Mike,

Requarding anular ring,  Before getting into the smallest a/r  what type of
board are you laying out?  Standard rigid board with 6/6 line and spacing
is using a minimum a/r of approx.  .015 over finished hole size.   This is
also based
on the minimum acceptible anular ring on the finished board.  The tighter
demand
placed on the a/r requirement the more costly the board will be.  The
standard rule
I like designers to use is the maximum anular ring for the design
allowable,  with .020 over the
finished holes size preferred.

Remember the hole drilled will be approx .005" larger in diameter to allow
for the plating in the hole.
So,  an a/r .015 over finished hole size will be .010 over the drilled hole
size, allowing .005" per side
of the hole for registration over a panel 18 x24.    The tighter the anular
ring the more difficult holding
the registration will be.

Also tear dropping pads with tight anular ring will help hold the
registration.

Last if a design with an anular ring too small their is a very good chance
you will recieve a call
from your board manufacturer.  Therefore,  if you have a questionable
design due to manufacturability
calling you board manufacturer for minimum requirments and any price
changes due to these requirements
might be a good idea.






----------
> I have a request from my CAD department on min. annular ring area (i.e.
> outside circumference - inside circumference).  What is the smallest
> annular ring vs hole size used in the industry!  Thank you in advance.
>
> Best Regards,
>
> Mike Forrester
> LeCroy Corp.
> [log in to unmask]
>
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