Silicone is a terrible thing to have around any conformal coating
process.   I have had some success with localized cleaning then touching
up the area.  For localized cleaning I use toluene.  You must remove the
poor conformal coat and the silicone that has caused the dewetting. The
key factor of success is to clean the area before the conformal coat has
time to set.  Whithin 24 hours seems to be the time frame.  If you have
baked the board to cure the conformal coat forget it.  Hope this helps.

Jon Hemstad
[log in to unmask]

>----------
>From:  [log in to unmask][SMTP:[log in to unmask]]
>Reply To:      TechNet Mail Forum.
>Sent:  Tuesday, October 28, 1997 8:12 AM
>To:    [log in to unmask]
>Subject:       [TN] CONFORMAL COATING REPAIR
>
>We conformal coat our assembled PCB's with polyurethane coating--typically
>there is a solder mask beneath the coating.  Occasionally at the end of the
>process (after curing) a board is discovered with a "dewetted" region in
>the form of a band.
>
>We know this is caused by the use of a plating/masking tape with a silicone
>adhesive  where the silicone has not been cleaned from the board (our
>supplier has discontinued use of such tapes).
>
>Does anyone know of a technique for repairing this region which is
>cosmetically "pretty good".  Just recoating--by machine or by hand--does
>not solve the problem.
>
>
>                                  Thanks for any tips.
>
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