JPS5922388A - Method of correcting curl of flexible printed circuit board - Google Patents

Abstract

(57) [Summary] This bulletin contains application data before electronic filing, so abstract data is not recorded.

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a method for straightening a flexible printed circuit board. More specifically, the present invention provides a method for mechanically correcting curls occurring in a flexible printed circuit board manufactured by forming a #82 layer made of aromatic polyamideimide or polyimide on a metal foil. It is related to .

A flexible printed circuit board is a board consisting of a metal foil such as copper foil and a thin resin film layered on top of each other.In recent years, it has been used as a wiring board for manufacturing flexible printed circuits, and has been used to simplify electronic circuits. It is increasingly being used mainly for the purpose of increasing density and density. Among them, aromatic polyamide-imide and polyimide have particularly excellent properties as resin materials for forming the resin thin film layer, so flexible printing consisting of a thin film layer of aromatic polyamide-imide or polyimide and metal foil Circuit boards are the mainstream.

As a method for producing a flexible printed circuit board comprising the above aromatic polyamide-imide or polyimide thin film layer and metal foil.

l) Heating an aromatic polyamide-imide film or an aromatic polyimide film and a metal foil using an adhesive,
2) A method for directly producing a substrate made of aromatic polyamideimide or aromatic polyimide and metal foil without using a contact agent, the method comprising:
Specifically, a solution of y'J aromatic polyamide-imide or aromatic polyimide, or a solution of an aromatic polyimide precursor is cast onto a metal foil, and then dried and solidified without applying heat. It has been known.

The above method 1) is a production method that has been generally used, and the thickness between the aromatic polyamideimide or aromatic polyimide film and the metal foil is 10 to 3.
A 0 gm adhesive layer is provided. The resin commonly used to form this adhesive layer has heat resistance, '1
[It is significantly inferior to aromatic polyamide-imide and polyimide in terms of physical properties, chemical resistance, mechanical properties, etc., and therefore, the performance of flexible printed circuit boards made of such a structure is This tendency is determined by the characteristics of the resin constituting the adhesive layer. Therefore, there has been a problem that the advantages of using aromatic polyamide-imide or (±aromatic polyimide) film, which exhibits excellent properties as an insulating layer of a flexible printed circuit board, cannot be fully utilized.

On the other hand, method 2) is simple and does not require the provision of an adhesive layer. It also has the advantage that the adhesion to metal foil does not deteriorate much even at high temperatures. however,
The flexible printed circuit board manufactured by this method has the drawback that curling is likely to occur due to volumetric shrinkage of the resin thin film layer. In other words, when a solution of aromatic polyamide-imide or an aromatic polyimide is cast onto a metal foil to form a solution@H'A layer, and this is dried to form a resin thin film layer, the process of evaporation of the solvent Volumetric shrinkage of the coating layer occurs, which causes curling. In addition, in a method in which a solution of an aromatic polyimide precursor such as aromatic polyamic acid is cast onto gold 1iA foil and then heated, the solvent is evaporated and polyimide is produced by ring closure of polyamic acid. Both solvent volatilization shrinkage and volume shrinkage due to ring-closing reaction occur, often causing severe curling. In addition to this, it is known that the difference in elongation of the wire 111v between the resin forming the thin film layer and the metal foil also promotes curling. The occurrence of such curling is a serious drawback for flexible printed circuit boards.
Not only is it inconvenient to handle in screen printing processes, chemical etching processes, etc., but it can also damage the resist and cause disconnection and short circuits of conductors.

Therefore, various improvements have been proposed for the purpose of preventing the occurrence of such curls or reducing the curls that have occurred.

For example, in order to prevent the occurrence of curl when forming an aromatic polyimide, which is most suitable for a flexible printed circuit board, as a thin film layer on a metal foil-1, it is possible to Other methods have been proposed, such as a method of reducing the volumetric shrinkage caused by the ring-closing reaction, or a method of casting a solvent-soluble aromatic polyimide. However, these methods also reduce solvent volatilization.
However, curling occurs due to the difference in coefficient of linear expansion between the resin forming the thin film layer and the metal foil, which remains a problem. In addition, when forming aromatic polyamide-imide as a thin film layer, volumetric contraction due to ring-closing reaction does not occur;
Curling still occurs due to volatilization of the solvent and the difference in linear expansion coefficient between the resin forming the thin film layer and the metal foil.

