Let's not get too complacent: there  are many more potential problems
than have been cited. One of the **essential** tests which will show up
many chemical and physical problems is the "pressure cooker" test or,
more scientifically, the "autoclave" test. Put a coated assembly in a
domestic pressure cooker with a litre of water, well above the water
level, and boil it vigourously for 48 hours (not letting it boil dry, of
course). If a microscopic examination reveals any vesication,
blistering, lifting of the coating or milkiness, you know you are in
DEEP trouble. This will reveal a whole host of problems, including some
prior contamination of the boards and/or components, hygroscopicity of
the flux residues, poor curing of the coating for whatever reason,
reaction between the flux chemistry and the coating chemistry etc.

Brian

Macko, Joe @ IEC wrote:

> Fellow Techeads,
>
> It has been suggested by one of our CMs that it is acceptable to conformal
> coat (type AR) over no clean flux residue.  Would anyone like to share their
> opinions or experience on this subject.  Conformal coating over residue does
> not sound like the correct thing to do.  thanks
>
> joe
>
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