GB2072428A

GB2072428A - Internally connecting flexible switch

Info

Publication number: GB2072428A
Application number: GB8111400A
Authority: GB
Original assignee: Brady Corp
Current assignee: Brady Corp
Priority date: 1978-01-25
Filing date: 1979-01-09
Publication date: 1981-09-30
Also published as: GB2013401A; GB2013401B; AU4327479A; BE873717A; DE2900633A1; GB2097588B; JPS54103584A; NL7812296A; GB2097588A; FR2415870A1

Abstract

A flexible touch switch has normally conductive material 62 inserted in apertures 72 in a spacer layer 18, for making electrical contact between electrical pathways 50, 60 carried by contact-carrying layers 16, 20. <IMAGE>

Description

GB 2 072 428 A 1

SPECIFICATION

Internally connecting flexible switch

5 This invention relates to flexible touch switches.

It is often desirable to provide backlighting for a flexible touch switch, either to indicate switch activation or continuously to identify 10 the individual touch switch locations. Prior efforts in touch switch backlighting have lit regions spaced from the individual touch switch locations, this being necessitated by the opaqueness of the contacts underlying the 1 5 touch locations. It would be desirable instead to provide backlighting at the centres of the touch switch locations, so as to provide both better identification of such locations and improved activation feedback to the operator. 20 U.S. Patent No, 3,732,389 of Kaelin et al and U.S. Patent No. 3,777,222 of Harris disclose a touch switch panel having conductors (gold or tin oxide) carried by one or two transparent flexible layers, which may be of 25 Mylar (Trade Mark), separated by an aper-tured transparent spacer layer (Mylar); light emitting diodes located in a substrate near the region of electrical contact product light indications through the transparent layers. 30 According to the present invention there is provided a flexible switch having contacts and comprising a first flexible layer carrying at least one electrical pathway, means including a spacer layer separating said first and second 35 layers whereby a portion of the first-mentioned electrical pathway operates as a movable switching contact, and normally conductive material inserted within at least one aperture in said spacer layer and in electrical 40 contact with said electrical pathways on both said first and second layers, thereby providing an internal electrical connection between said first and second layers.

In one embodiment of the invention back-45 lighting of the central portions of individual touch switches is achieved by providing holes in contacts carried by transparent layers. Transparent adhesive may be used to bond transparent layers in a backlighted flexible 50 touch switch according to the invention. In another embodiment of the invention manufacture may involve overlaying a flexible touch switch with a further layer having apertures with centres transversely positioned relative to 55 contacts carried by at least one lower layer of the switch, and placing over the apertured layer a continuous flexible outer layer, the apertures being small enough for touch forces centrally applied to an individual touch switch 60 to be transferred to the contacts and improve tactile feel.

In preferred embodiments two flexible layers carry aligned contacts on facing surfaces to provide an X-Y matrix, and a spacer layer 65 with apertures aligned with holes in the contacts separates the two contact-carrying layers; and a further layer with apertures aligned with and equal in size to the holes in the contacts overlies the upper contact-carrying 70 layer, and a continuous overlay underprinted with translucent ink portions at individual touch switches covers the further apertured layer, light being transmitted continuously from an incandescent light source beneath the 75 switch through the two apertures and through the two holes in the facing contacts.

The structure and operation of a preferred embodiment of the invention will now be described, by way of example, with reference 80 to the drawings, in which:—

Figure 1 is an exploded isometric view, partially broken away, of said embodiment;

Figure 2 is a partial sectional view through Fig. 1 at the centreline of the flexible tail 85 (thicknesses are exaggerated for clarity); and

Figure 3 is a partial sectional view through Fig. 1 at the location of one pair of transfer pads joined by a conductive epoxy insert.

Turning to Fig. 1, there is shown a flexible 90 switch panel 10 for telephone Touch-Tone (American Telephone and Telegraph Company trademark) switching. The panel 10 consists principally of five adhesively-joined transparent flexible layers; an overlay 12, a spreader 95 layer 14, an upper contact-carrying layer 16, a spacer layer 18, and a lower contact-carry-ing layer 20. A flexible tail 22 integral with the upper layer 16 is bent downward through slots 24, 26 in the spacer layer 18 and the 100 lower layer 20. An insert 28 occupies the void left in the upper layer 16 by bending the tail 22 downward. Below the panel 10 an incandescent light source (Fig. 2) provides backlighting. A frame (not shown) supports 105 the panel 10.

