Browse Prior Art Database

Liquid Crystal Electrical Continuity Tester

IP.com Disclosure Number: IPCOM000047291D
Original Publication Date: 1983-Oct-01
Included in the Prior Art Database: 2005-Feb-07
Document File: 2 page(s) / 46K

Publishing Venue

IBM

Related People

Kumar, AH: AUTHOR [+2]

Abstract

Continuity testing of dense circuit lines (e.g., on a multilayer ceramic substrate) by point-to-point contact probing is extremely cumbersome and costly. Disclosed herein is a continuity tester which utilizes the well-known ability of liquid crystals to orient under the influence of an electrical field, giving rise to a visually perceived indication. Referring to the figure, a substrate 11 includes metal vias connected to pads 13 on one surface thereof. To test continuity of vias 12, a liquid crystal device 14, comprising a layer of nematic or cholesteric liquid crystal material 15 sandwiched between two flexible transparent sheets 16 and 17, is placed on the substrate. A closely packed array of transparent conductor dots 20, corresponding to via locations, is formed on transparent sheet 17.

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Liquid Crystal Electrical Continuity Tester

Continuity testing of dense circuit lines (e.g., on a multilayer ceramic substrate) by point-to-point contact probing is extremely cumbersome and costly. Disclosed herein is a continuity tester which utilizes the well-known ability of liquid crystals to orient under the influence of an electrical field, giving rise to a visually perceived indication. Referring to the figure, a substrate 11 includes metal vias connected to pads 13 on one surface thereof. To test continuity of vias 12, a liquid crystal device 14, comprising a layer of nematic or cholesteric liquid crystal material 15 sandwiched between two flexible transparent sheets 16 and 17, is placed on the substrate. A closely packed array of transparent conductor dots 20, corresponding to via locations, is formed on transparent sheet 17. A transparent conductor sheet 22 is formed on sheet 16, and a dielectric spacer 21 is placed between substrate 11 and liquid crystal device 14. The substrate is placed on a metal mesh 18 which acts as a common bus for pads 13. When a suitable electrical potential, V, is applied between mesh 18 and electrode 22, an electrical potential develops between the conductor dots 20, adjacent electrically continuous vias 12, and electrode 22. The liquid crystal in these regions will orient with the potential, leading to a perceptible color change. The conductor dots 20 adjacent open-circuited vias 12 will not develop the potential, so that th...