On 03:49 PM 17/09/2002 -0700, JaMi Smith said:
><..snip..>> Nevertheless, this only takes place at extreme drill wander in 
>just the
> > wrong direction, and it is possible that a few mils of space could be
> > gained for routing by becoming dead-pad aware in DRC. Essentially, at some
> > value for the variables, the gain in yield from dropping the dead pads
> > could be balanced by the loss in yield due to extreme drill wander. One
> > might gain as much as a few mils of routing space.
> >
>
>Is this the exact same "extreme drill wander" that is coing to cause the
>exact same hole to short to an internal plane anyway?
>
>"Extreme drill wander" is not allowed in the manufacture of PCBs, only
>"controlled wander" within the intended design tolerances.

Drill wander is statistical not bound.  Abd ul-Rahman's "extreme wander" is 
a reference to the maximum permitted drill wander according to the PCB 
manufacturers stated (or unstated) performance.  It should not be read as 
extreme being outside the manufacturers limits but just at the limit (at 
the extreme).  Controlled wander - not really any such thing of course, but 
I know what you mean - you are talking the same thing - Abd ul-Rahman is 
simply discussing the worst case limit which is the situation likely to 
cause a drop in yield.

Ian Wilson


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