GB2562770A

GB2562770A - An electrical circuit

Info

Publication number: GB2562770A
Application number: GB1708368.4A
Authority: GB
Inventors: Youdan Paul
Original assignee: Jaguar Land Rover Ltd
Current assignee: Jaguar Land Rover Ltd
Priority date: 2017-05-25
Filing date: 2017-05-25
Publication date: 2018-11-28
Also published as: GB201708368D0

Abstract

An electrical circuit is described, which may be used to connect flat cables in a wiring harness 14 of a vehicle. An opening 15 is formed in a substrate. A first electrical conductor 20 is arranged onto a first surface 22 of the substrate. A second electrical conductor 24 is arranged onto a second surface 26 of the substrate. Each electrical conductor covers at least part of the opening 15. At least one electrical conductor is arranged to extend within the opening 15, to make contact with the other electrical conductor, and to form an electrical connection 32. A three dimensional electrical circuit is formed. The conductors may be fused together at the point of contact by heating, soldering, spot welding or ultrasonic welding. A sealer may fill the opening, preventing environmental contamination, and stiffening the electrical circuit. The electrical conductors 20,24 may be thin copper foil or aluminium. The substrate may be an elongate flexible film of polymer engineering material.

Description

(54) Title of the Invention: An electrical circuit

Abstract Title: An electrical circuit formed by contacting two electrical conductors arranged on different faces of a substrate through an opening in the substrate (57) An electrical circuit is described, which may be used to connect flat cables in a wiring harness 14 of a vehicle. An opening 15 is formed in a substrate. A first electrical conductor 20 is arranged onto a first surface 22 of the substrate. A second electrical conductor 24 is arranged onto a second surface 26 of the substrate. Each electrical conductor covers at least part of the opening 15. At least one electrical conductor is arranged to extend within the opening 15, to make contact with the other electrical conductor, and to form an electrical connection 32. A three dimensional electrical circuit is formed. The conductors may be fused together at the point of contact by heating, soldering, spot welding or ultrasonic welding. A sealer may fill the opening, preventing environmental contamination, and stiffening the electrical circuit. The electrical conductors 20,24 may be thin copper foil or aluminium. The substrate may be an elongate flexible film of polymer engineering material.

At least one drawing originally filed was informal and the print reproduced here is taken from a later filed formal copy.

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06 18

FIG. 1

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FIG. 2

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FIG. 3

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FIG. 4

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FIG. 5

AN ELECTRICAL CIRCUIT

FIELD OF THE INVENTION

The present disclosure relates to an electrical circuit and particularly, but not exclusively, to a method of manufacture of an electrical circuit. In particular, but not exclusively, the disclosure relates to a method for use in the manufacture of an electrical circuit for use in a vehicle. Aspects of the invention relate to an electrical circuit, a method of manufacture, an electrical harness and a vehicle incorporating such an electrical circuit or electrical harness.

BACKGROUND OF THE INVENTION

Flexible wiring or cabling is used extensively in modern vehicles to electrically connect the various systems of the vehicle with associated controllers. As the number of vehicle systems increases in modern vehicles so too does the complexity of the internal wiring, which must connect each of these systems together. In an attempt to reduce the complexity, improve packaging, and cost, of a vehicle’s internal wiring, flat cabling is increasingly being employed as a substitute for conventional insulated copper wires. Flat cables typically comprise a metal conductor sandwiched between two insulating substrates to form a uniform thin film. As with conventional wiring systems, it is necessary to join two or more sections of flat cabling together in order to construct an assembly of a suitable shape and/or length, and to provide the necessary electrical connections between different wiring paths.

An electrical connection is typically formed between two or more flat cables by first cutting, etching or drilling through the insulating substrate to expose the underlying conductive layer. The cables are then overlaid on top of each other to form a vertical stack. The holes in each cable are aligned to form vertically integrated access holes (VIAs) through which the conductive layers can then be joined together in order to form an electrical connection. The VIAs are then covered by either a soldering or an electroplating technique in order to form the necessary connection between the conductive layer on either side of the hole.

These methods for connecting the conductive layers of adjacent cables rely on the use of destructive processing techniques to remove at least one layer of insulating material so that an electrical connection can be formed between the conductive layers housed within the cables.

Insulation displacement riveting, or crimping, is often used to form the VIAs between the conductive layers of stacked cables. A significant drawback with this technique is that it is only able to form connections with a small contact area. The build-up of crimped insulating material causes an increase in the impedance of the connection between the conductive layers, thereby limiting this type of connection to low power applications. It can also reduce the robustness of the connection over time.

A typical soldering technique requires the use of substrate materials that withstand intense localised temperatures (e.g. polyesters). These materials are expensive which limits their applicability for use in circuits for use over large areas. Electroplating also requires the use of environmentally damaging chemicals or catalysts.

Metal laminating techniques are also used to form a connection between the conductive layers. However, this technique also requires the use of high temperatures in order to allow the metallic conductive layers to flow through the VIA to form a connection. This requires that the underlying substrate material is made from expensive heat resistant material in order that it can withstand the high temperatures associated with the metal laminating process.

It is an object of at least one embodiment of the present invention to address the aforementioned disadvantages of the prior art and to provide an improvement upon known methods.

SUMMARY OF THE INVENTION

Aspects and embodiments of the invention provide an electrical circuit, a method of manufacture, an electrical harness and a vehicle as claimed in the appended claims.

