GB2120837A

GB2120837A - Flexible circuit board

Info

Publication number: GB2120837A
Application number: GB08308988A
Authority: GB
Inventors: Hirofumi Matsumoto
Original assignee: Nippon Mektron KK
Current assignee: Nippon Mektron KK
Priority date: 1982-03-31
Filing date: 1983-03-31
Publication date: 1983-12-07
Also published as: FR2524759B1; GB2120837B; DE3311688C2; JPS58170095A; FR2524759A1; DE3311688A1

Abstract

A flexible circuit board or flat cable comprising a base sheet 12 conductors 13 and a cover sheet 15 bonded by adhesive 14 to the base sheet 12 has two metal or synthetic plastics shape fixation members 16 which maintain the shape of the circuit board in a desired configuration (Figure 3). The members 16 may be at the edge of the circuit board as shown, or between the base sheet and the cover sheet (10, Figure 2), or within the base sheet or the cover sheet (24, Figure 5). It is stated that the circuit board can be flexible enough to use as a moveable wiring part. <IMAGE>

Description

SPECIFICATION Flexible circuit board This invention relates to the field of flexible circuit boards. More particularly, this invention relates to new and improved printed circuit flexible circuit boards provided with a shaped or shapeable fixation member having plasticity.

Typically, flexible circuit boards in the prior art have the basic structure of a plastic base film, a circuit pattern on the base film and a plastic cover film adhesively fixed thereto. Because of the flexibility of the base and cover films, these circuit boards have often been used as a movable wiring part; and these flexible circuit boards have also been utilized in fixed wiring applications.

Unfortunately, prior art flexible circuit boards have considerable disadvantages when used in a fixed position. For example, after a conventional flexible circuit board has been formed to the desired installation shape (i.e., the shape of the installation location) and installed, the "memory" characteristics inherent in the flexible plastic base and cover films causes the circuit board to move in an attempt to resume its original shape. This non-conformity to the shape of its location results in movement of the flexible circuit board which may obstruct the arrangement of other internal parts along with unnecessary contact of the flexible circuit board with the walls of the instrument or container into which it is incorporated.

The above-discussed and other problems of the prior art are overcome or alleviated by the flexible circuit board of the present invention. In accordance with the present invention, in a conventional flexible circuit board, a shape fixation or retention member having plasticity (i.e., capable of being formed or shaped and retaining the form or shape) is attached to or provided within the base film and/or the cover film whereby the initially conforming shape of the circuit board at the time of installation will thereafter be maintained.

Thus, viewed from one aspect the invention provides a flexible circuit board having a base sheet with electrically conductive circuit means thereon, a cover sheet adhesively bonded to said base sheet, and shape fixation means incorporated in said flexible circuit board. Viewed from another aspect, the invention provides a flexible circuit board comprising a base sheet with electrically conductive circuit means thereon; and shape fixation means incorporated in said flexible circuit board.

Typically, the shape fixation member will be metal or synthetic resin formed as a circular rod or flat bar and located longitudinally along the two edges of the flexible circuit board or along a surface of the board. While the flexible characteristics of the metal or resin fixation members will still allow for use in movable wiring applications, the plasticity of the members will conform the flexible circuit to the shape of installation for those times where a fixed wiring application is desired.

The above-discussed and other advantages of the present invention will be apparent to and understood by those skilled in the art from the following detailed description of certain preferred embodiments thereof with reference to the accompanying drawings in which: Figure 1 is a cross-sectional view of a flexible printed circuit board in accordance with the prior art; Figure 2 is a cross-sectional side view of a flexible printed circuit board in accordance with the present invention; Figure 3 is a front perspective view looking down on the flexible circuit board of Figure 2; Figure 4 is a cross-sectional side view, similar to Figure 2, of a second flexible circuit board configuration incorporating and in accordance with the present invention; and Figure 5 is a cross-sectional side view of still another flexible circuit board configuration, similar to Figure 2, incorporating and in accordance with the present invention.

Referring first to Figure 1, aflexible printed circuit board in accordance with the prior art is shown. A film or base sheet 1, typically of thin flexible plastics, is shown having a series of conductors 4 thereon forming a circuit pattern. The circuit pattern may be formed by any conventional printed circuit or similar technique. A cover film 2, also typically of thin flexible plastics, covers and is bonded by adhesive 3 to the base sheet 1. The structure shown in Figure 1 is conventional and well known in the art. The flexible nature of the base and cover films provide highly desirable characteristics for use in movable wiring applications.

The flexible feature of the structure of Figure 1 is not desirable when used in a fixed wiring application. As a fixed wire part, the flexible circut board should ideally conform to the shape of the space into which it is being installed or be and remain in a planned fixed configuration in that space. This is desirable in order to avoid displacement and obstruction of other internal parts and to avoid physical contact with the walls of the container or instrument.

The prior art flexible circuit board devices have a tendency to move and displace as they attempt to revert to their original shape after placement into a fixed location, thereby creating the aforementioned problems. The structure of the present invention shown in Figure 2 overcomes these deficiencies by providing the necessary rigidity and conformity, while retaining an adequate amount of flexibility.

