JPH0115154B2 - - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a method for straightening a flexible printed circuit board. For more details,
The present invention relates to a method for mechanically correcting curls occurring in a flexible printed circuit board manufactured by forming a thin film layer of aromatic polyamide-imide or polyimide on a metal foil.

A flexible printed circuit board is a board consisting of a metal foil such as copper foil and a resin thin film layered on top of each other.It is used as a wiring board for manufacturing flexible printed circuits, and has been used in recent years to simplify and simplify electronic circuits. It is increasingly being used mainly for the purpose of increasing 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.

The method for manufacturing a flexible printed circuit board made of the thin film layer of aromatic polyamide-imide or polyimide and metal foil is as follows: 1. An aromatic polyamide-imide film or aromatic polyimide film and metal foil are bonded together using an adhesive. 2. A method for directly producing a substrate made of aromatic polyamideimide or aromatic polyimide and metal foil without using an adhesive, specifically, aromatic A method is known in which a solution of a group polyamide-imide or an aromatic polyimide, or a solution of an aromatic polyimide precursor is cast onto a metal foil, and then dried and solidified by heating or the like.

Method 1) above is a production method that has been commonly used in the past, and an adhesive layer with a thickness of 10 to 30 μm is formed between the aromatic polyamideimide or aromatic polyimide film and the metal foil. provided. The resins commonly used to form this adhesive layer are significantly inferior to aromatic polyamide-imide and polyimide in various properties such as heat resistance, electrical properties, chemical resistance, and mechanical properties. Therefore, the performance of a flexible printed circuit board having such a structure tends to be determined by the characteristics of the resin constituting the adhesive layer. Therefore, there has been a problem in that the advantages of using aromatic polyamide-imide or aromatic polyimide film, which have 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 an adhesive layer, so the properties of the resulting flexible printed circuit board are superior to those of the aromatic polyamide-imide or aromatic polyimide used. 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. That is, a solution coating layer is formed by casting a solution of aromatic polyamide-imide or aromatic polyimide onto metal foil,
When this is dried to form a thin resin film layer, volumetric shrinkage of the coating layer occurs due to volatilization of the solvent, 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 a metal foil and then heated, the solvent is evaporated and polyimide is produced by ring closure of the polyamic acid. Both volatilization shrinkage and volumetric shrinkage due to the ring-closing reaction occur, often causing severe curling. In addition to this, it is known that the difference in linear expansion coefficient between the resin forming the thin film layer and the metal foil also promotes curling.
The occurrence of such curls is a serious drawback for flexible printed circuit boards, and not only is it inconvenient to handle during screen printing processes, chemical etching processes, etc., but it can also damage the resist.
It can also cause conductor breaks and short circuits.

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, when forming aromatic polyimide, which is most suitable for flexible printed circuit boards, as a thin film layer on metal foil, curling can be prevented by using an aromatic polyimide precursor that has been partially dehydrated and ring-closed in advance. There have also been proposals for reducing the volumetric shrinkage, or for eliminating the volumetric shrinkage caused by the ring-closing reaction by using a method of casting a solvent-soluble aromatic polyimide. However, even with these methods, problems still remain, such as curling caused by volatilization of the solvent and the difference in linear expansion coefficient between the resin forming the thin film layer and the metal foil. Furthermore, when aromatic polyamide-imide is formed as a thin film layer, volume shrinkage does not occur due to the ring-closing reaction, but this is still caused by solvent volatilization and the difference in linear expansion coefficient between the resin forming the thin film layer and the metal foil. Curls occur.

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 period of time to remove distortion (Japanese Patent Application Laid-Open No. 54-66966); Inside diameter 70~1000mm
A method of straightening curls by wrapping the substrate around a cylindrical object having A method of straightening curls by wrapping the material around a cylindrical object as described above and leaving it in an organic solvent at high temperature for a long period of time (Japanese Patent Laid-Open Nos. 55-160489 and 56-23791) can be cited. can. 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, such as drying the curled metal foil surface of the board 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 direction of the bend (MD) can be mentioned (Japanese Patent Application Laid-Open No. 31480/1983).
However, in this method, the resin thin film layer and Both metal foils undergo plastic deformation. Therefore, this method not only requires a complicated process, but also tends to cause pinholes in the resin thin film layer, the difference in linear expansion coefficient between the resin thin film layer and the metal foil, or the complete removal of residual solvent, resulting in curling. Curls tend to reoccur after straightening treatment.

