Graham: Not Good !  Obviously the trick here is to remove the latex and
preserve board solderability and the integrity of the outerlayer materials,
i.e. laminate, soldermask etc.  Acrylic latex does not really solubilize
after this type of bake. The best you can hope for is to swell and soften
the material.
Try a solution of methanol and monoethanolamine  5:1 BV.  Immerse the
assembly at 50 C.(if possible ultrasonics will help). Take appropriate
precautions for heating flammables. Check every 10 - 15 mins for softening
of the latex and also look for attack of the soldermask and laminate
buttercoat. This may take a while, make sure you don't ruin the outerlayer
materials.  "If " and when it softens, the surface latex can be scrubbed off
with a stiff brush, try clearing out the holes with compressed air. You can
also try running it thru a high pressure spray system.

Another option if available to you  might be CO2 cleaning.

I've had a similar experience with over baked latex and finally got it off,
however I didn't pyrolyze the hell out of it as is your case.


Regards

Michael Barmuta

Staff Engineer

Fluke Corp.

Everett  Wa.

425-356-6076







-----Original Message-----
From: Graham Naisbitt [mailto:[log in to unmask]]
Sent: Thursday, August 12, 1999 7:44 AM
To: [log in to unmask]
Subject: [TN] Cooked Latex Mask



Fellow Techies,

Hope someone out there can help with this one:

We have a customer with a number of VERY EXPENSIVE assemblies onto which has
been put some peelable latex masking material. (NOT OURS BTW!)

These assemblies were then placed into an oven at 80Deg C (175Deg F - 176
for those who want precision :>) ) overnight. Unfortunately the fan in the
oven broke so they were exposed to 130 Deg C for some time, estimated at 6
hours.

As you might imagine, this has not done the latex any good at all. It pretty
much resembles the gum you leave on the bedpost overnight (for 5 days!).

We have tried up to and including MEK solvent without success. Of course we
tried peeling it - but, having lost its molecular bond, it fragments too
easily.

As if that was not enough of a problem, it is inside through hole vias and
empty sockets into which they must place some other leaded components and
then solder them.

Can anyone out there come up with a solution (liquid or metaphysical) that
will allow total removal? Rudy, you got any suggestions?

Regards,
Graham Naisbitt

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

WEB: http://www.concoat.co.uk <http://www.concoat.co.uk>

CONCOAT Ltd
Alasan House, Albany Park
CAMBERLEY GU15 2PL UK

Tel: +44 (0) 1276 691100  Fax: +44 (0) 1276 691227

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