ELECTRICAL CONNECTION

Abstract

An electrical connection (1) for electrically connecting a flat connector (2) and an electrical cable (3), the electrical connection (1) includes a flat connector (2) with an insulated portion (21) and an electrically conductive portion (20e) to which is secured a pressure sensitive adhesive (6) defining a window (6w), an electrical cable (3) which is secured to the flat connector (2) at the window (6w) to provide an electrical contact between the flat connector (2) and the electrical cable (3), and an enclosure (4) encasing the electrical contact.

Claims

1. An electrical connection for electrically connecting a flat connector, and an electrical cable, the electrical connection comprising a flat connector with an insulated portion and an electrically conductive portion to which is secured a pressure sensitive adhesive defining a window, an electrical cable which is secured to the flat connector at the window to provide an electrical contact between the flat connector and the electrical cable, and an enclosure encasing the electrical contact.

2. The electrical connection according to claim 1, wherein the electrical cable comprises an electrically conductive core encased in a non-conductive material to provide an exposed portion and wherein the exposed portion of the electrical cable is secured to the window.

3. The electrical connection according to claim 2, wherein the exposed portion of the electrical cable is secured to the window by material selected from the group consisting of lead-free solder; lead-containing solder and adhesive.

4. The electrical connection according to claim 1, wherein the electrical cable has an adhesive located thereon.

5. The electrical connection according to claim 4, wherein the adhesive is located fully about the cable.

6. The electrical connection according to claim 4, wherein the adhesive extends from a terminus of the non-conductive material in a direction away from the exposed portion of the cable.

7. The electrical connection according to claim 4, wherein the adhesive extends for a distance of less than 10 mm along the cable.

8. The electrical connection according to claim 4, wherein the adhesive has a first portion which lies adjacent the pressure sensitive adhesive and a second portion which extends beyond the end of the electrically conductive portion.

9. The electrical connection according to claim 1, wherein the insulated portion of the flat connector comprises polyimide film.

10. The electrical connection according to claim 1, wherein the electrically conductive portion of the flat connector has a first major surface and a second major surface.

11. The electrical connection according to claim 10, wherein the electrical cable is secured to the first major surface.

12. The electrical connection according to claim 10, wherein the second major surface of the electrically conductive portion comprises a second adhesive.

13. The electrical connection according to claim 12, wherein the second adhesive is configured to provide a second window and wherein the second window is positioned to correspond to the window.

14. An electrical connection for electrically connecting a flat connector, and an electrical cable, the electrical connection comprising a flat connector with an insulated portion and an electrically conductive portion to which is secured an adhesive defining a window, an electrical cable which is secured to the flat connector at the window to provide an electrical contact between the flat connector and the electrical cable, the electrical cable having an adhesive located therearound, and an enclosure encasing the electrical contact, the adhesive defining the window and the adhesive around the cable.

15. The electrical connection according to claim 14, wherein the enclosure comprises a unitary body.

16. A method of forming an electrical connection for electrically connecting a flat connector to an electrical cable, the method comprising: providing a flat connector having an insulated portion and an exposed portion; securing a pressure sensitive adhesive to the exposed portion to define a window; securing an electrical cable to the window to form an electrical contact; and encasing the electrical contact within an enclosure.

17. The method according to claim 16, comprising securing the pressure sensitive adhesive on the exposed portion by adhering the pressure sensitive adhesive using a pressure-sensitive adhesive located on a release liner.

18. The method according to claim 17, comprising a preliminary step of perforating the release liner and the adhesive located thereon to define a window.

19. The method according to claim 16, comprising providing the flat connector as a strip of plural flat connectors, wherein the strip of plural flat connectors are provided such that plural exposed portions are located in a side-by-side arrangement.

20. A windscreen assembly comprising an electrical connection according to claim 1, which further comprises at least one glass lamina and heating elements.

