JPH04273495A - Flexible printed wiring board - Google Patents

Abstract

PURPOSE:To prevent cracks generated in a peripheral part from spreading to the inside by forming a number of through holes in a specified region in the side part in cross direction of a base film and by so arranging the holes that an arbitrary line in a cross direction in the region crosses with one or more through holes. CONSTITUTION:A number of parallel linear circuit patterns 11 are printed on a flexible insulating base film 10. A cover lay is laminated to cover the circuit pattern 11. The base film 10 is rectangular and the circuit pattern 11 on a straight line is parallel in the longitudinal direction of the base film 10. A number of through holes 12, 12... are provided to a side region of a circuit pattern in each side part in cross direction of the base film 10. The through holes 12 are arranged in two lines along an outer periphery. The through holes 12 of each line are arranged zigzag in a region wherein the through holes 12 are so provided that an arbitrary line in a cross direction of the base film 10 crosses with any through hole of one line.

Description

[Detailed description of the invention]

0001

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a flexible printed wiring board having a circuit pattern printed on a flexible insulating substrate.

0002

[Prior Art] Flexible printed wiring boards are usually
A circuit pattern is printed on a base film having a thickness of approximately 25 to 75 μm, and a coverlay having a thickness of approximately 25 to 75 μm is laminated to the base film in order to protect the circuit pattern. As described above, flexible printed wiring boards are very thin and can be bent freely, and are often used after being processed into complex shapes. Flexible printed wiring boards with complex shapes are usually manufactured by punching the flexible printed wiring board using a mold corresponding to the shape (Kenji Numakura, "Functional Design of Flexible Boards", p. 55, KK)
Information Research Committee, published January 1, 1986). However, the die used for punching is expensive, so although it is suitable for mass production of printed wiring boards of a specific shape, it is uneconomical and inappropriate for small volume production. For this reason,
Printed wiring boards with specific shapes are manufactured manually using a knife or the like.

[0003] Furthermore, as mentioned above, since flexible printed wiring boards are very thin, there is a problem in that even if a small crack occurs in the peripheral portion, the crack propagates inside and expands. If the crack propagates inside, the circuit pattern provided on the base film may be disconnected or damaged.

[0004] In order to prevent cracks generated at the peripheral edge from propagating inside, for example, polyimide resin threads are interposed between the base film and the coverlay at the peripheral edge of the flexible printed wiring board. A method has been developed in which the threads are used to laminate a flexible printed wiring board and prevent cracks that occur at the peripheral edge of the board from propagating into the interior (see "Functional Design of Flexible Boards", p. 228).
.

[0005]

[Problems to be Solved by the Invention] As described above, in the method of using threads to prevent crack propagation, it is not easy to position the threads, and it is difficult to position the threads at a position away from the periphery of the flexible printed wiring board. If this happens, it becomes impossible to prevent cracks that occur around the periphery from propagating into the interior. Also,
Even when repeated stress is applied to a flexible printed wiring board, crack propagation cannot be reliably prevented.

[0006] Furthermore, when a flexible printed wiring board is manually processed into a specific external shape using a knife or the like, when forming concave corner portions, stress is applied to the portion where the corner portion is to be formed. There is also the problem that there is a risk that cracks may occur due to the formation of corner portions, and that it is not easy to form the corner portions. Furthermore, if stress is concentrated at the formed corner portions due to tearing force, there is a risk that cracks may occur from the corner portions.

The present invention solves the above-mentioned conventional problems, and its object is to provide a flexible printed wiring board that can reliably prevent cracks generated in the peripheral portion from propagating inside. Another object of the present invention is to provide a flexible printed wiring board that can suppress the occurrence of cracks in the portion where the corner portion is formed when the board is processed into an external shape having a concave corner portion.

[0008]

[Means for Solving the Problems] The flexible printed wiring board of the present invention is a flexible printed wiring board in which a circuit pattern is printed on a flexible insulating base film, at least on each side of the base film in the transverse direction. A large number of through holes are formed in a predetermined region of the section, and an arbitrary line along the transverse direction in that region is arranged so as to intersect one or more of the through holes. This achieves the above objective.

The flexible printed wiring board of the second invention is a flexible printed wiring board in which a circuit pattern is printed on a flexible insulating base film, and the portion corresponding to the position where the concave corner portion is formed is a flexible printed wiring board in which a circuit pattern is printed on a flexible insulating base film. It is characterized by having a through hole having a circular cross section, thereby achieving the above object.

0010

[Function] In the flexible printed wiring board of the present invention, even if a crack that occurs at the periphery propagates inward, the crack reaches one of the through holes, thereby preventing further propagation of the crack inward. Ru. Furthermore, in the flexible printed wiring board of the second aspect of the present invention, when forming the concave corner portion, the corner portion is formed in the through hole provided in the portion where the corner portion is to be formed. The generation of cracks is suppressed during formation.

[0011]

[Examples] Examples of the present invention will be described below.