On the other hand, there is also known a method of reducing curl by correcting the curl once it has occurred. Examples include a method of heating a curled substrate at high temperature for a long time to remove distortion (Japanese Patent Application Laid-open No. 54-66966); A method of straightening curls by wrapping the curl around a cylindrical object with a diameter of 70 to 1000 mm inside and leaving it at high temperature for a long time (Japanese Unexamined Patent Publication No. 108272/1982, No. 111673/1983, No. 55-72095) No. Publication), Curled No, (
A method of straightening the curl by rolling the plate into a cylindrical object as described in 2 and leaving it in an organic solvent at high temperature for a long time (Japanese Patent Application Laid-open No. 55-160489, No. 56'-2379)
Publication No. 1) can be mentioned. However, these methods require heat treatment at high temperatures and for a long time, making them unsuitable as methods for straightening curls that occur on long flexible printed circuit boards. This method is not preferable because the solvent may remain in the final product.

On the other hand, a method for straightening the curl of a long flexible printed circuit board is also known. For example, the curled metal foil surface of the board can be dried using a drying device with a curved surface such as a drum dryer. A method of reducing curl by bending under heating and stretching or rolling in the bent direction (MD) direction (Japanese Unexamined Patent Publication No. 11/54-31480)
can be mentioned. However, in this method, stretching or rolling is carried out under temperature conditions that soften the resin layer, such as at a high temperature close to the glass transition temperature, or at a temperature of at least 100°C or higher while a solvent remains. Both the resin thin film layer and the metal foil undergo plastic deformation. Therefore, this method is not only complicated, but also tends to cause pinholes in the resin thin film layer, the difference in the coefficient of linear expansion between the resin thin film layer and the metal foil, or the complete removal of residual solvent. Curls tend to reoccur after treatment.

The present invention provides flexible printing having a thin film layer of aromatic polyamide-imide or aromatic polyimide formed by a casting coating method on metal foil of various shapes such as elongated, rectangular, square, polygonal, circular, and oval. To provide a method for effectively correcting curls generated on a circuit board by a simple operation.

That is, the present invention can be applied by casting a solution containing an aromatic polyamideimide, an aromatic polyimide precursor, or an aromatic polyimide onto a metal foil, and drying and solidifying the solution coating layer. A flexible printed circuit board having a curl with the metal foil surface facing outward is manufactured by forming a thin film layer made of aromatic polyamide-imide or aromatic polyimide on a substrate with a radius of curvature of 0.5 to 25 mm.
Flexible printing characterized by sliding on the curved surface of a bar with the metal foil surface inside at a temperature of 80° C. or less while maintaining tension at a folding angle of 90 degrees or more. This method consists of a method for straightening curls on circuit boards.

According to the curl correction method of the present invention, the metal foil undergoes slight plastic deformation, but the resin thin film layer hardly undergoes plastic deformation, making it possible to effectively correct curl. Therefore, the deterioration in quality of the flexible printed circuit board that inevitably occurs in curl correction methods that involve treatment at high temperatures does not substantially occur in the correction method of the present invention.

In addition, since the curl straightening method of the present invention is carried out at a relatively low temperature, the straightened flexible printed circuit board is highly stable and is unlikely to curl again even if it is later heated to high temperatures. There are also advantages.

Next, the present invention will be explained in detail.

The flexible printed circuit board to be corrected in the curl correction method of the present invention is produced by casting a solution containing aromatic polyamideimide, an aromatic polyimide precursor, or an aromatic polyimide on metal foil of various shapes. The flexible printed circuit board is produced by drying and solidifying the solution coating layer to form a thin film layer made of aromatic polyamideimide or aromatic polyimide on the metal foil. As mentioned above, a flexible printed circuit board manufactured by such a method tends to curl with the metal foil surface facing outward.

In the present invention, typical compounds as aromatic polyamideimides are polymers having repeating units represented by the following general formulas CI) and (■).

0 00 1 1 (However, in the above formula, x is -CH2-, -0-, -9-
, -co-1-5Oz-, -9o-, etc.) Note that the aromatic polyamideimide in the present invention is a repeating atom represented by the above general formulas (I) and (II). It is not limited to polymers having units. That is, aromatic polyamide-imides other than those listed in "2" may be used as long as they contain both an amino acid group and an imide group in the molecule. Furthermore, the aromatic polyamide-imide does not need to be a single type, and may be a mixture of two or more types of aromatic polyamide-imides.