According to an aspect of the invention, there is provided a method of manufacturing an electrical circuit comprising the steps of: forming an opening in a first substrate, providing a first electrical conductor onto a first face of the first substrate to cover at least a part of the opening, providing a second electrical conductor onto a second face of the first substrate to cover at least a part of the opening; and arranging, at least one of the first electrical conductor and the second electrical conductor, at least partially within the opening in the first substrate to make contact with the other of the first electrical conductor and the second electrical conductor, thereby to form an electrical connection therebetween.

The openings define vertical connections between the horizontal conductors laid out on the substrate. Forming the electrical connection between the electrical conductors through the opening in the substrate creates a three dimensional electrical circuit. This allows a connection to be made from one side of the electrical circuit to the other, i.e. across the width of a given substrate, without disrupting the path of the second conductor. Advantageously, this can provide a greater number and variety of connections to be provided within a single electrical circuit without having to introduce an additional cable or wire. Advantageously, the enhanced dimensionality of the electrical circuit provides a means of connecting together a plurality of different electrical components using a single circuit assembly. In this way, the physical dimensions of the electrical circuit may be reduced whilst increasing the possible number of connections provided therein. The reduced physical dimensions mean that the electrical circuit can be more easily accommodated within the tight packaging requirements of a vehicle.

The formation of the hole prior to attaching the conductor means that conductors can be fused together by point application of fusing techniques, such as soldering or welding, through the hole. This advantageous method ensures that the adverse temperatures associated with the fusing techniques are localised on the conductors such that the substrate materials are not affected. This means that low temperature substrate materials can be used, which thereby reduces the cost of manufacturing the electrical circuit.

The method of forming the opening may occur prior to providing the first and second electrical conductor onto the first substrate.

The method may comprise arranging the second electrical conductor onto a first face of a second substrate.

The method may comprise forming an opening in the second substrate prior to arranging the second electrical conductor onto the first face of the second substrate

The method may comprise at least partially aligning the opening of the first substrate with the opening of second substrate prior to forming the electrical connection.

The method may comprise providing a third electrical conductor onto a second face of the second substrate.

The third electrical conductor may be configured to be arranged at least partially within the opening in the second substrate to form an electrical connection with one or more of the first and second electrical conductor.

The third electrical conductor may be configured to be arranged at least partially within the opening in the second substrate and the second conductor is configured to be arranged at least partially within the opening in the first substrate to form an electrical connection with the first electrical conductor.

Forming the electrical connection may comprise applying heat at the contact between the conductors to fuse the electrical conductors together. Heat may, thereby, be applied at the interface formed between the conductors. The step of forming the electrical connection may comprise spot-welding or ultrasonic-welding the electrical conductors together. A contact may be formed in this way between the first and second substrate, between the first and third conductor and/or between the second and third conductors.

The method may comprise arranging both the first and second conductors at least partially within the opening in the first substrate prior to forming the electrical connection. The first and second conductors may be protruded through the opening in the first substrate prior to forming the electrical connection.

The method may comprise filling the opening with a sealant following the formation of the electrical connection. The method may comprise filling the opening in the first substrate with a sealant following the formation of the electrical connection. The method may comprise filling the opening in the second substrate with sealant following formation of the electrical connection.

The sealant may be configured to flow in to the opening in the substrate when heat and pressure is applied to it by an external source. Upon application of the heat and pressure, excess sealant is caused to flow into the opening and thereby fill in the spaces around an adjoining region of the conductors.

Once the sealant has set it forms a protective barrier which prevents ingress of environmental contaminants into the opening. The sealant also helps to stiffen the region of the electrical circuit around the opening and provides stability to the electrical connection, or junction, formed therethrough. The sealant also reduces the susceptibility of the electrical circuit to vibration stress which may otherwise stress the electrical interconnections to fracture if they were left unsupported.

The method may comprise providing at least one outer surface of the electrical circuit with a stiffening substrate following the step of forming the electrical connection.

In some embodiments, the sealant may be added to the stiffening substrate before it is applied to the electrical circuit. Hence, the filling of the opening with a sealant may be carried out during the provision of at least one outer surface of the electrical circuit with a stiffening substrate.

The step of forming an opening may comprise at least one of hole-punching, drilling, lasercutting and drilling.

The method of providing at least one electrical conductor onto a substrate may comprise laminating.

Advantageously, laminating two of more substrates together to form a single assembly means that the electrical circuit can be more easily protected against the adverse effects of vibration, abrasion, and moisture, which it may experience during a lifetime of use within a vehicle. Furthermore, a single electrical circuit is easier for an installer to install into a vehicle compared to a bundle of multiple separate cables as is commonly the case with conventional cable harnesses. Consequently, the time taken to install the electrical circuit is decreased and the manufacturing process can be more easily standardised.

In one embodiment, the method comprises arranging the second electrical conductor onto a first face of a second substrate. A third electrical conductor may be provided onto a second face of the second substrate. An opening may be provided in the second substrate prior to arranging the second electrical conductor onto the first face of the second substrate.

The third conductor may be arranged upon a face of the second substrate which opposes the face of the second substrate on which the second conductor is arranged. Thus, the electrical circuit is configurable such that it defines a stacked construction of multiple conductors, which can be connected together in a variety of different configurations in order to form electrical connections between multiple components of the vehicle. For example, a hole in the first substrate and a hole in the second substrate may be aligned such that an electrical connection is formed between the first, second and third electrical connectors.

According to a further aspect of the invention there is provided an electrical circuit comprising: a first substrate comprising an opening; a first electrical conductor arranged onto a first face of the first substrate to cover at least a part of the opening; and a second electrical conductor arranged onto a second face of the first substrate to cover at least a part of the opening; wherein at least one of the first electrical conductor and the second electrical conductor is configurable to be arranged at least partially within the opening in the first substrate to make contact with the other of the first electrical conductor and the second electrical conductor, thereby to form an electrical connection therebetween.