Description

BRIEF DESCRIPTION OF THE DRAWINGS

[0055] Embodiments of the invention will now be described by way of example only with reference to the accompanying drawings in which:

[0056] FIG. 1A is a diagrammatic plan view of an electrical connection according to a first embodiment of the invention;

[0057] FIG. 1B is a diagrammatic side view of the electrical connection of FIG. 1A;

[0058] FIG. 1C is a diagrammatic cut-away plan view of the connection of FIG. 1A from a first side;

[0059] FIG. 1D is a diagrammatic cut-away plan view of the connection of FIG. 1A from a second side;

[0060] FIGS. 2A to 2E provide views of the stages of a method of manufacturing the electrical connection of FIG. 1A;

DETAILED DESCRIPTION OF PREFERRED EMBODIMENTS OF THE INVENTION

[0061] Referring firstly to FIGS. 1A and 1B, there is shown an electrical connection 1 according to one embodiment of the invention for electrically and mechanically joining a flat connector 2 to an electrical cable 3 at a first end 2a of the flat connector 2. The electrical connection 1 in the region of the first end 2a of the connector 2 is protected by an enclosure 4. The flat connector 2 has a second end (not shown), connected or connectable to electrical components, for example to one or more busbars or other electrical components.

[0062] Referring now to FIG. 1C, there is shown a cut-away view of the electrical connection 1 of FIGS. 1A and 1B, where the flat connector 2 comprises of a flat electrically conductive element 20 encased by a thin layer of electrically insulating material 21 to leave a free or exposed end portion 20e. The electrical cable 3 comprises an electrically conductive wire 30 of generally cylindrical form, e.g. of a generally circular cross-section surrounded by a thin layer of insulating material 31. Other shapes of cable 3 and connector 2 are possible, with the proviso that, at least in most cases, the connector 2 is flat or substantially flat and/or provides a flat conductive surface to which the cable 3 is to be attached. In this specification, by ‘flat’ we mean that the cross sectional width (W) of the connector is greater than the cross sectional depth or thickness (D), preferably where W>10 D, say W>50 D.

[0063] In a preferred embodiment the electrically conductive element 20 is flat and is from to 40 mm, e.g. 10 to 30 mm, say 15 to 20 mm, e.g. 17 mm, wide and about 10 to 1000 microns (1 micron is 10-6 m), say 50 to 500 microns, for example 100 microns thick, and is preferably formed from copper, which may or may not be coated. If the electrically conductive element 20 is coated, it may be coated with a protective substance, for example a substance capable of imparting at least a degree of environmental protection. One such coating material is tin or an alloy thereof. The insulating material 21 is preferably marginally wider than the electrically conductive element 20, for example to leave a marginal border outboard of the electrically conductive element 20 along the edges of the electrically conductive element 20. In an embodiment where the electrically conductive element 20 is 17 mm wide, the insulating material may be from 18 to 30 mm wide, e.g. 21 to 25 mm wide (for example 22 or 23 mm wide), and from 20 to 80, say 40 to 50 microns, e.g. 45 microns, thick at each major surface of the electrically conductive element 20. The insulating material 21 is preferably formed from a temperature-stable plastics material. One such plastics material is polyimide. The insulating material 21 may conveniently be formed from Kapton® film supplied by E.I. Dupont of Delaware, USA. The flat connector 2 may also include an adhesive patch 25 for attaching the flat connector to a site of use. The adhesive patch 25, where provided, may be located about 3 mm from an end of the insulating material 21 towards the second end of the connector 2. The adhesive patch 25, where provided, may be covered by a release liner (not shown). The adhesive patch 25, when exposed by removal of the optional release liner, may help to ensure accurate location of the flat connector 20 at a site of use. For example, the optional release liner may be removed to expose the adhesive patch 25 which can then be used to secure the electrical connection 1 at a site of use (e.g. on a windscreen component) whilst other components (for example a further pane of a windscreen) are assembled.

[0064] The flat connector 2 has an exposed portion or exposed end 20e of electrically conductive element 20 at its first end 2a. The exposed end 20e of the conductive material 2 may be from 2 to 20 mm long, e.g. from 5 to 18 mm long and in one embodiment is about 9 or 10 mm long. It will be appreciated that whilst the exposed portion 20e is shown as being of rectangular form it may also be other shapes. For example, the exposed end portion 20e may be of trapezoidal form.

[0065] The exposed portion 20e has an adhesive 6 located thereon. The adhesive 6 is provided around the exposed portion 20e to define a window 6w, which window 6w is preferably inboard of the edges of the exposed portion 20e. The window 6w may be surrounded on all sides by adhesive 6. The adhesive 6 may overlie an end portion of the insulating material 21.

