JPH0753801B2 - Method for manufacturing flexible printed circuit board - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION [Industrial field of application] The present invention is a heat-resistant, cold-resistant, electrical property obtained by directly casting a special polyamic acid solution on a metal foil and curing it by a special heating method. The present invention relates to a method for producing a curl-free flexible printed circuit board having excellent mechanical properties, abrasion resistance, chemical resistance, radiation resistance and the like.

[Prior art]

Conventionally, a flexible printed circuit board has been manufactured by bonding a polyimide film and a metal foil with an adhesive that can be cured at a low temperature. When it is a high temperature curing adhesive, due to the heat history during thermocompression bonding, when it is returned to room temperature, the curl of the substrate,
This is because twisting, warping, etc. occur and subsequent work such as patterning is impossible. However, even if a low-temperature curing adhesive is used, the adhesive originally has poor heat resistance, so that even if a polyimide film having good heat resistance is used as the substrate, the original heat resistance cannot be exhibited. Therefore, a method of manufacturing a flexible printed circuit board without using an adhesive has been studied. For example, U.S. Patent 3,179,634
The polyamic acid solution obtained by polymerization of a tetracarboxylic acid such as pyromellitic acid as shown in No. 4 and an aromatic primary amine such as 4,4′-diaminodiphenyl ether is directly applied to a copper foil, Then, the method is a method of producing a polyimide copper clad plate by heating to remove the solvent and generate a polyimide by the condensation reaction of the polyamic acid. However, in this method, since the condensation reaction described above is a dehydration condensation reaction, volume contraction occurs and a circuit board manufactured from a conventional general-purpose polyamic acid has curls, wrinkles, and
It has been considered practically impossible to manufacture a board for a flexible printed circuit by this method because of a problem such as crease.

[Object of the Invention]

The present invention, as a result of intensive studies to overcome such drawbacks so far, the flexible printed circuit board produced by using the curing method specified in the present invention polyamic acid specified in the present invention is excellent in heat resistance and the like curl. The present inventors have completed the present invention by obtaining the knowledge that the above phenomenon does not occur.

[Structure of Invention]

That is, the present invention is 3,3 ', 4,4'-biphenyl tetracarboxylic acid dianhydride 50-80 mol%, pyromellitic dianhydride
A tetracarboxylic dianhydride component consisting of 50 to 20 mol% and a diamine component consisting of 50 to 80 mol% of para-phenylenediamine and 50 to 20 mol% of 4,4'-diaminodiphenyl ether are added to the acid component / amine component ( Molar ratio) to 0.90-1.
In reacting with 00 with a laddering rate of 56 to 62%, 3,3 ′, 4,4′-biphenyltetracarboxylic dianhydride and paraphenylenediamine were previously reacted with pyromellitic acid. After preparing a reaction product of dianhydride and 4,4'-diaminodiphenyl ether, both were mixed,
Synthesize polyamic acid by reacting at 0 ℃ ～ 100 ℃ for 0.5 hours ～ 30 hours, cast and coat it on metal foil, and heat it from 100 ℃ to 300 ℃.
Continuously or stepwise over 0.5 hours to ℃, wrap the metal foil surface inside a cylinder with a diameter of 50 to 100 mm and continuously or stepwise from 300 ℃ to 350 ℃ 0.5
It is a method for manufacturing a flexible circuit board, which is characterized in that heating or holding and heating are performed over a period of time.

The tetracarboxylic acid dianhydride used in the present invention is 3,
3 ', 4,4'-biphenyltetracarboxylic dianhydride 50-8
0 mol% and pyromellitic dianhydride 50 to 20 mol%, but other acids, such as 2,3,3 ', 4'-biphenyltetracarboxylic 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) and the like can be used together. 3,3 ', 4,4'-biphenyltetracarboxylic dianhydride is preferably 50 to 80 mol%, 50 mol%
If it is less, curling occurs, and if it is more than 80 mol%, it becomes too rigid and lacks flexibility. The amount of pyromellitic dianhydride is preferably 50 to 20 mol%, and when it is more than 50 mol%, curling occurs, and when it is less than 20 mol%, flexibility is lost.