The present invention has long, rectangular, square, polygonal,
Effectively removes curls that occur on flexible printed circuit boards that have a thin film layer of aromatic polyamide-imide or aromatic polyimide formed by casting coating on metal foils of various shapes such as circular and oval shapes. It provides a method of correction.

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, which is manufactured by forming a thin film layer made of aromatic polyamide-imide or aromatic polyimide, on a fixed bar having a curved surface with a radius of curvature of 0.5 to 25 mm. On the curved surface of At,
The relative sliding speed between the bar and the substrate is 3 to 300
This method consists of a curl straightening method for a flexible printed circuit board, which is characterized by sliding the board at a speed of cm/min.

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 polyamideimide are polymers having repeating units represented by the following general formulas () and ().

(However, in the above formula, X is -CH ₂ -, -O-, -
divalent atoms or atomic groups such as S-, _-CO- , -SO2-, -SO-) The aromatic polyamideimide in the present invention is represented by the above general formulas () and (). It is not limited to polymers having repeating units. That is, aromatic polyamide-imides other than those mentioned above may be used as long as they contain both an amide 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 (), and a polymer obtained from an aromatic diamine having a repeating unit represented by the following general formula (). A polymer obtained from 3,3',4,4'-benzophenonetetracarboxylic dianhydride and an aromatic diamine having a repeating unit represented by the general formula (), and 3, having a repeating unit represented by the general formula (). Included are polymers obtained from 3',4,4'-biphenyltetracarboxylic dianhydride and aromatic diamine, and partially ring-closed polymers thereof.

(However, in the above formula, X is -CH ₂ -, -O-, -
divalent atoms or atomic groups such as S-, _-CO- , -SO2-, -SO-) The aromatic diamine component used in the production of the above polymer has the general formula (): (However, in the above formula, X is -CH ₂ -, -O-, -
The polyimide produced is a symmetric aromatic diamine that does not have a substituent represented by a divalent atom or atomic group such as S-, -CO-, -SO ₂ -, -SO-, etc. This is preferable in consideration of physical properties. Examples of such aromatic diamines include 4,4′-
Examples include diaminodiphenylmethane, 4,4'-diaminodiphenyl ether, 4,4'-diaminodiphenyl thioether, and 4,4'-diaminodiphenyl sulfone.

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

In addition, 3,3'-dimethyl-4, which is commonly used to make aromatic polyimide solvent-soluble,
Aromatic diamines such as 4'-diaminodiphenylmethane, 3,3'-diaminodiphenyl ether, 2,4-diaminotoluene, and m-phenylenediamine can also be used.

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

Furthermore, the aromatic polyimide precursor does not need to be a single one, and may be a mixture 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, the aromatic polyimide includes:
A polymer obtained from 3,3′,4,4′-benzophenonetetracarboxylic dianhydride and an aromatic diamine having a repeating unit represented by the following general formula (), and a polymer obtained by having a repeating unit represented by the following general formula (). Included are polymers obtained from 3,3',4,4'-biphenyltetracarboxylic dianhydride and aromatic diamine having the following repeating units.

(However, in the above formula, X is -CH ₂ -, -O-, -
divalent atoms or atomic groups such as S-, -CO-, _-SO2- , -SO-).

Considering the physical properties of the polyimide, the aromatic diamine component used in the production of the above compound is preferably a symmetrical aromatic diamine having no substituents represented by the above general 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 () and ().
For example, as a tetracarboxylic acid component, 2,3',
Also included are compounds containing 3,4'-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, among which it is 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 μm.

