Suggest that you review a copy of the paper:
"Protection Performance of Conformal Coatings in Harsh Environments" ,
Ling Zou and Christopher Hunt, DEPC-MPR 054, July 2006
You can request it through NPL (National Physics Lab) in England.
Very good discussion of moisture resistance of various CC types.
Not sure if the IPC has an archived copy of it somewhere.
Rich Kraszewski/ PLEXUS
-----Original Message-----
From: TechNet [mailto:[log in to unmask]] On Behalf Of Robert Kondner
Sent: Thursday, March 05, 2009 8:17 AM
To: [log in to unmask]
Subject: Re: [TN] Comformal Coating vs Potting
Brian and Blair,
From what I hear a sealed metal box will keep out water. A layer of
steel or glass does not allow water to pass.
Is this not the case for a "Thick" layer of silicone or epoxy?
What does "Thick" mean for different materials. How think does a
silicone adhesive need to be to equal the water penetration resistance
of 1/16 (or
1/8) inch of steel?
How do folks measure how water (or even any ionic material) passes
through a substance?
Thanks,
Bob Kondner
-----Original Message-----
From: TechNet [mailto:[log in to unmask]] On Behalf Of Blair Hogg
Sent: Thursday, March 05, 2009 8:38 AM
To: [log in to unmask]
Subject: Re: [TN] Comformal Coating vs Potting
Bob,
Most conformal coatings can and will pass moisture through to the
assembly in varying degrees, Thus, if there are any contaminants on the
assembly prior to coating that can activate with the addition of
moisture the coating will only slow down the effect. Also, if the
environment in which your module will be placed is humid for a
significant portion of the time, it will not have the opportunity to dry
out, and its performance may be affected.
Blair Hogg
On Wed, 4 Mar 2009 10:50:38 -0500, Robert Kondner
<[log in to unmask]> wrote:
>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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