The diamine used in the present invention is paraphenylenediamine.
50-80 mol% and 4,4'-diaminodiphenyl ether 50
~ 20 mol% but other amines such as 4,4'-
Diaminodiphenylmethane, 3,3'-dimethylbenzidine, 4,4'-diamino-p-terphenyl, 4,4-diamino-p-quaterphenyl, 2,8-diaminodiphenylene oxide and the like can also be used in combination.

Paraphenylenediamine is preferably 50 to 80 mol%, 50
If it is less than mol%, curling occurs, and if it is more than 80 mol%, it becomes stale. 4,4'-diaminodiphenyl ether is 50
-20 mol% is preferable, and if it is more than 50 mol%, curling occurs, and if it is less than 20 mol%, it becomes hard and loses flexibility. The reaction between the tetracarboxylic dianhydride component and the diamine component is the acid component / amine component (molar ratio) 0.90 to 1.
It is preferable to use 00, and if it is lower than 0.90, the degree of polymerization does not increase and the film properties after curing are poor. If it is more than 1.00, gas is generated during curing, and a smooth film cannot be obtained.

It is preferable that the polyamic acid produced by the reaction has a ladder rate of 56% or more and 62% or less per unit of polyimide molecule when it is cured by heating to become a polyimide resin.
Ladder ratio is the number of voids in the main chain bond of one unit of the polyimide molecule divided by the number of aromatic rings and heterocycles contained in it, for example pyromellitic dianhydride and 4,
Polyimide resin consisting of 4'-diaminodiphenyl ether, The number of bonds is 9 and the number of rings is 5, so the ladder rate is 5/9 x 100 = 55.6
%. A polyimide resin with a ladder rate of less than 56% has flexibility and flexibility but has low heat resistance and does not have the characteristics of a polyimide resin. A polyimide resin with a ladder rate of more than 62% has excellent heat resistance. Is too rigid and brittle, so it is not practically applicable.

The reaction is usually carried out in an organic polar solvent having a high dipole moment which does not react with tetracarboxylic dianhydride and diamines. Inert to the reaction system,
And besides being a solvent for the product, the organic polar solvent must be a solvent for at least one of the reaction components, preferably both. Typical examples of this type of solvent include N, N-dimethylformamide, N, N-dimethylacetamide, dimethyl sulfone, dimethyl sulfoxide, and N-methyl-2-pyrrolidone, and these solvents may be used alone or in combination. used. In addition to these, non-solvents such as benzene, dioxane, xylene, toluene, and cyclohexane that can be used in combination as a solvent can be used as a dispersion medium of a raw material, a reaction modifier, or a dispersion of a solvent from a product, a film smoothing agent. Used as such.

It is generally preferred to carry out the reaction under anhydrous conditions. This is because the tetracarboxylic acid dianhydride may be ring-opened by water and may be inactivated to stop the reaction. Therefore, it is necessary to remove the water content in the raw material and the water content in the solvent. On the other hand, however, water may be added to control the progress of the reaction and control the degree of resin polymerization. Further, the reaction is preferably carried out in an inert gas atmosphere. This is to prevent the oxidation of diamines. Dry nitrogen gas is generally used as the inert gas.

The synthesis reaction of the polyimide resin is generally performed by the following method.

(1) Diamines and tetracarboxylic dianhydride are mixed in advance, and the mixture is added little by little to an organic solvent while stirring. This method is relatively advantageous for exothermic reactions such as polyimide resins.

(2) On the contrary, there is also a method of adding a solvent to a mixture of diamines and tetracarboxylic dianhydride while stirring.

(3) A commonly-used method is to dissolve only diamines in a solvent and add tetracarboxylic dianhydride to this in a proportion that can control the reaction rate.

(4) Alternatively, the diamines and the tetracarboxylic dianhydride may be separately dissolved in a solvent, and the two solutions may be slowly added in the reactor.

(5) Furthermore, a polyamic acid product in excess of diamines and a polyamic acid product in excess of tetracarboxylic dianhydride may be prepared in advance and further reacted in a reactor.

(6) Also, among the diamines, there is a method in which a part of the diamine compound and the tetracarboxylic dianhydride acid are first reacted and then the remaining diamine compound is reacted, or the opposite method.

(7) In addition to this, there is also a method of mixing a part of a diamine compound of a diamine and a reaction product of a tetracarboxylic dianhydride before use.

