Electrostatic discharge protection in a portable communication device

• US 6,207,912 B1
• Filed: 03/02/1998
• Issued: 03/27/2001
• Est. Priority Date: 03/03/1997
• Status: Expired due to Term

• Current Assignee: Telefonaktiebolaget LM Ericsson
• Original Assignee: Telefonaktiebolaget LM Ericsson
• Inventors: Persson, Göran
• Primary Examiner(s): LUEBKE, RENEE S
• Application Number:
  US09/032,794
• Time in Patent Office: 1,121 Days
• Field of Search: 200/305, 200/306, 200/5.A, 200/512
• US Class Current: 200/305
• CPC Class Codes: H01H 13/702 with contacts carried by or formed from layers in a multilayer structure, e.g. membrane switches
• CPC Class Codes: H01H 2215/008 Part of substrate or membrane
• CPC Class Codes: H01H 2231/022 Telephone handset
• CPC Class Codes: H01H 2239/004 High frequency adaptation or shielding
• CPC Class Codes: H01H 2239/008 Static electricity considerations
• CPC Class Codes: H04M 1/0202 Portable telephone sets, e.g. cordless phones, mobile phones or bar type handsets constructional features of telephone transmitters or receivers, e.g. of speakers or microphones H04M1/03
• CPC Class Codes: H04M 1/23 Construction or mounting of dials or of equivalent devices; Means for facilitating the use thereof by improving visibility H04M1/22
• CPC Class Codes: H05K 9/0067 Devices for protecting against damage from electrostatic discharge

Abstract

A portable communication device has an electronic circuit board arranged inside a housing, and a keypad, the individual keys of which are arranged, when depressed, to collapse a respective tactile dome on a domefoil interposed between the keypad and the circuit board, so as to establish electric contact with a respective contact point on the circuit board. The domefoil is formed as a non-conductive sheet providing an airtight and/or electrostatic seal between the keypad and the circuit board. The domefoil protects the circuit board from electrostatic discharge.

Claims

1. A portable communication device, comprising an electronic circuit board arranged inside a housing, and a keypad, individual keys of which are arranged, when depressed, to collapse a respective tactile dome on a domefoil interposed between the keypad and the circuit board, so as to establish electric contact with a respective contact point on the circuit board, wherein

said domefoil is formed as a non-conductive sheet providing an electrostatic seal between the keypad and the circuit board, said domefoil thereby protecting the circuit board from electrostatic discharge (ESD);

and

an electrically conductive layer is provided in an interior of the domefoil and is connected to ground means, said layer thereby inhibiting electromagnetic interference between the device and its surroundings.

2. The communication device according to claim 1, wherein the device is a radio telephone.

3. The communication device according to claim 2, wherein the device is a cellular telephone.

4. A method of protecting a keypad-operated device from electrostatic discharge between a keypad and an electronic circuit board inside the device, comprising a step of

providing the device with a domefoil, comprising a set of tactile domes and at least an entire front surface of which being made from an electrically isolating material, as an electrostatic seal between the keypad and the circuit board;

and

providing an interior of the domefoil with an electrically conductive and grounded layer, said layer acting as an electromagnetic shield between the circuit board and electronic equipment external to the device.