[0066] The electrical cable 3 has an exposed portion of electrically conductive wire 30 at one of its ends. The exposed electrically conductive wire 30 at the end of the electrical cable 3 is soldered to the exposed electrically conductive element 20 at the end of the flat connector 2 in the region of the window 6w by solder 5 which may be of any suitable type, for example a solder 5 consisting of 60% tin and 40% lead, or alternatively and preferably a lead-free solder, for example SAC305 or 97Sn3Ag or even pure tin. Alternatively or additionally the connector 2 and wire 30 may be otherwise secured together so as to allow electrical conduction from the connector 2 to the wire 30, and/or vice versa.

[0067] A strip of adhesive 6a extends about (and completely around) the cable 3 so as to form a continuous fluid seal. The strip of adhesive 6a is located adjacent the exposed electrically conductive wire 30 at the end of the electrical cable 3 and at least a portion thereof lies adjacent a facing portion of the adhesive 6. Preferably, the adhesive 6A does not overlie the window 6w.

[0068] As shown in FIG. 1D, the other side of the exposed portion 20e of the flat connector 2 may also have an adhesive 6′ secured thereto. The adhesive 6′ may also be provided to define a window 6w′. The window 6w′ will preferably coincide with the window 6w on the first side (although it may be smaller), the reason for which will be explained below. As can be seen, the adhesive 6a around the cable 3 extends beyond the end of the exposed portion 20e.

[0069] The enclosure 4, which is preferably molded from a thermoplastic such as a polyamide, for example polyamide 6 (otherwise known as Nylon® 6 or PA6) or polyamide 6/6 (otherwise known as PA66) or polybutylene terephthalate (PBT) or polypropylene (and preferably glass reinforced PA6 or glass-reinforced PA66 or glass-reinforced PBT or glass-reinforced polypropylene) or Macromelt, is suitably sized and configured such that it encases the point of contact between the electrically conductive element 20 and the exposed end 30 of the wire 3 and extends from the flat connector 2 to the electrical cable 3 and over the adhesive 6a. Typically, the enclosure is formed by over-molding the electrical connection. Whilst the enclosure is shown as being rectangular in plan form, it may be other shapes, for example trapezoidal.

[0070] The provision of the adhesive 6 provides a surface which is more amenable to sealing of the electrical connection by the enclosure 4. We have found it particularly advantageous to use a pressure sensitive adhesive 6 such as a fully cured acrylic adhesive. The pressure sensitive adhesive that we prefer to use is 300LSE high strength acrylic adhesive supplied by 3M. Preferably the adhesive has a thickness of less than 100 μm, say 50 μm. The adhesive 6′ may comprise a pressure-sensitive adhesive such as a fully cured acrylic adhesive. The pressure sensitive adhesive that we prefer to use is 300LSE high strength acrylic adhesive supplied by 3M. Preferably the adhesive 6′ has a thickness of less than 100 μm, say 50 μm.

[0071] The manufacture of a heated windscreen entails providing a windscreen laminate comprising separate glass blanks between which are disposed a plurality of heating elements electrically connected to flat connectors of the type described herein. The flat connectors are electrically connected at their free ends to cables which are intended for future connection to a source of electrical power. The windscreen laminate, including the flat connectors and cables joined by an electrical connection, is then heated under vacuum in an autoclave at temperatures of up to 150° C. and for durations of around three hours in order to bind together the layers of the laminate (and also, in some cases, to solder electrical connections). It is imperative that the electrical connection is not damaged during this process and further that the electrical connection remains sealed against undesirable elements (particularly water and salt) which might otherwise corrode and hence degrade the connection.

[0072] The applicant has found that an electrical connection between a flat connector and an electrical cable and including an enclosure, and using the pressure sensitive adhesive, reliably prevents subsequent ingress of undesirable elements. Without wishing to be bound by any theory it is believed that movement and flexing of the cable and/or of the flat connector during the course of manufacture of the windscreen and automobile (and also during subsequent use of the automobile) may result in cyclical wear of the join between the cable and enclosure and/or of the join between the flat connector and the enclosure. This wear may produce gaps between the enclosure and the cable and/or flat connector through which undesirable elements may ingress. It is further believed that the adhesive 6 (and if present 6a), allows the thermoplastic material of the enclosure to effectively seal the electrical contact.

