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N_Cook N_Cook is offline
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Default Unusual pcb corrossion problem

Michael Karas wrote in message
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[This followup was posted to sci.electronics.repair and a copy was sent
to the cited author.]

In article , says...
I hope you meant FR4 fiberglass for the board when you wrote "fibre
board". If not, then I don't have a clue about how the board was
manufactured. Most circuit boards have a green solder mask layer with
writing on it showing, at least, the component id and perhaps a board
name and revision level. The solder mask is a very thin transparent
sheet of fiberglass that is laminated with the board. That is probably
what you are seeing.

Paul



Open up some remote controls. You will find that virtually all of them
use phenolic type circuit boards.

Solder mask is not a thin layer of fiberglass. Usually the stuff is a
photo sensitive coating that is spread across the board surface. It is
then exposed to light through the solder mask artwork layer which
changes the material that is exposed to the light. Afterwards a wash
process is used to remove the part of the solder mask that is over the
pads on the board.


--

Michael Karas
Carousel Design Solutions
http://www.carousel-design.com



Because somewhrre along the way the resistive-conductive black stuff has to
be in good reliable electrical contact with the underlying copper and then
no coating over those.