The step of forming a solution coating layer by casting a coating solution containing the aromatic polyamide-imide, aromatic polyimide precursor, or aromatic polyimide on the surface of the metal foil as described above is, for example, as follows. This can be done by any method.

A coating solution containing 5 to 30% by weight of the above polymer is discharged onto the surface of the metal foil from a film forming slit to coat the surface with a uniform thickness (the thickness is generally adjusted to 100 to 1000 μm). Continuous formation of membrane layers. 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 of the coating layer can be carried out under any conditions such as normal pressure, reduced pressure, or increased pressure. In addition,
If strong heating is performed before a polymer film is formed on the surface of the coating layer in this heating step, the rate of solvent volatilization will be excessively high, and the surface of the coating layer will therefore tend to become rough. Therefore, in the initial stage of removing the solvent by heating, it is desirable to perform heating at a relatively low temperature. 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 10 to 150 μm.

The flexible printed circuit board manufactured as described above has almost no apparent curl in the direction along the direction in which the casting process was performed (hereinafter referred to as MD direction), but A strong curl occurs in the direction perpendicular to the direction in which the work was performed (hereinafter referred to as the TD direction) 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 fixed bar having a curved surface with a radius of curvature of 0.5 to 25 mm is placed on the curved surface of the fixed bar with the metal foil surface of the board having the curl inside, and the bent angle is 135 mm. The tension of the board is 10 to 10 cm per 1 cm of board width.
80 while maintaining a tension state of 200g.
This is carried out by sliding the bar and the substrate at a relative sliding speed of 3 to 300 cm/min at a temperature of 0.degree. C. or lower.

The bar having a curved surface with a radius of curvature of 0.5 to 25 mm used in the present invention is a bar made of a highly rigid material such as glass, ceramics, metal, synthetic resin, or wood. The cross section (in the vertical direction) is a circle or 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 the radius of curvature 0.5~
It appears to be formed from a 25mm curved surface. The radius of curvature of the curved surface of the above bar is 1 to 10
Preferably in the range of mm, more preferably 2 to 6 mm
It is particularly preferable to be in the range of . Further, the front surface of the bar (the part that contacts the substrate) may be shaped so that the vicinity of the center in the width direction thereof slightly protrudes. Further, the length of the bar is selected to be longer than the width in the direction perpendicular to the moving direction of the substrate to be corrected.

In the straightening method of the present invention, a curled flexible printed circuit board with the metal foil side facing outward is placed on the curved surface of the bar having the above-mentioned curved surface, with the metal foil side facing inside, and folded at an angle of 135 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 or different directions.

In the above process, the folding angle means the angle formed by the extended surface of the flexible printed circuit board that is supplied so as to contact the bar and the board that contacts the bar and is folded and taken out. .
The folding angle is 135 degrees or more, and it is desirable that the elongated substrate be brought into contact with the bar in a "hairpin-like" folded state, for example.

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 depends on the degree of curl of the substrate, the material and thickness of the metal foil and resin thin film layer,
It varies depending on the radius of curvature of the bar, etc., but it is 10 to 200 per cm of width of the flexible printed circuit board.
g, preferably from the range of 15 to 200 g.

In the present invention, the speed at which the flexible printed circuit board is slid on the curved surface of the bar is 3 to 300 cm/min when the bar is held fixed and the board is slid on its surface. shall be.

By sliding the substrate onto the curved surface of the bar under the above conditions, the substrate can be handled on the curved surface of the bar.

The straightening method of the present invention is carried out at temperatures below 80°C. Temporary curl correction is possible even at temperatures exceeding 80°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 50°C,
More preferably, the temperature is 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,
The curl that occurs on a flexible printed circuit board consisting of a metal foil and an aromatic polyamide-imide or aromatic polyimide resin thin film layer provided on the surface without an adhesive layer is reduced or substantially eliminated. This is possible with a simple operation, and curling hardly occurs again after 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 50.06 g (0.25 mol) of 4,4'-diaminodiphenyl ether were
- Add to 1146 g of chlorphenol and raise the temperature to 160°C in 1 hour while stirring, then add this solution to 160°C.
The mixture was held at a temperature of 1 hour to perform polymerization and imidization to prepare an aromatic polyimide solution. The obtained aromatic polyimide had a logarithmic viscosity of 2.28.