The overlay 12, a 0.25 mm thick flexible non-conductive layer of General Electric Lexan (trade mark) polycarbonate film of grade 8B05 (which includes a velvet texture top 110 surface) and colour 112 carries on its under-surface translucent zones of graphic ink 36, 38 and opaque black and gray zones of graphic ink 35 and 40. These are acrylic-based System II inks obtained from KC Coat-115 ings, Incorporated, Kansas City, Missouri and applied by screening. The layers of ink form a black background 35, gray button areas 40, and white translucent indicia 36, 38 including button outlines and centrally-located lettering, 120 numbers, and symbols. Backlighting from an incandescent translucent white light source (not shown) is transmitted through indicia 36, 38.

Spacing the overlay 12 from the upper 125 layer 16 and adhering to each of these two layers is a spreader layer 14, a 0.075 mm thick transparent Mylar (DuPont trademark) polyethylene terephthalate layer 41 having on both its surfaces thermoset (after it is in place) 1 30 acrylic transparent pressure-sensitive adhesive

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GB2072428 A

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layers 42, 44. Each adhesive layer is 0.0375 mm thick. A suitable adhesive is the 3M Company's 467 Firm Acrylic Pressure Sensitive Adhesive. The spreader layer 14 is diecut 5 to provide openings 46 (approximately 6mm by 7.5 mm) underneath each button area. All indicia 36, 38 are aligned inside openings 46.

The upper contact-carrying layer 16 (0.125 10 mm thick transparent Mylar) has printed on its undersurface three columns of four 0.0175 mm thick conductive paint contacts 48. The conductive paint is sold by Acheson Colloids of Port Huron, Michigan, under the designa-15 tion Electrodag 415SS. The contacts 48 are conected by leads 50, which continue onto the tail 22. Each contact 48 has the form of a rectangle with a centre rectangle removed,

thus allowing light transmission through an 20 open and therefore transparent centre 52. The contacts are approximately 14 mm by 16 mm and the transparent centres are 6mm by 7.5mm, equal to the size of the spreader openings 46.

25 Extending from one edge of the upper layer 16 is the tail 22. Two cuts 54 each about 6mm long are made in the upper layer 16, and the tail 22 is bent downward inside the edge of the panel 10. The tail carries leads 50 30 from the contacts 48 on the upper layer 16 and leads 56 from transfer pads 58 located adjacent the bend in the tail. The transfer pads 58 are connected to transfer pads 59 and leads 60 on the lower layer 20 through 35 unhardened conductive epoxy inserts 62 in 1 the spacer layer 18. The conductive epoxy comprises an epoxy resin unmixed with hardener and having dispersed therein silver particles. The epoxy is supplied by Amicon, Lex-40 ington, Massachusetts, under the trademark 1 Uniset, type C-14. All leads and transfer pads are printed using the same conductive paint as used for the contacts 48. In all, the tail 22 carries seven leads, one for each column on 45 the upper layer 16 and one for each row on 1 the lower layer 20. By bending the tail 22 down inside the edge of the panel 10, leads 50, 56 can be connected to circuitry (not shown) beneath the supporting frame (not 50 shown) and the panel can be sealed to the 1 frame around the panel's entire periphery. The insert 28, made of the same 0.125 mm transparent Mylar as the upper layer 16, fits into the void between the cuts 54.

55 Spacing the upper layer 16 from and adher- 1 ing it to the lower layer 20 is the spacer layer 18. Identical in composition to the spreader layer 14, the spacer layer 18 consists of a 0.075 mm Mylar layer 64 sandwiched be-60 tween two 0.0375 mm adhesive layers 66, 1 68. Rectangular spacer holes 70 are diecut underneath the contacts 48. The spacer holes 70 are larger than the openings 46 in the spreader layer 14, and just slightly smaller 65 than the contacts 48 (Fig. 2). The slot 24

receives the tail 22. On either side of the slot 24 are four round holes 72, which receive unhardened conductive epoxy 62 during assembly for electrically connecting transfer pads 58 and 59. The holes 72 are all 6mm in diameter.

The lower contact-carrying layer 20 (0.125 mm thick transparent Mylar) has printed on its top surface conductive paint contacts 74,

leads 60, and transfer pads 59, and carries an adhesive layer 73 (3M adhesive described above) on its undersurface. The contacts 74 are connected by an extension of a lead 60 to a transfer pad 59. The contacts 74 are registered with the contacts 48 on the upper layer 16, and have the same rectangular shape with rectangular transparent centres 76. The slot 26 receives the tail 22. An adhesive layer 73 adheres the entire panel 10 to the supporting frame (not shown).

