KiCad autorouting working well - how do I disable (or delay) connecting GND?

[pentam]

re: pcbnew 4.0.7

For my 2000+ trace board, KiCAD autorouting is working well, better than FreeRouting on a layer-to-layer basis.

To clarify, it seems to me, when KiCAD autorouting is restricted to 1 (and perhaps 2) layer(s), KiCAD seems to beat FreeRouting (various metrics), so note to developers: please don’t get rid of built-in autorouting in the upcoming revisions.

Beyond 1 (and perhaps 2) layer(s), KiCAD autorouting seems to limit itself to a maximum of 2 layers at a time (by forcing to pick 2 layers to autoroute).

For now, I am letting KiCAD autoroute the top layer only (ie choosing the 2 layers to be the same, top layer), then passing that file to FreeRouting, to route on all 6+ layers.

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However, I desire to turn off KiCAD trying to route GND. To be sure, in the complete design, there will be lots of GND, but before then, traces of GND are cutting off my many other signals from getting routed.

I do have these 3 Net Classes, in this order (does the order make a difference?)

• default
• various POWER (+12, +5V, +3.3, etc)
• GND

but all 3 classes get routed together. Note that POWER or GND cannot be escalated to replace default at the top… I presume I’ll need to make another class and move everything else except POWER and GND into the new class, and order it: default, POWER, newClass, GND (in order to have POWER routed first).

QUESTION:
There must be a procedure to run the classes in a particular order such as (power, default, gnd). If so, please advise.

Thanks in advance

To answer Hermit:

@hermit

I generally hate it when people don’t answer the original question and push a view point, but…

There is a reason that Kicad is thinking of dropping auto-routing. There is more to board layout than connecting traces. Manual routing is not as hard as you might think, especially since you seem to indicate you are flexible on layers. You may have already spent more time on trying to figure out auto-routing as it would take to do the board. Been there done that.

I appreciate the comment, and I agree… but with thousands of traces, I need (ok, maybe I just want) a head start. I realize I will have to do some finish routing, or seeing how autorouting did it, start it off on a different scheme by first manually adding a few traces.

cheers

[PCB_Wiz]

KiCad is not great on Visibility and detailed NET controls generally.

One possible workaround, if you really want to wholesale ignore GND, would be to create a NET file minus GND (eg in a text editor, just delete the GND grouping)

• a quick check of this, and it seems to add/remove GND just fine, importing a pair of NET files.

If there are partial GND routes, those segments do not delete on the subset NET load, but a manual Edit.Cleanup Tracks does remove them.

This might work on thru-hole multi-layer designs, where inner layers connect naturally, but SMD parts would need some via-escapes which means partial GND routing would be required.

[SembazuruCDE]

Thought experiment here… (I haven’t tried this, so it may be a red herring…)

What about (temporarily?) doing a ground pour on a layer that isn’t being handed to the autorouter and manually stitching the SMT ground pads to vias before the autoroute. Would the THT pins and ground vias be recognized as routed by the autorouter even though the connections aren’t on layers being autorouted?

I hope my pre-caffeine thoughts are intelligible…