This aromatic polyimide solution was heated to approximately 100°C using a 35 μm thick electrolytic copper foil (MD direction: 24 cm x TD direction:
14cm) and coated at approximately 140℃ under reduced pressure.
Remove most of the solvent by heating for 300
C. to obtain a flexible printed circuit board having a 25 μm thick aromatic polyimide thin film layer. The obtained substrate had a curl with a radius of curvature of 4.6 cm with the resin thin film layer on the inside in the TD direction.

At the end of the above flexible printed circuit board
A load of 506.5 g was applied, and the curved surface of a glass bar with a radius of curvature of 4.0 mm was placed in a fixed state, with the copper foil surface on the inside, at room temperature, at a folding angle of 180 degrees.
Longitudinal direction (MD direction) at a sliding speed of 45 cm/min.
The curls were straightened. The radius of curvature of the curl in the TD direction after this straightening operation is 10.0cm
A clear reduction in curling was observed. Note that no curl was observed in the MD direction.

[Comparative Example 1] Regarding a flexible printed circuit board obtained by the same method as Example 1 (however, 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 increased to 2207 g. , and Example 1 except that a glass bar having a curved surface with a radius of curvature of 30 mm was used.
Corrective operations were performed in the same manner. After this corrective operation
The radius of curvature of the curl in the TD direction was 5.1 cm, and the degree of curl remained virtually unchanged.

[Comparative Example 2] For a flexible printed circuit board obtained by the same method as in Example 1, the straightening operation was performed in the same manner as in Example 1, except that the load applied to the edge of the board was reduced to 100 g. did. TD after this corrective operation
The radius of curvature of the directional curl was 4.4 cm, and the degree of curl remained virtually unchanged.

[Comparative Example 3] For a flexible printed circuit board obtained by the same method as in Example 1, the straightening operation was performed in the same manner as in Example 1, except that the load applied to the edge of the board was increased to 5500 g. did. TD after this corrective operation
The radius of curvature of the curl in the direction is −4.1 cm, i.e.
A similar curl in the opposite direction occurred.

[Comparative Example 4] Regarding the flexible printed circuit board obtained by the same method as in Example 1, the sliding speed of the board was
The straightening operation was carried out in the same manner as in Example 1 except that the speed was increased to 350 cm/min. The radius of curvature of the curl in the TD direction after this straightening operation was 3.1 cm, and the curl was only slightly reduced.

[Example 2] A glass bar with a curved surface with a curvature radius of 6.2 mm was used for a flexible printed circuit board obtained by the same method as in Example 1 (however, the radius of curvature of the curl in the TD direction was 4.7 cm). Example 1 except that
Corrective operations were performed in the same manner. After this corrective operation
The radius of curvature of the curl in the TD direction was 6.2 cm, and a clear reduction in curl was seen. Note that no curl was observed in the MD direction.

[Example 3] A glass bar with a curved surface with a curvature radius of 3.5 mm was used for a flexible printed circuit board obtained by the same method as in Example 1 (however, the radius of curvature of the curl in the TD direction was 4.5 cm). Example 1 except that
Corrective operations were performed in the same manner. As a result of this correction operation, the curl in the TD direction virtually disappeared. However, weak curling occurred in the MD direction with the copper foil side facing inside.

[Example 4] Regarding a flexible printed circuit board obtained by the same method as in Example 1 (however, the radius of curvature of the curl in the TD direction was 4.4 cm), the load applied to the edge of the board was changed to 1006.5 g. The straightening operation was carried out in the same manner as in Example 1 except for the above. TD after this corrective operation
The radius of curvature of the curl in the direction was 10.6 cm, and a clear reduction in curl was observed. Note that no curl was observed in the MD direction.

[Example 5] A flexible printed circuit board having a resin thin film layer with a thickness of about 40 μm 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 on the inside in the TD direction.