At least one of the first and second electrical conductors may be a substantially flat cable.

The thickness of at least one of the first and second substrates may be dependent on the diameter of the opening formed in the respective substrate. Alternatively, the diameter of an opening formed in at least one of the first and second substrates may be dependent on the thickness of the respective substrate. At least one of the first and second substrates may have a thickness of between 0.1mm and 5mm. The thickness of the substrate may be dependent on the material from which at least one of the first and second conductors is formed.

The first substrate may be flexible. The substrate may be a flexible thin film. The inherent flexibility of the substrates allows the electrical circuit to more easily conform to the curved and non-uniform surfaces of a vehicle interior. It also enables the electrical circuit to bend and flex in response to external stresses being applied to it when in use, which may otherwise increase the risk of shorts forming in the electrical circuit.

The first and or second substrate may be formed from an engineering polymer material.

Both the first and second electrical conductors may be configured to be arranged at least partially within the opening in the first substrate to form the electrical connection.

The second electrical conductor may be provided onto a first face of a second substrate.

The second substrate may comprise an opening which may, for example, be arranged to be at least partially aligned with the opening formed in the first substrate.

The opening formed in the second substrate may be arranged to be at least partially aligned with the opening formed in the first substrate.

A third electrical conductor may be provided onto a second face of the second substrate.

The third electrical conductor may be configured to be arranged at least partially within the opening in the second substrate to form an electrical connection with at least one of the first and second electrical conductor.

Alternatively, the third electrical conductor may be configured to be arranged at least partially within the opening in the second substrate and the first conductor is configured to be arranged at least partially within the opening in the first substrate to form an electrical connection with the first electrical conductor.

At least one of the openings formed in any of the substrates may be polygonal. A rounded edge may be provided between the first face of the first substrate and an interior face of the opening

At least one of the openings formed in any of the substrates may be substantially circular.

The first and second substrates may be elongate films. The first and second substrates may be arranged in parallel or at an angle to each other.

According to a still further aspect of the invention there is provided an electrical harness for use in vehicle, the electrical harness comprising the electrical circuit as described in any of the preceding paragraphs.

According to a yet further aspect of the invention there is provided a vehicle comprising the electrical circuit or the electrical harness as described in the preceding aspects of the invention.

Within the scope of this application it is expressly intended that the various aspects, embodiments, examples and alternatives set out in the preceding paragraphs, in the claims and/or in the following description and drawings, and in particular the individual features thereof, may be taken independently or in any combination. That is, all embodiments and/or features of any embodiment can be combined in any way and/or combination, unless such features are incompatible. The applicant reserves the right to change any originally filed claim or file any new claim accordingly, including the right to amend any originally filed claim to depend from and/or incorporate any feature of any other claim although not originally claimed in that manner.

BRIEF DESCRIPTION OF THE DRAWINGS

One or more embodiments of the invention will now be described, by way of example only, with reference to the accompanying drawings, in which:

Figure 1 is a schematic plan view of a vehicle provided with an electrical circuit according to an embodiment of the invention;

Figure 2 is a representation of a laminating step in a method of manufacture of the electrical circuit according to an embodiment of the invention;

Figure 3 is a perspective view of an electrical circuit according to an embodiment of the invention;

Figure 4 is a cross-sectional side view of an electrical circuit according to an embodiment of the invention; and

Figure 5 is a cross-sectional side view of an electrical circuit according to an embodiment of the invention.

DETAILED DESCRIPTION OF EMBODIMENTS

A specific embodiment of the invention will now be described in which numerous specific features will be discussed in detail to provide a thorough understanding of the inventive concept as defined in the claims. However, it will be apparent to the skilled person that the invention may be put into effect without these specific details and that, in some instances, well known methods, techniques and structures have not been described in detail in order not to obscure the invention unnecessarily.

To place the embodiments of the invention in a suitable context, reference will firstly be made to Figure 1, which illustrates a top view of a vehicle 10 including a plurality of components 12 that are connected by a cable harness 14. Note that although only a single cable harness 14 is shown here for convenience, the components 12 may be connected by any number of harnesses 14 arranged in any suitable configuration according to the requirements of the particular vehicle design. It would be also understood by the skilled person that the vehicle 10 may comprise any number of electrically connected components 12, each configured to perform a variety of different functions within the context of the operation of a vehicle 10.

The cable harness 14 is an electrical circuit comprising a plurality of electrical conductors. The circuit is arranged to transmit electrical signals and/or electrical power between the components 12a, 12b, 12c of the vehicle 10. The cable harness 14 may also be referred to as a wiring harness or alternatively as a cabling or wiring assembly. As shown in Figure 1, the cable harness 14 comprises a first cable 14a which connects a first component 12a to a second component 12b whilst a second cable 14b connects the first cable 14a to a third vehicle component 12c. A junction 16 is formed at the point where the first 14a and second 14b cables meet such that an electrical connection is established between each of the three vehicle components 12a, 12b, 12c.

It will now be described how the cable harness 14 is fabricated according to an embodiment of the present invention. Figure 2 shows a stage in the roll-to-roll fabrication process by which cables 14a and 14b are produced. Considering the construction of cable 14a, the cable’s structure comprises a substrate 18 arranged to support a conductor 20. Both the substrate 18 and the conductor 20 are flexible such that they can be wound around a respective spool in preparation for being assembled into a uniform cable body having a laminate structure. During fabrication, a pair of rollers 17a, 17b is arranged to pull the assembled cable 14a in the direction designated by the arrow A, in order to unravel the substrate 18 and conductor 20 from their respective spools and then laminate them together to form the cable 14a.

