Flexible electrical connectors

Abstract: A flexible electrical connector 1 connects two rigid members, a plug 2 and printed circuit board 3. The connector 1 has a tendency to produce a tear 16, but by including reinforcing thread members 12 and 13 between two layers 8 and 9 of the connector 1, the tear 16 is prevented from growing further.

Description: This invention relates to flexible electrical connectors, i.e. connectors which comprise a flexible insulating material bearing a conductive track. FR-A-2 524 759 discloses an electrical connector in which stiffening members are included to hold it in a desired configuration. EP-A-0 066910 describes an electric cable in which continuous mechanical elements are included for absorbing longitudinal tractional forces. The use of flexible electrical connectors is particularly advantageous where electrical connections must be made between two rigid members in a confined volume, since a desired arrangement of the members may be more readily realised. More efficient use of the available space may thus be achieved than if a rigid connector is used, or the members to be connected are placed immediately adjacent to one another. However, the insulating material can be prone to tearing, and a tear, once started, may continue across a great portion of the material, and also across the conductive track or tracks carried by it. Such a tear may be difficult and expensive to repair and could entail the dismantling of one of the connected parts. This might be a printed circuit board of a type which has a continuation of the flexible connector sandwiched between rigid sheets carrying circuitry and components. If the tear occurs near the printed circuit board it may be necessary to remove the components it carries to effect a repair, and in doing so, the components are almost inevitably damaged, or at least may be tested to ascertain whether any damage has been sustained. In fact it may be more economical in these circumstances to reject the printed circuit board and flexible connector rather than attempt to repair the tear, and to fit a new board and connector, even though this may be expensive, costing perhaps, hundreds of pounds. The inventor has now realised that this problem can be overcome in a very simple and inexpensive way. According to a first aspect of the invention there is provided a flexible electrical connector comprising a layer of insulating material bearing a flat thin conductor characterised by a flexible reinforcing thread attached to a surface of the layer between one edge thereof and the conductor, the thread being of greater strength against tearing than the conductor and being sufficiently flexible not to impair the flexibility of the connector. Preferably, there are two layers of insulating material having a conductor between them. The member may be secured along its whole length or along only part of its length and may be readily incorporated in the connector with little disruption to the techniques applied in manufacturing conventional flexible connectors. Where there are two layers, the member may be located between them or may be present on a surface of one layer which does not face the other layer. It could be present on the same surface of the layer as the conductor or on the other surface of the layer. The thread may be a single fibre or a plurality of twisted fibres or yarn. It could be of a natural material or synthetic, such as nylon, and preferably it is of an aromatic polyamide, such as Kevlar (Registered Trade Mark). A thread can have great strength and yet is flexible so that it does not impair the flexibility of the connector. The use of a thread, i.e. an elongate member having substantially circular cross-section, is of particular significance, in that it is likely to be more resistant to tearing than other possible reinforcing members in the form, for example, of flat strips etc. It is preferred that the reinforcing thread is attached along substantially its entire length to a layer of insulating material, although it could be secured only at spaced points along its length. Preferably the thread is attached to one layer of insulating material by adhesive, which may, for example, be a heat setting adhesive, in which case the thread must be of a type undamaged by the heat required during manufacture. Preferably the two layers of insulating material are a polyimide, such as Kapton (Registered Trade Mark). Apparatus may include a connector as described above to connect a rigid member having electrical circuitry to other circuitry. A method of manufacturing a flexible electrical connector includes: taking a sheet of insulating material having adhesive on one surface thereof; taking a sheet of insulating material having a conductor on one surface thereof; arranging the surfaces of the sheets having adhesive and the conductor thereon to face each other; characterised by placing a reinforcing elongate member between them , the member being of greater strength against tearing than the conductor and being sufficiently flexible not to impair the flexibility of the connector; and bringing them together. Preferably the conductor is defined by etching a layer of conductive material initially present on the sheet. Also preferably the sheets and the member are bonded by heating them when they are brought together to heat set the adhesive. One way in which the invention may be performed is now described by way of example, with reference to the accompanying drawings, in which: Figure 1 shows schematically, and partially broken away, a flexible electrical connector in accordance with the invention; and Figure 2 illustrates the manufacture of the flexible connector of Figure 1, like parts having like references throughout. With reference to Figure 1, a flexible electrical connector 1 is arranged to electrically connect two rigid members, a plug 2 and a printed circuit board 3, the surface of which carries various components and inter-connecting tracks 4 which are only schematically indicated. The printed circuit board 3 includes a continuation 5 of the flexible connector 1 sandwiched between two rigid sheets 6 and 7. The flexible connection comprises first and second layers 8 and 9 of Kapton (Registered Trade Mark), which is an insulating material, held together by an intermediate adhesive layer 10 (shown cross-hatched), and, sandwiched between the Kapton layers 8 and 9, a plurality of copper conductors 11 and two reinforcing thread members 12 and 13. The reinforcing thread members 12 and 13 are of Kevlar (Registered Trade Mark), which is a a strong, flexible material capable of withstanding the temperature required to heat set the adhesive during manufacture. One thread member 12 is positioned substantially parallel to and between the top edge 14 of the connector 1 as shown and the conductor 11A nearest to it, and the other member 13 is positioned between the bottom edge 15 of the connector and the conductor 11B, which is closest to it. A tear 16 is shown as having developed in the connector 1 from its top edge 14 and close to the printed circuit board 3. This is a common place for a tear to occur in this arrangement, for example during assembly, even a slight twist between the printed circuit board 3 and connector 1 being liable to result in a tear. The tear 16 only extends downwards as far as the top thread member 12, which, because of its resistance to tearing, prevents the tear 16 from growing further, which it would otherwise do, and hence eliminates the need for any costly and difficult repairs. In manufacturing the flexible connector 1, the second layer 9 prior to assembly as shown in Figure 2, has copper laid down on one surface which is etched, using conventional techniques to obtain the desired conductors 11. The first layer 8 has a heat-setting adhesive layer 10 on its surface which is arranged to face the conductors 11. The first and second layers 8 and 9 are brought together and the thread members 12 and 13 inserted between them in the correct position. Heat is then applied to cause the adhesive to bond together the two layers 8 and 9 and the intermediate thread members 12 and 13, and conductors 11. Although in the embodiment described above with reference to Figures 1 and 2 the reinforcing thread members 12 and 13 are substantially the same length as the strip of flexible electrical connector 1 between the two rigid members 2 and 3, they could be shorter. This might be the case where a particular portion of a certain configuration of flexible connector tends to tear, the flexible reinforcing member being included at that portion only. For example if the flexible connector includes a right angled bend the reinforcing member could be present across the turn and for a short distance on either side of it only. In an alternative embodiment (not shown) the flexible reinforcing member could be secured to one surface of an insulating layer, the other surface of which is adjacent a second insulating layer, with a conductor being present between the two layers. The flexible reinforcing member could be secured by adhesive or by some other means, such as a further insulating layer placed over it.

