We've just put a CCR System on line and I like it much better than chemical
striping, especially for spot removal. The ESD features are also good. The
best thing about spot removal on many assemblies is that you can make a mask
which exposes only the areas to be removed and blast away.
Jim Marsico
Senior Engineer
Production Engineering
EDO Electronics Systems Group
[log in to unmask] <mailto:[log in to unmask]>
631-595-5879
-----Original Message-----
From: Steve Gregory [SMTP:[log in to unmask]]
Sent: Wednesday, June 04, 2003 2:44 PM
To: [log in to unmask]
Subject: [TN] Urethane Coating Spot Removal...
Hi All!
First I would like to thank everyone for all the dialog about ISO
and Prototypes. There has been some extremely good discussion!
My next subject has been talked about recently, but I would like to
get a little more detailed about some things.
We are about to embark on a task up-grading a bunch of assemblies
(1200+) that have been coated with urethane conformal coating. The upgrades
will consist of removing just a handfull of parts, and replacing them, maybe
adding a jumper wire or two, and replacing part number labels with new rev
ones. So we're going to spot remove and spot re-coat.
The -7721 lists a preferred removal method order table, and it lists
Thermal as number 1, Grinding / Scraping number 2, Solvent number 3, and
Micro Blasting number 3.
I've searched the achives and picked-up a bit of info, and there was
a thread asking about what chemical to use removing urethanes from plastic
SMT parts. I also did a search of the 'NET for some info, which prompts me
to ask some questions.
Why would Micro-blasting be listed as one of the least desirable
methods? I understand the ESD issue, but from what I learned in looking at
two companies that I found that make this equipment (Crystal Mark and CCR
Company), they address the ESD issues. Are their claims over stated? There's
a *.PDFdocument that CCR has up on the web, that makes for some interesting
reading. Go to:
http://www.ccrco.com/study.pdf
In that document, they state that using a thermal method is
hazardous because the coating will produce toxic gases when burnt. I called
Conathane and they said that if it is overheated, there is some cyanide
given off. But I would think that only happens when you actually burn and
char the coating, true? I've been playing around with a hot air pencil and a
orange stick, and that works with no charring or burning, but that's dead
slow.
I really don't want to use chemicals because it is so messy and
takes forever, and we're only going to be doing a handful of places on each
board.
So what method would you use if you had 1200 boards staring you in
the face, with just a handfull of places on each board?
-Steve Gregory-
P.S. I'm looking into the possibilities of leasing a micro-blasting
system, unless somebody says that's the worst thing I could do...
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