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Voltage Short Detection by Liquid Crystal Sheets

IP.com Disclosure Number: IPCOM000044939D
Original Publication Date: 1983-Jan-01
Included in the Prior Art Database: 2005-Feb-06
Document File: 1 page(s) / 12K

Publishing Venue

IBM

Related People

Press, RM: AUTHOR

Abstract

In card testing, certain cards fail due to a voltage-ground plane short. A large percentage of these cards are scrapped because of the time involved to find the short. The scrap process may be avoided for most of these cards by using a heat sensitive - liquid crystal sheet, such as that made by Edmond Scientific Co.

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Voltage Short Detection by Liquid Crystal Sheets

In card testing, certain cards fail due to a voltage-ground plane short. A large percentage of these cards are scrapped because of the time involved to find the short. The scrap process may be avoided for most of these cards by using a heat sensitive - liquid crystal sheet, such as that made by Edmond Scientific Co.

The liquid crystal sheets come in several different temperature ranges. However, for the process of short detection, the temperature range should be just above the normal working environment temperature. In most cases the range would be from 25 degrees to 30 degrees centigrade.

The nature of a short will produce heat. It is this heat that is used to detect the shorted point. The liquid crystal sheet is placed in contact (the flat block surface of the sheet) with the pin side of the shorted card. The card must be at room temperature. Too much handling will place heat on the card which will show on the crystal sheet. A low voltage (5V) at 1 amp (maximum of 2 amps) will produce enough heat for detection. The liquid crystal sheet (on the glossy side) will change color as heat is applied; the more heat (up to a point without damaging the sheet) will cause the most dramatic change in the color of the surface area on the sheet. The voltage applied should only be applied long enough to observe the heat pattern of the shorted lands or point.

When observing the surface, notice the point with the most color change...