JPS6242482A - Flexible wiring board - Google Patents

Abstract

(57) [Summary] This bulletin contains application data before electronic filing, so abstract data is not recorded.

Description

[Detailed description of the invention] Industrial applications The present invention relates to a flexible wiring board.

2. Description of the Related Art In recent years, electronic devices have become more multi-functional and smaller, and flexible wiring boards have been used more frequently to achieve higher reliability and space savings, and various problems have been raised in their use. . One of them is a piece of copper foil on a 7 lexiple wiring board. The causes are excessive stress applied to the surface of the copper foil and repeated amplitude stress.

FIG. 8 is a cross-sectional view of the bent copper foil of the flexible wiring board, and shows the inner bending radius f, R of the copper foil of the flexible wiring board.
4. If the thickness of the copper foil is t, its elongation δ is δ=−1, and if the thickness of the copper foil is constant, the elongation δ of its surface is also constant. Since t is about 35μ, the strain on the outer surface of the copper foil is as follows.If R4 is small, ε becomes large. This strain ε is proportional to the stress within the elastic range, and if it becomes large enough to cause the elastic range, the copper foil will break.

An example of the above-mentioned flexible broken line board will be described below with reference to the drawings.

FIGS. 9 and 10 are cross-sectional views of an example of a reinforcing portion of a conventional flexible wiring board and its label. 1 is a base film, 2 is a copper foil provided in parallel, 3 is a reinforcing plate, 6 is a cover film, 7 is a double-sided tape for adhering the reinforcing plate 3 and the base film 1, and is used by inserting it into a connector (not shown). be done.

FIG. 11 is a cross-sectional view of FIG. 10 when a force in the bending direction is applied, and the reinforcing plate 3 attached to the base film 1 is made of polyester film or the like to increase the rigidity of the reinforced part. It will be done.

Problems to be Solved by the Invention However, in conventional devices, the base film 1 is usually made of polyimide with a thickness of about 26 μm, and the copper foil 2 is made of polyimide with a thickness of about 36 μm, which are highly flexible, and the end face 11 of the reinforcing plate has an acute angle. All bones are easily bent. Therefore, there was a problem in that excessive stress as described above is applied to the copper foil 2, making it easy to break the wire.

In view of the above-mentioned problems, the present invention provides a flexible wiring board that completely reduces the stress applied to the copper foil and is less likely to break, even if it has a reinforcing portion of the same structure.

Means for Solving the Problems In order to solve all of the above problems, the flexible wiring board of the present invention includes a plurality of copper foils provided in parallel on a base film and a base film sandwiched between the plurality of copper foils and facing the above-mentioned plurality of copper foils. The reinforcing part is provided at a position where the reinforcing part is perpendicular to the copper foil, and the part facing the copper foil on the end face perpendicular to the copper foil of the reinforcing part is formed in a concave shape, and the part facing the hot steel gap between the copper foils is formed in a convex shape. It is something.

Function The present invention can provide a highly reliable flexible wiring board by reducing the stress applied to the copper foil wire, eliminating the causes of wire breakage, etc. with the above structure.

Embodiment FIGS. 1, 2, and 3 are examples of the present invention, and correspond to the conventional examples shown in FIGS. 9, 10, and 11, respectively. 4 and 5 are one end surface of the reinforcing plate 3 perpendicular to the copper foil 2;
The area between adjacent copper foils 2 facing the copper-free portion is a convex part 4, and the area facing the copper foil 2 is a concave part 5.

With this configuration, when an external force is applied to the flexible wiring board with low rigidity to bend it, the point of displacement occurs on the boundary with the reinforcing plate 3 where the rigidity changes significantly, and the convex portion 4, The copper foil portion tends to be displaced along the concave portion 5.

Therefore, the bending radius of the copper foil can be increased as indicated by 8 in FIG. 3, and the stress applied to the copper foil can be reduced. Fourth
6 to 6 show other embodiments, and similar effects can be obtained in each case. FIG. 4 shows a double-sided flexible board, and FIG. 6 is a cross-sectional view taken along the line Bo-B. In the figure, reference numeral 9 denotes a copper foil or a dissimilar metal located at a position facing the copper foil 2 of the double-sided flexible wiring board, which has high rigidity with respect to the copper foil 2 and functions as a reinforcing portion.

FIG. 6 shows a flexible wiring board attached to a printed wiring board, and FIG. 7 shows its C3-C4 cross section.

In the figure, 10 is a printed wiring board, which has high rigidity.

Effects of the Invention As described above, according to the present invention, although the structure is the same as the conventional one, by making the end face of the reinforcing plate uneven, it is possible to significantly improve reliability against the problem of wire breakage.

[Brief explanation of the drawing]

FIG. 1 is a plan view showing a flexible wiring board according to one embodiment of the present invention, FIGS. 2 and 3 are cross-sectional views of the flexible wiring board according to another embodiment of the present invention, and FIG. 5 is a sectional view taken along line BB, FIG. 6 is a plan view showing a flexible wiring board according to another embodiment of the present invention, FIG. 7 is a sectional view taken along line 0-C, and FIG. FIG. 9 is a plan view of a conventional flexible wiring board, and FIGS. 10 and 11 are cross-sectional views thereof. 1...Base film, 2. River...Copper foil, 3.
・Mountain/reinforcing plate, 4... Convex portion, 5...
Concave portion, 6... River/cover film, 7... Double-sided tape, 9... Copper foil, 11... Printed wiring board. Name of agent: Patent attorney Toshio Nakao and one other person: Kawadai. Figure 3 Figure 4 Figure 5 Figure 6 Figure 7 Figure 8 Figure 9

Claims (1)

[Claims] It is composed of a plurality of copper foils provided in parallel on a base film, and a reinforcing part provided at a position facing the plurality of copper foils while sandwiching the base film, and the reinforcing part is orthogonal to the copper foils of the reinforcing part. 1. A flexible wiring board characterized in that a portion of the end surface facing the copper foil is formed in a concave shape, and a portion facing the copper-free portion between the copper foils is formed in a convex shape.