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

HTH,

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.

Redwire,

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.