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August 2011

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Subject:
From:
Jack Olson <[log in to unmask]>
Reply To:
TechNet E-Mail Forum <[log in to unmask]>, Jack Olson <[log in to unmask]>
Date:
Fri, 19 Aug 2011 09:33:13 -0500
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text/plain
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text/plain (33 lines)
IPC will only provide the recommended MINIMUM clearance between planes, and from that point of view, it would be no different than any other "copper to copper" feature; pad-to-trace, via-to-trace, trace-to-plane, etc.

Knowing that, I still can't resist the urge to increase the gap width on most of my designs. So, even though I might be comfortable using 6 mil lines and 6 mil spaces, I still use 25 mil or 50 mil gaps between planes if I can.

Also keep in mind that if your plane copper thickness is different from the thickness you are using for signal layers, you should use wider gaps for EVERYTHING because of etching heavy copper.

Regarding vias: 
.
1) if you are talking about stitching vias around the edges of the planes to join them to adjacent layers (an isolated ground on one layer stitched to a full ground plane on another layer, for example) you have no worries, just place them any way you can, hopefully without blocking too many routing channels on other layers.
.
2) if you are talking about placing vias in the gap between planes, I do this all the time. Your CAD system will automatically remove the copper around the via to the distance you specify in your routing rules, and by putting them between planes you can avoid some of the swiss-cheese effect you would get in the plane area. The only consideration I know of in this scenario is if you WANT a large gap between planes, say 50 mils, and you plop a via pad in the middle of it, your via-to-plane clearance on that layer should be set for at least 25 mil clearance ring, otherwise you are providing a "bridge" between planes that might be risky at higher voltages. (and depending on your CAD system, that might add 25mil clearances around ALL your vias, which will really mess up a good plane)
 
p.s. ignore Dewey 

Jack


.
On Thu, 18 Aug 2011 09:56:41 -0500, Micahel T. Handy <[log in to unmask]> wrote:

>To all, is there an IPC specification for design of split/mixed plane design. I'm looking for design parameters for the gap spacing between split planes and how to place thru hole vias between the isolated planes. Any help would be greatly appreciated.
>Mike Handy

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