Re: Murphy Strikes again!

[Lee Hart <leeahart@earthlink.net>]

Michael Haseltine wrote:
> Is conformal coating something that could be used in this case? It's
> been mentioned on the list before, but I don't really know much about
> it and would like to learn.

Conformal coatings work, but not as well as you might think. In general,
they SLOW the rate of water reaching the parts, but do not stop it
completely.

The four basic types of conformal coating are acrylics, urethanes,
2-part  epoxies, and silicone rubbers.

Arcryics are the cheapest and easiest to apply, but work the worst. They
provide a hard, very thin, crystal clear, rather brittle coating. You
can melt right through it with a soldering iron if necessary to change
parts.

Urethanes are slightly more expensive, about as easy to apply, and work
better because they resist water and most solvents. The coating isn't
quite as hard, is thin, and slightly yellow, and rather difficult to
burn off or scrape off if you need to change parts.

Epoxies are typically used by the military or someone who wants to make
it impossible for you to see or service the circuit. They are a thick
honey-like coating, or often dyed black or opaque so you can't see the
parts. They are difficult to apply, but extremely moisture and
solvent-resistant -- it is next to impossible to get them off for
servicing.

Silicones are a thick rubbery coating. They can be clear, white, or
other colors. They are easy but messy to apply, and take a long time to
set. Their solvent resistance is almost as good as epoxies. Heat
dissipation through them is poor. You can dig parts out of it if you
have to.
--
Lee A. Hart                Ring the bells that still can ring
814 8th Ave. N.            Forget your perfect offering
Sartell, MN 56377 USA      There is a crack in everything
leeahart_at_earthlink.net  That's how the light gets in - Leonard Cohen