The conductor 20 is arranged such that it substantially covers the width of an upper face 22 of the substrate 18. Prior to laminating the conductor 20 on to the upper surface 22 of the substrate 18, a hole cutter 19 is used to form a series of circular holes 15, or openings, in the substrate 18 at strategic positions along its length. Once the holes 15 have been formed in the substrate 18, an adhesive (not shown) is added to the upper face 22 of the substrate 18. The conductor 20 and the substrate 18 are then both pulled through the rollers 17a, 17b, which apply an opposing pressure which bonds the conductor 20 and substrate 18 together to form the foil clad laminate cable structure. The resulting structure comprises regions of the conductor 20 which are fixedly attached to the substrate 18 and other regions where the conductor 20 is suspended above the holes 15 which have been formed by the hole cutting operation.

According to the embodiments described herein, the conductor 20 takes the form of a thin copper foil. It is envisaged, however, that the conductor 20 may also take the form of a wire and/or may be formed from any other suitably conductive material such as aluminium, for example. The conductor may be a continuous sheet of foil, as shown in Figure 2, or it may comprise a number of individual conductive strips, which are then joined together once they have been arranged on to the upper surface 22 of the substrate 18. It is envisaged that the individual conductor 20 strips may be connected together using known processing methods including chemical etching, laser cutting or laser ablation.

As shown in Figure 2, the lamination of the conductor 20 onto the substrate 18 causes the conductor 20 to cover the plurality of holes 15 that are provided in the substrate 18. The conductor 20 may be substantially narrower than the substrate 18 such that it at least partially covers only a single hole 15. Alternatively, the conductor 20 may comprise a plurality of conductor strips arranged in parallel along the upper surface 22 of the substrate such that they each cover a different hole 15. These individual conductor strips may have different and/or varying dimensions such that they can be arranged to cover multiple holes 15 that are provided along the length of the substrate 18.

For the purpose of this specification, reference to ‘providing’ shall be taken to mean, for example, the process of arranging or applying one constituent element of the harness 14 (such as, for example, a substrate or a conductor) on top of, or adjacent with respect to, another element. Alternatively, when referring to the process of providing a hole in a substrate of the harness 14, the term providing is used in this context to describe the forming or creating of the hole.

The substrate 18 is formed from a low-cost polymer material such as, for example, polyethylene terephthalate (PET), polyester polycarbonate or plasticised polyvinyl chloride (PVC). The substrate 18 may be substantially flexible such that it can used in the roll-to-roll continuous fabrication of the cables 14a, 14b, as described previously. The skilled person would understand that an engineering polymer material would be any polymer material that exhibits physical and electrical characteristics suitable for use in an electrical harness for a vehicle. The substrate is flexible thin film and has a thickness of between 0.1 mm and 5mm.

The hole cutter comprises a plurality of hole punching tools arranged in an array across the width of the substrate 18. The hole punching tools are used to punch holes 15 in the substrate as it is wound off a spool. As will described in more detail below, the holes 15 provide vertical interconnect access holes (VIAs) through the substrate 18 at positions which correspond to electrical junctions that will be formed later on in the fabrication process.

Hole punching provides a simple and low cost hole formation technique for producing multiple holes of uniform shape and size. Punching tools with different shapes, sizes and cutting surfaces may be used to produce holes with different shapes, sizes and finishes. At least one of the holes 15 formed in the first and second substrates 18, 28 may be substantially polygonal (i.e. polygon-like) or circular. In some embodiments, the holes 15 may have substantially rounded edges.

Alternatively, laser cutting processes allow high definition control of the cutting process to produce holes with a precise perimeter, or outline. It is envisaged that the cutter may be fitted with multiple punching tools in order to form holes with different shapes and sizes in a single section of substrate material during a single processing step. Alternatively, a laser cutter may be programmed to produce different sized and shaped holes in a single section of substrate according to a computer aided design (CAD) protocol.

The adhesive used to laminate the conductor 20 to the substrate 18 may be applied to the upper surface of the substrate using, for example, spray coating or drop coating methods. The adhesive is pressure activated such that the pressure applied by the rollers 17a, 17b causes a permanent bond to form between the opposing surfaces of the substrate 18 and conductor 20 films. Alternatively, a heat activated adhesive may be used.

Following the above described fabrication process the cable 14a may be wound onto a receiving spool on which it can be stored for later use. Alternatively, the assembled cable 14a can be fed directly into the next stage of the harness fabrication process in which the cable 14a is cut to a desired length using a cable-cutting machine such as would be readily known to the skilled person. In this way, both cables 14a and 14b are formed from the same strip of cable.

The resulting cable sections 14a, 14b are then arranged vertically one above the other such that their respective holes 15 are in direct alignment as shown in Figure 3. In order to secure the overlapping cables 14a, 14b together, a heat activated adhesive (not shown) is applied to either an underling face 26 of cable 14a or an upper face 30 of cable 14b in an adjoining region 32 where the two cables meet.

Turning now to Figure 3, which shows a perspective view of the harness 14 according to an embodiment of the invention, the first and second cables 14a, 14b of the harness 14 are arranged in a stacked cable assembly. In other words, the first cable 14a is overlaid onto the second cable 14b to form the junction 16 of the harness 14, as first described with reference to Figure 1. It will be appreciated by the skilled person that the arrangement of the first and second cables 14a, 14b shown in Figure 3 is an example representation of one possible configuration of the cables. In this case, the first cable 14a is arranged orthogonally with respect to the second cable 14b. However, the cables 14a, 14b may also be overlaid in parallel with each other or at any other intermediate angle therebetween.

