Recently we encounter exposed copper problem after electroless nickel gold
process ,
we wish to know if there any way to determine the stubborn film on top of
the copper
that prevent the plating to take place . We understand that soldermask on pad or
poor rinsing after final development could give rise to such problem . Such
problem
of soldermask on pad could be easily found after HAL but cases of minor
soldermask
on pad could not be detected in HAL . Please advise .