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April 2006

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From:
R Sedlak <[log in to unmask]>
Reply To:
TechNet E-Mail Forum <[log in to unmask]>, R Sedlak <[log in to unmask]>
Date:
Thu, 20 Apr 2006 14:40:44 -0700
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Hmmmm, if as Dewey has said, THF works, I am willing to bet I could find another, somewhat more gentle...from the same sort of family..

I would look at:

Dimethyl Formamide (DMF)
N-Methyl Pyrollidone  (NMP)
even, our old friend, DMSO (Dimethyl Sulfoxide) famed for carrying stuff through your skin...

And there is one more... much less well known, Furfuryl Alcohol, derived from oats, I believe...

And just because, if you want, I will send you 4 ounces of each, for free, and at no extra charge, just to play with... with the understanding, that you are responisible for digging up your own MSDS off the internet.

Rudy Sedlak
RD Chemical Company


Steve Gregory <[log in to unmask]> wrote: Hi All!

I've always thought that when it comes to removing parylene coating,
about the only way you can remove it is with some sort of mechanical
means, i.e.; microabrasion, or scraping. Burning through it with a
soldering iron when trying to do rework it is very, very
difficult...I've tried it...it doesn't work well at all.

I was just told that a chemical that I haven't heard of before might
work, it's called THF, or Tetrahydrofuran. I was told that it won't
dissolve the coating, but will cause it to lift from the PCB where it
can be brushed away. Have any of you ever heard of this stuff? I'm not a
chemist, and I'm not about to use it until I learn more about it.

The issue that I have is with a little tiny assembly that has been built
and parylene coated with some bad programmable hall effect switches
installed. The board is so small, and there are other components
installed really close to where the coating has to be removed. I'm
afraid of getting them microblasted because I'm afraid of damaging the
other components. See the assembly at:
http://stevezeva.homestead.com/files/8001_assy_backside.JPG ...the small
components are 0402's, so that gives you a visual scale of how big the
assembly is...

I've got the information in to a company that I found that does laser
ablation to remove coatings to give us a quote, so I'm waiting on that.
But if that turns out to be really expensive, I was contemplating using
the THF as plan "B" (provided the stuff will work and it doesn't hurt
anything else on the assembly).

Kind regards,

-Steve Gregory-
Senior Production Engineer
OAI Electronics
East 12th Street
Tulsa, Oklahoma 74112

(918) 836-9077 Ext.-507
(918) 706-2779 CELL

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