I live in southwest Florida...we get those blasted
things on the
outside of our houses down here. I have no idea what they are, but they
are indeed difficult to remove. The standard solution is to use a
pressure washer. I doubt that'd be appropriate for a PCB though. :-(
I forgot the english name for it, in portuguese is called "vespa", is a
bitter insect (has a point on back that hurts) and they build their houses
with this hard material. You can take it off scrapping but I doubt you will
save this board, mostly anything animal that glues is corrosive, so I doubt
there are integral traces on bottom of it. Oh, I just remember...WASP is
their name. They are not good to mess up with, they bite and it hurts. If
this is a replaceable unit, just throw it away and put some poison on it :o)