JPH0227572Y2 - - Google Patents

Description

[Detailed Description of the Invention] [Industrial Application Field] This invention relates to a flexible printed wiring board (hereinafter referred to as FPC) with improved mechanical strength.

As is well known, FPC is a polyimide film,
A wiring pattern is formed by fixing a conductive material (currently mainly copper foil) onto the surface of a thin base film such as polyester film that is both insulating and flexible, saving mounting space and improving reliability. It is widely used in computer-related equipment, audio products, communication equipment, etc.

[Prior art]

Because FPC uses a thin base film due to its essential material composition, it is vulnerable to external mechanical forces and has the disadvantage of being easily torn, especially when polyimide film is used. Also, FPC
Because of the purpose for which it is used, it has a very complex shape, and the external forces that are applied to it vary. In particular, L-shaped or U-shaped planes as shown in Figure 1 A and B
In a letter-shaped FPC, stress tends to concentrate in one part, making it easy to tear. In other words, Fig. 1A is L-shaped in plan,
FIG. 4B shows an FPC in which a wiring pattern 2 is formed on a base film 1 having a planar U-shape. Stress is concentrated in these corner portions 3, making them easy to tear.

As a conventional method for protecting such easily tearable parts, there is a method of leaving reinforcing foil 4 on the corner part 3, as shown in FIG. 2A and B. That is, on the inner peripheral edge of the corner part 3, there is a substantially L-shaped or U-shaped shape.
The purpose is to form a reinforcing foil having a letter shape and a constant width, thereby preventing cracks in the corner portions 3.

According to such a method, although the strength of the corner portion 3 is greatly improved, both ends 4a of the reinforcing foil 4,
There was a drawback that stress tends to concentrate near 4a, and cracks 5 as shown by broken lines in FIG. 1A and B are likely to occur.

[Purpose of invention]

In view of the above-mentioned circumstances, the purpose of this invention is to provide an FPC that prevents cracks from occurring at the corners and improves the overall mechanical strength.

[Structure of the idea]

In order to achieve the above object, the gist of the present invention is to change the shape of the reinforcing foil and create a structure in which the width gradually decreases toward both ends.

[Example of idea]

Embodiments of the present invention will be described below based on the drawings.

FIG. 3 is a plan view showing the configuration of essential parts of an embodiment of the present invention, and A and B in the same figure correspond to A and B in FIG. 2, respectively. The present embodiment shown in FIG.
The difference from the conventional FPC shown in FIG. 2 is the shape of the reinforcing foil. That is, the reinforcing foil 6 in FIG. 3A,
The reinforcing foil 7 shown in FIG.
The width gradually decreases toward a and 7a, and as a result,
The reinforcing foil 6 has a tapered V-shaped structure, and the reinforcing foil 7 has a tapered U-shaped structure.

According to such a structure, the corner portion 3 is sufficiently reinforced, stress is not concentrated on both end portions 6a and 7a, and cracks can be prevented from occurring at these locations.

Next, Fig. 4 shows an example in which the present invention is applied to a double-sided FPC, and Fig. 4 shows an example in which the present invention is applied to a double-sided FPC.
When the shapes of a and 9a and the back reinforcing foils 8b and 9b are different, C and D in the figure are the front reinforcing foils 10a and 11a.
This is an example in which the formation positions of the back reinforcing foils 10b and 11b are shifted.

That is, in the figure A, the back reinforcing foil 8b is made of a V-shaped copper foil that is one size larger than the front reinforcing foil 8a, and in the same figure B, the back reinforcing foil 9b is made of copper foil that is wider than the front reinforcing foil 9a. Made of foil. on the other hand,
In C and D of the same figure, an asymmetrical reinforcing foil 1 is shown.
0a and 10b, and 11a and 11b are formed on both the front and back surfaces so as to be offset from each other.

According to such a configuration, since the reinforcing foil is formed on both sides, the strength of the corner portion 3 is further strengthened, and the reinforcement strength gradually decreases as the distance from the corner portion 3 increases. Such stress is dispersed and cracks can be prevented.

In addition, in each of the above embodiments, the reinforcing foils 6, 7,
8a, 8b, 9a, 9b, 10a, 10b, 11
It is also possible to cover a and 11b with a coverlay film. Thereby, the degree of reinforcement and stress distribution can be further improved, and the effect of preventing cracks can be further enhanced.

Moreover, the same effect can be obtained by attaching a thin insulating film having a similar shape to the corner portion 3 instead of the reinforcing foils 6 to 11b. That is, polyester film, polyimide film, polyethylene film, polypropylene film, polyvinyl chloride film, paper, etc. are cut into the same shape as the reinforcing foils 6 to 11b,
These are adhered to the corner portion 3 using a suitable adhesive or adhesive. Such a configuration is an FPC
This is particularly effective when the circuit density is high and there is no room for reinforcing foil. This is because the reinforcing film made of these insulating films can be adhered onto the wiring pattern.

[Effect of idea]

As explained above, this invention uses reinforcing foil or reinforcing membrane whose width gradually decreases toward both ends.
Since it is formed on the surface of the corner part of the FPC, it is possible to avoid concentration of stress on a specific part of the corner part, thereby preventing cracks in the corner part.

[Brief explanation of drawings]

Fig. 1 is a plan view showing a conventional example of an FPC having a corner portion, Fig. 2 is a plan view showing a conventional example of reinforcing foil provided at the corner portion, Fig. 3 A, B, and Fig. 4 I-- D is a plan view showing the configuration of essential parts of an embodiment of the present invention. 3... Corner part, 6, 7, 8a, 8b, 9a,
9b, 10a, 10b, 11a, 11b...Reinforcement foil.

Claims (1)

[Claims for Utility Model Registration] (1) A flexible printed wiring board having a reinforcing foil on the surface of a corner portion, wherein the reinforcing foil has a shape whose width gradually decreases toward both ends. wiring board. (2) The flexible printed wiring board according to claim 1, wherein the reinforcing foil having the shape described above is formed on both the front and back surfaces. (3) The flexible print according to claim 2 of the utility model registration claim, characterized in that the shapes of the reinforcing foils formed on both the front and back surfaces are different and/or the formation positions are shifted from each other. wiring board. (4) The flexible printed wiring board according to any one of claims 1 to 3 of the claims registered as a utility model, characterized in that a plastic film or paper of the same shape is used in place of the reinforcing foil.