The reaction method of the polyimide resin according to the present invention is a novel method that does not correspond to any of the above, and has excellent heat resistance, film characteristics, flatness, etc., as a polyimide resin used for a flexible printed circuit board, It is the best one. That is, the method of the present invention, previously reacted with 3,3 ', 4,4'-biphenyltetracarboxylic dianhydride and paraphenylenediamine, and pyromellitic dianhydride with 4,
This is a method in which a reaction product with 4'-diaminodiphenyl ether is prepared, and then both are mixed and reacted at 0 ° C to 100 ° C for 0.5 hour or more. If the both are simply mixed, the appearance will be poor due to the appearance of a scratchy surface on the polyimide resin film surface of the final product. According to the method of the present invention, when both are reacted at 0 ° C. to 100 ° C. for 0.5 hours or more, surprisingly there is no such pattern as above,
Moreover, excellent products such as heat resistance and flatness of film characteristics can be obtained.

The reaction temperature is preferably 0 to 100 ° C. This is because if the temperature is 0 ° C. or lower, the reaction rate becomes slow, and if the temperature is 100 ° C. or higher, the generated polyamic acid gradually starts the ring-closing reaction. Usually, the reaction is carried out at around 20 ° C.

The reaction time is preferably 0.5 hours or more. If it is 0.5 hours or less, the reaction between the two is insufficient and the stain pattern cannot be eliminated. If the reaction is carried out for 30 hours or more, the ring-closing reaction of the polyamic acid proceeds to become imidized, the solubility is lowered, and it becomes difficult to maintain the varnish state, and the polyamic acid is hydrolyzed by the condensed water. Usually, the reaction is carried out for about 3 hours.

The degree of polymerization of polyamic acid can be systematically controlled. For example, when the viscosity becomes too high or the molecular weight becomes too high, aging at 80 to 90 ° C. may be performed for adjustment. Further, in order to control the degree of polymerization, it is also possible to block the end with phthalic anhydride or aniline, or to add water to deactivate one of the acid anhydride groups by ring-opening.

The polyamic acid product produced by the method of the present invention, various silane coupling agents in use,
Borane coupling agent, titanate coupling agent,
Aluminum-based coupling agents and other chelate-based adhesion / adhesion improvers, various solvents, and flow agents may be added. In addition to these, ordinary acid curing agents, amine curing agents, imidazoles, tertiary amines, etc. A small amount of a curing accelerator may be added, or a flexibility-imparting agent such as rubber or low molecular weight epoxy or a viscosity modifier, or polyamide imide, polyether imide, polyester imide, etc. may be blended, talc, mica, A small amount of a filler such as quartz powder, a coloring agent such as carbon black and phthalocyan blue, a flame retardant such as tetrabromophenylmethane, and a flame retardant auxiliary such as antimony trioxide may be added.

The metal foil used in the present invention is generally a copper foil, but an aluminum foil, a nickel foil, or the like can also be used. The metal foil having a thickness of 10 to 100 μm is used, and the surface of the metal foil is preferably subjected to a graining treatment.

The method of applying the polyamic acid solution to the metal foil may be a method of casting to a uniform thickness of 50 to 1000 μm by a known application means such as a rotary coater, a knife coater, a doctor blade, and a flow coater. Next, the solvent of the polyamic acid is removed by heating and the imide ring is formed.However, if strong heating is performed from the beginning before the polyimide film is formed, the surface becomes rough or tight, so heating is not possible. It is preferable to gradually increase from low temperature. For example, heating is continuously performed from 100 ° C. to 300 ° C. for 0.5 hours or more. If it is less than 0.5 hours, it may depend on the film thickness, but the solvent removal may be insufficient, or the ring closure of the imide may be insufficient, so that the characteristics may not be sufficiently exhibited. Also, for example, 10
30 minutes at 0 ℃, then 30 minutes at 150 ℃, 30 minutes at 200 ℃, 250 ℃
The temperature may be raised stepwise such as 30 minutes and 300 ° C. for 10 minutes. The heating atmosphere may be in the air in some cases, but it is often preferable to carry out under reduced pressure or under a non-oxidizing state while flowing an inert gas. Also, in order to relieve residual stress during curing or heating that remains in the polyimide film and flatten the substrate, wrap it around a cylinder with a diameter of 50 to 100 mm with the metal foil surface inside and the polyimide resin surface outside. , Continuously anneal from 300 ℃ to 350 ℃ for 0.5 hours or more, or at 300 ℃ for 30 minutes,
Then, annealing is performed stepwise at 350 ° C. for 30 minutes. After annealing, the method of returning to room temperature is preferably cooling. If the diameter of the cylinder is less than 50 mm, it will reverse warp and
If it is larger than 0 mm, there is no effect of warping. Further, if the annealing time is less than 0.5 hours, the effect of annealing is insufficient.