Claims: A flexible electrical connector comprising a layer (9) of insulating material bearing a flat thin conductor (11), of the type formed by printed circuit and similar techniques, characterised by a flexible reinforcing thread (12, 13) attached to a surface of the layer (9) between one edge thereof and the conductor (11), the thread (12, 13) being of greater strength against tearing than the conductor (11) and being sufficiently flexible not to impair the flexibility of the connector. A flexible connector as claimed in claim 1 comprising two layers (8, 9) of insulating material having the conductor (11) between them. A connector as claimed in claim 1 or claim 2 wherein the thread is a single fibre. A connector as claimed in claim 1 or claim 2 wherein the thread comprises a plurality of twisted fibres. A connector as claimed in any preceding claim and wherein the thread (12, 13) is attached along substantially its entire length to one layer of insulating material. A connector as claimed in any preceding claim and wherein the thread (12, 13) is of Kevlar (Trade Mark). A connector as claimed in any preceding claim and wherein the thread (12, 13) is attached to one layer (8) of insulating material by adhesive (10). A connector as claimed in any preceding claim and wherein the conductor (11) is defined by etching a conductive material deposited on one layer of insulating material. A connector as claimed in any preceding claim and wherein the conductor (11) is of copper. A connector as claimed in any preceding claim and wherein the layer or layers (8, 9) are of Kapton (Trade Mark). Apparatus including a rigid member (3) having electrical circuitry (4) connected to other circuitry by a connector (1) as claimed in any preceding claim.

Inventors: SMITH ARTHUR RONALD, SMITH, ARTHUR RONALD
Applicants: GEN ELECTRIC CO PLC, THE GENERAL ELECTRIC COMPANY, P.L.C.
Application year: 1985
Main classification: H01R9
IPC codes: H05K1, H01R12, H05K3, H01B7