[0073] Referring now to FIGS. 2A to 2D, there is shown sequential steps in a method of forming the electrical connection 1 shown in FIGS. 1A to 1D.

[0074] The method involves a first step (FIG. 2A) of perforating a tape T comprising a pressure sensitive adhesive which is provided with a release liner RL to form plural apertures A through both the release liner RL and the adhesive.

[0075] In a second step (FIG. 2B) an array of elongate flat conductive strips 20′ which are longitudinally aligned in side-by-side relations and encapsulated on both sides by a non-conductive polymeric film 21′ are provided. The non-conductive polymeric film 21′ does not extend to the ends of the flat conductive strip 21′ thereby to leave an exposed portion 20e and another exposed portion 21e′. At one end 21a′, the tape T is secured to the exposed portion 20e′ such that each aperture A is located inboard of the edges of a respective exposed portion 20e′.

[0076] A similar tape T (where the apertures may be the same size or smaller) may be secured to the other face of the exposed portion 20e′ at the first end 21a′. The apertures A on the two surfaces will generally coincide. Between the adjacent exposed portions 21e′ the adhesive of the tapes T will be secured together.

[0077] The so formed laminate may be passed through a roller (not shown), for example a heated roller to ensure that the adhesive of the tape T is firmly secured to the exposed portion 21e′ and the marginal portion of the non-conductive polymeric film 21′ and, where present, the tape T secured to the other surface of the exposed portion 21e′ is firmly secured to the exposed portion 21e′ and the marginal portion of the non-conductive polymeric film 21′ In a third step (FIG. 2C) individual encapsulated flat conductive strips 20′ are cut from the array. The cutting stage may shape the exposed end 21e′, the adhesive and the release liner RL′. The individual aperture A′ is shown coincident with the exposed end 20e′.

[0078] In a fourth step (FIG. 2D), the release liner RL′ is removed to expose the adhesive 6″ and a window 6w″ corresponding to the aperture A. An exposed end 30′ of a conductive cable 3′ is presented to the window 6w″. An adhesive 6a′ provided about the conductive cable 3′ lies adjacent, preferably in abutting relations, with the adhesive 6″ defining the window 6w″. The exposed end 30′ carries a solder composition. The conductive cable 3′ comprises insulation 31′ away from the exposed end 30′. The adhesive 6a′ is located about the terminal portion of the insulation 31′ to a length of less than 10 mm. Accordingly, a first portion of the adhesive 6a′ will lie adjacent adhesive 6″ and a further portion of the adhesive 6a′ will extend beyond the end of the exposed end 20e′. The adhesive is preferably a pressure sensitive acrylic adhesive, which may be 300LSE high strength acrylic adhesive supplied by 3M.

[0079] In a fifth step (FIG. 2E) heat is applied to melt the solder composition carried by the exposed end 30′ of the cable 3′ and thereby form an electrical contact between the cable 3′ and the flat conductive strip 20′.

[0080] Heat is applied to the window provided in the adhesive located on the other major surface of the exposed end 20e′ (i.e. the non-shown surface in FIG. 2E). The heat applied (typically for 1-2 seconds) is sufficient to melt the solder and cause it to flow. Once heat is removed the solder rapidly cools thereby securing the cable 3′ to the flat conductive strip 20′ to make a robust electrical connection. The release liner RL on the heated side of the exposed end 20e′ may be removed before or after heating. We prefer to remove the release liner RL on the adhesive on the heatable major surface after heating so as to make the window more visible for the application of heat. The window provided in the adhesive located on the other major surface of the exposed end 20e′ (i.e. the non-shown surface in FIG. 2E) is typically smaller than the window 6w″ provided by adhesive 6″ as the application of heat can be performed accurately.

[0081] The connected part is then moved to an overmolding machine (not shown) where the electrical contact is overmolded to make an electrical connection 1 in which the end of the cable 3′ and end of the flat connector 20′ are encapsulated in thermoplastic material. The cycle time to achieve the overmolding is typically less than 60 s, and may be less than 45 s, say around 30 s. The provision of the pressure sensitive adhesive on the two major surfaces of the exposed end 20e the marginal surface of the polymeric film 21′ and around the cable 3 provides a suitable surface for forming an environmentally stable seal with the overmolded thermoplastics material. Because the adhesive 6″, 6a′ does not need to cure (i.e. it is not a heat activated or heat cured adhesive) overmolding cycle times can be reduced. In some cases the connected part may be subjected to a heat stage before overmolding, for example by passing the connected part through a heat tunnel or storing at an elevated temperature for a period of time. Additionally or alternatively, the parts may be subjected to a heating stage after the second step and before the third step.

