 100°C and heated to 250°C continuously over a period of 2 hours.

t! on the printed circuit board manufactured in this way! A circuit was formed by etching 4fi.

The resin surfaces of the flexible printed circuit boards on which this circuit was formed were overlapped and heated at 350°C and 60°C using an electric press.
The mixture was heated under pressure for 40 minutes at 0 g/c 2.

The flexible printed circuit board manufactured in this manner was free from curls and wrinkles and had excellent heat resistance and flame resistance.

(Example 2) Using the same apparatus and method as in Example 1*1, a polyamic acid solution consisting of phenylene diamine and 3,3',4,4-biphenyltetracarboxylic dianhydride was prepared. .4ζ Polyamic acid solution consisting of diaminodiphenyl ether and pyromellitic dianhydride 8! (Set as B)
Synthesized 0. 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 a copper foil, placed in a dryer at 100°C, and heated to 200°C over 1 hour.

A circuit was formed by etching the copper foil on the flexible printed circuit board manufactured in this manner.

The resin surfaces of the flexible printed circuit boards on which this circuit was formed were overlapped and heated at 400°C and 200°C using an electric press.
The mixture was heated under pressure for 20 minutes at 0 g/c 2.

The flexible printed circuit board manufactured in this manner was free from curls and wrinkles and had excellent heat resistance and flame resistance.

(Comparative Example 1) A polyamic acid solution prepared using the same apparatus and method as in Example 1 was directly cast onto a copper foil, and the temperature was continuously raised to 100 to 380°C over 2 hours.

The tR foil surface of the thus obtained two-layer flexible printed circuit board was etched to form a circuit, and then an epoxy adhesive was applied to the polyimide surface, and the two sheets were stacked and press-bonded. A flexible printed circuit board was fabricated.

The thus obtained double-sided flexible printed circuit board had poor heat resistance and flame resistance, and when heated to 350° C., the adhesive layer carbonized and deteriorated, causing peeling.

(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, and 4 , 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 60/40.

This polyamic acid solution was cast onto a copper foil and then placed in a dryer and heated at 120° C. for 2 hours.

When the copper foil on the flexible printed circuit board manufactured in this manner was etched to form a circuit, it curled severely and could not be overlaid.

(Comparative Example 3) A polyamic acid P# solution (referred to as A) consisting of paraphenylene diamine and 3.3', 4.4°-biphenyltetracarboxylic dianhydride was prepared using the same apparatus and method as in Example 1.
Then, 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.

After casting this polyamic acid solution on copper foil,
The mixture was placed in a dryer at 0°C and heated to 320°C over 2 hours.

A circuit was formed by etching the steel foil on the flexible printed circuit board manufactured in this way.

The resin surfaces of the flexible printed circuit boards on which this circuit was formed were overlapped and heated at 400°C and 200°C using an electric press.
Although the resin surface was heated under pressure at 0g/cs+2 for 20 minutes, the resin surface did not adhere and a double-sided flexible printed circuit board could not be obtained.

(Effects of the Invention) The flexible printed circuit board manufactured by the method of the present invention has excellent heat resistance and flame resistance because it does not have an adhesive layer, does not curl, and has 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.

Claims (3)

[Claims] (1) Metal foil/heat resistant resin obtained by laminating the resin surfaces of a two-layer flexible printed circuit board obtained by directly casting a heat resistant resin onto the metal foil without using an adhesive. /Flexible printed circuit board made of metal foil. (2) The heat-resistant resin contains a tetracarboxylic dianhydride component and a 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 a polyamic acid solution (A) obtained by reacting phenylene diamine, pyromellitic dianhydride, and 4,4'-biphenyltetracarboxylic dianhydride.
A/B=55/45~
The flexible printed circuit board 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) A flexible printed circuit board obtained by directly casting a heat-resistant resin on metal foil,
A circuit pattern is etched on the material that has been heated to a state before it is completely cured at ℃, and then the resin surfaces are overlapped and heated at a temperature of 300 to 450℃ and a pressure of 1 to 100 kg/cm^2. 2. The method for manufacturing a flexible printed circuit board according to claim 1, wherein the flexible printed circuit board is pressurized by pressure.