Paul -

Section 6 of IPC-2221 will give you most of the necessary "design standards"
type information.  Much of the answer you seek is dependent on the specifics
of the circuit application and the laminate used.

May I also suggest you try to take a close look at microsections of the failed
areas of the board, on the off chance that a process variance may have entered
into this situation.  Any item which will allow "wicking" of the barrel
plating to extend beyond the normal perimeter of the drilled hole can also
promote a situation like this.  I ran into a few of these type situations back
in the years before we had the high class drills and laminates available today.

I assume you've already cleared registration, hole location, etc., as
contributors.

Good luck - Kelly

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