Jan
The order from good to bad, at temperatures < 40°C, but ONLY, say again,
ONLY FOR MOISTURE RESISTANCE.
paraxylylene (Parylene (R) ) 1
acrylics 2
epoxy 3
polyurethane 4
silicone 5
For mechanical resistance, the order is 3, 1, 4, 2, 5
For chemical resistance. 1, 3, 5, 4, 2
For electrical properties (dry conditions) 2, 1, 5, 4, 3
For ease/cost 2, (3, 4, 5), 1
Repairability 2, 4, 5, 3, 1
Obviously, these orders may vary somewhat with individual coatings, and
are just a rough categorisation, but they will give you an idea
according to which characteristics are most interesting for your
application. Where there is a choice between single and 2-component
products, go for solventless 2-component ones for best results, PROVIDED
you can meter and mix them accurately, otherwise forget them. The reason
there is such a choice is because there is no single ideal solution and
you have to compromise somewhere along the line. If you draw up a
"league table" from the above scores, you will find them all roughly
equal, certainly within the tolerances between individual products.
FWIW
Brian
Jan Satterfield wrote:
>
> Someone asked the questions regarding high humidity and the best conformal
> coating to use and I read 4 different answers: Acrylics, urethanes,
> paralyene and Silicone. I have always understood that acrylics were the
> least moisture resistant, paralyene the most moisture resistant and
> urethanes the most commonly used for moisture resistance on CCA's. Anyone
> care to clarify?
>
> -----Original Message-----
> From: [log in to unmask] [mailto:[log in to unmask]]
> Sent: Wednesday, March 06, 2002 9:22 AM
> To: [log in to unmask]
> Subject: Re: [TN] Conformal coating: high humidity environment.
>
> Acrylics tend to have the best performance in high moisture environments, as
> long as the temperatures are not extremely high.
>
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