The first cable 14a comprises a first substrate 18 on to which a first electrical conductor 20 is provided. As described previously, the first conductor 20 is arranged onto the first face 22 of the first substrate 18 such that it at least partially covers the first face 22 of the first substrate 18.

A second electrical conductor 24 is arranged onto a second face 26 of the first substrate 18 such that it at least partially covers the second, underlying, face 26 of the first substrate 18. The second face 26 of the first substrate 18 is arranged in an opposite orientation to the first face 22 such that the first and second electrical conductors 20, 24 are separated from each other by the first substrate 18.

The first electrical connector 20 is fixedly attached to the substrate 18 of the first cable 14a, which defines the first substrate 18 of the harness 14, and the second electrical connector 24 is fixedly attached to the substrate of the second cable 14b, which defines the second substrate 28 of the harness 14. Therefore, the second electrical connector 24 is arranged in parallel with the first, upper, surface 30 of the second substrate 28 of the harness 14. Owing to the substantially perpendicular arrangement of the first and second cables 14a, 14b, the second electrical connector 24 is arranged perpendicular to the first substrate 18.

The first substrate 18 further comprises a hole 15 that the first and second electrical connectors 20, 24 both cover, at least partially. The first and second electrical connectors 20, 24 are each configured to be at least partially arranged within the opening 15 in the first substrate 18 in opposing directions in order to form an electrical contact therebetween. Put another way, first and second electrical connectors 20, 24 are protruded into the opening 15 in the first substrate 18. The adjoined region 32 of the overlapping portions of the first and second electrical connectors 20, 24 forms an interface which defines an electrical connection between the first and second cables 14a, 14b of the harness 14.

Advantageously, the circular shape of the hole 15 helps to prevent the formation of splits in the substrate material, which could otherwise run along the length of the substrate 18. The formation of splits in the substrate may disrupt the electrical connections formed by the conductor 20 and thereby cause failure of the electrical circuit. It is easier to fabricate circular holes using conventional cutting, punching and drilling techniques. In embodiments, the circular holes may be provided with at least one substantially straight edge where the conductor passes over the edge of the hole 15. The straight edge allows the conductor 20, 24 to fold more easily into the hole 15 in such a way that it may conveniently protrude into the hole 15 without having to twist or stretch. Accordingly, in some embodiments, at least one of the openings or holes 15 in one or more of the substrates 18, 28 may comprise a superellipse or a squircle.

Referring once again to Figure 3 in which a junction 16 is formed at the interconnection of two conductors 20, 24 arranged at right angles to each other, the hole 15 may be provided with straightened edges as described above so as to accommodate the folding of conductors into the hole 15 in order to form the junction 16. A first pair of opposing straight edges of the hole perimeter would coincide with the section of the hole edge where the first conductor 20 starts to protrude into the hole 15. A second pair of opposing straight edges, arranged at right angles to the first, would therefore correspond to the section of the hole edge where the second conductor 24 starts to protrude into the hole 15. Thus, it is envisaged that the hole 15 may be configured to accommodate a variety of different arrangements of the conductors. For example, a substantially triangular or hexagonal hole shape may be used for a junction configuration in which three electrical connectors intersected at 60 degrees to each other. In order to prevent splits forming in the substrate material at the intersection between two straightened edges of a hole perimeter, the holes 15 may be provided with corners that have a substantially rounded profile. In this way, a hole may be provided which is substantially square but rounded edges (otherwise known as a squircle). To further aid the bending of the conductor as it protrudes into the hole 15, the edge of the hole may be rounded where the upper 22 or lower 26 face of the first substrate 22 meets an interior face 17 of the hole 15. In this way, the rounded edges are provided between the face of the substrate and the interior face 17 of the opening 15.

Turning now to Figure 4, which shows a side on section view of a harness 14 according to an embodiment of the invention. In contrast to Figure 3, the cables 14a, 14b are arranged in parallel such that the substrates 18, 28 and conductors 20, 24 are all aligned with one another. As can be seen in Figure 4, the second substrate 28 is provided with a hole 15b which is aligned with the hole 15a of the first substrate 18. In this way the holes 15a, 15b of the first and second substrates 18, 28 combine to define the hole 15 of the harness 14.

A number of adhesive layers are provided to fixedly attach the cables 14a, 14b to each other and to secure the conductors 20, 24 to their respective substrates 18, 28. A first adhesive layer 38 is provided between the first face 22 of the first substrate 18 and the first conductor 20. A second adhesive layer 38 is also provided between the second face 26 of the first substrate 18 and the second conductor 24. A third adhesive layer 38c is further provided between the first face 30 of the second substrate and the second conductor 24.

The adhesive layers 38 are provided to hold the components of the cables 14a, 14b together such that the alignment of the holes 15a, 15b can be maintained during the formation of the junction 16. The adhesive layers 38 also help to isolate the portions of the conductors 20, 24 which are suspended above the hole 15, and which are therefore susceptible to external stresses which may be exerted on the harness 14 when it’s in use.

As the conductors 20, 24 are each suspended above the holes 15a, 15b in the their respective substrates 18, 28, this allows for the exposed portion of each conductor to protrude into the hole 15 and to form a contact therebetween. Advantageously, the conductors 20, 24 can be directly adjoined together without being hindered or obstructed by the substrate 18, 28.

