Orcad layout questions

[Carl_at_xrite]

Howdy all,
I recently helped a "newbie" designer at one of our sister companies, they use Orcad 9.2 layout (I use ppcb,PCAD,protel).
One issue that I keep seeing in orcad is the router populates the board with errors - vias over vias etc.

All design rules were setup how I wanted them, this was an 8 layer brd. with 4 signal layers and over 1500 nets when the router had finished there was 1000 errors in the file.

Anyone know what the deal is with this? or is Orcad this for lack of a better word lame?

Thanks in Advance,
Carl

[Jackie Oh!]

Hi Carl,

I have the exact same problem. Although I haven't had time to play with it too much, I have noticed that it does it more if you do an Add Only ECO compared to an Auto ECO.

I've sent one of my board files to Cadence support to look at the issue. I'll let you know what they say.

[mhowell]

It would help if you stated the type of DRC error you are seeing. Orcad 9.2 seems to have a bug which causes the DRC routine to perform checks on non-selected types, such as bad-pad-exit or via-off-grid, and flags these as violations.

A workaround I use is to do 2 DRC checks. In the first, select all the rules, and let it run. In the second, select only the rules pertinent to what you want (i.e. placement, net spacing, via location, etc), and all those errors should go away.

[Jackie Oh!]

Sorry guys,

I guess I wasn't clear enough with my post.

The errors I get are via over via errors and I get them because the program adds free vias on top of free vias when I do an ECO. Sometimes it adds them to ALL the free vias on the board and sometimes just some of them. They are not attached to any net so when eliminating them, one has to be very careful to make sure the left over one is attached to the net. It doesn't seem to matter whether they're locked or not.

[mhowell]

The problem you describe sounds like the via-grid-set-to-zero error. I used to get this all the time, then talked with Cadence's AE's and thats what they told me.
In the system options dialog box, look at your via grid settings. If it is zero, try setting it equal to your route grid, then try autorouting again.

If you are getting free vias placed during autorouting, check the fanout settings dialog box and look to see if the "use free vias" box is checked.

Another fix for this involves downloading a patch from orcad which fixes this problem.

[Jackie Oh!]

Hi Michael,

I don't do any autorouting on my boards. This "feature" only happens when I do an auto eco. My via setting is at "0", tho, so I will try it with the via setting the same as the route setting.

Thanks for the info!

[Carl_at_xrite]

Howdy Mike,
I know when I helped set up the design rules the via grid was definately not set at zero.
Orcad did not actually place "free" vias on the board but it did populate via to via errors, double trace errors etc.
Nice to know there may be a patch though.
Did not have enough time to investigate the problem only had a week to stay.. in ,out and gone as they say...
Thanks for the information
Carl