Bill,

Amendment 1 to IPC-2221 is in the release process. This amendment  changes
para 9.1.1 - Variable "a" add: Note: For external layers, the requirement is
the maximum diameter of the finished hole. For external layers, the drilled
hole diameter is used.

Also - Variable "b" add: Note: Etchback must be included within the
calcualtion.*

I trust that this revision addresses your concerns.

Regards,

Gary Ferrari
Executive Director
IPC Designers Council
860-350-9300
fax 413-771-5386

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