[volt-nuts] PCB cleaning and sealing

[shalimr9 at gmail.com]

Parylene is for all practical purposes an effective moisture barrier. However, it is very difficult to apply, and even harder to remove. We use it in extreme cases wen the environmental requirements are such that the normal urethane coating will not do. 

Didier

Sent from my Verizon Wireless BlackBerry

-----Original Message-----
From: Bob Paddock <bob.paddock at gmail.com>
Sender: volt-nuts-bounces at febo.com
Date: Sun, 26 Sep 2010 07:23:24 
To: Discussion of precise voltage measurement<volt-nuts at febo.com>
Reply-To: Discussion of precise voltage measurement <volt-nuts at febo.com>
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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