Hello Technet

We here and some others use a method called "Via Capping".  It is spec'ed
as follows:

                         VIACAPPING
                                   An exception to soldermask in plated
                                   through holes will be made for boards
                                   requiring via caps.

                                          VIACAP REQUIREMENTS
                                          When viacaps are required the
                                          following requirements must be
                                          met:

a.   TThe documentation supplied by Teradyne will specify which holes are
to be capped.

b.   TThe finished hole size for these holes will be .018 + 003 / .018
inches.

c.   TThe LPI soldermask on the circuit side of the board will encroach
onto the pads.

d.   TThe viacap will be of liquid epoxy soldermask and applied to the
circuit side of the board so as to overlap on the LPI mask (see figure 1).

e.   AAll required holes must be capped.
















               Regards,
               Dave Tyler