NZ201186A - Membrane push button switch array:conductive elastomeric pad screens contacts from electrostatic discharges - Google Patents

Description

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PubHcation Date: £.8, S£P. 199A P.O. Joum:!, No: NEW ZEALAND THE PATENTS ACT, 1953 COMPLETE SPECIFICATION "PUSH-BUTTON SWITCH1 WE, INTERNATIONAL STANDARD ELECTRIC CORPORATION, a Corporation of the State of Delaware, United States of America, of 320 Park Avenue, New York 22, New York, United States of America, hereby declare the invention, for which we pray that a patent may be granted to us, and the method by which it is to be performed, to be particularly described in and by the following statement 1 - 201186 This invention relates to "dimple pad" switching arrangements, such as used in electrical push-button switches.

Such pads use conductive elastomeric materials, and, see Fig. 1, are usually made from a sheet 1 of a non-conductive material such as rubber or a rubber-like insulating material. The sheet has for each switch a dimple such as 2 which is of dome or conical form to which is bonded a small disc or pill 3 of an electrically conductive material. When the push-button for the dimple 2 is depressed, the pill 3 is driven down to bridge two adjacent contacts 4 on an insulating substrate 5. As used in a telephone for push-button"dialling", the two contacts 4 would be row and column contacts which are bridged to control the "dialling".

The keypad contacts are often connected directly to the inputs of electronic devices which may be susceptivle to electrostatic damage, e.g. if the user of the keyset is himself electrostatically charged. An object of the invention is to provide an improved contact pad of the above type in which this difficulty is minimised ot overcome.

According to the invention there is provided a switching arrangement which includes a contact pad formed of an electrically conductive elastomeric material which includes a plurality of elements each of which is of a trusto-conical shape with its top portion thickened with respect to its walls, and an insulating material layer on which the contact pad is 2 0118 6 mounted with each said thickened portion aligned with a pair of contacts on the insulating layer, in which to complete a connection a said element is collapsed so that its thickened region bridges the contacts thereunder and connects both of them to a common point.

An embodiment of the invention will now be described with reference to the accompanying Pig. 2.

In the arrangement of Fig. 2, the sheet 6 of elastomeric material is a conductive material, with for each contact-making region a somewhat thickened disc 7. The sheet itself has a connection 8 to a common point in the circuit, which may be earth. This gives two make contacts per button, i.e. row-common and column-common. In addition, the use of a conductive elastomer for the sheet provides an electrostatic screen for the contacts and thus for circuitry connected thereto. When the common point is earth it will be clear that any electrostatic discharge due to the user is coupled directly to the circuit earth.

Claims (2)

01186 What we claim is:

1. A switching arrangement which includes a contact pad formed of an electrically conductive elastomeric material which includes a plurality of elements each of which is of a frusto-conical shape with its top portion thickened with respect to its walls, and an insulating material layer on which the contact pad is mounted with each said thickened portion aligned with a pair of contacts on the insulating layer, in which to complete a connection a said element is collapsed so that its thickened region bridges the contacts thereunder and connects both of them to a common point.

2. A switching arrangement substantially as described with reference to Fig. 2 of the accompanying drawings. INTERNATIONAL STANDARD ELECTRIC CORPORATION P.M. CONRICK Authorized Agent 5/1/1053 - 4 -