Les,
Removing 1A33 after it has cured for over a week or two is indeed difficult.
Per Mr. Caswell's response, most solvents that will remove the cured coating
are likely to attack any other markings or coatings, too.  I have found that
tetrahydrofuran will remove the coating.  My employment of the solvent is
for removal of splashes and splatters after coating and drying of 1A33
through a conveyorized oven.  In such an application it is almost
instantaneous (we use a cotton swab).  It is much slower (like minutes to
hours) on cured 1A33.  I have never had to remove the coating from an entire
assembly and don't know what prolonged to exposure to tetrahydrofuran would
do to inks, soldermask or components.  THF is slightly more volatile than
isopropyl alcohol and I believe the NFPA ratings are about the same.  It
would have to be kept in a closed vessel for the period of time required to
soften or dissolve the coating.  Be sure to employ good ventilation.

I have also used Kyzen 4402 to remove cured 1A33 from aluminum carriers.  At
room temp it requires about a day's soak and gentle brushing.  At elevated
(120-140F) it takes much less time, but requires ventilation.  I would
suspect that while the Kyzen will remove the polyurethane with no attack to
metals or plastic, the markings and soldermask might suffer.  I haven't
tried this, myself, on populated assemblies.

George Carroll
[log in to unmask] <mailto:[log in to unmask]>

-----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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