JPH09205256A - Flexible printed-circuit board - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a flexible printed-circuit board which is bent by a small force by a method in which a flexible base member on which a circuit pattern is formed is formed in such a way that a part which is covered with a cover lay film in the direction of a bend line on a base member at a flexible board covered with the cover lay film and a part which is not covered with the cover lay film are formed side by side. SOLUTION: A plurality of opening parts 5 are formed in the extension direction of a bend line L in a desired bend region A on a base film 1. The respective opening parts 5 are formed in parts between end edges of the base film 1 and circuit patterns 3 and in parts between the circuit patterns 3, 3, and the respective circuit patterns 3 are covered with parts adjacent to the opening parts 5 in the cover lay film 4. Thereby, in the bend region A, parts which are covered with the cover lay film 4 in the direction of the bend line and parts which are not covered with the cover lay film are formed side by side. A bend resistance is reduced by a portion in which the thickness of parts in which the opening parts 5 are formed becomes thinner than the parts covered with the cover lay film 4, and an FPC can be bent by a small force.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a flexible printed board in which a circuit pattern is covered with a coverlay film (particularly a photosensitive coverlay film).

[0002]

2. Description of the Related Art Flexible printed circuit boards (hereinafter referred to as FP
(Referred to as C), for example, as shown in FIG. 4, a copper foil is bonded onto a polyimide base film 41 with an adhesive 42, and the copper foil is subjected to an etching treatment to form a circuit pattern 43.
Made by forming. The circuit pattern 4 is formed on the base film 41 and the circuit pattern 43.
In order to protect 3, the cover lay film 44 made of polyimide in which the required holes and the like are formed in advance is adhered by the adhesive 45.

The FPC manufactured in this way has the structure shown in FIG.
As shown in FIG. 5, copper foil is adhered to the front surface and the back surface of the base film 51 using adhesives 52a and 52b, respectively,
By etching these copper foils, the circuit patterns 53a,
There is also a double-sided FPC with 53b formed. Then, in this double-sided FPC, the coverlay films 54a and 54b are adhered to the front surface and the back surface of the base film 51 using adhesives 55a and 55b, respectively.

If a coverlay film is provided on the FPC, the bending resistance of the coverlay film itself may increase the force required to bend the FPC. In particular, in the double-sided FPC, since bending resistance of the two coverlay films is added, it is necessary to increase the strength of the parts supporting the FPC and the driving force of the operating means connected to the FPC.

Therefore, like the double-sided FPC shown in FIG. 5, a portion E not covered with the coverlay film is provided on the back surface side of the base film 51 over the entire bending direction L of the base film 51. Is easily bent along the bending line L. In addition, this double-sided FPC is
It has already been disclosed in Japanese Examined Patent Publication No. 63-48143.

[0006]

However, even if there is only the bending resistance of one coverlay film as in the single-sided FPC of FIG. 4 and the double-sided FPC of FIG. 5, the resistance may be increased depending on the device using these FPCs. May be too large, and there is a demand to use an FPC that can be bent with a smaller force.

Further, when a strong bending force is applied to the double-sided FPC of FIG. 5, stress concentration occurs around the edges F and G of the coverlay film 54b, which may lead to disconnection of the circuit pattern 53a.

Therefore, a first object of the present invention is to provide a flexible printed circuit board which can be bent with a small force even if a coverlay film is provided.

A second object of the present invention is to provide a flexible printed circuit board capable of preventing the disconnection of the circuit pattern when it is bent.

[0010]

In order to achieve the above object, in the first invention of the present application, a flexible printed board in which a flexible base member having a circuit pattern is covered with a coverlay film is bent. A portion covered with a coverlay film and a portion not covered with the coverlay film are arranged side by side in the line direction.

That is, by covering the circuit pattern formed so as to intersect with the bending line of the base member with a coverlay film, the circuit pattern is surely protected and, for example, between the circuit patterns. The cover lay film is not covered with an opening or the like at a portion that does not need to be protected, thereby reducing the bending resistance of the FPC.

It is desirable to use a photosensitive film as the coverlay film in the present invention so that fine openings and the like are formed at accurate positions of the coverlay film.

In the case of a double-sided flexible printed circuit board in which the front surface and the back surface of the base member are respectively covered with a coverlay film, a part covered with the coverlay film and a part not covered with the coverlay film on one side of the front surface and the back surface. It is desirable to arrange and in parallel with the bending line direction, and to provide the other side with a portion not covered with the coverlay film over the entire bending line direction.

In the second invention of the present application, in such a double-sided flexible printed circuit board, the positions of the end portions of the front surface and the back surface which are not covered with the coverlay film (in other words, the end portions of the covered portion) are set. The circuit patterns are prevented from breaking due to different stresses.

