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Orcad Layout split planes drive me nuts...

I usually subcontract multilayer boards, but I had to keep this one and seem to get a pb with split planes.

So I have 2 different GND areas, namely GND, and GND_MB on the same GND plane layer.

According to the Layout documentation, I've set the GND net (by far the most important one) to the GND plane layer. Then I added 2 copper pour obstacles, one for each net. The final DRC is OK.

When post processing, it generates correctly all the planes (negative as it is a plane layer), except that the void area between the GND and GND_MB planes is filled with copper. So I have 3 copper areas, the 2 plane regions delimited by a fine copper free "track" and the in between region.

I've tried almost all I could think of to not avail.

Any hint?

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Thanks,
Fred.
Reply to
Fred Bartoli
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Generally, Layout does a decent job on split planes. Almost all my boards use split planes these days. It appears that you have done everything properly. For your particular case:

  1. Set your GND net to the ground plane layer via the Net Spread Sheet. I usually do this for the net that has the most connections to the particular plane.
  2. Use copper pour obstacle for your other plane pour net(s). In your case, GND_MB. Width will be the spacing between your GND_MB and GND. Very important that the obstacle type is copper pour. Set your obstacle layer, in your case, GND. Good idea to set a clearance like 10 mils (0.25mm) if you're using a routing layer. Not necessary to set clearance on a plane layer. Set your net attachement to GND_MB. You may need to set a Z-order if you overlap your planes.
  3. Hit OK and draw in your GND_MB plane making sure you hit at least one of the pins connected to GND_MB.
  4. Your planes should be correct. You can view your Gerber file results in GerbTool.

If you still have problems, you can send me a small sample board and I may be able to tell you how to correct the problem. qrkjunk@zzxxzzcom zzxxzz = yahoo.

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Mark
Reply to
qrk

Poster qrk provided the correct procedure.

From your description, I think the only error you made was to try to put two copper pours in the ground plane layer, when you only need to connect two nets in that layer. The ground plane layer, by itself, provides the connectivity for one of your ground nets. You only need to add a SINGLE copper pour to the ground layer to add an additional net.

If you put two pours on the ground plane layer, and don't put their boundaries close enough, then there will be room left for Orcad to place some copper for the "real" ground plane. That may be why you are seeing some copper between your split planes.

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NOTE: to reply, remove all punctuation from email name field

Ned Forrester        n_f_orrester@whoi.edu         508-289-2226
Applied Ocean Physics and Engineering Dept.
Oceanographic Systems Lab                 http://adcp.whoi.edu/
Woods Hole Oceanographic Institution, Woods Hole, MA 02543, USA
Reply to
Ned Forrester

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