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STATIC DISCHARGE GUARD DEVICE

IP.com Disclosure Number: IPCOM000005623D
Original Publication Date: 1986-Oct-01
Included in the Prior Art Database: 2001-Oct-22
Document File: 2 page(s) / 62K

Publishing Venue

Motorola

Related People

Theodore V. Lester: AUTHOR

Abstract

Electrostatic discharge (ESD) protection of electronic circuitry often involves the use of guards and shunt discharge paths. An example of such protection involves protection of a DIP switch, accessible through a slot in a plastic enclosure, from direct discharge while the switch is being accessed.

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0 MOTOROLA

Technical Developments Volume 6 October 1966

STATIC DISCHARGE GUARD DEVICE

by Theodore V. Lester

   Electrostatic discharge (ESD) protection of electronic circuitry often involves the use of guards and shunt discharge paths. An example of such protection involves protection of a DIP switch, accessible through a slot in a plastic enclosure, from direct discharge while the switch is being accessed.

   A metal guard ring or aperture plate connected to a ground return has been used in the past to conduct discharges to ground, protecting the DIP switch and associated circuitry from a direct discharge. This often creates problems, however, due to the high peak currents that result when the guard conducts the discharge to ground; the high peak currents are known to reach 15Kv. In fact, ESD simulation testing typically involves discharging a 15OpF or larger capacitor, charged to 15KV, through 150 ohms.

   While the high peak discharge current can be reduced by placing a series resistor in the ground return for the guard plate, a method using less parts is possible by making the aperture guard out of plastic film with a screened carbon resistance material. Carbon based inks have sheet restivities of 40 to 90 ohms/square when applied to plastic sheet.

   By screen printing a resistive ink in a spiral pattern on the plastic film, sufficient ground path resistance can be included to substantially reduce discharge currents while adding an inductive component to lengthen discha...