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Text Fixture for High-Density Circuit Cards

IP.com Disclosure Number: IPCOM000117213D
Original Publication Date: 1996-Jan-01
Included in the Prior Art Database: 2005-Mar-31
Document File: 2 page(s) / 78K

Publishing Venue

IBM

Related People

Anderson, G: AUTHOR [+3]

Abstract

Modern circuit board assemblies are being designed to accommodate components at higher and higher densities. This is happening primarily on mobile products where size is one of the main design points. This evolution is causing problems for the "bed of nails" fixtures used to electrically test the cards after assembly at "In Circuit Test".

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Text Fixture for High-Density Circuit Cards

      Modern circuit board assemblies are being designed to
accommodate components at higher and higher densities.  This is
happening primarily on mobile products where size is one of the main
design points.  This evolution is causing problems for the "bed of
nails" fixtures used to electrically test the cards after assembly at
"In Circuit Test".

      The decreasing free space on the cards is forcing the card
designers to reduce or even ignore the test points used by the "bed
of nails" fixtures and the test points which are provided are on a
decreasing pitch and diameter.  These two scenarios mean that the
fixtures must have probes on a tighter pitch and must be able to prob
areas of the card other than test points, such as solder joints or
even component leads themselves.

      Conventional designs for these fixtures cannot accomplish this
as the individual probes are unguided, which means they can be
deflected away from their target test point, and the mechanical
precision of the probes mounting is low.  So when a conventional test
fixture is used to probe a modern mobile card, the test will fail due
to poor electrical contact and eventually the probes will become bent
or broken.

      A conventional fixture (Fig. 1) has the probes secured to a
probe plate.  When this is pushed down onto the card under test,
stops on the fixture stop the downwards travel of the guide plate a
predetermined height above th...