In use of the switch, a person selects the desired button and presses it with his finger generally in the centre of the button outline. The force applied by the finger is radially spread in the spreader layer 14 to the periphery of the corresponding opening 46 (Fig. 2). The spread out force pattern thus bears directly on the rectangular contact ring 48, and assures engagement between contacts 48 and 74. Without the spreader layer, a centrally applied force might not exert enough force at the contact periphery to engage the periphery. When the contacts 48 and 74 touch, a circuit is completed between one row lead 60 on the lower layer 20 and one column lead 50 on the upper layer 16. The layers 16 and 20 thus form an X-Y matrix. The circuit is complete through the unhardened conductive epoxy 62 connecting one pair of corresponding transfer pads 58, 59. The incandescent light source (not shown) illuminates the button outlines 36 and the other centrally-located indicia 38 to identify buttons in low light or night conditions. Light is transmitted through the transparent centre 76 in the lower layer 20, the spacer hole 70, the transparent centre^ 52 in the upper layer 16, the opening 46 in the spreader layer 14, and the translucent indicia 36, 38 in the overlay 12. >

The contacts 48 and 74 need not be connected in an X-Y matrix. One contact could be a pattern of two spaced-apart circuit paths and the other an electrical bridging element to complete the circuit between the circuit paths. The appropriate conductive pattern could be provided on a surface of the substrate or frame to which the flexible switch is attached. The spacer layer 18 need not be included in the flexible switch panel, but could be built into the surface of the substrate or frame, as could any adhesive that is used for mounting the switch panel. Air channels could connect the adjacent apertures 46, 70, to soften the tactile feel of the switch.

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GB 2 072 428 A 3

Claims

1. A flexible switch having contacts and comprising a first flexible layer carrying at least one electrical pathway, a second layer

5 carrying at least one electrical pathway,

means including a spacer layer separating said first and second layers whereby a portion of the first-mentioned electrical pathway operates as a movable switching contact, and normally *10 conductive material inserted within at least one aperture in said spacer layer and in electrical contact with said electrical pathways on both said first and second layers, thereby providing an internal electrical connection be-15 tween said first and second layers.

2. A flexible switch as claimed in claim 1 wherein said conductive material is unhardened conductive epoxy resin.

3. A flexible switch as claimed in claim 1 20 wherein said conductive material is hardened conductive epoxy.

4. A flexible switch as claimed in claim 1 wherein said conductive material is conductive grease.

25 5. A flexible switch as claimed in claim 1 wherein said conductive material is conductive ink.

6. A flexible switch as claimed in any one of the preceding claims wherein said first 30 flexible layer further includes conductive switch pads supported on a first surface, said switch pads being arranged in rows and said swich pads in each row being connected by one of said electrical pathways. 35 7. A flexible swich as claimed in claim 6 wherein said second layer is flexible and further includes conductive switch pads supported on a surface facing said first surface of said first flexible layer, said switch pads being 40 aligned with said switch pads in said first layer ana arranged in columns perpendicular to said rows on said first flexible layer and said switch pads in each column being connected by one of said electrical pathways. 45 8. A flexible switch as claimed in any one of the preceding claims wherein said first and second layers further include individual conductive transfer pads connected to said electrical pathways and said spacer layer includes a '50 plurality of apertures filled with said conductive material, each said pad on said first layer being aligned with one said aperture and one said pad on said second layer and said aligned pads each being in electrical contact 55 with said conductive material in said aligned aperture, whereby a larger area of contact is formed between said conductive material and said electrical pathways than the minimum necessary to provide an electrical pathway. 60 9. A flexible switch as claimed in any one of the preceding claims wherein said first flexible layer includes a tail carrying extensions of said electrical pathways carried by said first layer, at least one of said extensions 65 being in electrical contact with one of said inserts of conductive material, thereby providing an electrical connection between said second layer and said tail.

10. A flexible switch substantially as here-70 inbefore described with reference to, and as shown in, the accompanying drawings.

CLAIMS (11 Jun 1981)

1. A flexible switch having contacts and 75 comprising a first flexible layer carrying at least one electrical pathway, a second layer carrying at least one electrical pathway,

means including a spacer layer separating said first and second layers whereby a portion of 80 the first-mentioned electrical pathway operates as a movable switching contact, and at least one aperture in said spacer layer aligned with said electrical pathways on both said first and second layers and filled with a material which 85 is sufficiently conductive of electricity when in an uncompressed condition as to provide an operative electrical connection between said first and second layers.

Printed for Her Majesty's Stationery Office by Burgess & Son (Abingdon) Ltd.—1981.

Published at The Patent Office, 25 Southampton Buildings,

London, WC2A 1AY, from which copies may be obtained.