Well now, it depends.  Is the low residue flux from eutectic tin-lead or 
lead free?  The latter may have harder residues.  What I have generally 
found is that the solvent from 1B31 (toluene, xylene, MEK) will have a 
tendency to bite into the flux residues creating a little better adhesion. 
 A coating with a less aggressive solvent may not be the same.  The 
question that arises is there some sort of negative impact of the solvent 
on the flux residue.  Depends on the residue.    Will it stick long 
enough? Depends on your definition of "long enough", whether for the 
design life of the product, or just until the warranty period is up.

We use toluene and cotton swabs and wipes to remove 1B31 prior to rework 
and repair.  Labor intensive, but it works. 

As for the white residue - go with what Mike Sewell said.

Doug Pauls




Ioan Tempea <[log in to unmask]> 
Sent by: TechNet <[log in to unmask]>
09/09/2008 02:45 PM
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Subject
[TN] Coating over no-clean






Dear Technos,

 

There are cases when we need to rework components on conformally coated
boards. In some cases the boards cannot be completely stripped due to
funky components, so we need to locally remove the CC, repair with
no-clean (a few weeks ago I've got answers on Technet that acylic cc
cannot be sent into the washer) and then re-apply coating.

 

The questions I have now are regarding cc over no-clean:

*         Will acrylic, namely 1B31, properly stick to the no-clean
residue and for long enough? 

*         Oftenly when soldering we need to add liquid no-clean flux,
which will spread and leave that white residue. Should it be wiped with
alcohol?

 

I know there are tons of issues with improperly cleaned residue and
alcohol will only spread the stuff around, etc., but I would like to
have a pragmatic point of view: what do you do in cases like this?

 

Thanks,

 

Ioan


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