The polyimide film layer formed in this way is generally 10
~ 200μ.

〔The invention's effect〕

The flexible printed circuit board manufactured by the method according to the present invention is excellent in heat resistance because it does not have an adhesive layer, has good processability because it has no curl, and is excellent in that it has strong film properties. It was a flexible substrate.

The circuit board obtained by the present invention is used not only for various electric and electronic equipment wiring boards, but also for acoustic diaphragms, flat motors, tape carriers, liquid crystal lead wires, floppy disk heads, high frequency antennas, electromagnetic shield plates, etc. It

〔Example〕

 The present invention will be described below with reference to examples.

[Example 1] 59.4 g of purified anhydrous paraphenylenediamine (55 of amine component) in a four-neck separable flask equipped with a thermometer, a stirrer, a reflux condenser and a dry nitrogen gas inlet.
Mol%), and a mixed solvent of 90% by weight of anhydrous N-methyl-2-pydrine and 10% by weight of toluene was added thereto in an amount such that the solid content ratio in all the charged raw materials was 15% by weight. Dissolved. Dry nitrogen gas was allowed to flow throughout the entire process from the reaction preparation stage to the product removal. Next, 158.5 g of purified anhydrous 3,3 ', 4,4'-biphenyltetracarboxylic dianhydride (55 mol% of the acid component) is added little by little with stirring, but since it is an exothermic reaction, it is added to the external water tank. It was cooled by circulating cold water at about 15 ° C. After adding the internal temperature
It was set at 20 ° C and reacted for 5 hours [A]. Reaction of anhydrous 4,4'-diaminodiphenyl ether 90.0 g (45 mol% of amine component) and purified anhydrous pyromellitic dianhydride 96.1 g (45 mol% of acid component) purified by the same apparatus and method [B]. Next, [A] synthesized in this way,
[B] Two kinds of polyamic acid solutions were charged into an apparatus similar to the above, the internal temperature was set to 20 ° C., and the mixture was stirred for 3 hours to complete the reaction.

The acid / amine (molar ratio) in the reaction was 0.98, and the ladder rate was 58.9%. The obtained product was a yellowish brown transparent extremely viscous polyamic acid solution, and the intrinsic viscosity of a 0.5 wt% solution in N-methyl-2-pyrrolidone was 0.89 (a
t30 ° C). This polyamic acid solution was cast-coated on a copper foil and then placed in a dryer to continuously raise the temperature from 100 ° C to 300 ° C over 2 hours. Furthermore, a copper foil surface was wound inside and a resin surface was wound outside on a cylinder of 60 mmφ and annealed at 300 ° C. for 30 minutes and at 350 ° C. for 30 minutes.

The flexible printed circuit board manufactured in this way has no curl, and the heat resistance of the film after etching the copper foil is 505 ° C, the tensile strength is 22 kg / mm, and the elongation is 28%. there were.

Example 2 Using the same apparatus and method as in Example 1, 81.0 g of paraphenylenediamine (75 mol% of amine component) and 205.1 g of 3,3 ′, 4,4′-biphenyltetracarboxylic dianhydride ( 75 of the acid component
(Mol%) was reacted at 20 ° C. for 5 hours [A]. Similarly, 4,
4'-diaminodiphenyl ether 50.0g (of amine component
25 mol%) and 50.7 g of pyromellitic dianhydride (2 of acid component)
5 mol%) was reacted at 20 ° C. for 5 hours [B].

Next, both [A] and [B] were reacted at 15 ° C. for 5 hours. The acid / amine (molar ratio) in the reaction was 0.93, and the ladder rate was 59.7%. The intrinsic viscosity of the product was 0.95. This polyamic acid solution is cast and applied on a copper foil and then placed in a drier, 100 ° C. for 30 minutes, 150 ° C. for 30 minutes,
After heating at 200 ° C for 30 minutes, 250 ° C for 20 minutes, and 300 ° C for 10 minutes, wind it around a 90mmφ cylinder,
Annealing was performed by continuously raising the temperature to 50 ° C. over 1 hour.

