What is the smallest acceptable plated through hole diameter in a .063" 
thick FR4 board without running into barrel-cracking problems?

Our suppliers are saying that a .010" drill dia. is acceptable for vias, but 
this exceeds the 3 to 4 aspect ratio (hole diameter to board thickness) that 
many books specify.  Are our books out of date?

Thanks in advance
Jack Tippit
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