Re: conformal coating

From: Robert Baer (robertbaer_at_earthlink.net)
Date: 11/09/04 

Date: Tue, 09 Nov 2004 09:31:28 GMT

John Larkin wrote:
>
> Hi,
>
> can anybody suggest a good conformal coating? I have a PCB that is
> moisture sensitive; apparently the PCB itself absorbs enough moisture
> to change the laminate dielectric constant enough to cause me trouble.
> We coated the critical oscillator section with household polyurethane
> varnish, and it helped a lot; absorption after 48 hours at 100%
> humidity is down by about 3:1, and the recovery time constant is much
> better (shallower moisture penetration?). But this stuff is thin, and
> we'd like something gloppier that we can apply a bit thicker. We'll
> brush it on by hand, to keep it exactly where we want it.
>
> Any suggestions? We'd prefer something that sticks well, goes on
> fairly thick (high viscoscity) and is reasonably easy to rework. Who
> makes good stuff these days?
>
> John

  How about changing the PCB type?
  Try Megtron 5 from MEM: http://www.mem-or.com/
  I have some sample material if you have need for immediate delivery,
but i would have to make a box for shipping and you would have to
specify the *** size and thickness (20 mil and 40 mill, up to 18x22).

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