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