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1996

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From:
[log in to unmask] (Steve Mikell)
Date:
Thu, 21 Mar 1996 17:18:18 -0600
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Jack Tippet asked

>Since starting to use aqueous cleaning with Armakleen E-2001A saponification 
>for removal of RMA flux, have experienced some problems with removal of PWB 
>silk sceen marking and one case where solder mask has came off traces on a 
>CCA.  This case has soldermask over bare copper using a dry film mask.  We 
>are a military environment and have multiple cleaning steps i.e., after SMT, 
>wave solder, and final assembly.
>Have others experienced problems between solder mask coatings and aqueous 
>cleaning using saponification?

Yes Jack, all of us.  The alkalinity of your cleaning solution will destroy
any dryfilm soldermask I have encountered to date.  It will also destroy a
soldermask known as Conformask.  As a result of our experiences during both
SMT reflow and saponified cleaning, no dryfilm soldermasks are approved for
new buys of PWBs.  All new orders use a tested LPI type solder mask, with a
few holdovers using a liquid epoxy silk screened soldermask.

The marking ink problems with both legend markings on the PWB, and markings
applied internally for rev level and serial number, will be wiped out if
proper precleaning, mixing and curing processes are not followed.
Additionally, if the surface is not properly designed for the ink to adhere,
it may still come off.  I refer specifically to glossy soldermask or to
areas of glossy ink applied as a contrasting background.  Similar problems
occur on plated parts, plastic parts ..especially connector bodies, and others.

That's the bad news.  I had three major programs in design when we tested
all "current materials" for compatibility in 1993.  When we finally went
operational with our alternate cleaning process in 1995, we painfully
discovered the dryfilm problem on these new military programs.  Fortunately,
I had also ordered a solvent-only, tank-type cleaner and a dishwasher type
cleaner.  For dryfilm PWBs, we soak the CCA in the agitated solvent, rinse
in IPA, dry, and then rinse the CCA in hot DI water in the dishwasher.  We
also tossed a number of raw PWBs.

If you wish further info on cleaner models, cleaning solutions, dryfilm
suppliers, qualified LPIs and the rest, contact me directly at
       [log in to unmask]

Steve Mikell,  Process Engineer, Soldering and Cleaning
SCI Systems, Government Division, Plant 13



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