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January 2008

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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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