Referring now to a joint consideration of Figures 2 and 3, a flexible printed circuit board shown in Figures 2 and 3 has the same general components as in the prior art structure of Figure 1; a film or base sheet 6, a series of conductors 7 forming a circuit pattern thereon and a cover sheet or film 8 bonded by adhesive 9 to base sheet 6. Located longitudinally along and between the edge portions of the base and cover sheets 8 are two shape fixation members 10. These members 10 are made of a material such as metal or synthetic resin and shaped in the form of a circular rod. As shown in Figure 2, when the shape fixation members 10 are manufactured from conductive metal, the surrounding adhesive material 9 functions also as an insulating material for members 10.

The flexible circuit board having the above de scribed structure of Figures 2 and 3 is particularly suitable for use as a fixed wiring part by virtue of the plasticity of the circuit board shape fixation parts 10.

For example, when a flexible circuit board of the present invention is to be intalled in a shape resembling the letter "S" and the shape is to be kept fixed, all one has to do is to shape the board in conformity with the shape of the installation location as shown in Figure 3; the conforming shape is maintained thereafter by virtue of the plasticity of the circuit shape fixation members 10.

An alternative embodiment of the present invention is shown in Figure 4. This embodiment includes a film or base sheet 12, a series of conductors 13 forming a circuit pattern thereon and a cover sheet or film 15 bonded by adhesive 14 to base sheet 12.

Shape fixation members 16 similar to those described in Figure 2 are enclosed within and supported by edge covering members 18 which are attached longitudinally along the two respective edges of the circuit board by adhesive 17. The edge members 18 are made of an insulating synthetic resin material while the adhesive can be any type of conventional polymeric adhesive materials.

The flexible circuit board in Figure 4 has an advantage over the previously discussed embodiment in Figure 2, in that the shape fixation members 16 are attached to the sides of the circuit board by a separate edge members 18 instead of being incorporated within the main body of the board. Thus, the thickness of the circuit board will not have to increase in order to internally accommodate the added shape fixation members.

Another variation to the present invention is to locate the shape fixation members either only in the base sheet or only in the cover sheet. One illustration of this embodiment is shown in Figure 5 and includes a base sheet or film 20, a series of conductors 21 forming a circuit pattern thereon, an intermediate cover sheet 23 bonded by adhesive 22 to base sheet 20, two rectangular rod shaped fixation members 24 locked by adhesive 25 and embedded longitudinally in surface channel 23A along the respective edges of intermediate cover sheet 23, and an outer cover sheet 26 bonded by adhesive 27 to intermediate cover sheet 23. Although not shown, the embodiment in Figure 5 could have an equivalent structure whereby the rectangular rod shaped fixation members 32 are located in the base sheet 20.

The rectangular rod shaped fixation members of Figure 5 provide a lesser amount of flexibility and resilience after plastic deformation then in the previous embodiments utilizing the circular rod shape fixation members. Less resilience will, in turn, result in better shape stability after the installation of a flexible circuit board in a fixed wiring application.

Similarly, many other variations of the present invention may be desired depending on the particular circumstances. For example, the location of the shape fixation member may be altered and its configuration may be changed (i.e., rod shaped, tubular shaped, plate shaped, etc.).

It should also be noted that, while primarily intended to be used for fixed wiring applications, circuit boards of the present invention may, depend- ing on the nature and characteristics of the shape fixation member, retain enough resilience and flexibility to also be used as a movable wiring part. Thus, the present invention provides plasticity as well as flexibility to the conventional flexible circuit board and hence creates a flexible circuit which can be suitable as a movable wiring part as well as a fixed wiring part, thereby expanding the possibilities of uses and applications.

While preferred embodiments have been shown and described, various modifications and substitutions may be made thereto without departing from the spirit and scope of the invention. Accordingly, it is to be understood that the present invention has been described by way of illustrations and not limitation.

Claims

1. Aflexible circuit board having a base sheet with electrically conductive circuit means thereon, a cover sheet adhesively bonded to said base sheet, and shape fixation means incorporated in said flexible circuit board.

2. A flexible circuit board comprising a base sheet with electrically conductive circuit means thereon and shape fixation means incorporated in said flexible circuit board.

3. Aflexible circuit board according to claim 1 or 2 2wherein said shape fixation means is located longitudinally along the respective edge portions of said base sheet and said cover sheet.

4. Aflexible-circuit board according to claim 1,2 or 3 wherein said shape fixation means is located between said base sheet and said cover sheet.

5. A flexible circuit board according to claim 3 including edge elements adhesively attached to said base sheet and said cover sheet said edge elements being located longitudinally along the outside edges of said base sheet and said cover sheet; and said shape fixation means being within said edge elements.

6. Aflexible circuit board according to any of claims 1 to 4 including an intermediate sheet adhesively fixed between said base sheet and said cover sheet said intermediate sheet having a plurality of longitudinal channels, and said channels being geometrically shaped to receive and house said shape fixation means.

7. Aflexible circuit board accord to claim 6 wherein said shape fixation means is of rectangular rod shape, and said channels having a cooperating rectangular cross-sectional shape.

8. A flexible circuit board according to any of claims 1 to 5 wherein said shape fixation means is connected to said base sheet.

9. A flexible circuit board according to any of claims 1 to 5 wherein said shape fixation means has the shape of a circular rod.

10. A flexible circuit board substantially as hereinbefore described with reference to Figures 2 to 5 of the accompanying drawings.