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...