The solvent for preparing the aromatic polyamide-imide coating solution can be selected from various known solvents, and among them, amide solvents such as N,N-dimethylformamide and N-methyl-2-pyrrolidone are preferred.

In the present invention, the aromatic polyimide precursor includes a polymer obtained from pyromellitic dianhydride and an aromatic diamine having a repeating unit represented by the following general formula (III), a polymer obtained by the general formula ('IV ) with a repetitive potential expressed as 3,
3″, 4,4″-Bensiff.

A polymer obtained from mentetracarboxylic dianhydride and an aromatic diamine, and a 3,3",4.4°-biphenyltetracarboxylic dianhydride having a repeating unit represented by the general formula (V). These include polymers obtained from aromatic diamines, partially ring-closed polymers thereof, and the like.

(However, in the above formula, x is -cH2-, -0-, -S
-, -co-, -so□-1-8O- or other divalent atoms or Jg groups)' The aromatic diamine component used in the production of the above polymer has the general formula (VIH): , -1-, x is -CI(2-, -o-t
' -3-, -Go-1-9O2-, -3o-natonodi(lli(7) is an atomic group) symmetrical aromatic diamine without substituents. Considering the physical properties of the polyimide produced, it is preferable that the Examples of such aromatic diamines include 4,4'-diaminodiphenylmethane, 4,4'-diaminodiphenyl ether, 4,4'-diaminodiphenylthioether, 4,4'-diaminodiphenyl sulfone, and the like. .

However, it is also possible to use other symmetrical diamines that are not included in the above general formula (VIII), such as p-phenylenediamine.

In addition, 3,3'-dimethyl-4,4'-diaminodiphenylmethane, 3,3'-diaminodinoenyl ether, and 2,4-diaminotoluene, which are commonly used to make aromatic polyimide solvent-soluble, are also available. Aromatic diamines such as , lo-phenylene diamine can also be used.

Note that the aromatic polyimide precursor in the present invention is not limited to the polymers having repeated coordination represented by the above general formulas (IIF) to (V).

Further, the aromatic polyimide precursor does not need to be a single one, and may be a compound of two or more aromatic polyimide precursors.

The solvent for preparing the coating solution of the aromatic polyimide precursor can be selected from various known solvents, among which amide solvents such as N,N-dimethylformamide and N-methyl-2-pyrrolidone are preferred. .

In the present invention, aromatic polyimides include 3, 3°, 4° repeating units having the following formula (VI):
．． 4'-benzophenone tetracarpone decoction [polymer obtained from water and aromatic diamine, and general formula (
VII) 3, 3', 4.
Included are polymers obtained from 4'-biphenyltetracarboxylic dianhydride and aromatic diamine.

(However, the above formula -7"X is 10) +2-, -0-
, -9-, -co-1-5o2-, -'so-, etc.) The aromatic diamine component used in the production of the above compound is represented by the above general formula (VIII). Considering the physical properties of polyimide, it is preferable to use a symmetrical aromatic diamine having no substituent represented by the following formula.

Note that the aromatic polyimide in the present invention is not limited to a polymer having repeating units represented by the above general formulas (VI) and (VII).

For example, 2,3', 3.
Also included are compounds having 4'-biphenyltetracarboxylic dianhydride as an acid component. Moreover, the various tetracarboxylic acid components described above can also be used as a mixture in one molecule. Furthermore, the aromatic polyimide does not need to be a single type, and may be a mixture of two or more types of aromatic polyimides.

The solvent for preparing the aromatic polyimide coating solution can be selected from known solvents such as phenolic solvents, but it is particularly preferable to use halogenated phenolic solvents, particularly 4-chlorophenol.

The metal foil that is the constituent material of the flexible printed circuit board used in the present invention may be made of various metal materials that have been conventionally used as constituent materials of the flexible printed circuit board or that have been proposed for use. You can choose any shape of metal foil. Copper foil is generally used, and it is particularly preferable to use electrolytic copper foil whose surface has been roughened. However, metal foils made of other conductive metals such as aluminum foil and nickel foil can also be used. The metal foil typically used has a thickness of 10 to 100 lumens.