The flexible printed circuit board thus manufactured had no curl at all, and the heat resistance of the film after etching and removing the copper foil was excellent at 565 ° C. tensile strength of 18 kg / mm and elongation of 20%.

Comparative Example 1 In Example 1, 86.4 g (30 mol%) of 3,3 ′, 4,4′-biphenyltetracarboxylic dianhydride and 149.5 g (70 mol of pyromellitic dianhydride) were used. %) And reacted. The acid / amine (molar ratio) is 0.98 and the ladder rate is 59.5%.

A flexible circuit substrate was prepared in the same manner as in Example 1, but the amount of 3,3 ′, 4,4′-biphenyltetracarboxylic dianhydride was low, probably because there was too much pyromellitic dianhydride. It has curled greatly because it passed.

Comparative Example 2 In Example 1, 259.3 g (90 mol%) of 3,3 ′, 4,4′-biphenyltetracarboxylic dianhydride and 21.4 g (10 mol of pyromellitic dianhydride were used. %) And reacted. The acid / amine (molar ratio) is 0.98, and the ladder rate is 58.2%.

A flexible circuit board was prepared in the same manner as in Example 1, but there was no curl, but the film elongation after etching away the copper foil was only 5%, which was unsuitable as a circuit board.

Comparative Example 3 In Example 2, 32.4 g (30%) of paraphenylenediamine was added.
Mol%), 4,4'-diaminodiphenyl ether 140.0
g (70 mol%) and reacted. Acid / amine (molar ratio)
Is 0.93 and the ladder rate is 55.9%.

A flexible circuit board was prepared in the same manner as in Example 2, but it curled greatly because there was too much 4,4'-diaminodiphenyl ether or because there was too little paraphenylenediamine.

[Comparative Example 4] In Example 2, 97.2 g (90%) of paraphenylenediamine was added.
Mol%), 20.0 g of 4,4'-diaminodiphenyl ether
(10 mol%) and reacted. Acid / amine (molar ratio)
0.93, ladder rate is 61.3%.

A flexible circuit board was prepared in the same manner as in Example 2, but there was no curl, but the elongation after etching and removing the copper foil was only 4%, which was unsuitable as a circuit board.

Comparative Example 5 Using the same apparatus and method as in Example 1, 59.4 g of paraphenylenediamine (55 mol% of amine component) and 142.3 g of 3,3 ′, 4,4′-biphenyltetracarboxylic dianhydride ( Acid component of 55
Mol%) was reacted. Similarly, 90.0 g of 4,4'-diaminodiphenyl ether (45 mol% of the amine component) and 86.3 g of pyromellitic dianhydride (45 mol% of the acid component) were reacted.

Next, both of them were reacted, and the acid / amine (molar ratio) in the reaction was 0.88, and the ladder rate was 57.5%.

A flexible circuit board was prepared in the same manner as in Example 1, but there was no curl, but the tensile strength of the film after etching and removing the copper foil was only 7.0 kg / mm, which is unsuitable as a circuit board. there were.

Comparative Example 6 By the same apparatus and method as in Example 2, 81.0 g of paraphenylenediamine (75 mol% of amine component) and 242.6 g of 3,3 ′, 4,4′-biphenyltetracarboxylic dianhydride ( 75 of the acid component
Mol%) was reacted. Similarly, 50.0 g of 4,4'-diaminodiphenyl ether (25 mol% of the amine component) and 60.0 g of pyromellitic dianhydride (25 mol% of the acid component) were reacted. Next, both of them were reacted with each other.
The amine (molar ratio) is 1.10 and the ladder rate is 61.8%.

A flexible circuit board was prepared in the same manner as in Example 2, but there was no curl, but there were many creases and pinholes on the film surface, making it unsuitable as a circuit board.

