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 Confused by program names, autoroute more than 6 layers, tricks (auto route) 

Last post Tue, Oct 5 2010 12:48 AM by OrCAD Flo. 5 replies.
Started by DrLightning 02 Oct 2010 09:24 AM. Topic has 5 replies and 2737 views
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  • Sat, Oct 2 2010 9:24 AM

    Confused by program names, autoroute more than 6 layers, tricks (auto route) Reply
    I'm new to Cadence/OrCAD/Allegra, although I have 15+ years Eagle experience. Cadence/OrCAD/Allegra seems a big confusing mess of program names, so I don't know what is what.

    My company recently purchased OrCAD PCB Designer Suite 16.3, that includes OrCAD Schematic CIS and OrCAD PCB Editor. It cost around $6000 or $7000.

    I hear the autorouter is limited to 6 layers. This makes me concerned and leads me to look for more capability. The salesperson says I can upgrade to "Allegra L" for $3200, whatever that is. If I understand correctly, this does NOT in itself get more layer routing. Instead, we have to add another $9400 (holy mother of God!). After that, we should be able to route as many layers as we want.

    Meanwhile, on this forum, I read about many other program names.

    QUESTION ONE: How do the program names I'm offered to purchase relate to the program names mentioned on this forum? Is "SPECCTRA" the $9400 piece that goes with Allegra L? (SPECCTRA is mentioned on the older OrCAD community) I'm totally confused.

    QUESTION TWO: This is all part of a big complex problem (at least in my eyes) that I'm trying to solve. I've broken this problem up into several questions. Of course, I did this over at the older OrCAD community, not knowing there was a newer community here. Rather than repost all this stuff, might you be SO KIND as to look at these links. You might then reply there, or reply here with a quote from there (to get that text dragged over to this forum). Thanks very much.

    Ref http://www.orcad.com/forums/ShowPost.aspx?PostID=33283#33283

    Ref http://www.orcad.com/forums/ShowPost.aspx?PostID=33286#33286

    Ref http://www.orcad.com/forums/ShowPost.aspx?PostID=33285#33285

    Ref http://www.orcad.com/forums/ShowPost.aspx?PostID=33288#33288

    Ref http://www.orcad.com/forums/ShowPost.aspx?PostID=33284#33284

    Thanks for your help.
    • Post Points: 20
  • Sat, Oct 2 2010 7:23 PM

    • redwire
    • Top 10 Contributor
    • Joined on Thu, Jul 17 2008
    • Allen, TX
    • Posts 876
    • Points 13,500
    Re: Confused by program names, autoroute more than 6 layers, tricks (auto route) Reply

     Dr L.: I read your post on the OrCad forum and it looks like you need some good PCB stackup consulting.  Talk  to your fabricator or hire a consultant to help you.  That stackup is not reliable and will produce some noise/crosstalk issues.


    Regarding the products.  The basic package includes a signal layer routing limitation of 6 layers.  Your stackup would not qualify unless you turned off routing on top and bottom.  

    Specctra is the name of the pcb autorouter from older days -- it remains basically unchanged but renamed in the newer products called PCB Router.

     Allegro L will get you more constraint capability but it won't increase layer count.  That is a different product "Router Performance"

    I have been on the product for more than 15 years and have not *truly* needed the additional routing layers.  There are some tricks you can play by turning off routing layers but 6 signal layers covers a *lot* of pcb designs.  Power planes and stackup play an important part and contribute to the high layer count like your reference design has.

    Here is a link to the Cadence datasheet: http://www.cadence.com/rl/Resources/datasheets/7432_PCB_Designs_FINAL.pdf


    • Post Points: 20
  • Mon, Oct 4 2010 6:59 AM

    Re: Confused by program names, autoroute more than 6 layers, tricks (auto route) Reply

    Thanks *very* much for your answers. Please allow me to ask for some clarification...

    1) Regarding the limit of 6 signal layers, does that include power planes or not? Logically, from my point of view, the power plane is included in the routing task, because sometimes a via is consumed by the plane and sometimes not. This is an electrical connection of a node to the plane's net or not, which is indeed a routing function. If I can get 2 power planes PLUS 6 signal layers, then I think I'll be fine. But if I only get 2 power planes plus 4 signal layers, it's going to be a problem.

    2) That Allegro L won't get more layer count is consistent with my understanding. However, I believe it then gets you the platform upon which you can subsequently run a [very expensive] program that WILL increase the layer count. Is my understanding correct?

    3) My initial foray into these forums was to find exactly those "tricks". Can you give me some keywords for searching the forums, or hints on how to do the tricks? I'm imagining routing half the circuitry with one set of perhaps 4 layers, and another half of the circuitry with a different set of 4 layers. But with that, I can also imagine a whole bunch of problems arising -- not to mention the question of "is it possible to tell the autorouter to only route half the signals".

    x) Be clear that I take no offense at your suggestion of hiring a consultant. Nevertheless, I do have 20 years experience of my own in board design, albeit never more than 4 layers. Also, my current task uses a 529 pin BGA (23 x 23). This has the distinct possibility of running into a roadblock with only 6 signal layers, but it might not. In theory, the worst case need is 11 signal layers (that being N-1 for N=ceiling(23/2); I believe the ceiling is necessary for an odd pin count along one dimension). (I realize you may have picked up on both these points while reading one or more of the OrCAD community posts.)

