Bob,

Surface cleanliness prior to any type of coating would be of paramount
concern.  So that would be task #1

In the automotive industry, one would use paralyene as a superb
environmental barrier layer.  It is thin, relatively transparent, but not
altogether cheap, or convenient.

I assume that SCS would coat up some boards for you [at little to no cost]
so that you could do side by side environmental test comparison between
paralyene, conformal coating, and potting.  They may even have some
suggestions for testing.

Most of my work experience has been with hermetic components, so I am not a
conformal coating/potting guru.  I have been told that moisture will
certainly pass through urethane and silicone CC and pottings.  The trick is
not to allow the water molecules to form a continuous film on the surface of
your part - going back to cleanliness and adhesion of the coating material.

Doesn't necessarily answer your question, but provides another option

Steve



-----Original Message-----
From: TechNet [mailto:[log in to unmask]] On Behalf Of Robert Kondner
Sent: Wednesday, March 04, 2009 10:51 AM
To: [log in to unmask]
Subject: [TN] Comformal Coating vs Potting

Hi,

 

  I have been playing with some conformal coating material and I have a
couple of general questions.

 

1.	Coatings get VERY thin around sharp corners. Using a number of coats
seems like the only way to build up any serious thickness.


2.	Potting seems like another name for "Very Thick Conformal Coating". 



 I am looking as an application where a sensitive electronic module will be
placed in a wet humid environment. It is a sensor going into the cooling
tower of a HVAC system.

 

  After reading about conformal coating and playing with some sprays and
brush on material I think thick potting is the only option to keep moisture
out of circuits. We need at least 20 Meg ohm between circuits spaced 10 mils
on FR4 material.

 

 Can anyone verify I am on the correct track and can they point me towards
selecting the proper materials and process?

 

Thanks,

Bob Kondner


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