We occasionally have to spot remove polyurethane coating, mostly to remove and
replace a component.  It's not easy, but we use DMF (Dimethylformanide).  A
small piece of cotton cloth is cut to the size of the coating which needs to be
removed, the cloth is saturated in DMF and placed on the board and presses in
place to make good contact.  As the DMF slowly attacks the coating, the cloth
is removed and replaced with a fresh saturated piece.  This process is repeated
until all visible signs of coating are removed.  One word of caution, though,
DMF will attack the solder mask and even the epoxy in the PWB if left on long
enough.

Jim Marsico
(516) 595-5879
[log in to unmask]

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