[Comparative Example 7] In Example 2, 81.0 g of paraphenylenediamine (75 mol% of the amine component) and 205.1 g of 3,3,4,4'-biphenyltetracarboxylic dianhydride (75 mol of the acid component) %) And 4,4 ′
-Diaminodiphenyl ether 50.0 g (25% of amine component)
Mol%) and 50.7 g of pyromellitic dianhydride (25% of acid component)
(Mol%) and the mixture was reacted at 20 ° C. for 10 hours. The acid / amine (molar ratio) is 0.93, and the ladder rate is 59.7%.

A flexible circuit substrate was prepared in the same manner as in Example 2, but it was curled, and it was found that the reaction method of this example is inappropriate.

[Comparative Example 8] In Example 2, 81.0 g of paraphenylenediamine (75 mol% of the amine component) and 205.1 g of 3,3 ', 4,4'-biphenyltetracarboxylic dianhydride (75 of the acid component) Mol%) and 20
The reaction was carried out at ℃ for 5 hours. Separately, 50.0 g of 4,4′-diaminodiphenyl ether (25 mol% of amine component) and 50.7 g of pyromellitic dianhydride (25 mol% of acid component) were reacted at 20 ° C. for 5 hours. After blending both of them to form a uniform varnish, a flexible circuit board was prepared in the same manner as in Example 2. Although there was no curl, the film surface after the copper foil was removed by etching had a faint pattern of cod, a tensile strength of only 11 kg / mm and a heat resistance of only 420 ° C.

[Comparative Example 9] In Example 1, after the polyamic acid solution was cast and applied, the temperature was raised from 100 ° C to 300 ° C in 20 minutes. Further, the film was wound on a cylinder and processed in the same manner, but blistering occurred on the film surface of the obtained substrate.

[Comparative Example 10] In Example 1, the polyamic acid solution was cast and coated, and then heated at 80 ° C for 2 hours and at 200 ° C for 2 hours. Further, the film was wound on a cylinder and processed in the same manner, but blister was generated on the film surface of the obtained substrate.

[Comparative Example 11] The same treatment as in Example 1 was performed after the cylinder size was changed to 30 mmφ. However, in the obtained substrate, the copper foil surface was curled inward and the film surface was curled outward.

[Comparative Example 12] The same treatment as in Example 1 was performed after the cylinder size was changed to 150 mmφ. However, the obtained substrate was curled with the copper foil surface outside and the film surface inside.

[Comparative Example 13] In Example 1, the substrate was wound around a cylinder and then annealed at 300 ° C for 1 hour, but the obtained substrate had a copper foil surface on the outside and a film surface on the inside.

[Comparative Example 14] In Example 1, the substrate was wound around a cylinder and then annealed by continuously raising the temperature from 300 ° C to 350 ° C in 15 minutes. The obtained substrate had a copper foil surface on the outside and a film surface on the outside. It was curled inside.

[Comparative Example 15] In Example 1, after wrapping the foil with the same foil, at 300 ° C for 30 minutes, 3
After annealing at 50 ℃ for 30 minutes, 400 ℃ for 30 minutes, and 450 ℃ for 30 minutes, the obtained substrate turned black.

Claims (1)

[Claims] 1. 50 to 80 mol% of 3,3 ', 4,4'-biphenyltetracarboxylic dianhydride and 50 to 50% of pyromellitic dianhydride.
A tetracarboxylic dianhydride component consisting of 20 mol% and a diamine component consisting of 50 to 80 mol% of para-phenylenediamine and 50 to 20 mol% of 4,4'-diaminodiphenyl ether were added to the acid component / amine component (molar ratio). ) To 0.90 to 1.00 and the laddering rate to 56 to 62%, and the reaction is carried out in advance with 3,
A product obtained by reacting 3 ', 4,4'-biphenyltetracarboxylic dianhydride with paraphenylenediamine [A] and a product obtained by reacting pyromellitic dianhydride with 4,4'-diaminodiphenyl ether After preparing [B], both [A] and [B] are mixed, and the mixture is heated at 0 ° C to 100 ° C for 0.5 hours to 30 hours.
After reacting for a time to synthesize polyamic acid, it is cast and coated on a metal foil and heated continuously from 100 ℃ to 300 ℃ or in steps over 0.5 hours, and then a cylinder with a diameter of 50 to 100 mm is formed. A method for manufacturing a flexible circuit substrate, comprising winding a metal foil surface inside and continuously or stepwise heating or holding and heating from 300 ° C. to 350 ° C. over 0.5 hours or more.