Re: gEDA-user: High voltage caps in small places

[Bob Paddock <graceindustries@xxxxxxxxx>]

On Thu, Jun 9, 2011 at 9:13 PM, Kai-Martin Knaak <kmk@xxxxxxxxxxxx> wrote:
> Ethan Swint wrote:
>
>> I wonder what materials are available for soldermask and
>> if they have higher moisture resistance?
>
> Maybe "conformal coating" fits your needs.
>   http://en.wikipedia.org/wiki/Conformal_coating

A very common misconception is that Conformal Coating is a Hermetic
Seal. It is used a lot in the Coal Mines, and the Electronic Industry
in general, to keep the caustic dust etc. off circuit boards.

As Conformal Coating is not a hermetic seal, what real happens is the
impurities in the water are kept away from the circuit, but the water
itself reaches the traces. Since the water is now fairly devoid of
contaminates the water acts more like a dielectric insulator. You
never notice it in a low impedance digital circuit, but unless
debugging is an obsession don't let it get near a RF tuning circuit or
a high impedance sensor.  For example Analog Devices for their
(obsolete?) electrostatic grade OpAmps say to "expose to air" rather
than coat.

Conformal Coating has lots of applications, however the application
and environment that the product is going to be used in has to be
understood when the system is being designed.


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