JPS6347359B2 - - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a method for straightening a long flexible printed circuit board. More specifically, the present invention aims to continuously eliminate curls occurring in a long flexible printed circuit board manufactured by forming a thin film layer made of aromatic polyamideimide or polyimide on a metal foil using a mechanical method. It concerns a method of correction.

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 above-mentioned thin film layer of aromatic polyamide-imide or polyimide and metal foil includes: (1) bonding the aromatic polyamide-imide film or aromatic polyimide film and the metal foil with adhesive (2) A method for directly producing a substrate made of aromatic polyamide-imide or aromatic polyimide and metal foil without using an adhesive, the method comprising: Specifically, a method is known in which a solution of aromatic polyamide-imide, 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. is 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 with such a structure tends to be determined by the characteristics of the resin that makes up the adhesive layer, and it has excellent properties as an insulating layer of a flexible printed circuit board. There has been a problem in that the advantages of using an aromatic polyamideimide or an aromatic polyimide film having the following properties are not fully utilized.

On the other hand, in method (2), the manufacturing method itself is simple and there is no need to provide 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. That is, when a solution coating layer is formed by casting a solution of aromatic polyamide-imide or an aromatic polyimide onto a metal foil, and this is dried to form a thin resin layer, the coating layer is formed by volatilization of the solvent. Volumetric shrinkage of the 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 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 ring closure 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 and chemical etching processes, but it can also damage the resist, cut conductors, and cause short circuits. It can also be the cause of

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.

Therefore, the present invention provides a method for easily drying curls that occur on a long flexible printed circuit board having a thin film layer of aromatic polyamide or aromatic polyimide formed on a long metal foil by a casting coating method. This provides an effective method for correcting the condition by

In particular, the present invention provides a method for correcting curls occurring or latent in the longitudinal direction (MD direction) and/or width direction (TD direction) of a long flexible printed circuit board by a continuous series of operations. It is something to do.

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 long metal foil, and drying and solidifying the solution coating layer. A long 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 the metal foil, and the width of the long board is The first bar has a curved surface with a radius of curvature of 0.5 to 25 mm and is installed at an angle of 20 to 70 degrees with respect to the direction. At a temperature below 80℃ while maintaining a tension state of 10 to 200g per 1cm,
The relative sliding speed between the first bar and the substrate is 3~
Slide it in the longitudinal direction of the board at a speed of 300cm/min.
Next, a second bar having a curved surface with a radius of curvature of 0.5 to 25 mm was placed at an angle of 70 to 110 degrees with respect to the first bar, and the metal foil surface was placed on the inside with the above tension. 80 while maintaining the tension of
Curling correction of a flexible printed circuit board, characterized by sliding the substrate in the longitudinal direction at a temperature of ℃ or less such that the relative sliding speed between the second bar and the substrate is 3 to 300 cm/min. It consists of a method.

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 in the longitudinal direction (MD direction) and/or the long flexible printed circuit board. Alternatively, curls that have occurred or are latent in the width direction (TD direction) can be effectively corrected. Therefore,
The deterioration in quality of flexible printed circuit boards that inevitably occurs in curl straightening methods that involve treatment at high temperatures does not substantially occur in the straightening 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 prepared by casting a solution containing aromatic polyamideimide, an aromatic polyimide precursor, or an aromatic polyimide on a long metal foil. This is a long flexible printed circuit board manufactured by drying and solidifying the solution to form a thin film layer made of aromatic polyamideimide or aromatic polyimide on the metal foil. As mentioned above, the elongated flexible printed circuit board manufactured by such a method is particularly prone to curling in the width direction. Furthermore, although curling does not normally occur in the longitudinal direction (MD direction) of the long flexible printed circuit board as described above,
If the long object is cut so that the MD direction is shorter than the TD direction, curls often appear in the MD direction as well. Therefore, it can be said that curl is latent in the longitudinal direction (MD direction) of the long flexible printed circuit board as described above, that is, it is often generated latently.

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-, -S
-, -CO-, _-SO2- , -SO-, etc.) Note that the aromatic polyamideimide in the present invention is a repeating compound represented by the above general formulas () and (). It is not limited to polymers having 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-, -S
-, -CO-, _-SO2- , -SO-, etc.) 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-, -S
-, -CO-, -SO ₂ -, -SO-, etc.) is a symmetric aromatic diamine without a substituent group, which is a divalent atom or atomic group such as -, -CO-, -SO 2 -, -SO-, etc. It is preferable to take this into account. Examples of such aromatic polyamines 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 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-, -S
-, -CO-, _-SO2- , -SO-, etc.) The aromatic diamine component used in the production of the above compound is represented by the general formula () above. Considering the physical properties of polyimide, it is preferable to use a symmetrical aromatic diamine having no substituents.

