Dry film solder mask is now about dead.  At least that is what
I see.  LPI is being spec'd out in 90% of the $250M worth of
boards my company does.  Dry film is very easy to use for
tenting purposes while LPI is not that easy and requires more
than one process.  However, the benefits of LPI is worth the
xtra problem.  Most of the people I deal with require 'plugging"
with LPI on the circuit side only.  They also prepare a special
artwork to show which holes get plugged.  Some people use'
epoxy screening ink to plug, some plug from both sides with
more LPI, some use other screening techniques.
The winner I think is plug from circuit side only (this prevents
entraped gases and use an epoxy ink as the plugging agent.
There will be a lot of no's and yes's, and they may be right,
but I am speaking from personal experience both as a user
 a producer and a seller.
I don't want to knock dry film mask on the air, and if you want
my views on this, email me direct.
On another note, you realy do not need to fill unused holes unless
you are worried about whistling testers.......

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