    4) Finally, you say "That stackup is not reliable and will produce some noise/crosstalk issues." I'd like to be certain of to *what* stackup are you referring? I can only imagine that you're referring to the one describing the existing reference design. If so, I don't see any specific problems with it and would like to know one example of why you think it does.

    Thanks in advance for all your help.

    • Post Points: 20
  • Mon, Oct 4 2010 7:02 PM

    • redwire
    • Top 10 Contributor
    • Joined on Thu, Jul 17 2008
    • Allen, TX
    • Posts 876
    • Points 13,500
    Re: Confused by program names, autoroute more than 6 layers, tricks (auto route) Reply

     Working from #4 on your reply backwards.

    The stackup? You posted it:

    Here is the detail of the reference design layers:
    1- Top
    2- GND
    3- ML1
    4- VCC
    5- ML2
    6- ML3
    7- VCC1
    8- ML4
    9- ML5
    10- ML6
    11- Bottom

    4 signal layers (ML4, ML5, ML6, Bottom) is not consistent with good signal integrity and power integrity practice.  11 layer boards are not standard.  Check with your fabricator and / or hire a specialist.


    #3)  The tricks are complex to write out in one sentence to a newbie on a forum.  I'd suggest practicing with the tool for a while and ask specific questions.

    #2) No.  Router Performance is an option.   Perf. L gets you constraints.

    #1) 6 signal layers is 6 signal layers.  Power planes don't count no matter how hard you try.

    • Post Points: 20
  • Mon, Oct 4 2010 11:05 PM

    Re: Confused by program names, autoroute more than 6 layers, tricks (auto route) Reply

    Thanks for responding again. I sincerely appreciate your advice.

    #4) Please note that this is NOT my stackup. This is the stackup from the reference design. Please note that I'm used to using a term different from "stackup" for this, so I wasn't sure what you meant. Also, I do believe I described in the post the oddness of this adding up to 11. I know for certain it's possible that they may have a blank layer in there. I also know for certain that the documentation says it's a 14 layer board. I don't know how they get from this to that! More likely, however, the gerber documentation accidentally excluded a layer or three. For example, if there were actually a power plane between ML5 and ML6, then this would help dramatically by providing a return path reference plane for ML5 & ML6. That still leaves Bottom out in the cold, however, and it still leaves 2 layers unaccounted for. Perhaps those two are a missing ML7 and absent additional power plane. These would straighten it all out. Again, this was not MY stackup. I realize I asked "are there any tricks to make this work." I wasn't referring to the signal quality of the this stackup. I was merely referring to the layer count and routing.

    #3) I agree things would be easier if I get more familiar with the tool first. I will indeed do that as soon as my task schedule allows. At this time, I'm just trying to establish FEASIBILITY so that I know whether or not to broach the subject of additional cost with my boss, and doing so in enough time for decisions to be made and software purchased. I don't have the scheduling liberty to come up to speed on one tool, only to have to change to another later. Therefore, I don't have to UNDERSTAND the tricks specifically. Might you comment with a general waving hand guestimate of how much of a pain it is to use these tricks and thus route more layers?

    #2) I'll feed this info back to the EMA salesperson to try to get some clarity. He definitely said we had to buy Allegro L plus the other router in order to get more layers. He thus implied that the router with more layer capability was compatible with Allegro L but not compatible with OrCAD PCB Editor.

    #1) Your grammar here has a slight amount of ambiguity in it. Please allow me to rephrase more clearly. Do you mean "power planes are not counted in the limitation of 6 signal layers for the autorouter"? Note I'm not "trying" to count them. I'm "hoping" they are not counted for the limit.
    • Post Points: 20
  • Tue, Oct 5 2010 12:48 AM

    • OrCAD Flo
    • Not Ranked
    • Joined on Tue, Aug 11 2009
    • Celle, Lower Saxony
    • Posts 7
    • Points 125
    Re: Confused by program names, autoroute more than 6 layers, tricks (auto route) Reply


    just to #1)

    - you would place the parts by hand

    - you will decide about the stackup of the board (brainwork in collaboration with your boardshop)

    - you will fanout (automatically or by hand) just the GND and PWR nets (that means 4-6 layers are done)

    - now you disable the done nets from routing and you autoroute the last 4 - 6 layers, that means your actually autorouter will be fine...

    Thats the way I understand redwires posts.




    Greetings Flo I am using OrCAD Capture (16.0.0.s003) and OrCAD Layout (16.0.0 Build s003)
    • Post Points: 5
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Started by DrLightning at 02 Oct 2010 09:24 AM. Topic has 5 replies.