Its nothing that any DRC or ERC can ever pick up.
Its a manufacturing problem which should be avoided.
For starters your PCB house should be made aware
before hand that the plane clearences are less than
20mil.

The reason for this is due to the PCB house drilling
an oversized hole and then plating the hole size back
to the desired size.  A slight miss-alignment of the
drilling machine will result in a break into the
plane.

been there .. got the tee-shirt.. :-)

Best thing to do is to only reduce the plane clearence
where absolutly nessassary and if you need to reduce
the size, make sure that your drilled hole size is the
same as the manufactures drill.. if they go up a size
it could make things worse.

Simon


 --- Dave Eloranta <[EMAIL PROTECTED]> wrote: > 
> Mike
> I have no split planes passing thru the hole. I do
> have traces drawn in the
> planes that channel currents.
> 
> Dave
> 
> -----Original Message-----
> From: Mike Reagan [mailto:[EMAIL PROTECTED]]
> Sent: Thursday, November 21, 2002 11:25 AM
> To: Protel EDA Forum
> Subject: Re: [PEDA] shorted planes due to alignment
> pin holes with no
> plane expansion
> 
> 
> Dave,
> 
> You didnt mention if this was a result of  a split
> plane passing thru the
> hole.....This  is the only time I have ever
> encountered a short in which the
> DRC did not catch it.  Actually it is the only DRC
> that has ever failed for
> me.
> 
> Mike
> 
> ----- Original Message -----
> From: Dave Eloranta <[EMAIL PROTECTED]>
> To: 'Protel EDA Forum'
> <[EMAIL PROTECTED]>
> Sent: Thursday, November 21, 2002 10:07 AM
> Subject: [PEDA] shorted planes due to alignment pin
> holes with no plane
> expansion
> 
> 
> > Hi
> > I just got a 10 layer board back with the +3.3
> plane shorted to the ground
> > plane at 2 alignment pins. The design rules were
> set for a 14 mil power
> > plane clearance. The alignment holes are plated
> but do not electically
> > connected to any net. The DRC found no problem and
> the gerber generator
> did
> > not flash a plane clearout in the plane layers for
> these 2 holes.
> > We were able to remove the connector and ream the
> holes to isolate the
> > planes.
> >   The other feature of the rules that are
> different on this board from
> > others that I have done is that I have 3
> additional plane clearance rules
> > that apply to regions of the board under BGAs that
> require a smaller plane
> > clearance of 12mils.
> > I am surprized that I have not run into this
> problem before.
> >
> > Dave Eloranta
> > [EMAIL PROTECTED]
> > Locus Inc.
> > 5540 Research Park Dr.
> > Madison, WI
> >
> >
> 
> 
> 
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