Bob Vanech 

The statement in IPC-D-275 requiring 0.001 annular ring is for design
purposes.  You always design to have an annular ring, you do not design for
breakout.  IPC-RB-276 accepts no breakout for Class 3, but allows a 90 degree
breakout for Class 2 and a 180 degree breakout for Class 1.   This is the
manufacturing acceptance criteria which allows some "not entirely perfection"
in the board for some Classes.  If you read the same paragraph in the
forthcoming issue of the replacement for IPC-D-275 which is IPC-2221 you will
find words to the effect that the annular ring number is for desig
calculation and that the performance specifications may allow breakouts for
some classes.

Phil Hinton 
Hinton "PWB" Engineering 
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