The step of forming a solution coating layer by casting the coating solution containing the aromatic polyamide-imide, aromatic polyimide precursor, or aromatic polyimide on the surface of the metal foil as described in 2. This can be done by a method such as:

A coating solution containing 5 to 30% by weight of the above-mentioned polymer is discharged onto the surface of the metal foil from a film forming slit I to obtain a uniform thickness (the thickness is generally adjusted to 11,000p to 1000p). Continuously forms a coating layer. As this coating means, it is also possible to use other coating means such as a roll coater, knife coater, doctor blade, and flow coater.

Next, the polymer coating layer prepared as described above is heated to volatilize the solvent. However, when an aromatic polyimide precursor such as aromatic polyamic acid is used as the polymer, in addition to removing the solvent, a ring-closing reaction is caused to convert it to polyimide on the metal foil.

The heating step for the 11-minute coat can be carried out under any conditions such as normal pressure, reduced pressure, or increased pressure. In addition, if strong heating is performed before the polymer skin 11A is formed on the surface of the coating layer in this heating step, the volatilization rate of the solvent will become excessively fast, which will cause the surface of the coating layer to become rough. Tend. Therefore, in the initial stage of removing the solvent by heating, it is preferable to perform heating at a relatively low Ijlll.

Then, the heating temperature is gradually increased until the heating temperature reaches 150 to 400°C to complete the removal of the solvent (including the ring-closing reaction when an aromatic polyimide precursor is used). The thickness of the aromatic polyamide-imide layer or aromatic polyimide layer formed in this way is generally 0 to 150 ILm.

The flexible printed circuit board manufactured as described above shows almost no apparent curl in the direction in which the casting process was performed (hereinafter referred to as the MD force direction); In the direction perpendicular to the direction in which the coating operation was performed (hereinafter referred to as the TD force direction), a strong curl occurs with the metal foil surface facing outward. Here, the curl is the curl measured in a state where the influence of its own weight is eliminated, for example by hanging the flexible printed circuit board in an upright state.

The strong curling of the flexible printed circuit board as described above can be effectively corrected by the correction method of the present invention, that is, the curling can be reduced or substantially eliminated.

In the curl correction operation of the flexible printed circuit board of the present invention, a bar having a curved surface with a curvature of 0.5 to 25 mm is placed on the curved surface of the bar with the metal foil surface of the curled board on the inside, and the folding angle is At a temperature of 80°C or less while maintaining tension at 90° or more, move this substrate in any direction, for example, in approximately the same direction as the direction in which the curl is occurring, or in a direction approximately perpendicular to the direction of the curl. It is carried out by sliding it on, etc.

The radius of curvature used in the present invention is 0.5 to 25 mn]
8 with a curved surface of glass, ceramics, gold 1K
It is a bar made of a highly rigid material such as synthetic resin or wood, and its horizontal (that is, in the direction perpendicular to the length of the bar) is a circle or an ellipse with a radius of curvature of 0.5 to 25 mm. Or, the cross section has any shape such as a rectangle, square, or polygon, but the cross section of the contact surface with the metal foil is formed from a curved surface with a radius of curvature of 0.5 to 25 mm. It is. The radius of the curved surface of the bar is preferably in the range of 1 to 10 mm, and particularly preferably in the range of 2 to 6 mm. Further, the front surface of the bar (the part that contacts the substrate) may be shaped so that the center of the bar in the width direction slightly protrudes. Also, the length of the circle is selected to be longer than IIVX in the direction perpendicular to the moving direction of the nol plate to be corrected.

In the correction method of the present invention, a flexible printed circuit board having a curl with the metal foil side facing outward is placed on the curved peak of the above-mentioned curved bar with the metal foil side facing inside, and is folded at an angle of 90 degrees or more. The process consists of sliding the material once in any direction at a temperature of 80° C. or less while maintaining tension, or a total of two or more times in the same direction or different directions.

In the above process, the folding angle refers to the angle formed by the extended surface outside the flexible printed circuit system that is supplied in contact with the bar and the board that contacts the bar and is folded back and taken out. means.

A preferable folding angle is 135 degrees or more, and for example, it is desirable to bring the elongated substrate into contact with the bar in a state where it is folded back into a hairpin shape.

The flexible printed circuit board and the curved surface of the bar are brought into contact while maintaining tension. Such tension is maintained by applying tension to the substrate. The appropriate tension range varies depending on the degree of curl of the board, the material and thickness of the metal foil and resin thin film layer, the radius of curvature of the bar, etc., but it is usually within the width 1c of the flexible printed circuit board.
It is selected from the range of 10 to 200 g per m, preferably 15 to 20 g.