The above flexible printed circuit board was subjected to a straightening operation in the same manner as in Example 1. After this straightening operation, the radius of curvature of the curl in the TD direction was 6.5 cm, indicating that the curl was clearly reduced. In addition,
No curl was observed in the MD direction.

[Example 6] Pyromellitic dianhydride 15.27g (0.07mol)
and 14.02 g of 4,4'-diaminodiphenyl ether
(0.07 mol) and N-methyl-2-pyrrolidone 117
g and reacted for 24 hours to prepare an aromatic polyamic acid solution having a concentration of 20% by weight and a logarithmic viscosity of 0.96.

This aromatic polyamic acid solution was heated to about 100°C.
Cast coating onto 35 μm thick electrolytic copper foil (MD direction: 14 cm x TD direction: 14 cm) and dry in a hot air dryer for 120 µm.
Remove the solvent by heating for 2 hours at 300°C.
The mixture was heated for 30 minutes to imide, thereby obtaining a flexible printed circuit board having a 25 μm thick aromatic polyimide thin film layer. The obtained substrate had a curl with a half-curvature of 1.8 cm in the TD direction with the resin thin film layer on the inside.

Regarding the above flexible printed circuit board,
Using a glass bar with a curved surface with a radius of curvature of 2.5 mm,
The straightening operation was carried out in the same manner as in Example 1, except that the slide was made in the TD direction. The curl in the TD direction after this straightening operation has a radius of curvature of 8.5cm with the copper foil side inside.
On the other hand, a curl with a radius of curvature of 7.6 cm was generated in the MD direction with the resin thin film layer on the inside.

The curvature radius of the above-mentioned straightened substrate is further increased.
The same correction operation as in Example 1 (sliding operation in the MD direction) was performed except that a glass bar with a curved surface of 6.25 mm was used. This correction operation substantially eliminated the curl in the TD direction and the curl in the MD direction.

[Example 7] Using a commercially available aromatic polyamideimide varnish (solid content: 30% by weight) synthesized from trimellitic anhydride and 4,4'-diaminodiphenylmethane, the thickness was reduced by the method described in Example 6. A flexible printed circuit board having a 25 μm aromatic polyamideimide thin film layer was obtained. The obtained substrate had a curl with a radius of curvature of 2.6 cm with the resin thin film layer on the inside in the TD direction.

Regarding the above flexible printed circuit board,
The straightening operation was carried out in the same manner as in Example 1, except that a glass bar having a curved surface with a radius of curvature of 3.0 mm was used.
The radius of curvature of the curl in the TD direction after this straightening operation is
It became 6.8cm, and a clear reduction in curls was seen.
Note that no curl was observed in the MD direction.

[Comparative Example 5] Instead of a fixed glass bar,
A freely rotating glass bar (radius: 4.0 mm) with a circular cross section is used, and the bar rotates as the flexible printed circuit board moves, so that the flexible printed circuit board and the circumferential surface of the bar are The straightening operation was carried out in the same manner as in Example 1, except that the relative sliding speed with respect to the sample was set to 0 cm/min.

The radius of curvature of the curl in the TD direction after this straightening operation was 5.0 cm, and the degree of curl remained essentially unchanged.

Claims (1)

[Claims] 1 Casting a solution containing aromatic polyamideimide, an aromatic polyimide precursor, or an aromatic polyimide onto metal foil, drying the solution coating layer,
A flexible printed circuit board having a curl with the metal foil surface facing outward, manufactured by forming a thin film layer of aromatic polyamideimide or aromatic polyimide on the metal foil by solidifying,
Place the board on the curved surface of a fixed bar having a curved surface with a radius of curvature of 0.5 to 25 mm, with the metal foil surface inside, at a folding angle of 135 degrees or more, and apply tension to the board by 1 width of the board.
It is characterized by sliding the bar and the substrate at a relative sliding speed of 3 to 300 cm/min at a temperature of 80°C or less while maintaining a tension state of 10 to 200 g per cm. A curl correction method for flexible printed circuit boards.