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Date: | Sun, 6 Jan 2008 23:56:42 EST |
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If you go back and read the original 1972 work by the Navy on the
development of MIL-P-XXXXX, which became MIL-P-28809, the original reason for PWA
cleanliness testing was to make sure the assembly was clean prior to the
application of conformal coating. The services were also concerned since MIL-RA fluxes
were coming into use at about that time; these had significantly higher
activator levels compared with the traditional RMA formulations.
Before just concluding that since you don't conformally coat assemblies
there is no need to do cleanliness testing, remember that component density,
solder joint spacing etc. were crude compared to today's complex, high density
multilayer assemblies. So cleanliness testing will provide a safety net that
protects the PWA maker as the industry packs more and more with higher
reliability requirements into a fraction of the space allowed in the early 1970's
While on the topic of the changes in complexity and density since the '70's,
let us not forget that the 'no clean' fluxes came into use (primarily in
customer premise telephone circuitry) in the late '80's-- think how much has
changed since then. [It always helps to consider things in context!]
Bill Kenyon
Global Centre Consulting
3336 Birmingham Drive
Fort Collins, CO 80526
Tel: 970.207.9586 Cell: 970.980.6373
**************Start the year off right. Easy ways to stay in shape.
http://body.aol.com/fitness/winter-exercise?NCID=aolcmp00300000002489
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