[PCB_FORUM] Re: Removing unused pad rings on inner layers DURING design...
- From: "Austin Franklin" <austin@xxxxxxxxxxxx>
- To: <icu-pcb-forum@xxxxxxxxxxxxx>
- Date: Fri, 1 Apr 2005 12:23:16 -0500
Hi Matt,
> The via pad your discribing, 10 mil finished hole with a 24 mil
> pad...
The drill is actually 10.
> is sized to
> allow for tangency of the
> hole to the pad edge. All the pad allows for is a 10 mil manufacturing
> tolerance. The hole will be drilled with a 13 or 14 mil drill in
> order to plate
> and finish at 10. The hole can endup anywhere within that pad
> including at the
> edge.
>
> Under those conditions you do not gain any usable space by removing the
> unconnected pads.
> By removing unconnected pads, you get to use the designed in
> space that was for
> annular ring. In this case that is zero.
You do gain clearance though...simply for DRC...doing it the way I
described. The trace doesn't impinge on the actual pad area (if it was
there), it simply has a clearance to it that is better done (IMO, from a DRC
prospective) by removing/reducing the pad instead of setting up area
constraints (as was suggested can be done), and then having the pad ring
removed during manufacture.
I've done many boards this way, and this technique seems to work just fine
(never a failed board due to this issue)...and the PCB manufacturers have
not had a problem with it. The drill can't hit the trace, as we specify a
minimum amount of ring left, that includes all tolerances, just to avoid
such potential problems.
Regards,
Austin
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