Can someone please explain why the internal pad size is calculated (per
IPC-D-275 and IPC-2221) based upon the maximum diameter of the plated hole
instead of the drilled hole diameter?  Many suppliers drill the holes a
little larger than the maximum diameter of the finished hole.  It seems like
the pad size should be based upon the drilled hole since the annular ring is
measured at the foil.  The fabrication allowances don't seem to be quite
enough to accommodate this.  I'm sure this has been discussed before, I just
need a refresher.

Bill Dieffenbacher
Lockheed Martin

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