WO2007011807A2

WO2007011807A2 - Elastomeric membrane switch

Info

Publication number: WO2007011807A2
Application number: PCT/US2006/027539
Authority: WO
Inventors: Alexander L. Darbut; Thomas Bruce Odegard
Original assignee: Soundquest, Inc.
Priority date: 2005-07-18
Filing date: 2006-07-18
Publication date: 2007-01-25
Also published as: WO2007011807A3

Abstract

An elastomeric membrane switch having an elastomeric connector comprising a plurality of alternating vertically disposed conductive layers and non-conductive layers extending between upper and lower contact surfaces. The lower surface of the elastomeric connector is disposed over a substrate having electrically isolated, first and second contact pads of an electrical switch circuit. Each of the first and second contact pads is in electrical contact with different ones of the exposed ends of conductive layers of the lower contact surface. A resilient membrane having an electrically conductive interior surface is spaced a distance above the upper contact surface, whereby upon applying a downward force to the resilient member, the otherwise electrically isolated contact pads are electrically connected through the electrically conductive layers of the elastomeric connector and the electrically conductive interior surface of the resilient member.

Description

ELASTOMERIC MEMBRANE SWITCH

CROSS-REFERENCE TO RELATED APPLICATIONS This application is a continuation-in-part of U.S. Patent Application No. 11/184,604 filed July 18, 2005 and claims priority to Provisional Application No. 60/700,548 filed July 18, 2005.

BACKGROUND

Membrane switches are used in many small-scale consumer applications because they provide a substantially waterproof cover, have a low profile, and are easy to operate. Membrane switches generally have a membrane that covers a conventional electro- mechanical pushbutton switch or a switch that comprises two electrically conductive elements on flexible substrates separated by an air gap. On a "normally open" switch, for example, by depressing the flexible membrane, at least two electrically isolated contact points within the pushbutton switch or on the respective separated flexible substrates are forced to make contact, thereby completing the circuit, and thereby allowing electrical current to flow between the previously separated contact points.

Pushbutton and flexible substrate switches that are typically located under the flexible membrane require small-scale, movable elements. These small-scale movable elements can wear and fail over time after repeated use. Additionally, pushbutton switches generally require wires or soldering, which prove difficult or impractical in many small-scale applications. Similarly, flexible substrate switches generally require a connector on each spaced substrate layer that in turn must connect to a mating connector by soldering or other means of affixing to a printed circuit board (PCB) or flexible circuit. Other disadvantages associated with pushbutton switches is that older people who have lost tactile sensation in their fingertips cannot feel whether the membrane switch has been depressed. Unfortunately, such pushbutton switches are often found on hearing aids and other small-scale devices used by older people who have lost tactile sensation.

Accordingly, there is a need for a membrane switch that eliminates or reduces the need for tactile sensitivity to open and close the switch. There is also a need for such a switch that can be used in small-scale applications that does not require soldering and that overcomes the other attendant disadvantages and shortcomings associated with conventional membrane switches utilizing push-buttons or flexible circuit switches.

Elastomeric connectors, such as Z-Connectors, available from Z- Axis Connector Company, Warminster, PA, are made from alternating layers of a conductive and non- conductive layers. Such elastomeric connectors are often used to connect electronic components such as connection pads on adjacent PCBs because they eliminate the need for soldering and/or drilling of holes. Therefore, it is desirable to provide a switch that utilizes the features and advantages of elastomeric connectors for a membrane switch.

SUMMARY The present invention is directed toward an elastomeric membrane switch. In the preferred embodiment, the elastomeric switch includes an elastomeric connector comprising a plurality of alternating vertically disposed conductive layers and non- conductive layers extending between upper and lower contact surfaces. The lower surface of the elastomeric connector is disposed over a substrate having electrically isolated, first and second contact pads of an electrical switch circuit. Each of the first and second contact pads is in electrical contact with different ones of the exposed ends of conductive layers of the lower contact surface. A resilient membrane having an electrically conductive interior surface is spaced a distance above the upper contact surface, whereby upon applying a downward force to the resilient member, the otherwise electrically isolated contact pads are electrically connected through the electrically conductive layers of the elastomeric connector and the electrically conductive interior surface of the resilient member.

