CIRCUIT TO A CONNECTOR

Field of the Invention

This invention relates to a method for attaching a connector to a flexible and compliant electronic circuit to form a mechanical and an electrical interface between the flexible and compliant electrical circuit and another electrical circuit.

Background of the Invention

Conventional electronic circuits such as Printed Circuit Boards (PCBs) are made from rigid materials and there are many off-the shelf solutions for electrically and mechanically tethering them together either directly via a plug and socket for example, or by using a cable or cable assembly. Flexible Printed Circuit Boards (FPCs) are effectively thin PCBs that can mechanically bend but cannot stretch. FPCs have many connector options specifically designed for them, and, because they do not stretch, are compatible with many of the existing connector and cable solutions that have been designed for conventional PCBs.

New electromechanical circuits however are both flexible and compliant. It is highly desirable to be able to combine these circuits with conventional PCBs or FPCs in larger systems. For example, dielectric elastomers are

electromechanical devices that are made from elastomeric materials such as silicones, polyurethanes, or acrylic polymers, and can elastically stretch and deform by a factor of 2 or more relative to their original dimensions. These large stretches present a challenge when it comes to creating an electrical and mechanical interface with conventional PCBs or FPCs. Direct connection of a rigid connector component to a soft circuit creates a mechanical stress concentration that results in the interface degrading with repeated

mechanical cycling of the soft circuit, leading to mechanical and/or electrical failure of the connection.

It would therefore be of advantage to have a means for connecting a plug to a flexible and compliant circuit that enables it to be connected to a PCB or FPC which overcomes or at least ameliorates one or more disadvantages of the prior art, or alternatively to at least provide the public with a useful choice.

Definitions:

Compliant, a compliant material - a compliant material can bend, is able to stretch, and had a resilient character which returns this material to

approximately its initial size and shape after each occurrence of a bending or stretching action.

Disclosure of the Invention

According to one aspect of the present invention there is provided a flexible and compliant circuit formed from multiple layers of material which includes at least one support material bonded to at least one surface of the circuit, the support material defining functional apertures capable of receiving at least one tooth of a clamping connector so that the flexible and compliant circuit can be connected to another electrical circuit. According to a further aspect of the present invention there is provided a method of manufacturing a flexible and compliant circuit which includes the steps of i. covering at least one layer of electrically conductive material with a layer of encapsulation material, and

ii. bonding at least one support material to a layer of the circuit.

According to yet another aspect of the present invention there is provided a method of connecting a flexible and compliant circuit which includes the steps of i. clamping a first clamping connector around a support material bonded to one region of a layer of the circuit, and

ii. clamping a second clamping connector around a support material

bonded to another region of a layer of the circuit. Preferably the first and second connectors are connected to support materials bonded to the same layer of the circuit.

Preferably at least one tooth of a connector is inserted through a tooth aperture defined by the support material during clamping of the connector around the support material.

The present invention seeks to provide a simple and effective method for bonding a support material with functional apertures to the flexible and compliant circuit, and attaching a clamping style connector to the resultant layered structure so that the flexible and compliant circuit can be electrically and/or mechanically connected to another electrical circuit.

A flexible and compliant circuit provided by the invention can bend, is able to stretch, and had a resilient character which returns this material to

approximately its initial size and shape after each occurrence of a bending or stretching action.

Reference and general throughout the specification will be made to the invention providing a flexible and compliant circuit. References are also made to invention providing a soft circuit where those skilled in the art will appreciate that these terms refer to the same form of circuit.

Preferably a flexible and compliant circuit provided by the invention includes a layer of electrically conductive material covered by a layer of encapsulation material.

Preferably, the flexible and compliant circuit has electrical connections that are exposed on at least one surface. For example in some preferred embodiments at least one portion of the layer of conductive material is exposed on at least one exterior surface of the circuit.

Electrical connections for the circuit may be exposed by the provision of a slit or aperture formed in any circuit layers which cover a layer of electrically conductive material to be contacted. The slits or apertures formed in covering layers of the circuit therefore allow contacts or contact areas to be exposed to the making of which were connections.

In a preferred embodiment a support material may be bonded to a layer which forms at least part of the exterior surface of the circuit.