[0015]

BEST MODE FOR CARRYING OUT THE INVENTION

(First Embodiment) FIG. 1 shows a single-sided flexible printed circuit board (single-sided FPC) according to a first embodiment of the present invention. In this figure, reference numeral 1 is a base film formed of polyimide in a strip shape. Reference numeral 3 denotes a circuit pattern, which is formed by adhering a copper foil on the base film 1 using the adhesive 2 and then etching the copper foil.

Reference numeral 4 is a photosensitive coverlay film. As shown in FIG. 2, the coverlay film 4 is formed by laminating a photosensitive dry film on the surface (upper surface) of the base film 1 on which the circuit pattern 3 is formed, and exposing the film using a phototool and performing chemical treatment. By developing
In consideration of the manufacturing error, only the width necessary for protecting the circuit pattern 3 is left and the unnecessary portion is removed to form the required shape.

By using the photosensitive film as described above, it is possible to eliminate the sticking misalignment of the coverlay film 4 with respect to the base film 1 and the circuit pattern 3, and to form fine openings in the coverlay film 4. Therefore, it is possible to obtain a finer coverlay film shape as compared with the conventional case where a polyimide film is used.

Here, in this embodiment, a plurality of openings 5 are formed in a desired bending region A of the base film 1 in the extension direction of the bending line L (bending line direction). Each opening 5 is formed between the edge of the base film 1 and the circuit pattern 3 and between the circuit patterns 3 and 3 in the bending region A, and each circuit pattern 3 is adjacent to the opening 5 in the coverlay film 4. It is covered by the part.

As a result, in the bending region A, a portion covered by the coverlay film 4 (a portion where the circuit pattern 3 is formed) and an uncovered portion (a portion facing the opening 5) are arranged in the bending line direction. And are formed side by side (alternately).

Therefore, in the bending region A, the thickness of the portion where the opening 5 is formed is smaller than that when the whole is covered with the coverlay film 4. The thinner it is, the smaller the bending resistance becomes. Therefore, this FPC can be bent with a small force, and the FP can be used in devices using this single-sided FPC.
The member that supports C can be downsized, and the force required to drive the actuation means connected to the FPC can be reduced.

(Second Embodiment) FIG. 3 shows a second embodiment of the present invention.
Double-sided flexible printed circuit board (double-sided F
PC) is shown. In this figure, 11 is a base film formed of polyimide in a strip shape. 13
a and 13b are circuit patterns, and the base film 11
On the front surface (upper surface) and the back surface (lower surface) of the adhesive 12a, 1
2b is used to bond copper foils, and then these copper foils are subjected to etching treatment.

Reference numerals 14a and 14b denote photosensitive cover lay films. A photosensitive dry film is laminated on the entire front surface and the back surface of the base film 11, and the manufacturing error is taken into consideration by exposure and development as in the first embodiment. Only the width required to protect the circuit pattern 3 is left, and unnecessary portions are removed to form a desired shape.

In this embodiment, a plurality of openings 15 are formed in the extension direction of the bending line L (bending line direction) on the surface side of the desired bending region B of the base film 11. Each opening 15 is formed in the bending region B between the edge of the base film 11 and the circuit pattern 13 and between the circuit patterns 13a and 13a.
a is covered by a portion of the cover lay film 14a adjacent to the opening 15.

As a result, the surface side of the bending region B is covered with the portion covered with the coverlay film 14a (the portion where the circuit pattern 13a is formed) in the bending line direction, as in the first embodiment. The non-existing portion (the portion facing the opening 15) is formed alternately.

Therefore, on the front surface side of the bending region B, the thickness of the portion where the opening 15 is formed is covered with the coverlay film 14a as compared with the case where the whole is covered with the coverlay film. The bending resistance becomes smaller as the thickness becomes thinner than that of the bent portion.

On the other hand, on the back surface side in the bending region B, the cover lay film 14b is provided with an opening 16 extending over the entire direction of the bending line L. Therefore, also on the back surface side of the bending region B, the thickness of the portion in which the opening 16 is formed is smaller than that in the portion covered with the coverlay film 14b, as compared with the case where the whole is covered with the coverlay film. As the thickness decreases, the bending resistance decreases.

Therefore, since the bending resistance on the front surface side and the back surface side is reduced in this way, the bending region B can be bent with a small force, and the member supporting the FPC in a device or the like using this double-sided FPC is downsized. Alternatively, the force required to drive the actuating means connected to the FPC can be reduced.

