The guideline for edge to hole is in IPC-2222, not IPC-2221
in IPC-2222 10.1.1 it says board edge or unplated hole to conductor
shall not be less than Table 6-1 of IPC-2221 plus .4mm
(and Table 6-1 is your minimum clearance based on voltage)

The MINIMUM from Table 6-1 (.05mm) plus .4mm works out to 17mils!

The discussion you remember was regarding IPC-2222 requirement
for haloing, and I'm not sure it was ever resolved, but I remember
we DID change some wording for the next revision.
You could get the new changes from John Perry for your own interest,
but of course it won't mean much until it is officially published.

And the haloing rule it won't help if your designers are disregarding the
clearance guideline, but I'm sure you know THAT (grin)
good luck!
Jack
On Fri, Mar 12, 2010 at 10:11 AM, Wendi Boger <[log in to unmask]> wrote:

> Everyone,
>
>
>
>   I seem to remember a discussion about Haloing of edges and non plated
> holes at one of our recent meetings.   The requirement for the haloing
> to be less than 50% the distance to nearest conductor works assuming the
> design has a reasonable space from conductor to edge.  I looked in
> IPC2221 but did not find a guideline for suggested minimum distance.  We
> are seeing non-plated tolling holes with surface ground rings at <10mils
> hole edge to copper.  Depending on the material and hole size it's
> difficult to meet the 50% rule.
>
>
>
>   Is there a section in 2221 I can send the designers to so we can
> avoid this type of issue?
>
>
>
> Thanks,
>
> Wendi Boger
>
>
>
>
>
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