However in other alternative embodiments a support material may be bonded to an internal layer of the circuit, with the support material covered by an intervening additional layer.

Reference in general throughout the specification will primarily be made to a flexible and compliant circuit provided by the invention including two support materials bonded to the same exterior surface of the circuit.

However those skilled in the art will appreciate that in other embodiments potentially one, or three or more supporting materials may be integrated into a circuit provided in accordance with the present invention.

Furthermore, those skilled in the art will also appreciate that a supporting material need not necessarily be bonded to the exterior surface of a circuit, nor do the circuit's supporting materials need to be bonded to the same layer of the circuit. In addition various alternative circuit geometries other than the provision of support materials at opposite ends of the circuit are also envisioned and within the scope of the invention.

Preferably the support material is bonded to a layer of the circuit using the same compound used to form a layer of the circuit.

Preferably, a support material has a higher stiffness than a layer of the circuit it is bonded to. For example in some embodiments, a PET support material (for example) can be bonded to one (or both) sides of the exterior surface of flexible and compliant circuit.

Preferably the support material is formed from plastic. Preferably, the support material is thin and flexible.

Preferably the support material is formed into a flat sheet which defines a plurality of functional apertures.

Preferably, a support material employed with a circuit is resistant to stretching forces. Preferably this support material resists stretching forces applied substantially perpendicular to the major surface of the support material.

Preferably, a support sheet defines one or more functional rivet apertures that facilitate the bonding of the support layer to the flexible and compliant circuit through the formation of soft rivet-like structures. Preferably the support material defines one or more functional tooth apertures arranged to receive at least one tooth of a clamping connector. In particular, a support sheet may define one or more functional tooth

apertures arranged to align with exposed electrical connections of the circuit. In a preferred embodiment a clamping connector may clamped around the support material and the exposed electrical connections of the soft circuit. A mechanical connection is created by elements of the connector clamping around the support material when the connector is placed in a closed configuration. An electrical connection is created by at least one tooth of the connector penetrating a tooth aperture and the exterior surface of the circuit to contact a layer of electrically conductive material of the circuit.

Various forms of clamping connector may be used with the invention. For example in some embodiments a pivoting double jaw clamping connector may be used which deploys two jaws presenting set of opposing projecting teeth, where the jaws are moved towards each other when the connector is to be closed. Reference throughout this specification will also be made to various embodiments of the invention employing this form of clamping connector, described as a clincher-style connector.

However in alternative embodiments a clamping connector may be formed from a crimping style connector which includes a single base plate from which a number of projecting teeth extend. These teeth may initially project substantially perpendicular to the base plate when in an open configuration, and may be bent over towards the base plate when placed in a close configuration to clamp the teeth and base plate around a substrate or layer of material.

In some embodiments a circuit provided by the invention may also include at least one clamping connector. Preferably the teeth of the connector deform or are deformed when placed in a closed configuration. In one further preferred embodiment when placed in a closed configuration the teeth of the connector come into contact with an opposing jaw of the connector and deform to grip the circuit. Alternatively, in other embodiments the invention may employ a connector other than a clincher-style connector, but which has teeth that are capable of penetrating the flexible and compliant circuit, and that are capable of protruding through the aperture in the support material. Those skilled in the art will appreciate that any equivalent clamping connector may be used to grip the support material in order to create both a secure mechanical connection between the connector, the flexible and compliant circuit, and the support layer, and to create a firm contact between the connector and the electrical connection of the flexible and compliant circuit, may be used without departing from the scope of the invention.

Reference throughout this specification will in general be made to the invention using a clincher clamping jaw connector to make both mechanical and electrical connections with a soft circuit. However those skilled in the art should appreciate that other forms of clamping connectors may be used with the invention and reference to the above only throughout this specification should in no way be seen as limiting.