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 polymers 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. Further, 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 is a long sheet made of a metal material that has been conventionally used as a constituent material of the flexible printed circuit board or a metal material that has been proposed for use. You can choose any type 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 casting the aromatic polyamide-imide, aromatic polyimide precursor, or coating solution containing the aromatic polyimide on the surface of the long metal foil as described above is carried out, for example, by the following method. be able to.

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 heat removal of the solvent, 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 long flexible printed circuit board manufactured as described above is manufactured in the longitudinal direction (hereinafter referred to as MD).
In the width direction (hereinafter referred to as the TD direction), there appears to be almost no curl, but in the width direction (hereinafter referred to as the TD direction), strong curls occur with the metal foil surface facing outward.
Curling in the MD direction generally does not appear in long products as described above, but it is necessary to cut the long flexible printed circuit board into an almost square shape or Saga TD
If you cut it so that it is shorter than the length in the direction,
Similar curls often occur in the MD direction as well. Here, the curl refers to the curl measured in a state in which the influence of its own weight is eliminated, for example, by hanging the flexible printed circuit board in an upright state.

Both the strong curls in the TD direction and the latent curls in the MD direction of the long flexible printed circuit board as described above can be effectively corrected by a continuous series of operations by the correction method of the present invention. Curl reduction or substantial elimination of curl can be achieved.

The curl correction method for a flexible printed circuit board of the present invention includes: (1) straightening a curled long flexible printed circuit board so as to form an angle of 20 to 70 degrees with respect to the width direction of the long flexible printed circuit board; The radius of curvature installed in the
Place the substrate on the curved surface of the first bar with the metal foil side inside, and heat the substrate to a temperature of 80°C or less while maintaining the tension of 10 to 200 g per 1 cm of width of the substrate. (2) Slide the substrate in the longitudinal direction so that the relative sliding speed between the first bar and the substrate is 3 to 300 cm/min, and then (2) slide the substrate at an angle of 70 to 110 degrees with respect to the first bar. A second bar having a curved surface with a radius of curvature of 0.5 to 25 mm is placed so that the metal foil surface is on the inside, and while maintaining the above-mentioned tension state, a temperature of 80°C or less is applied. This is achieved by sliding the substrate in the longitudinal direction such that the relative sliding speed between the second bar and the substrate is 3 to 300 cm/min.

In order to facilitate understanding of the relationship between the flexible printed circuit board and the first bar and the second bar in the correction method of the present invention, a description will be given with reference to the accompanying drawings.

FIG. 1 schematically depicts a plan view of an example of a situation in which a straightening operation is performed using bars with circular cross sections as the first bar and the second bar.

That is, the flexible printed circuit board 11 wound up on the roll 10 is moved in the direction of the arrow, and the first bar 12 (in FIG. The folding angle is 180 degrees (that is, the state where the plane to which the substrates supplied to the first bar 12 belong and the plane to which the substrates taken out from the first bar 12 belong are in a parallel relationship) while touching the curved surface of the ) is wrapped. The substrate taken out from the first bar 12 is then moved in the direction of the arrow, and the second bar 13 (in FIG. 1, it is installed so that the angle β with respect to the first bar 12 is 90 degrees). While contacting the curved surface, the folding angle is 180 degrees (that is, the state where the plane to which the substrates supplied to the second bar 13 belong and the plane to which the substrates taken out from the second bar 13 belong are in a parallel relationship)
It is folded back. The substrate taken out from the second bar 13 further moves in the direction of the arrow and is wound up onto a roll 14. In addition, in FIG. 1, roll 1
In the process of moving from zero to the first bar 12 and the process of moving from the second bar 13 to the roll 14, the flexible printed circuit board moves with the resin thin film layer on the upper side, and moves from the first bar 12 to the second bar 13. During the moving process, the metal foil is moved as the upper side.

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 Curvature radius 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. The length of the bar is selected to be longer than the length of the long substrate in the width direction. Note that the first bar and the second bar may be the same bar or may be of different types.

The first bar is arranged at an angle of 20 to 70 degrees (an angle corresponding to α in Fig. 1) with respect to the width direction of the long flexible printed circuit board (direction perpendicular to the direction of movement of the board). Install. This angle is 40~
Preferably it is in the range of 50 degrees, and particularly preferably about 45 degrees. Also, the first bar is
Preferably, the first bar is disposed substantially in the same plane as the roll for supplying the elongated flexible printed circuit board.

