Impedance rule isn't applied?

[zphaze]

Hi,

I just noticed today I was doing my DRCs with "Signal Integrity/Impedance" unchecked.

After checking the option, I can only assume the impedance constraint rules I applied to a few nets, simply doesn't seem to be applied.
I was expecting Altium would just modulate the impedance width to modulate the impedance.



I'm not necessarily trying to have perfect impedance matching (I think for that to happen the fab must control your stackup, and for *now* I want to use a generic stackup).
That said, I would expect there is some kind of functionnality to make Altium "decide" of the width of a trace so that it can match the impedance constraint, so that the DRC can pass (I understand there will be incertitudes, but not a >2x factor like I'm getting). I thought setting a rule would be sufficient, but it doesn't seem to have any impact.

TL;DR Is there a way to make Altium strictly apply the impedance rule I previously set (by imposing a width)?

Thanks!

[T3sl4co1l]

Do you have planes in the layer stackup?  It only calculates impedance to the nearest plane(s).  Regardless of what's on the layers.  Although I don't recall it producing a result in case of no planes...  Those numbers would actually be reasonable for parallel differential pairs with no plane.

Planes aren't very nice to use, better to simply calculate the expected trace width and go with it.  There's no inter-layer check for grounding copper, so it's down to a visual inspection either way.

Tim

[zphaze]

I have a 4 layer stackup, but the inner "plane layers" are declared as "Signal" because I much prefer working with polygons.

Why would we need planes? Since the traces are on the top layer, I'm not sure I understand why Altium would require planes 

Is there any tools available for manual calculations?

[Codex]

I find Altium impedance tool difficult/impossible to use and it often just does not work correctly or as expected.

I use impedance tools like Saturn PCB.
https://saturnpcb.com/pcb_toolkit/

And you tell the PCB maker that you have controlled impedance on your PCB.