This is late but as once said...
You may have more of an issue than CC blisters if you don't repair this
correctly. If the cc bubbles up and the product is in a moist dirty
area you can have the contamination pass through the cc as a gas and
then form as a chemical soup inside the blister.
eric
-----Original Message-----
From: TechNet [mailto:[log in to unmask]] On Behalf Of Phillip Bavaro
Sent: Friday, November 23, 2007 11:50 AM
To: [log in to unmask]
Subject: Re: [TN] RTV contamination and conformal coating
In a former position, I had the benefit of being able to still use a
freon
vapor degreaser to easily strip the acrylic 1B31 from any board that
needed
better prep (non-adhesion qualifies as that), but I don't know if there
is
a equivalent stripping method these days.
My recommendation is to locally scrub the area that has the problem, IF
it
is flat and easily rubbed with a cotton swab. The RTV can be rubbed off
using a suitable solvent (but be very careful not to drip the solvent
onto
any good areas).
Adhesion of the touch up 1B31 to the "clean" surface will be just a good
as
the rest of the board has long as you do a good job cleaning. Don't
forget
to bake the board before reapplying the 1B31.
Covering up the spots (that you are no doubt seeing under ultraviolet
light) with more 1B31 is not recommended as you are right, you have not
fixed the problem. However it depends on what the environment is that
you
are using the 1B31 for. Typically such an environment is not one which
would bubble up an area like you are mentioning (if the pull-aways are
in
fact only due to RTV).
I am just curious, are you applying the RTV after prepping the boards
for
the 1B31? Is it possible to coat the board and then apply the RTV
afterwards. Typically the RTV is applied to external surfaces which
could
be easily locally stripped and then covered up with RTV. It would seem
obvious that you don't have a requirement to put 1B31 on top of the RTV.
Hope this helps.
Phil
At 02:31 PM 11/22/2007 -0500, Ioan Tempea wrote:
>Dear Technos,
>
>
>
>I am having a few boards that have spots of Dow Corning 3-1744 RTV
where
>they should not. We need to CC with acrylic 1B31 from Humiseal and,
>guess what, the CC does not catch on the silicone.
>
>
>
>If the problem spots are touched up with CC thinner or CC, after 2-3
>passes we manage to cover the problem. Now, there will probably be no
>adherence under the touch-ups, since there was no adherence in the
first
>place and on the long run, or maybe not so long, the CC will bubble and
>peel off. Do I see it right?
>
>
>
>I would appreciate an idea on how to work this out, have never been
>involved with CC before. Will patching work? Should I strip and clean
>locally? What to clean with and how, and so on? Any post-cleaning
>cleanliness worries?
>
>
>
>Thanks for your input,
>
>
>
>Ioan
>
>
>
>
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