The first bar is installed so as to form an angle of 70 to 110 degrees (an angle corresponding to β in FIG. 1) with respect to the second bar. Preferably, this angle is in the range 80 to 100 degrees, particularly preferably about 90 degrees. Moreover, it is preferable that the first bar and the second bar are installed so as to be substantially on the same plane. Moreover, it is preferable that the roll for winding up the elongated flexible printed circuit board taken out from the second bar is installed so as to be substantially on the same plane as the second bar.

In the present invention, the "folding angle" refers to the angle formed by the extended surface of the long flexible printed circuit board that is supplied so as to contact the bar and the board that contacts the bar and is folded back and taken out. means. The preferred folding angle is 135 degrees or more, and it is desirable that the elongated substrate is brought into contact with the bar in a state where it is folded, for example, in a "hairpin shape." The elongated 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 elongated 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.
The amount is selected from the range of 10 to 200 g, preferably 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.
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 above range.

The straightening method of the present invention is carried out at a temperature of 80°C or lower. 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
-50°C, more preferably 5-40°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.

In addition, when implementing the straightening method of the present invention, it is preferable to perform the manufacturing process of the long flexible printed circuit board and the straightening process continuously, and by implementing such an aspect, the straightening effect of the present invention can be further enhanced. improves.

As described above, according to the straightening method of the present invention, a long metal foil and an aromatic polyamide-imide or aromatic polyimide resin provided on the surface of the metal foil without an adhesive layer are provided. It is possible to reduce or substantially eliminate curls that have actually or potentially occurred on a long flexible printed circuit board consisting of a thin film layer with a simple operation, and the re-occurrence of curls after straightening treatment is almost impossible. Never. Therefore, the present invention can be said to be a method for straightening the curl of a long flexible printed circuit board 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'-bisphenyltetracarboxylic dianhydride and 50.06 g (0.25 mol) of 4,4'-diaminodiphenyl ether were mixed with 4-chlorophenol. The mixture was added to 1146 g of the mixture, heated to 180° C. over 1 hour with stirring, and maintained at this temperature for 1 hour for polymerization and imidization to prepare an aromatic polyimide solution (10% by weight solution). The rotational viscosity of the obtained aromatic polyimide solution at 100°C was about 5000 poise.

After degassing this aromatic polyimide solution, it was placed on a long electrolytic copper foil (width: 25 cm) with a thickness of 35 μm held on a steel belt with a T-shaped tube with a slit interval of 0.28 mm.
A coating layer was formed by extrusion under pressure from a die and continuous casting coating. Next, hot air at about 115 to 200°C was supplied to the surface of the coating layer, and about 80% by weight of the solvent was removed while the foil was held on a steel belt to form a thin film layer on the electrolytic copper foil. Finally, it was heated to 400°C in a short time in a high-temperature drying oven to substantially completely remove the solvent from the thin film layer 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 5.5 cm with the resin thin film layer on the inside in the TD direction.
This board did not show any curl in the MD direction when it was long, but it was cut to a length of 25 cm and
When the substrate is square cm x 25 cm, the radius of curvature is also changed in the MD direction before cutting.
A curl of 5.8 cm had occurred.

2 at the end of the above flexible printed circuit board.
On the curved surface of the first glass bar (see Figure 1), which has a curved surface with a radius of curvature of 6.25 mm and is fixed at an angle of 45 degrees with respect to the TD direction of the board, a load of 1 kg is applied. Fold at room temperature on the curved surface of the second glass bar (see Figure 1), which has a curved surface with a radius of curvature of 11.0 mm and is set at an angle of 90 degrees to the first bar. Each angle is 180
The curl was corrected by sliding the substrate in the longitudinal direction (MD direction) at a sliding speed of 45 cm/min. After this correction operation, the curl in the TD direction had virtually disappeared, and no curl was observed in the MD direction. Even when the substrate after this straightening operation was cut to a length of 25 cm to form a square substrate of 25 cm x 25 cm, no curl was observed in both the MD and TD directions.

Comparative Example 1 Regarding a flexible printed circuit board obtained by the same method as in Example 1 (the curl state is also the same), a flexible printed circuit board with a curved surface with a radius of curvature of 6.25 mm and an angle of 90 degrees with respect to the MD direction of the board was used. Slide the board in the longitudinal direction (MD direction) at a sliding speed of 45 cm/min at room temperature with the copper foil surface on the inside at a folding angle of 180 degrees on the curved surface of the installed first glass bar, and curl it. A corrective operation was performed. The second bar was not used.

