JPH04296089A - Flexible printed wiring board - Google Patents

Abstract

PURPOSE:To surely prevent fissures induced at the peripheral edge of a circuit layer from reaching to a circuit pattern propagating inward. CONSTITUTION:A circuit layer 2 where a circuit pattern 21 is provided and an overlay 1 which is laminated on the surface of the circuit pattern 21 of the circuit layer 2 are provided. A large number of through-holes 11 and 12 are provided to both the sides of the overlay 1 corresponding to a region between the side edges of the circuit layer 2 and the circuit pattern 21. Fissures are prevented from propagating inward at the through-holes 11 and 12.

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 capable of preventing propagation of cracks occurring in circuit layers.

0002

[Prior Art] Flexible printed wiring boards are usually
It has a circuit layer with a circuit pattern printed on a flexible insulating base film with a thickness of about 25 μm to 75 μm,
To protect the circuit pattern of this circuit layer, the thickness is 25 mm.
A coverlay of about μ to 75 μ is laminated on the circuit layer. Since the flexible printed wiring board is thus very thin, even if a slight crack occurs at the peripheral edge of the circuit layer, the crack easily expands inside and may damage the circuit pattern.

Conventionally, in order to prevent the propagation of cracks in flexible printed wiring boards, Kevlar threads (polyimide threads) have been used between the base film and the coverlay at the peripheral edge of the flexible printed wiring board. A method has been proposed in which the fibers are interposed and laminated to prevent cracks that occur at the peripheral edge of a flexible printed wiring board from propagating into the interior (Kenji Numakura, "
"Mechanical Design of Flexible Substrates" P. 288, Information Research Committee Co., Ltd., published on January 1, 1988).

0004

[Problems to be Solved by the Invention] However, in the method of preventing crack propagation using threads, it is not easy to accurately position the threads. Once the thread is placed in that position, it is no longer possible to prevent cracks formed at its peripheral end from propagating into the interior. Further, even when repeated stress is applied to the flexible printed wiring board, propagation of cracks cannot be reliably prevented.

The present invention has been made to solve the above problems, and its purpose is to provide a flexible printed wiring board that can reliably prevent cracks generated at the peripheral edge of the circuit layer from propagating inside. It is about providing.

[0006]

[Means for Solving the Problems] The flexible printed wiring board of the first invention includes a circuit layer having a circuit pattern printed on a flexible insulating base film, and a circuit layer laminated on the surface of the circuit pattern of the circuit layer. A flexible printed wiring board having a coverlay, wherein a large number of through holes are provided on both sides of the coverlay at positions corresponding to areas between both side edges of the circuit layer and the circuit pattern. This achieves the above objective.

The flexible printed wiring board of the second invention includes a circuit layer having a circuit pattern printed on a flexible insulating base film, a coverlay disposed on the circuit layer, and a combination of the circuit layer and the cover. A flexible printed wiring board having a crack propagation prevention layer disposed between the circuit layer and the circuit pattern, wherein the crack propagation prevention layer is provided at a position corresponding to a region between both side edges of the circuit layer and the circuit pattern. A large number of through holes are provided on both sides of the layer, thereby achieving the above objective.

The insulating base film used in the present invention is usually formed into a rectangular shape, and a circuit pattern is printed on this base film to form a circuit layer. A region where no circuit pattern is provided is formed between both side edges of the circuit layer and the circuit pattern, and a large number of through holes are provided on both sides of the coverlay at positions corresponding to this region. ing. This through hole is designed to prevent damage to the circuit pattern by preventing the crack from progressing further when it reaches the through hole when a crack occurs for some reason at the side edge of the circuit layer. Therefore, in order to ensure that the cracks that occur are captured by the through holes, when the coverlay is laminated on the circuit layer, it is necessary to A large number of through holes are arranged so that a running line hits at least one through hole.

The method for forming such a through hole is not particularly limited, and the hole may be formed by drilling, punching, etc. in the coverlay before lamination. By laminating the coverlay on the circuit layer with the through-hole provided, the through-hole can be formed easily and at an accurate position.

[0010] The size of the through-hole is not particularly limited, but if it is too large, the size of the flexible printed wiring board will become large, and if it is too small, the number of holes must be extremely large, so it should be about 3 mm to 10 mm. is preferred. The shape of the through hole is preferably circular or oval to avoid stress concentration.

