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Orcad Layout split planes drive me nuts...
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Fred Bartoli
electronics forum Guru


Joined: 02 May 2005
Posts: 457

PostPosted: Wed Jun 07, 2006 9:41 pm    Post subject: Orcad Layout split planes drive me nuts... Reply with quote

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?


--
Thanks,
Fred.
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qrk
electronics forum Guru Wannabe


Joined: 07 May 2005
Posts: 167

PostPosted: Thu Jun 08, 2006 1:28 am    Post subject: Re: Orcad Layout split planes drive me nuts... Reply with quote

On Wed, 7 Jun 2006 23:41:49 +0200, "Fred Bartoli"
<fred._canxxxel_this_bartoli@RemoveThatAlso_free.fr_AndThisToo> wrote:

Quote:
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?

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.

---
Mark
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Ned Forrester
electronics forum beginner


Joined: 02 Feb 2005
Posts: 5

PostPosted: Thu Jun 08, 2006 4:36 pm    Post subject: Re: Orcad Layout split planes drive me nuts... Reply with quote

Fred Bartoli wrote:
Quote:
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?

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.

--
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
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