After this correction operation, the curl in the TD direction had virtually disappeared, and no curl was observed in the MD direction. However, when the substrate after this straightening operation was cut to a length of 25 cm to form a square substrate of 25 cm x 25 cm, a curl with a radius of curvature of 8.5 cm appeared in the MD direction.

Example 2 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 at room temperature for 24 hours to prepare a polyamic acid solution with a concentration of 10% by weight. The rotational viscosity of the obtained aromatic polyamic solution at 100°C was about 4000 poise.

A coating layer was formed on an electrolytic copper foil using this aromatic polyamic acid solution in the same manner as in Example 1, and then the solvent was removed and the ring was dehydrated to form a flexible printed circuit having a 25 μm thick aromatic polyimide thin film layer. A substrate for use was obtained.

The obtained substrate had a curl with a radius of curvature of 1.8 cm with the resin thin film layer on the inside in the TD direction.
This board did not show any curl in the MD direction when it was in a long form, but it was cut into 25cm lengths and 25cm long.
When using a square board of cm x 25 cm, before cutting
The radius of curvature is 2.1 in the MD direction as well.
A cm curl had occurred.

3 on the edge of the above flexible printed circuit board.
A load of Kg was applied, the curved surface had a radius of curvature of 2.5 mm, and the angle of 45 degrees with respect to the TD direction of the board (the first
(See figure) On the curved surface of the installed glass first bar,
Next, a second glass bar with a curved surface with a radius of curvature of 2.5 mm was placed at an angle of 90 degrees to the first bar (see Figure 1), and the copper foil surface was placed on the inside at room temperature. Each folding angle is 180 degrees,
The curl was corrected by sliding the substrate in the longitudinal direction (MD direction) at a sliding speed of 101 cm/min. After this correction operation, the curl in the TD direction had virtually disappeared, and no curl was observed in the MD direction. The length of the board after this straightening operation is 25
When cut into 25cm x 25cm square substrates, there is a weak curl with a radius of curvature of 13.8cm in the TD direction, and a radius of curvature in the MD direction.
Only a weak curl of 10.9 cm appeared.

Example 3 A commercially available aromatic polyamide imide varnish (solid content: 30% by weight) synthesized from trimellitic anhydride and 4,4'-diaminodiphenylmethane was cast on the electrolytic copper foil described in Example 1. A coating layer was formed by coating. After heating this coating layer to 120°C to remove the solvent (N-methyl-2-pyrrolidone),
The solvent was completely removed by heating to 400° C. for a short time to obtain a flexible printed circuit board having a 25 μm thick aromatic polyamideimide thin film layer. 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.

The same correction operation as in Example 2 was performed on the above flexible printed circuit board. After this correction operation, the curl in the TD direction had virtually disappeared, and no curl was observed in the MD direction.
Then, even if the board after this correction operation is cut into a length of 25 cm and made into a square board of 25 cm x 25 cm,
Almost no curls were observed in both MD and TD directions.

[Brief explanation of the drawing]

FIG. 1 is a schematic plan view schematically showing an embodiment of the method for straightening a flexible printed circuit board according to the present invention. 10: Roll for supplying flexible printed circuit boards, 11: Flexible printed circuit boards, 1
2: first bar, 13: second bar, 14: roll for winding up a flexible printed circuit board.

Claims (1)

[Claims] 1. A solution containing aromatic polyamide-imide, an aromatic polyimide precursor, or an aromatic polyimide is cast onto a long metal foil, and the solution coating layer is dried and solidified to coat the metal foil. A long 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
The radius of curvature installed at an angle of 20 to 70 degrees
On the curved surface of the first bar having a curved surface of 0.5 to 25 mm,
With the metal foil side on the inside, the tension on the board is set to 1 the width of the board.
While maintaining a tension state of 10 to 200 g per cm, at a temperature of 80 degrees Celsius or less, the longitudinal length of the substrate is adjusted such that the relative sliding speed between the first bar and the substrate is 3 to 300 cm/min. Then, place the metal foil surface on the inside on the curved surface of a second bar having a curved surface with a radius of curvature of 0.5 to 25 mm, which is installed at an angle of 70 to 110 degrees with respect to the first bar. , while maintaining the above-mentioned tension state, the relative sliding speed between the second bar and the substrate is 3 at a temperature of 80°C or less.
A curl correction method for a flexible printed circuit board, characterized by sliding the board in the longitudinal direction at a speed of ~300 cm/min.