The method of adjoining the two conductors 20, 24 together comprises first applying solder or solder paste (not shown) to an upper surface of the second, lower, conductor 24. Pressure is then applied by two probes 40 from above and below the first and second conductors 20, 24 in order to compress the conductors together. Thermal energy is conducted from a heat source, through the probes 40, and into the adjoining region 32 of the conductors 20, 24, which causes the solder to flow throughout the adjoining region 32. Once the heat source is removed the solder solidifies thereby fusing the conductors 20, 24 together to form an electrical connection. The solder is a low temperature melting point metal alloy paste such as would commonly be known in the art.

In embodiments, the conductors may be adjoined using ultrasonic welding wherein two probes are used to compress the conductors together while high frequency vibrations are transmitted into the conductors 20, 24 in order to generate localised thermal energy at the interface between the two conductors 20, 24. Alternatively, spot welding may be used to fuse the conductors 20, 24 together, whereby an electric current is passed from one probe to the other in order to generate intense heat at the interface between the conductors 20, 24, which thereby causes them to fuse together to form an electrical connection therebetween.

Advantageously, the provision of a hole in both the first and second substrate 18, 28 allows the use of any of the above described adjoining methods due to the fact that the holes 15a, 15b enable the direct application of a probe 40 onto each conductor. It is envisaged that the holes 15a, 15b in the first and second substrates 18, 28 may be configured for different purposes in the construction of the harness 14, which may require that they exhibit different shapes and sizes. For example, in the embodiment described in Figure 4, the hole 15a may be configured to allow the first and second conductors 20, 24 to at least partially protrude through it in order to form an electrical connection therebetween. Therefore, the shape and size of the hole 15a may be configured so that it doesn’t inhibit the bending of the conductors 20, 24 as they protrude into the hole 15a. In contrast, the hole 15b in the second substrate 28 may not be required to meet these same requirements since it is merely provided to enable the lower probe 40 to reach the underside of the second conductor 24 so that it can form the electrical connection at the adjoined region.

In the embodiments described herein, only two overlapping cables have been shown. However, it is envisaged that additional conductors and substrates could be added to the presently described harness 14. Furthermore, the electrical conductors can also be configured such that a single electrical connection is made both above and below the junction 16, as shown in Figure 4, in order to form connections across multiple substrates. For example, in the case of a threelayered junction, a third electrical conductor may be provided on a second face of the second substrate. The second face opposes the first face of the second substrate 28 such that the third electrical conductor is arranged at the bottom of the harness 14. In this arrangement, the third electrical conductor is configured to protrude through the hole 15b in the second substrate 28 arranged above it. The first electrical conductor 20 is configured to protrude through the hole 15a in the first substrate 18 and the second electrical conductor 24 remains substantially level. In this configuration, the second electrical conductor 24 is arranged such that it does not protrude through either the first or second substrates 18, 28. However, both the first and third electrical conductors have to bend across the thickness of the first and second substrates 18, 28, respectively, in order to make contact with the second electrical conductor 24 and thereby form the electrical connection.

In an alternative embodiment, at least two of the three electrical conductors may be configured to form an electrical connection in isolation from the other conductor. For example, a first electrical connection may be formed between the first and second electrical conductors 20, 24 through a hole 15a in the first substrate 18. A separate connection may be formed between the second and third electrical conductors through a hole 15b in the second substrate 28, wherein the hole 15b in the second substrate 28 is positioned away from the hole 15a in the first substrate 18. In a yet further alternative configuration, the hole 15a in the first substrate 18 and the hole 15b in the second substrate 28 may be aligned with each other and yet positioned along their respective substrates such that the second electrical conductor 24 does not at least partially cover either hole 15a, 15b. Thus, an electrical connection may be formed directly between the first and third electrical conductors which completely bypasses the second electrical conductor 24.

Once the adjoining process is complete, the final fabrication step can take place. Turning now to Figure 5, which shows a finished electrical circuit according to an embodiment of the invention, a pair of stiffening substrates 42a, 42b are provided above and below the harness 14 in the region of the junction 16. The stiffening substrates 42a, 42b are fixedly adhered to the outer surfaces of the cables 14a, 14b by a thick layer of adhesive 44. In particular, a first substrate 42a is attached to the first substrate 18 and a second stiffening substrate 42b is attached to the second substrate 28 of the harness 14.

The stiffening substrates 42a, 42b are made from an engineering polymer, such as polyvinyl chloride acetate (PVCA), which exhibits a substantially greater stiffness than the cable substrate 18, 28. The stiffening substrates 42a, 42b have a thickness of between 0.1mm and 5mm.

The filling adhesive 44 is a heat activated resin or sealant, which is configured to flow in to the hole 15 of the harness 14 when heat and pressure is applied to the substrates 42a, 42b by an external source, as indicated by the arrows labelled B. Upon application of the heat and pressure, excess adhesive 44 is caused to flow into the hole 15 following the trajectory of the arrows labelled C. The excess adhesive 44 is thereby configured to fill in the spaces around the adjoining region 32 of the conductors 20, 24.

Once the adhesive 44 has set, it forms a protective barrier which prevents ingress of environmental contaminants into the hole 15. The adhesive 44 also helps to stiffen the region of the electrical circuit around the holes 15a, 15b and provides stability to the junction 16 formed therethrough. The adhesive 44 also reduces the susceptibility of the electrical circuit to vibration stress which would otherwise stress the interconnections to fracture if they were left unsupported. In some embodiments, the adhesive 44 may be added to the stiffening substrates 42a, 42b before they are applied to the harness 14. Alternatively, the adhesive 44 comprises a heat activated resin which, once applied to harness 14, is configured to set hard in order to form a protective barrier for the junction 16 region. It is envisaged that a single process will be used to fill a plurality of holes 15 in any given portion of the harness 14.