Preferably, the mechanical connection between the connector and the support material prevents the flexible and compliant circuit from deforming around the electrical connection between the connector and the exposed electrical connection of the flexible and compliant circuit, thus limiting the potential for significant cyclical deformation of the soft circuit around the connection between connector and flexible and compliant circuit, thus substantially reducing the opportunity for the electrical connection to degrade. Preferably, the functional apertures for the teeth of the clincher prevent the act of closing the jaws of the clincher from tearing and/or otherwise damaging the electrical connections of the soft circuit due to warping of the flexible and compliant circuit or support material layer, skewing of the upper jaw of the clincher relative to the lower jaw, or improper penetration of the clincher's teeth, for example.

Preferably a layer of electrically conductive elastomer covers the areas of the connector and the exterior surface of the circuit which are in contact with one another.

Preferably the material used to cover the contacting areas of the connector and the exterior surface of the circuit is formed from the same material used to form a layer of electrically conductive material of the circuit. For example in some preferred embodiments the connection between the flexible and compliant circuit and the connector is further reinforced with the addition of an electrically conductive elastomer or similar material over the join between the clincher and the flexible and compliant circuit. Those skilled in the art will appreciate that the flexible and compliant circuit provided by the invention can be readily mechanically and electrically connected to a further circuit or component. A user simply needs to attach a first clamping connector around a first - preferably sheet like - support material while ensuring a tooth or teeth of the connector penetrates through the tooth apertures of this support material sheet. The user can then attach a second clamping connector around a second support material sheet while again ensuring a tooth or teeth of the second connector projects through the tooth apertures of the second support material sheet. These support material sheets may be bonded to the same layer of the circuit, or may be bonded to different layers if required. Brief description of the drawings

Additional and further aspects of the present invention will be apparent to the reader from the following description of embodiments, given in by way of example only, with reference to the accompanying drawings in which :

Figure 1 : shows a schematic diagram of the basic structure of an example of flexible and compliant circuit: a dielectric elastomer

Figure 2: shows a schematic diagram of one embodiment of the invention providing a dielectric elastomer strip with intermediary support material sheets bonded to each end in the unstretched state (left), and stretched state (right)

Figure 3a, 3b: show schematic diagrams of a "clincher"-style connector used in some embodiments when in open and closed configurations

Figure 4a, 4b: show a schematic diagram of a crimping style connector used in alternative embodiments in open and closed configurations.

Figure 5a 5b, 5c: show examples embodiments of the structure of support sheet materials and a single layer dielectric elastomer that is built up of several layers.

Figure 6a, 6b, 6c: Show exploded views of a dielectric elastomer sensor

fabricated from the layers described in Figure 5a, 5b, 5c.

Figure 7a, 7b: Show cross-section views of an embodiment which uses

clincher connectors clamped onto the dielectric elastomer of each terminal of a two terminal DE sensor.

Figure 8: Shows an embodiment with the addition of electrically conductive material over the join between the connector and the electrical connection of the dielectric elastomer sensor.

Figure 9: Provides a cross-sectional view of one embodiment where rivet like structures are formed by the material used to bond support material sheets to the dielectric elastomer flowing through the functional rivet apertures of the sheets Figure 10a, 10b, 10c: Provide views of the different forms of support material sheet used in the embodiments illustrated in figures 5 and 6.

Further aspects of the invention will become apparent from the following description of the invention which is given by way of example only of particular embodiments.

Best modes for carrying out the invention A type of flexible and compliant circuit that demonstrates enormous potential as a technological platform is the dielectric elastomer (DE). DEs are soft electromechanical transducers that can be used as actuators, sensors, or power generators. Figure 1 shows the basic structure of a DE in the form of an insulating soft polymer 1 sandwiched between compliant electrodes 2.

The invention is described throughout this specification as being

implemented as part of a DE sensor, but could equally be applied to DE actuators or generators, or other flexible and compliant electrical circuits. DE sensors are low stiffness, high strain devices that are ideally suited for the instrumentation of flexible and compliant structures such as the human body, for example. The electrical parameters of a DE sensor, such as its capacitance of electrode resistance for example, are intimately coupled to the mechanical state of the DE. By sensing these parameters while the DE is deforming, information can be derived regarding the deformation itself.

With any sensor however, it is important to have a robust method for attaching the sensor to the substrate to be measured. Figure 2 shows a DE sensor 3, configured as a narrow strip, with intermediary supports materials 4 bonded to either end to facilitate the attachment of the sensor to an underlying substrate.

