Diagnosis of Malfunctions in Complex Electronic Assemblies. Final Report. Page: 36 of 66
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However, since both detectors must be developed and proven feasible, and
since switching, fixturing, and general testers could be evaluated separately,
the following development plan was chosen as the most economical' approach.
" A complete tester would be developed to include a functional type of
detector that would make functional checks of individual stages of circuitry.
" A separate detector would be developed and evaluated for checking indi-
vidual passive components. -
" The tester would be evaluated under actual production line conditions to
evaluate such areas as speed of testing, fixturing, operating simplicity,
attitudes 6f'the assembly workers concerning the tester, and the general
effectiveness of tester performance.
" Recommendations for production equipment would be made on the basis -
of the combined effectiveness of the two detector types.
Fixture Design an'd Development. The two most important dimensions in the
fixture design were: . .
" Speed required to mount: the printed circuit board; and
" The reliability of electrical contact.
Since this type of tester is to be operated by unskilled operators, false indi-
cations needed particularly. to be avoided. A study of spring-type fixtures
showed that failures were often caused .by:
" Uneven holding pressures resulting in circuit board tilt;
" Isolation at the point of contact due to oxide films, flux or other foreign
material, or irregular solder surfaces; and
" Spring contact failures because of faulty contact and bent contacts.
The fixture is shown in Figure 4. Installation of the board to the fixture
requires approximately 15 seconds. The spring contact design has a cupped
head with a lip around the periphery of the cup, allowing better probability
of contact than a pointed configuration, and the cup mates well with the nor-
mal contour of a solder joint. This mounting arrangement provides clamps
that pick up'tooling holes approximately 120 degrees apart and clamp the
printed circuit assembly down against standoff posts. The platform plane
containing the spring contacts is raised into the board by pushing a levee
forward. The' lever is mechanically linked to an eccentric cam. Rotation
of the cam by the forward motion of the lever applies an upward force to a
rod riding on the cam. The rod, in turn, lifts the platform containing the
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Losure, J. A. Diagnosis of Malfunctions in Complex Electronic Assemblies. Final Report., report, January 1, 1971; Kansas City, Missouri. (https://digital.library.unt.edu/ark:/67531/metadc1031893/m1/36/: accessed March 22, 2019), University of North Texas Libraries, Digital Library, https://digital.library.unt.edu; crediting UNT Libraries Government Documents Department.