1B31 coating may stick to your no clean residues - you'd have to
evaluate it or see if Humiseal or your flux manufacturer has any data.

Ensuring that the flux is fully activated when you hand apply flux and
hand solder is difficult.  Flux pens vs. a bottle may help limit the
amount applied, or you can pretin the components and solder with only
the flux core in the solder wire.  If you try to heat the coated
assembly post soldering to kill the flux the 1B31 will get "sticky" and
be prone to imprinting until it has cooled - you'd might need to support
the assembly.

I've taped areas off with kapton to locally strip coating, remove and
replace with RMA, clean, then recoat.  Time consuming but it can be
done.

Don't wipe 1B31 with alcohol - it will dissolve the coating and/or leave
fibers from your wipe.  

Mike

-----Original Message-----
From: TechNet [mailto:[log in to unmask]] On Behalf Of Ioan Tempea
Sent: Tuesday, September 09, 2008 2:45 PM
To: [log in to unmask]
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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