[volt-nuts] PCB cleaning and sealing

Alan Scrimgeour scrimgap at blueyonder.co.uk
Sun Sep 26 12:00:03 UTC 2010

Do silicone based conformal coatings allow water in too?


----- Original Message ----- 
From: "Bob Paddock" <bob.paddock at gmail.com>
To: "Discussion of precise voltage measurement" <volt-nuts at febo.com>
Sent: Sunday, September 26, 2010 12:23 PM
Subject: Re: [volt-nuts] PCB cleaning and sealing

> On Sun, Sep 26, 2010 at 3:20 AM, Dr. Frank Stellmach
> <drfrank.stellmach at freenet.de> wrote:
>> sealing to avoid corrosion, oxydation, leakage currents.
> A very common misconception is that Conformal Coating is a Hermetic
> Seal. It is used a lot in the Coal Mines [Where I've done many
> designs], and the Electronic Industry in general, to keep the caustic
> dust 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 circuit.
> The quality of the coating determines how long it will take the water
> to reach the traces, it could be months, but it will reach the traces.
> -- 
> http://blog.softwaresafety.net/
> http://www.designer-iii.com/
> http://www.wearablesmartsensors.com/
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