[0012] The flexible printed wiring board of the present invention includes:
As shown in FIG. 1, a large number of parallel linear circuit patterns 11 are printed on a flexible insulating base film 10. A coverlay (not shown) is then laminated to cover the printed circuit pattern 11. The base film 10 has a rectangular shape in this embodiment, and the linear circuit pattern 11 is parallel to the longitudinal direction of the base film 10. A large number of through-holes 12,
12, . . . are provided respectively. The through holes 12 provided on each side are arranged in two rows along the outer periphery.
In each region provided with through-holes 12 on each side, each of each row of The through holes 12 are arranged in a zigzag pattern.

Each through hole 12 has a diameter of, for example, 5 mm, and is located 5 mm from each side edge of the base film 10.
One row of through holes 12 is formed along each side edge at a distance, and the other row of through holes 12 is formed along each side edge at a distance of 12 mm from each side edge. be done.

[0014] Each through hole is easily and accurately formed at any position by drilling or punching. Each through hole 12 may be formed in the base film 10, but may also be formed in a coverlay laminated on the base film 10. Therefore, the state in which the coverlay is laminated on the base film 10 in,
It may be formed on the base film 10 together with the coverlay. Although the size of each through-hole is not limited, if it is too small, the number of through-holes increases, resulting in decreased workability. In order to keep the base film 10 to an appropriate size so as not to increase in size, it is preferably about 3 to 10 mm. The cross-sectional shape of each through hole 12 is preferably circular or elliptical in order to avoid stress concentration.

In the flexible printed wiring board of the present invention having such a structure, even if a crack occurs at the periphery of each side in the transverse direction of the base film 10, the crack will not propagate by reaching any of the through holes 12. This prevents cracks from expanding.

Next, the flexible printed wiring board of the second invention will be explained. This flexible printed wiring board has a rectangular shape in which a plurality of parallel linear circuit patterns 21 are printed on a flexible base film 20, for example, as shown in FIG. 2(a). As shown in FIG. 2(b), this flexible printed wiring board has a circuit pattern 21 on a base film 20.
A rectangular shape having a pair of concave corner portions 23 and 23 is manually cut out from each side using a knife to form the outer shape. As shown in FIG. 2(a), the flexible printed wiring board has each corner 2
Each of the holes 24 has a through hole 24 in a portion corresponding to 3. Each through hole 24 is formed by drilling or punching. When shaping the wiring board using a knife, each side portion is cut along the broken line in FIG. 2(a). At this time, a knife is inserted from each side edge of the wiring board, and after the knife reaches each through hole 24, the space between each corner portion 23 is cut by the knife. Then, each corner portion 23 is cut out in a rectangular shape.
are formed respectively. As a result, when forming each corner portion 23, there is no fear that stress will be concentrated on the corner portion and cracks will occur. Since each of the formed corner portions 23 is formed by a portion of each through hole 24, it has an arc shape. Therefore, even if stress is concentrated on the corner portion 23 due to tearing force, the stress will not be absorbed by the corner portion 23. Since it is distributed along the circumferential surface, there is no risk of cracking.

If each through hole 24 is too small, the arcuate portion of the corner portion 23 formed therein will become small, making it impossible to sufficiently disperse the stress caused by the tearing force. Furthermore, if the through hole 24 is too large, the area cut as the corner portion 23 becomes large, which is not economical. For this reason, about 3 to 10 mm is preferable.

[0018]

Effects of the Invention In the flexible printed wiring board of the present invention, cracks generated from the periphery of the base film are reliably prevented from propagating into the inside of the base film due to the through holes. There is no risk of the formed circuit pattern being disconnected or damaged. Also,
The flexible printed wiring board according to the second aspect of the present invention is used when processing an external shape having a concave corner portion, and has a through hole in a portion corresponding to the position where the corner portion is formed. , work for machining the corners becomes unnecessary. As a result, there is no risk of cracks occurring when forming the corner part, and since the corner part is formed by a part of the through hole, the stress caused by tearing force is dispersed and the corner part is formed. The occurrence of cracks in the corner portions is suppressed.

[Brief explanation of the drawing]

FIG. 1 is a plan view of a flexible printed wiring board of the present invention.

FIG. 2(a) is a plan view of the flexible printed wiring board of the second invention. (b) is a plan view of a flexible printed wiring board whose external shape has been processed.

[Explanation of symbols]

10 Base film 11 Circuit pattern 12 Through hole 20 Base film 21 Circuit pattern 23 Corner part 24 Through hole

Claims (2)

[Claims] 1. A flexible printed wiring board in which a circuit pattern is printed on a flexible insulating base film, wherein a large number of through holes are formed in predetermined areas at least on each side of the base film in the transverse direction. A flexible printed wiring board characterized in that the area is arranged such that any line along the transverse direction intersects one or more through holes. 2. A flexible printed wiring board in which a circuit pattern is printed on a flexible insulating base film, which has a through hole having a circular cross section in a portion corresponding to a position where a concave corner portion is formed. A flexible printed wiring board featuring: