Brant,

The fabricators phototool should be compensated for his production. The
amount depends on his specific process requirements. We advocate that the
data files sent to the fabricator be at 1:1. No matter what process allowance
you may place, it will probably not match the fabricators specific
requirements.

However, the designer should include process tolerances in his design, for
such features such as lands. A standard fabrication allowance is specified in
IPC-D-275, in table 5-10. This allowance should be included in the
calculation for the minimum land size, for a given hole.

Regards,

Gary Ferrari
Tech Circuits
(203) 269-3311