BRIEF DESCRIPTION OF THE DRAWINGS FIG. 1 is a perspective view of a membrane switch in accordance with the present invention disposed on a surface of a device.

FIG. 2 is a cross-sectional view of the membrane switch of FIG. 1 as viewed along lines 2-2 of FIG. 1.

FIG. 3 is a partially broken top plan view of the membrane switch.

FIG. 4 illustrates a device where two membrane switches of FIG. 1 are disposed on opposite sides of a device using a single circuit panel.

DETAILED DESCRIPTION Referring now to the drawings wherein like reference numerals identify corresponding or like parts throughout the several views, FIG. 1 is a perspective view of a membrane switch 100 disposed on a surface 101 of an electrical or electro-mechanical apparatus where a membrane switch may be utilized to open and close an electrical connection. FIG. 2 is an enlarged cross-sectional view of the membrane switch 100 as viewed along lines 2-2 of FIG. 1. FIG. 3 is a partially broken top plan view of the switch 100. The cross-sectional view of FIG. 2 and the plan view of FIG. 3 of the switch 100 are obviously greatly exaggerated in order to better illustrate the structure of the preferred membrane switch 100.

The membrane switch 100 includes a flexible, resilient membrane 102 extending over an opening 103 in the surface 101 of the apparatus on which the switch is used. The flexible membrane 102 may be made from any suitably flexible and resilient material such as a polymer or rubber material. In the preferred embodiment, the membrane 102 is preferably dome shaped and sealed over the opening. An electrically conductive coating 106 is preferably disposed on at least a portion of the interior surface 104 of the membrane 102. The conductive coating 106 can be any type of conductive material that adheres or which can otherwise be bonded to the flexible membrane 102 and which is sufficiently resilient so as to move and flex with the membrane 102 while maintaining electrical continuity. In the preferred embodiment, the conductive coating 106 is a conductive carbon paint.

Disposed below the flexible, resilient membrane 102 is an elastomeric connector designated generally by reference numeral 200. The elastomeric connector 200 is preferably a Z-Connector, available from Z- Axis Connector Company, Warminster, PA, which comprises alternating layers of electrically conductive elements 202 and non- conductive elements 204, such that, as illustrated in FIG. 2, the exposed ends of the conductive layers 202 form upper and lower contact surfaces 206, 208, respectively. An insulating or non-conductive support layer 210 preferably surrounds the perimeter of the connector 200 leaving only the upper and lower contact surfaces 206, 208 exposed.

In the preferred embodiment, the conductive layers 202 preferably comprise carbon-silicon, but other conductive materials such as carbon, gold, silver or any of a number of other conductive materials may also be suitable for the conductive layers 202. In the preferred embodiment, the non-conductive layers 204 and support layer 210 preferably comprise silicone rubber, but any suitable non-conductive material may be utilized. An advantage of using silicone rubber as the material for the non-conductive layers 204 and support layer 210 is that the connector 200 is somewhat flexible and resilient, which may be beneficial in some applications.

It should be appreciated, that connector 200 can have different conductive properties and/or resistance values desired based on the conductive layer materials and their dimensions. Additionally, the connector 200 can have different materials and dimensions for the support layer 210 as desired depending on the particular application for the switch.

Disposed below the connector 200 and preferably pressure sealed or otherwise secured to the support layer 210, is a PCB or other substrate 300 on which is disposed electrically conductive tracings or contact pads 302, 304 of the switch circuit. It should be appreciated that the contact pads 302, 304 of the switch circuit are electrically isolated from each other. As shown, different conductive layers 202 from the connector 200 are preferably in contact with each contact pad 302, 304.

In the embodiment illustrated in FIG. 2, the switch is a "normally open" switch. Thus, the electrical contact pads 302, 304 on the substrate 300 remain electrically isolated until the resilient member 102 is sufficiently depressed to close the switch circuit. It should be understood that upon the electrically conductive coating 106 on the underside of the membrane 102 making electrical contact with the ends of the electrically conductive layers 202 of the upper contact surface 206, the otherwise electrically isolated contacts 302, 304 will be electrically connected. This is so because the electrically conductive layers 202 extend between the upper and lower contact surfaces 206, 208, and because the exposed ends of the electrically conductive layers 202 of the lower contact surface 208 are in electrical contact with the contact pads 302, 304. Likewise, when down pressure is released from the membrane 102, the electrically conductive coating 106 on the underside of the interior surface 104 of the membrane 102 returns to its original position, thereby breaking the electrical contact with the upper contact surface 206 of the connector 200 and thereby returning the switch to its "normally open" condition.