When the flexible printed wiring board of the present invention has a crack propagation prevention layer, it corresponds to the area between both side edges of the circuit layer and the circuit pattern, as in the case where the coverlay is provided with through holes. A large number of through holes are provided on both sides of the crack propagation prevention layer at the positions shown in FIG. In other words, the holes provided in the crack propagation prevention layer are such that when the crack propagation prevention layer is laminated on the circuit layer, there is at least one line passing through both regions of the circuit layer and running between both ends of the circuit layer. It is placed so that it hits the through hole. The method for forming the through holes is not particularly limited, and the holes may be formed by drilling, punching, etc. in the crack propagation prevention layer before lamination. By laminating the crack propagation prevention layer on the circuit layer provided with the through hole, the through hole can be formed easily and at an accurate position. The size of the through hole is not particularly limited, but if it is too large, the size of the flexible printed wiring board will become large, and if it is too small, the number of holes will have to be extremely large, so it is preferably about 3 mm to 10 mm. . The shape of the through hole is preferably circular or oval to avoid stress concentration. The through holes may be formed over the entire surface of the crack propagation prevention layer, or may be formed only in a portion corresponding to the vicinity of the peripheral edge of the flexible printed wiring board.

The material of the crack propagation prevention layer used in the present invention is not particularly limited, but in order not to reduce the strength, heat resistance, etc., it should be made of the same material as the base film of the coverlay or circuit layer. It is desirable that there be.

[0013]

[Function] In the flexible printed wiring board of the present invention, even if a crack occurs inward from the edge of the circuit layer, if the crack reaches the through hole provided in the coverlay or crack propagation prevention layer, the crack will crack. By dispersing the stress caused by the tearing in the through-hole portion, it is possible to prevent the crack from progressing.

[0014]

Embodiments An embodiment of the present invention will be described with reference to the drawings.

Embodiment 1 FIG. 1 is a perspective view of a coverlay 1 before lamination and a circuit layer 2 provided with a circuit pattern 21. One row of holes 11 each having a diameter of 5 mm were arranged on both sides of the coverlay 1 at a pitch of 8 mm at a position 5 mm inside from both side edges 13, 13. Similarly, one row of holes 12 each having a diameter of 5 mm were arranged at positions 12 mm inside from both ends of the coverlay 1 at a pitch of 8 mm. Further, each hole 12 was positioned between the holes 11, 11.

Next, the coverlay 1 and the circuit layer 2 were laminated by pressing to obtain a flexible printed wiring board of the present invention.

The side edges 13 of the obtained flexible printed wiring board were scratched with a knife to generate cracks. When force was further applied to the cracked part to cause the crack to progress, when the crack reached the holes 11 and 12, the crack stopped there and did not expand further inside.

Embodiment 2 FIG. 2 is a perspective view of a coverlay 2, a crack propagation prevention layer 4, and a circuit layer 3 provided with a circuit pattern 31 before being laminated. One row of holes 41 each having a diameter of 5 mm were arranged at a pitch of 8 mm on both sides of the crack propagation prevention layer 4 at positions 5 mm inside from the edges 43 on both sides. Similarly, the 5 mm diameter hole 42 is placed 12 mm inside from both ends at a pitch of 8.
One row was arranged in each mm. Further, each hole 42 is connected to the hole 41
, 41.

The coverlay 5, crack propagation prevention layer 4, and circuit layer 3 were laminated by pressing to obtain a flexible printed wiring board of the present invention.

The side edges 43 of the obtained flexible printed wiring board were scratched with a knife to generate cracks. When further force was applied to the crack to cause the crack to progress, when it reached the hole, the crack stopped growing there and did not expand further inside.

[0021]

[Effects of the Invention] Even if a crack occurs in the flexible printed wiring board of the present invention, the crack stops growing at the through hole and does not expand any further, so there is no damage to the circuit pattern. .

[Brief explanation of drawings]

FIG. 1 is an exploded perspective view of an embodiment of a flexible printed wiring board of the present invention.

FIG. 2 is an exploded perspective view of another embodiment of the flexible printed wiring board of the present invention.

[Explanation of symbols]

1 Coverlay 11 Crack propagation prevention hole 12 Crack propagation prevention hole 2 Circuit layer 21 Circuit pattern 3 Circuit layer 31 Circuit pattern 4 Crack propagation prevention layer 41 Crack propagation prevention hole 42 Crack propagation prevention hole 5 Coverlay

Claims (2)

[Claims] 1. A flexible printed wiring board comprising: a circuit layer having a circuit pattern printed on a flexible insulating base film; and a coverlay laminated on the surface of the circuit pattern of the circuit layer; A flexible printed wiring board in which a large number of through holes are provided on both sides of the coverlay at positions corresponding to areas between both side edges of the layer and the circuit pattern. 2. A circuit layer having a circuit pattern printed on a flexible insulating base film, a coverlay disposed on the circuit layer, and a coverlay disposed between the circuit layer and the coverlay. A flexible printed wiring board having a crack propagation preventing layer, wherein a large number of through holes are provided on both sides of the crack propagation preventing layer at positions corresponding to areas between both side edges of the circuit layer and the circuit pattern. A flexible printed wiring board equipped with