[PCB_FORUM] Re: Why would auto router create L-L DRCs?

Hi Gene:

  You are running into the fundamental method of Specctra.

  It is an iterative tool. On some board where we route all the nets it
starts with 16000 crosses and clearnace problems then as we introduce more
and more passes of the router it reduces that number in a process called
convergence. On designs with 5000 nets and 15000 connections it will wind up
with 10 or 20 crosses which you have to clear manually in the cleanup
process.

   In general it is best to give Specctra the whole routing problem and fix
in cleanup where it fails.

  It makes sense if you are  routing all or at least most of the connections
on the board.

  Take a look at the papers published on the CopperCad web site from
previous UG conferneces.
 They are to be found under the Specctra Coaching Tab (at the very bottom).
                              www.coppercad.com

  If you really want it to route with no short. use "limit cross 0" command.
  I do not recommend this as it defeates the very strenght of the
autorouter.


 Hugh Allen
 Specctra Specialist
 CopperCad Design Inc.
 www.coppercad.com
 hugh@xxxxxxxxxxxxx


-----Original Message-----
From: icu-pcb-forum-bounce@xxxxxxxxxxxxx
[mailto:icu-pcb-forum-bounce@xxxxxxxxxxxxx]On Behalf Of Gene Carman
Sent: Wednesday, December 21, 2005 6:04 PM
To: icu-pcb-forum@xxxxxxxxxxxxx
Subject: [PCB_FORUM] Why would auto router create L-L DRCs?


This is pretty fundamental...  as a designer you wouldn't cross two
different nets with a short and expect to "get away with it." Why is the
autorouter making this choice.  The constraint is set, yet the autorouter is
violating it.  Very odd.

CONSTRAINT:      Line to Line Spacing
  CONSTRAINT SET:  DEFAULT
  CONSTRAINT TYPE: NET SPACING CONSTRAINTS
    Constraint value: 4 MIL
    Actual value:     0 MIL

BTW I am selectively autorouting nets by selection.

But the whole issue to me is that the autorouter is making shorts, and that
just does not make sense.
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