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Re: gEDA-user: chip scale package soldering
On Fri, Jul 16, 2010 at 7:26 PM, Armin Faltl <[1]armin.faltl@xxxxxx>
wrote:
How good is varnish to protect solder joints from humidity and dirt
and enhance insulation (assuming it was clean)?
Conformal Coating is not a hermetic seal.
A very common misconception is that Conformal Coating is a
Hermetic Seal. It is used a lot in the Coal Mines, 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 Wireless
Sensor Network circuit like a pH meter.
This is why some high impedance OpAmp data sheets tell you "expose to
air", like the (obsolete?) AD549 and OP128.
--
[2]http://blog.softwaresafety.net/
[3]http://www.designer-iii.com/
[4]http://www.wearablesmartsensors.com/
References
1. mailto:armin.faltl@xxxxxx
2. http://blog.softwaresafety.net/
3. http://www.designer-iii.com/
4. http://www.wearablesmartsensors.com/
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