Reference IPC-D-275 Para 5.3.2.4 (Page 65).

Senario:  4 layer board with power and ground planes.  Via size .012 max 
finished diameter.  Electrical clearance requirement .010 on inner layers.
Board size 5x10 (2 per panel).  What size antipads required??

Per table 5-18, begin at the OD of the max drilled hole (figure is unclear 
whether it is max drilled hole or max finished hole).  I assumed this should 
be the max drilled hole (.016/2=.008).  Add to this the electrical clearance 
(.010) and manufacturing allowance from table 5-10 (.016) for boards to 12".

(.008+.010+.016)x2=.068 dia antipad.  

Is this overkill?  Most board houses can live with a diameter .030 over the 
finished hole to get the normal electrical clearance of .004 min. This 
thinking would get me an antipad of .054 

	.012 - finished hole
	.030 - fab allowance
	.012 - extra electrical clearance over nonimal (.010 -.004)x2
	-----
	.054  antipad diameter.

What is the rest of the world doing??

Any comments ???

gary ...