Preferably, the intermediary supports 4 are fabricated from a thin, flexible material that has a higher stiffness than that of the DE sensor itself, such as PET or polyimide for example. As a result, when the DE sensor goes from the unstretched state (Figure 2, left) to the stretched state (Figure 2, right), the deformation primarily occurs in the DE sensor and not the support materials 4. Consequently, this typically results in the necking illustrated at the interface between the support and DE sensor.

As well as attaching the sensor to a substrate, it is also important to be able to make an electrical connection to the sensor.

Figure 3a, 3b illustrate a common clincher jaw style connector used in the description of the present invention. Clinchers are electrical connections consisting of an open set of jaws 5 with teeth 6. Using the method of the invention a thin substrate to which an electrical and mechanical connection is desired is inserted into the jaws, and the jaws are clamped shut. The teeth penetrate the substrate before deforming in a manner similar to that of a common staple for fastening sheets of paper so that the jaws and/or teeth grip the substrate to prevent it from being released.

At the same time the jaws clamp the substrate, forming a robust electrical and mechanical connection between the clincher and the substrate. Figure 3a is a detail view of a single clincher connection in the open state (top view) and while figure 3b shows the clincher in a closed state (bottom view). As the jaws come together, the teeth of clincher come into contact with the opposing jaw and deform to grip the substrate. Figures 4a, 4b show a schematic diagram of a crimping style connector used in alternative embodiments in open (figure 4a) and closed configurations (figure 4b). With this form of a crimping connector a single base plate 5 is provided instead of the upper and lower jaws of a jaw style clamping connector as discussed with respect figure 3. A number of projecting teeth 6 extend from the base plate 5.

In the open configuration these teeth are orientated substantially

perpendicular to the base plate, allowing the teeth to project through to the apertures formed in a support material. In a close consideration these teeth are crimped or bent over to clamp in place a substrate layer between the teeth and base plate. In this embodiment cropping or ending of the teeth is completed with the assistance of an additional handle (not shown) such as for example a set of pliers.

As referenced above, alternative connectors other than a clincher connector, but that have teeth that are capable of penetrating the flexible and

compliant circuit, and that are capable of protruding through the aperture in the support material, and that preferably deform when crimped/installed to grip the support material in order to create both a secure mechanical connection between the connector, the flexible and compliant circuit, and the support layer, and to create a firm contact between the connector and the electrical connection of the flexible and compliant circuit, will be apparent to those skilled in the art and may be used without departing from the scope of the invention. Such connectors are available from manufacturers such as Nicomatic, FCI Connect, and TE Connectivity, for example.

Figures 5a-c and 6a-c disclose three example embodiments illustrating the several of the layers of a DE suitable for use with the present invention. Figure 5 provides a cross section view of each embodiment while figure 6 provides a corresponding expanded view after assembly of the

corresponding embodiment.

The basic DE itself consists of five layers: a long base layer 7 made from an electrically insulating elastomeric material, such as silicone for example; a first electrode 8 made from an electrically conductive compliant material that has a small protrusion 9 defined at one end for making an electrical connection; a short elastomeric dielectric layer 10 that covers the first electrode 8 but leaves the small protrusion 9 of the first electrode exposed; a second electrode 11 with a small protrusion 12 for making an electrical connection that is offset from the protrusion 9 of the first electrode 8 to prevent the second electrode 11 from electrically contacting the first electrode 8; and a final, short, electrically insulating elastomeric material 12 that covers the second electrode 11 but leaves both the first and second electrode protrusions 9, 12 exposed. Additional layers can be added to modify the nominal parameters of the DE.

Attached to the base of this DE structure is a pair of intermediary support material sheets 13, which are made from the thin flexible material PET. The sheets 13 are adhered to the base layer 7 of the DE using the same material as that used to make the base layer - being silicone in this embodiment. Functional apertures 14 in the sheets 13 serve two purposes: they allow the adhesive to flow through the sheet to form a soft rivet structure for enhanced mechanical robustness (provided by a functional rivet aperture); and they enable a connector to be crimped or clamped shut without the teeth having to penetrate the relatively hard sheet material and warping and/or damaging the DE or the sheet in the process (provided by a

functional tooth aperture).