Each of the above-described processing steps may be performed using hand held tooling, including the hole formation, the foil lamination, the cable alignment and the interconnection formation. Alternatively, the above process steps may be performed as part of an automated fabrication process. Furthermore, the fabrication may be adapted for use in a continuous process, whereby for example, the substrates and foils are provided form a rolled source and/or the soldering is printed onto the substrate.

In addition to the electrical connections formed through the holes 15 which are provided in the substrate 18, the substrate 18 may also be selectively stripped away to expose the conductor 20, which can then be connected to an external connector port to provide a connection to a component of the vehicle. In this way, a plurality of cables may be connected end-to-end using connector ports according to the requirements of a particular circuit design. Individual cables may also be bound together by straps, cable ties, cable lacing, sleeves, electrical tape, or any combination thereof.

In a conventional vehicle harness an element of stiffness is necessarily introduced where external connector ports are attached to the bundles of cables at the point where connections are made with the electrical components of the vehicle. These bulky and cumbersome connectors are difficult to incorporate within the body of a vehicle. Advantageously, the electrical circuit according to the present invention allows the junctions 16 to be partially flexible so that they may fit into cramped or crowded portions of the vehicle’s interior. Furthermore, the localised stiffening of the junction 16 regions allow electrical connections to be formed along a length of the otherwise flexible cable harness 14 without having to introduce a separate connecting component. Moreover, separate branching cables can be connected to a central cable, as shown in Figure 1, without causing a significant reduction in the overall flexibility of the harness 14. In this way, the harness 14 can provide multiple point-to-point connections from a single length of flexible cable.

A conventional wiring harness is made of a bundle of individually coated wires, each forming a point-to-point connection from one component to another within the vehicle. When designing an electrical circuit within a vehicle, it may be necessary to make additional connections to multiple components within the vehicle. It may also be necessary to move an existing connection from a single wire within the bundle to a different wire in order to attach an external connector, for example. This is not possible with a conventional harness without disrupting the other wires within the bundle or without disrupting the existing connections between the vehicle components.

As explained above, the method of fabrication according to the present invention allows a plurality of interconnects to be formed between the conductors of overlapping cables 14a, 14b. The interconnects define vertical connections between the horizontal circuits laid out on the substrate of each cable. Thus, the structure of the harness 14 provides a three-dimensional electrical circuit. This allows a connection to be made from one side of the harness 14 to the other, i.e. across the width of a given substrate, without disrupting the path of a second conductor. Advantageously, this can provide a greater number and variety of connections to be provided within a single cable of the harness 14, without having to introduce an additional cable or wire.

The three dimensional nature of the electrical circuits formed within the harness 14 means that a plurality of different electrical components can be connected together using a single harness assembly. In this way, the physical dimensions of the harness 14 are reduced whilst increasing the possible number of connections provided therein. The reduced physical dimensions mean that the harness 14 can be more easily accommodated within the tight packaging requirements of a vehicle. This is of particular importance in modern vehicles where an increasing number of features has increased the number of connections that must be made between different components of the vehicle 10. This must be balanced with a need to provide sufficient internal space for passengers and luggage, and weight considerations. Consequently, the space between the interior and external panels of the vehicle provide little space to accommodate electrical cabling.

Further advantages are achieved through the advantageous configuration of the harness 14 as described above. For example, the inherent flexibility of the substrates 18, 28 allows the harness 14 to more easily conform to the curved and non-uniform surfaces of a vehicle interior. It also enables the harness 14 to bend and flex in response to external stresses being applied to it when in use, which may otherwise increase the risk of shorts and open circuits forming in the electrical circuit. Advantageously, fixing two of more cables together to form a single assembly means that the harness 14 can be more easily protected against the adverse effects of vibration, abrasion, and moisture, which it may experience during a lifetime of use within a vehicle 10. Furthermore, a single harness 14 is easier for an installer to install into a vehicle 10 compared to a bundle of multiple separate cables as is commonly the case with conventional cable harnesses. Consequently, the time taken to install the harness 14 is decreased and the manufacturing process can be more easily standardised. The single cable harness 14 may also be more easily bound into a sleeve.

Furthermore, the conventional methods of forming electrical connections in a printed circuit board (PCB) typically require that a metal conductor or foil is pushed through a hole, which is formed by simultaneously piercing the underlying substrate, in order to form a connection with a conductor located on an underlying surface of the substrate. Alternatively, the connection may be made by filling a pierced hole with a metal solder which is baked solid at an elevated temperature. In order to withstand the high temperatures used in such reflow soldering techniques, a thermally stable substrate material such as polyamide is used. Such materials are commercially unviable for use in large scale electrical circuits such as those used in vehicle cable harnesses. The destructive techniques that are used in these conventional fabrication methods take place whilst the conductor is attached to the substrate, which increases the risk of causing damage to both the conductor and the substrate. These destructive processing steps tend to cause contamination of the junction formed between the conductors, which causes shorts and regions of high impedance to form in the electrical circuit.

By contrast, the formation of the hole prior to attaching the conductor, as required by the present invention, means that the conductor remains exposed in the region that overlaps the pre-formed holes. When the holes of overlapping cables are aligned with each other, the corresponding conductors can be fused together by point application of soldering or welding processes. By welding the conductors together through the hole, the advantageous method ensures that the adverse temperatures caused by the fusing techniques are localised on the conductors such that the substrate materials are not exposed to the adverse conditions associated with the welding process. This means that low temperature substrate materials can be used, which thereby reduces the cost of the electrical circuit.

