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March 2011

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Subject:
From:
Brian Ellis <[log in to unmask]>
Reply To:
TechNet E-Mail Forum <[log in to unmask]>, Brian Ellis <[log in to unmask]>
Date:
Tue, 22 Mar 2011 18:47:08 +0200
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text/plain (71 lines)
Very difficult! As I see it, why is there corrosion there, in the first 
place? A good acrylic coating should protect the boards, even better 
than most other coating types. As it apparently doesn't, this implies 
that moisture is being "pumped" in through the coating, in turn implying 
you have bad ionic/hygroscopic contamination between the board and the 
coating. What are your flux type, cleaning process and process control 
method before applying the coating?

Your first step towards recovery, if it is possible (not certain) is a 
good removal of all traces of acrylics. Consult your supplier to find 
out the best solvent for this and hope it does not damage any of the 
components. You must then remove all traces of the corrosion and any 
other residual contamination. My best guess, for a first try, would be 
methanol (warning! TOXIC/FLAMMABLE),preferably with strong agitation.

Brian

On 22/03/2011 17:00, Hetal Shah wrote:
> Hello,
>
>
> We have been using the acrylic  coating and it is failing.  My application
> is a small, expensive  copper/solder circuit board which must operate
> exposed in a greenhouse environment with humidity up to at least 80 per cent
> and temperature from about 55 to 85 deg F.  There is evidence of green
> corrosion products and peeling conformal coating which presumably need a
> more appropriate coating.
>
> We have to do rework and use agin same pcb boards. We would be very grateful If
> anyone can be advised how to remove corrosion from the board.
>
>
>
> thanks
>
> Hetal Shah
>
> MG Chemicals
>
>
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