GB2102626A

GB2102626A - Contact dimple pad

Info

Publication number: GB2102626A
Application number: GB08122393A
Authority: GB
Inventors: Frederick John Howett
Original assignee: Standard Telephone and Cables PLC
Current assignee: STC PLC
Priority date: 1981-07-21
Filing date: 1981-07-21
Publication date: 1983-02-02
Also published as: AU553429B2; NZ201186A; AU8607382A; GB2102626B

Abstract

In a block of push button switches for use in a telephone set, including a dimple pad with a dimple per switch, the dimple pad is a sheet (6) of an electrically conductive elastomer with a number of frusto-conical dimples each having its flat top thickened to form a contact (7). The sheet has a connection (8) for earthing so that when depressed it bridges and earths two contacts on an underlying insulating substrate. This overcomes the effect of electrostatics. <IMAGE>

Description

SPECIFICATION Contact dimple pad 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 susceptible 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 or 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 frusto-conical shape with its top portion thickened with respect to its walls, and an insulting 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.

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

1. A switching arrangement which includes a contact pad formed of an electically 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.

CLAIMS (3rd Dec 1981) 3. 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 the frusto-conical walls, and an insulating material layer on which the contact pad is mounted with each end said thickened portion aligned with a pair of contacts on the insulating layer, in which each said thickened portion is of cylindrical form with its end face substantially parallel with the 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, and in which when the switching arrangement is in use the contact pad is electrically connected to a common point at a reference potential so that the contact pad also acts as an electrostatic screen for the contacts.

**WARNING** end of DESC field may overlap start of CLMS **.

Claims

**WARNING** start of CLMS field may overlap end of DESC **. SPECIFICATION Contact dimple pad 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 susceptible 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 or 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 frusto-conical shape with its top portion thickened with respect to its walls, and an insulting 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. An embodiment of the invention will now be described with reference to the accompanying Fig. 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

CLAIMS (3rd Dec 1981)

3. 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 the frusto-conical walls, and an insulating material layer on which the contact pad is mounted with each end said thickened portion aligned with a pair of contacts on the insulating layer, in which each said thickened portion is of cylindrical form with its end face substantially parallel with the 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, and in which when the switching arrangement is in use the contact pad is electrically connected to a common point at a reference potential so that the contact pad also acts as an electrostatic screen for the contacts.