The embodiment shown with respect to figures 5a, 6a includes a pair of support material sheets 13a, 13b. These sheets are discussed in further detail with respect to figures 10a and 10b. As can be seen from figures 5a, 6a each different sheet of support material is bonded to the exterior surface of the base layer 7 and defines both tooth and rivet functional apertures, as discussed further with respect to figures 10a, 10b.

The embodiment shown with respect to figures 5b, 6b includes a pair of support material mesh sheets 13c. Again each sheet is bonded to the exterior surface of the base layer. These sheets are discussed in further detail respect to figure 10c.

The embodiment shown with respect to figures 5c, 6c again includes a pair of support material sheets 13a, 13b as discussed in further detail with respect to figures 10a and 10b. These sheets are bonded to the internal elastomeric dielectric layer 10 of the circuit, and are covered by the interviewing layers of the circuit.

Figures 7a, 7b illustrate how a clincher jaw connector makes an electrical and mechanical connection with the DE. For comparison cross section schematics of a clincher attaching to each of the two exposed electrical connections of the example DE sensor structure are described in Figure 5 a-c are provided for comparison. As shown by figure 7a, by crimping the clincher jaws shut, the intermediary support provided by support sheet 13, base layer 7 and the exposed area of electrode 11 are clamped together, and the upper jaw 5 of the clincher is pressed in firm contact with the exposed electrical connection protrusion 12 of the electrode 11. Figure 7b illustrates the connection made in respect of the uppermost electrode 8 and associated connection protrusion 9. The teeth 6 of the clincher pass through the functional tooth aperture 14a in the support sheet 13 and deform once they come into contact with the opposing jaw 5. The tooth apertures in the support sheet prevents the teeth from being deformed prematurely, which can result in undesirable effects such as warping of the support sheet, damage to the electrode connection or base layer, or failure of the clincher to properly secure the DE, for example.

Figure 8 is a simple illustration of applying additional electrically conductive material 8a to the join between the jaw of the clincher 5 and the electrode 8 connection to create a more robust electrical and mechanical connection. In this embodiment the conductive material used is the same material as that used to produce the electrodes.

Figure 9 illustrates the formation of elastomer rivets 15 that occur when the adhesive used to bond the intermediary support sheets to the base layer 7 of the DE is allowed to flow through the functional rivet apertures 14b in the sheets. In the current embodiment the same material is used to adhere the sheet as was used to form the base layer, so the sheet is effectively absorbed into the base layer, improving the robustness of the mechanical connection between sheet and DE and helping to prevent delamination of the DE from the sheet when the DE is deformed.

Figures 10a, 10b and 10c illustrate support material sheets used in three different embodiments of the invention.

Fig 10a and 10b show enlarged views of the support material sheets deployed in the embodiments discussed with respect to figures 5a, 6a and figures 5c, 6c. Each of these support material sheets defined a number of functional apertures including tooth apertures 14a and rivet apertures 14b.

Fig 10c show an enlarged view of the support material mesh sheet 13c deployed in the embodiments discussed with respect to figures 5b, 6b. The mesh used to form the support material defines a regular array of apertures rivet aperture.

Fig lOd shows an enlarged view of a support material sheet 13d provided in accordance with a further embodiment of the invention where the sheet defines a number of regular functional apertures 14. In this application the functional apertures shown may perform as both rivet and tooth apertures.

In the preceding description and the following claims the word "comprise" or equivalent variations thereof is used in an inclusive sense to specify the presence of the stated feature or features. This term does not preclude the presence or addition of further features in various embodiments.

It is to be understood that the present invention is not limited to the embodiments described herein and further and additional embodiments within the spirit and scope of the invention will be apparent to the skilled reader from the examples illustrated with reference to the drawings. In particular, the invention may reside in any combination of features described herein, or may reside in alternative embodiments or combinations of these features with known equivalents to given features. Modifications and variations of the example embodiments of the invention discussed above will be apparent to those skilled in the art and may be made without departure of the scope of the invention as defined in the appended claims.