Test Results

[0082] Electrical connections 1 according to the invention were tested according to the following tests:

[0083] Connector Fabrication [0084] Electrical connections 1 according to the invention were prepared from a pre-tinned copper strip having a width of 15 mm and a thickness of 100 μm. Polyimide tape (19 mm wide, total thickness 45 μm) provided with an epoxy adhesive was secured to either side thereof to leave exposed ends. A pressure sensitive adhesive was secured to both sides of one of the exposed ends, the pressure sensitive adhesive defining an adhesive fee window on both sides of the exposed end. A 2.5 mm.sup.2 Radox® cable, which was pre-tinned was secured to one of the windows by the application of heat, sufficient to melt the tin and cause the tin material to flow. Removal of the heat allowed the tin to solidify and to secure the cable to the exposed end. The entire connection was overmolded with nylon 6 to form a flat connector to cable electrical connection.

[0085] Test 1—Insulation Resistance Following Forming [0086] A 5% salt water solution at approximately 20° C. was prepared. Each electrical connection 1 was then tested in turn by partially submerging it in the solution such that the enclosure 4 was submerged in the solution but not the second end of the flat connector 2. The insulation resistance of each electrical connection 1 was tested by measuring the resistance between the free second end of the flat connector 2 and the solution (using an ohmmeter). [0087] Result: 50 electrical connections were tested and all successfully passed this test.

[0088] Test 2—Insulation Testing Following Bending Cycles [0089] Each electrical connection 1 was subjected to cyclic bending by fixing the enclosure 4 and bending the flat connector 2 around the enclosure 4 by an arc of 180°, five times. Each electrical connection 1 was also subjected to cyclic bending by fixing the enclosure 4 and bending the cable 3 around the enclosure 4 by an arc of 180°, five times. The purpose of this bending is to mechanically stress the joins between the enclosure 4 and the flat connector 2 and/or cable 3 and to therefore test the efficacy of the seal provided by the enclosure 4 and the adhesive 6, 6a. [0090] The same test protocol was used as in Test 1. [0091] Result: 50 electrical connections were tested and all successfully passed this test. [0092] Test 3—Insulation resistance following thermal cycling [0093] Electrical connections 1 were prepared as described in relation to Test 1. [0094] Two 5% salt water solutions were prepared, one at a temperature of 65° C., the other at 0° C. [0095] Each electrical connection 1 was submerged in the first solution for a period of 30 minutes before being transferred to the second solution for another period of 30 minutes. The time taken to transfer the electrical connections 1 between first and second solutions was less than 10 seconds. This procedure was repeated five times in total for each of the electrical connections 1. The purpose of this thermal cycling is to test the efficacy of the seal provided by the enclosure 4 and first and second seals 6a, 6b. [0096] The insulation resistance of the thus thermally cycled electrical connections 1 was then measured as described above in Test 1. [0097] Result: 50 electrical connections were tested and all successfully passed this test.

[0098] As will be appreciated, the test results demonstrate that the electrical connections 1 of the invention are able to withstand repeated physical stress as well as thermal cycling stress. The testing of 150 samples with no fails is particularly encouraging.

[0099] It will be appreciated by those skilled in the art that several variations to the aforementioned embodiments are envisaged without departing from the scope of the invention. For example, the solder 5 may be lead free and/or may include any suitable combination of solder materials. Although we prefer to use a pressure sensitive acrylic adhesive, other pressure sensitive adhesives may be used. We prefer to use a pressure sensitive adhesive rather than a heat activated adhesive because we have found that using an adhesive which is fully cured before the encapsulation is applied leads to a more robust connection which is less susceptible to environmental ingress.

[0100] It will also be appreciated by those skilled in the art that any number of combinations of the aforementioned features and/or those shown in the appended drawings provide clear advantages over the prior art and are therefore within the scope of the invention described herein.