In the present invention, there is no particular limit to the speed at which the flexible printed circuit board is slid onto the curved surface of the bar. When the bar is held fixed and the substrate is slid on its surface, the moving speed of the substrate is usually 1 cm/min, preferably 3-3 cm/min.
The speed shall be 300 cm/min. If the cross section of the bar is circular, it can also be made to rotate around its axis, and in that case, the relative speed between the moving speed of the substrate and the rotational speed (surface speed) of the bar can be adjusted. It is sufficient if the difference is within the range shown in 2.

The straightening method of the present invention is carried out at a temperature of 80° C. or lower. 80
Temporary curl correction is possible even at temperatures exceeding °C, but curling often occurs again due to temperature changes when the substrate is returned to room temperature, and at even higher temperatures, plastic deformation of the resin thin film layer occurs. This is not desirable as it may also occur. The preferred temperature range when carrying out the straightening method of the present invention is 0 to 5
0°C, more preferably 5 to 40°C, for example room temperature. It is preferable to straighten curls at a temperature close to room temperature because the re-occurrence of curls due to subsequent temperature changes is negligible.

As described above, according to the correction method of the present invention, flexible printing is made of a metal foil and an aromatic polyamide-imide or aromatic polyimide resin thin film layer provided on the surface thereof without an adhesive layer. Curling that has occurred on the circuit board is almost never re-occurred after the curling or straightening treatment. Therefore, the present invention can be said to be a method for straightening curls of flexible printed circuit boards which is particularly advantageous in practice.

Next, Examples and Comparative Examples of the present invention will be described.

[Example 1] 73.56 g (0.25 mol) of 3.3',4,4'-biphenyltetracarboxylic dianhydride and 5.0,06 g (0.25 mol) of 4.4'-diaminodiphenyl ether was added to 1146 g of 4-chlorophenol, heated to 160°C in 1 hour without stirring, and then held at 160°C for 1 hour for polymerization and imidization to form aromatic compounds. A polyimide solution was prepared. The logarithmic viscosity of the obtained aromatic polyneuimide was 2.28.

This aromatic polyimide solution was heated at approximately 100°C using a 35pm thick electrolytic copper foil (MD side 1rij: 24cm).
XTD direction: 14cm) Top
'fr & I top (needle heated at 140°C for 1 hour to remove the large N content of the solvent, then heated to 300°C to form a flexible film with a thin 11 layer of aromatic polyimide of 25 m). A printed circuit board was obtained.The obtained board number is TD force direction and has a curvature of half iX4 with the resin thin film layer on the inside.
．． A 6cm curl had occurred.

iiA sound R4ko5 of the above flexible printed circuit board
A curved surface made of glass with a curved surface with a radius of curvature of 4.0 mm was placed in a fixed state under a load of 0.06.5 g, with the copper foil surface facing inside, at room temperature, at a folding angle of 180 degrees, and at a sliding speed. The curl was straightened by sliding it in the longitudinal direction (MD force direction) at a speed of 45 cm/min.
The radius of curvature of the curl in the D force direction was 10.0 cm, and a clear reduction in curl was observed. By the way, I couldn't see the MD direction.

[Comparative Example 1] For a flexible printed circuit board obtained by the same method as in Example 1 (the radius of curvature of the curl in the TD direction was 5.0 cm), the load applied to the edge of the board was 22
07g and a curved surface with a radius of curvature of 30mm. 1. ) The straightening operation was carried out in the same manner as in Example 1 except that. After this straightening operation, the radius of curvature of the curl in the TD force direction was 5°1 cm, and there was no substantial change in the degree of curl.

[Example 2] A flexible printed circuit board obtained by the same method as Example 1 (however, the radius of curvature of the TD force direction curl was 4
', 7 cm), radius of curvature 6, . 2 mm
The straightening operation was carried out in the same manner as in Example 1, except that glass with a curved surface of /<- was used. T after this straightening operation
The radius of curvature of the curl in the D force direction was 6.2 cm, and a clear reduction in curl was observed.

Note that no curl was observed in the MD force direction.

[Example 3] Same method as Example 1! Curved flexible printed circuit board (curvature of TD force direction curl is half 1)
(a is 4.5 cm), the straightening operation was carried out in the same manner as in Example 1 except that a glass par with a curved surface with a radius of curvature of 3.5 mm was used. As a result of this correction operation, the TD force direction curl substantially disappeared. However, in the MD force direction, weak curling occurred with the copper foil side facing inside.