Further, the positions of the ends C and D of the opening 16 and the positions of the ends of the openings 15 on the front side are different from each other in the longitudinal direction of the base film 11. Therefore, even if a force to bend along the bending line L acts on the double-sided FPC, stress concentration is unlikely to occur around the ends C and D and around the end of the opening 15, and the circuit pattern 13a, 1
It is possible to reliably prevent disconnection of 3b.

In each of the above embodiments, the flexible printed circuit board using the polyimide base film (base member) has been described, but the present invention can also be applied to the flexible printed circuit board using a base member other than polyimide. . Further, in each of the above-described embodiments, the flexible printed circuit board using the cover lay film made of a photosensitive film has been described, but the present invention can be applied to the flexible printed circuit boards using other cover lay films.

Further, the present invention may be used by combining the above-described embodiments and modified examples, or their technical elements as needed.

(Relationship Between Embodiments and Claims) The base films 1 and 11 in the above embodiments are the base members described in the claims, and the circuit patterns 3, 13a and 13b are the circuit patterns described in the claims. The coverlay films 4, 14a, 14b cover the coverlay film in the claims, and the portions of the base films 1, 11 facing the openings 15, 16 of the coverlay films are covered by the coverlay films in the claims. The extension direction of the bending line L corresponds to the bending line direction referred to in the claims.

The above is the correspondence relationship between each configuration of the present invention and each configuration of the embodiment, but the present invention is not limited to the configuration of these embodiments, and the mechanism or the embodiment shown in the claims is not limited. Any structure may be used as long as the function of the structure can be achieved.

[0033]

As described above, according to the first invention of the present application, the cover lay film is provided with the portion covered with the cover lay film and the opening and the like in the bending line direction of the base member. The parts that are not covered with are arranged side by side. Therefore, according to the present invention, the circuit pattern formed so as to intersect the bending line of the base member can be covered with the coverlay film to surely protect the circuit pattern, and the coverlay film may be provided with an opening or the like. The resistance to bending along the bending line of the FPC can be reduced by the amount provided.

Therefore, the FPC can be bent along the bending line with a small force, and it is necessary for downsizing the member supporting the FPC in an apparatus or the like using the FPC and for driving the operating means connected to the FPC. You can reduce the power.

If a photosensitive film is used as the coverlay film in the present invention, it is possible to form a fine opening or the like at an accurate position of the coverlay film.
A high-definition coverlay film shape can be obtained.

In the case of a double-sided flexible printed circuit board, a portion covered by the coverlay film and a portion not covered by the coverlay film are provided side by side in the bending line direction on one side of the front surface and the back surface, and the bending line is formed on the other side. If a portion not covered with the coverlay film is provided over the entire direction, a double-sided flexible printed circuit board having a small bending resistance can be obtained as in the single-sided flexible printed circuit board.

In the second invention of the present application, in such a double-sided flexible printed circuit board, the positions of the end portions of the front surface and the back surface which are not covered with the coverlay film are different. Therefore, according to the present invention, it is possible to prevent stress concentration from occurring at the same position on the front surface side and the back surface side of the base member, and it is possible to reliably prevent disconnection of the circuit pattern.

[Brief description of drawings]

FIG. 1 is a cross-sectional perspective view of a flexible printed circuit board according to a first embodiment of the present invention.

FIG. 2 is a cross-sectional view of an FPC using a photosensitive coverlay film.

FIG. 3 is a sectional perspective view of a flexible printed circuit board according to a second embodiment of the present invention.

FIG. 4 is a cross-sectional perspective view of a conventional flexible printed circuit board.

FIG. 5 is a cross-sectional perspective view of a conventional flexible printed circuit board.

[Explanation of symbols]

 1,11 Base film 2,12a, 12b Adhesive 3,13a, 13b Circuit pattern 4,14a, 14b Photosensitive coverlay film 15,16 (Coverlay film) opening

Claims (4)

[Claims] 1. A flexible printed board in which a flexible base member having a circuit pattern formed thereon is covered with a coverlay film, wherein a portion covered with the coverlay film and a portion not covered with the coverlay film are arranged in the bending line direction of the base member. A printed circuit board characterized by being provided. 2. The flexible printed circuit board according to claim 1, wherein the coverlay film is made of a photosensitive film. 3. A front surface and a back surface of the base member are respectively covered with the coverlay film, and a portion covered with the coverlay film and a portion not covered with the coverlay film are provided on one side of the front surface and the back surface. The flexible printed circuit board according to claim 1 or 2, wherein the flexible printed circuit board is provided side by side in the bending line direction, and a portion not covered with the coverlay film is provided on the other side over the entire bending line direction. 4. The flexible printed circuit board according to claim 3, wherein the front surface and the back surface are different from each other in the position of the end of the portion not covered with the coverlay film.