Wade,
Further to what Doug wrote,  you can also correlate cleanliness tester
readings to what you "normally" (or otherwise ;(  )   see on your boards.
In the early 90's, while I was with Nortel Networks, through a two-lab test
program we found that most circuit packs manufactured with wave or foam
fluxers and no-clean fluxes gave values of 2.5 to 4.5 SOD for a particular
brand of cleanliness tester.  6-8 we took as yellow light and above 10 as a
red light situation - the board probably took a bath in a flux wave and you
usually had flux residues in your edge connectors - not a good scenario.
Pretty seat-of-the -pants, but better than nothing.

Bev Christian
XLTEK

-----Original Message-----
From: Douglas Pauls [mailto:[log in to unmask]]
Sent: March 24, 2000 7:53 AM
To: [log in to unmask]
Subject: Re: [TN] process control of final cleanliness in a no-clean
world


In a message dated 03/22/2000 4:11:05 PM US Eastern Standard Time,
[log in to unmask] writes:

>         How do all of you in the no-clean world monitor and control board
>  cleanliness.  In the days of OA flux, we used an Ionograph or Omegameter
to
>  monitor our 'cleaning' process.  Do some of you still use an ionic
>  contamination tester or do you use SIR testing or nothing or what?

Wade,
How did you do process control before you went no-clean?  You can still use
an Omegameter or Ionograph (or other such instrument) as PROCESS CONTROL,
but
you have to throw out everything you know about "good" adn "bad" numbers.
Those instruments work for process control, but not for accept-reject.   The
result that you get will probably be higher, because the weak organic acid
activators come off of the board and make the isoproapnol-water solution
conductive.  The materials are benign on a board surface.  You should do
some
correlation studies between accelerated electrical testing, such as burn-in
or life tests, and Omegameter readings.  Determine what maximum reading
correlates to failures in such accelerated testing.  Then use that as your
maximum control limit.

Doug Pauls
CSL

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