FIG. 4 illustrates an application where two switches 100 are disposed on opposing side walls 101 of an apparatus. In this example, the two switches 100 are shown disposed back-to-back against a single PCB or substrate having contact pads or traces 302, 304 on opposing sides. A particular application for the back-to-back switch is on a behind-the- ear (BTE) auditory device as disclosed in U.S. Patent Application No. 11/184,604, incorporated herein by reference.

The foregoing description is presented to enable one of ordinary skill in the art to make and use the invention and is provided in the context of a patent application and its requirements. Various modification to the preferred embodiment of the apparatus and its method of use and the general principles and features described herein will be readily apparent to those of skill in the art. Thus, the present invention is not to be limited to the embodiments of the apparatus and methods described above and illustrated in the drawing figures, but is to be accorded the widest scope consistent with the spirit and scope of the appended claims.

Claims

Claims:

1. An elastomeric switch comprising:

(a) an elastomeric connector having upper and lower contact surfaces comprising a plurality of alternating, exposed ends of conductive layers and non- conductive layers extending between said upper and lower contact surfaces;

(b) a substrate having electrically isolated first and second contact pads of an electrical switch circuit, each of said first and second contact pads in electrical contact with different ones of said exposed ends of conductive layers of said lower contact surface;

(c) a resilient membrane having an electrically conductive interior surface spaced a distance above said upper contact surface, whereby upon applying a downward force to said resilient member, said electrically conductive interior surface electrically contacts said exposed ends of conductive layers of said upper contact surface which are in electrical contact with said different ones of said exposed ends of conduct layers of said lower contact surface in electrical contact with said first and second contact pads of said substrate, thereby closing the electrical switch circuit.

2. The elastomeric switch of claim 1, wherein the conductive layers comprise carbon.

3. The elastomeric switch of claim 1, wherein the conductive layers comprise gold.

4. The elastomeric switch of claim 1 , wherein the conductive layers comprise silver.

5. The elastomeric switch of claim 1 , wherein the non-conductive layers comprise silicone.

6. A back-to-back elastomeric switch, comprising:

(a) a first elastomeric switch, disposed on a first surface, said first elastomeric switch comprising:

(i) a first elastomeric connector having upper and lower contact surfaces comprising a plurality of alternating, exposed ends of conductive layers and non-conductive layers extending between said upper and lower contact surfaces;

(ii) a first resilient membrane having an electrically conductive interior surface spaced a distance above said upper contact surface of said first elastomeric connector

(b) a second elastomeric switch, disposed on a second surface opposing said first surface, said second elastomeric switch comprising:

(i) a second elastomeric connector having upper and lower contact surfaces comprising a plurality of alternating, exposed ends of conductive layers and non-conductive layers extending between said upper and lower contact surfaces; (ii) a second resilient membrane having an electrically conductive interior surface spaced a distance above said upper contact surface of said second elastomeric connector;

(c) a substrate having a first side and a second opposing side, both said first and second sides having electrically isolated first and second contact pads of an electrical switch circuit, each of said first and second contact pads of said first side in electrical contact with different ones of said exposed ends of conductive layers of said lower contact surface of said first connector, each of said first and second contact pads of said second side in electrical contact with different ones of said exposed ends of conductive layers of said lower contact surface of said second connector; whereby upon applying a downward force to either said first or second resilient member, said electrically conductive interior surface thereof electrically contacts said exposed ends of conductive layers of said upper contact surface of said respective connector which are in electrical contact with said different ones of said exposed ends of conduct layers of said lower contact surface of said respective connector in electrical contact with said respective first and second contact pads of said substrate, thereby closing the electrical switch circuit.

7. The back-to-back elastomeric switch of claim 6, wherein the conductive layers comprise carbon.

8. The back-to-back elastomeric switch of claim 6, wherein the conductive layers comprise gold.

9. The back-to-back elastomeric switch of claim 6, wherein the conductive layers comprise silver.

10. The back-to-back elastomeric switch of claim 6, wherein the non- conductive layers comprise silicone.