Claims

1. A method of manufacturing an electrical circuit the method comprising:

forming an opening in a first substrate, providing a first electrical conductor onto a first face of the first substrate to cover at least a part of the opening, providing a second electrical conductor onto a second face of the first substrate to cover at least a part of the opening; and arranging, at least one of the first electrical conductor and the second electrical conductor, at least partially within the opening in the first substrate to make contact with the other of the first electrical conductor and the second electrical conductor, thereby to form an electrical connection therebetween.

2. The method of claim 1, wherein forming the opening occurs prior to providing the first and second electrical conductors onto the first substrate.

3. The method of claim 1 or claim 2, wherein the method comprises arranging the second electrical conductor onto a first face of a second substrate.

4. The method of claim 3, wherein the method comprises forming an opening in the second substrate prior to arranging the second electrical conductor onto the first face of the second substrate.

5. The method of claim 4, wherein the method comprises at least partially aligning the opening of the first substrate with the opening of the second substrate prior to forming the electrical connection.

6. The method of any of claims 3 to 5, wherein the method comprises providing a third electrical conductor onto a second face of the second substrate.

7. The method of claim 6, wherein the third electrical conductor is configured to be arranged at least partially within the opening in the second substrate to form an electrical connection with one or more of the first and second electrical conductors.

8. The method of claim 7, wherein the third electrical conductor is configured to be arranged at least partially within the opening in the second substrate and the second conductor is configured to be arranged at least partially within the opening in the first substrate to form an electrical connection with the first electrical conductor.

9. The method of any of claims 1 to 8, wherein forming the electrical connection comprises applying heat at the contact between the conductors to fuse the electrical conductors together.

10. The method of claim 9, wherein forming the electrical connection comprises spotwelding.

11. The method of any of claims 1 to 10, wherein forming the electrical connection comprises ultrasonic-welding.

12. The method of any of claims 1 to 11, wherein the method comprises arranging both the first and second conductors at least partially within the opening in the first substrate prior to forming the electrical connection.

13. The method of any of the preceding claims, wherein the method comprises filling the opening with a sealant following the formation of the electrical connection.

14. The method of any of the preceding claims, wherein the method comprises providing at least one outer surface of the electrical circuit with a stiffening substrate following the formation of the electrical connection.

15. The method of claim 14, when dependent on claim 13, wherein filling the opening with a sealant is carried out during the provision of the at least one outer surface of the electrical circuit with the stiffening substrate.

16. The method of any of the preceding claims, wherein forming an opening comprises holepunching.

17. The method of any of the preceding claims, wherein forming an opening comprises laser-cutting.

18. The method of any of the preceding claims, wherein forming an opening comprises drilling.

19. The method of any of the preceding claims, wherein providing the at least one electrical conductor onto a substrate comprises laminating.

20. An electrical circuit comprising:

a first substrate comprising an opening;

a first electrical conductor arranged onto a first face of the first substrate to cover at least a part of the opening; and a second electrical conductor arranged onto a second face of the first substrate to cover at least a part of the opening;

wherein at least one of the first electrical conductor and the second electrical conductor is configurable to be arranged at least partially within the opening in the first substrate to make contact with the other of the first electrical conductor and the second electrical conductor, thereby to form an electrical connection therebetween.

21. The electrical circuit of claim 20, wherein at least one of the first and second electrical conductors is substantially flat.

22. The electrical circuit of claim 21, wherein the substrate has a thickness which is dependent on the diameter of the opening formed therein.

23. The electrical circuit of claim 21 or claim 22, wherein the substrate has a thickness which is dependent on the material from which at least one of the first and second conductors is formed.

24. The electrical circuit of any of claims 20 to 23, wherein the first substrate is a flexible film.

25. The electrical circuit of any of claims 20 to 24, wherein the first substrate is formed from an engineering polymer material.

26. The electrical circuit of any of claims 16 to 20, wherein both the first and second electrical conductors are configured to be arranged at least partially within the opening in the first substrate to form the electrical connection.

27. The electrical circuit of any of claims 20 to 26, wherein the second electrical conductor is provided onto a first face of a second substrate.

28. The electrical circuit of claim 27, wherein the second substrate comprises an opening.

29. The electrical circuit of claim 28, wherein the opening formed in the second substrate is arranged to be at least partially aligned with the opening formed in the first substrate.

30. The electrical circuit of any one of claims 27 to 29, wherein a third electrical conductor is provided onto a second face of the second substrate.

31. The electrical circuit of claim 30, wherein the third electrical conductor is configured to be arranged at least partially within the opening in the second substrate to form an electrical connection with at least one of the first and second electrical conductors.

32. The electrical circuit of claim 31, wherein the third electrical conductor is configured to be arranged at least partially within the opening in the second substrate and the second conductor is configured to be at least partially arranged within the opening in the first substrate to form an electrical connection with the first electrical conductor.

33. The electrical circuit of any of claims 20 to 32, wherein at least one of the openings formed in any of the substrates is polygonal.

34. The electrical circuit of claim 33, wherein a rounded edge is provided between the first face of the first substrate and an interior face of the opening.

35. The electrical circuit of any of claims 20 to 34, wherein at least one of the openings formed in any of the substrates is substantially circular.

36. The electrical circuit of any of claims 20 to 35, wherein the first and second substrates are elongate films.

37. The electrical circuit of claim 36, wherein the first and second substrates are arranged 5 parallel to each other.

38. The electrical circuit of claim 36, wherein the first and second substrates are arranged at an angle to each other.

10

39. An electrical harness for use in a vehicle, the electrical harness comprising the electrical circuit according to any of claims 20 to 38.

40. A vehicle comprising the electrical circuit according to any of claims 20 to 38 or the electrical harness according to claim 39.

Application No: GB1708368.4

Intellectual

Property Office