[Example 4] Example 1 and l? ? ] Example 1 except that the load applied to the edge of the substrate was changed to 1006.5 g for the flexible printed circuit board obtained by the method (however, the radius of curvature of the TD force direction curl was 4.4 cm). Corrective operations were performed in the same manner. After this straightening operation, the radius of curvature of the curl in the T'D direction was 10.13 cm, indicating that the curl was clearly reduced. Note that no curl was observed in the MD force direction.

[Example 5] A flexible printed circuit board having a resin thin film layer with a thickness of about 40 pm was obtained by the same method as in Example 1. The obtained substrate had a curl with a radius of curvature of 3.8 cm with the resin thin film layer in the TD force direction on the inside.

Example 1 of the flexible printed circuit board described in ``2''
Correcting operations were performed in the same manner. After this straightening operation, the radius of curvature of the curl in the TD force direction was 6.5 cm, and a clear reduction in curl was observed. Note that no curl was observed in the MD force direction.

[Example 6] Pyromellitic dianhydride 15.27 g, (0.07 mol) and 4,4'-diaminodiphenylethyl 14.
02g (0.07 mol) and N-methyl-2-pyro91
An aromatic polyamic acid solution having a concentration of 20% and a logarithmic viscosity of 0.96 was prepared by reaction.

This aromatic polyamic acid solution was heated to about 100°C using an electrolytic copper foil (MD force direction 100m
Direction: 14cm) and apply by casting in a hot air dryer for 12cm.
The solvent was removed by heating at 0 °C for 2 h, then at 30 °C.
0'C! Heat 30 volumes to imidize it to a thickness of 257
A flexible printed circuit board having a pm aromatic polyimide film layer was obtained. A curl with a curve L+4 radius of 1.8 cm was generated on the rubbed substrate with the resin thin film layer in the TD force direction on the inside.

-1; For flexible printed circuits (tentatively,
The straightening operation was carried out in the same manner as in Example 1, except that a glass par with a curved surface with a radius of curvature of 2.5 mm was used and it was slid in the TD force direction. The curl in the TD force direction after this straightening operation becomes a curl with a radius of curvature of 8.5 cm with the copper foil side on the inside, while the curl in the MD force direction has a radius of curvature of 7.5 cm with the resin thin film layer on the inside. , a 6 cm curl was generated.

With the above-mentioned straightened substrate, the radius of curvature is 6, 25.
Example 1 except that a glass par with a curved surface of mm was used.
A similar correction operation (operation of sliding in the MD force direction) was performed. This correction operation substantially eliminated the TD force direction curl and MD force direction curl.

[Example 7] Using a commercially available aromatic polyamide imide varnish (solid content 230% by weight) synthesized from trimellitic anhydride and 4,4°-diaminodiphenylmethane, a thickness of 25 l was prepared by the method described in Example 6. A flexible printed circuit board having an aromatic polyamideimide thin film layer of m was obtained. The obtained substrate had a curl with a radius of curvature of 2.6 CI with the resin thin film layer in the TD force direction on the inside.

A straightening operation was performed on the flexible printed circuit board described in Example 1 in the same manner as in Example 1, except that a glass par with a curved surface with a radius of curvature of 3 and 0 mm was used. After this straightening operation, the radius of curvature of the curl in the TD force direction was 6.8 cm, and a clear reduction in curl was observed. Note that no curl was observed in the MD force direction.

Patent applicant Ube Industries Co., Ltd. Agent: Patent attorney: Yasuo Yanagawa

Claims (1)

[Claims] Aromatic polyamide-imide, an aromatic polyimide precursor, or a solution containing aromatic polyimide is cast onto a metal foil, and the solution coating layer is dried and solidified to form an aromatic polyamide-imide onto the metal foil. Or, the curved surface of a bar having a curved surface with a radius of curvature of 0.5 to 25 mm can be used to produce a flexible printed circuit board for curing curls with the metal foil surface on the outside, which is manufactured by forming a thin film layer made of aromatic polyimide. Second, with the metal foil side inward, fold at an angle of 9.
Curling m, iEυ, of a flexible printed circuit board, characterized in that it is slid at a temperature of 80° C. or less while maintaining a tension state at a temperature of 0° C. or less.