Hi Les,

This sounds very similar to a process I've used for removing acrylic
conformal coating (Humiseal 1B31 & 1B73).

I agree with what Charles already said 100%.  In addition to dissolving the
silkscreen printing (argh!) you may see the RTV get an attacked.

As with any manual operation, success will depend on goal-oriented workers.
The process goal should be to completely remove the coating as quickly as
possible.  Duh - that would costs them less money to do and you get the card
sooner.   A single soak to strip the coating can take a very long time to
work.  How long does your OEM expect the process to take?  Using an
appropriate brush to manually remove softened coating can speed things up.
We also used several (3 - 4) pans in a cascade wash - start with the
dirtiest solution first and keep transferring to cleaner ones. I'd also want
to know, how many assemblies they expect to clean before replenishing a
bath?  (I've seen assemblies soaking in totally loaded solutions, a huge
ring of conformal coating surrounding the bath and the assembly workers are
"stuck" because the coating isn't coming off.)  Your OEM may want to try
using a UV light as an in-process check for coating residue before the final
clean - especially electrical contacts.  I needed a forceful spray
(something like 15 - 30 psi, 0.5 gallon/hour) to get stripping solution
under components and flush the coating out.  They'd want to do a spray
process in a fume hood because conformal coating/stripper solution doesn't
taste good - trust me.  And as you know, the Omega meter test won't be valid
unless the alcohol can dissolve any remaining stripper residue into
solution.

Hans

Integrity First  -  Service Before Self  -  Excellence in All We Do
~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
Hans M. Hinners
Electronics Engineer
Warner Robins - Air Logistics Center (WR-ALC/LUGE)
Special Operations Forces System Program Office (SOF - SPO)
Gunship Section
226 Cochran Street
Robins AFB GA 31098-1622

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Com: (478) 926 - 5224
Fax:   (478) 926 - 4911
DSN Prefix: 468

-----Original Message-----
From: Bogert [mailto:[log in to unmask]]
Sent: Tuesday, October 02, 2001 5:25 PM
To: [log in to unmask]
Subject: [TN] Seeking Conformal Coating (Type UR) Removal Process by Solvent
Dipping


10/2/2001

Folks, I am seeking technical help on the pros/cons of removing Humiseal
Type 1A33 conformal coating (MIL Spec Type UR) using Humiseal 1063 Stripper
Solvent, or any other solvent that can remove the coating by dipping.  We
are returning boards from the field for a significant amount of rework where
removal of coating by conventional means such as by soldering iron or spot
application of solvents is not practical.  The boards are FR4 base material
(0.063 to 0.125 inch thick) with all parts being plated-thru-hole military
specification parts.  There are parts such as connectors and numerous
Integrated Circuit sockets where the stripper material could get into. There
are also a significant number of teflon insulated stranded wire jumpers that
are fastened to the board using RTV covered over with conformal coating. The
OEM plans on dipping the complete board in a pan of Humiseal 1063 liquid and
leaving it sit till the coating is dissolved.  Cleaning will then be done
using alcohol with DI water applied manually followed by automatic cleaning
via in-line cleaner using solvent and DI water.  Omega Meter type ionic test
will then be done on sample basis to verify the ionic contamination has been
removed (Humiseal 1063 stripper is highly conductive).

Has anyone out there removed conformal coating using Humiseal 1063 stripper
or other solvent dipping process.  If so, please advise if you found the
process technically acceptable, and please provide specific process details,
including the post cleaning method used.  I would appreciate an answer as
soon as possible.Thanks.

I can be reached at following contact:

Les Bogert
Bechtel Plant Machinery Inc.
412-829-8489
[log in to unmask] <mailto:[log in to unmask]>
FAX 412-825-8997




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