Steven,
we tried that coating many years ago for RF. The epsilon is not ideal,
that's true, but as that coating can be rather well controlled (repeated)
the disadvantages can as best be tuned for. However, we found also, that
repair was messy and the licence and machine was pretty expensive, so we
did not go on with Parylene C. So, it all depends, can you accept certain RF
losses, distorted signal and take time for tuning, you may use this coating.
(With tuning, I don't mean old time's tuning by trimming caps, inductors and
shortening stubs with scalpel and other sorts. Today, most so called tuning
is done by means of software).
If I was asked for giving advice today, I'd rather recommend some of the
'dielectric' sprays that are available since some years. These are sort of
very thin organic 'oils' that protect from corrosion, humidity and water
droplets. You get a 'fat' surface but the layer is so thin that the
electromagnetic fields won't be affected. I did a search a couple of years
ago, and rember there are also some plasma deposition methods today, kind of
nanotech methods. So, the kilometer thick coatings are probably out one day
and superseded by such methods.
Inge
----- Original Message -----
From: "Steven Creswick" <[log in to unmask]>
To: <[log in to unmask]>
Sent: Monday, June 01, 2009 8:33 PM
Subject: Re: [TN] humidity test failure
> Inge,
>
> Would you ever consider the application of parylene C on an RF board as a
> moisture barrier? Up to what freq?
>
> I believe the dielectric constant for parylene C is nearly 3 at 1 MHz,
> compared to ~1+ for air?
>
> Steve Creswick
>
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