Delay tuning - time not length possible?

Hi all,

I’m just starting work on a more complex board than I have done before, which will include some fairly high-frequency signals. I’d like to be able to tune trace length based on delay (taking in to account propagation speed on different layers, as well as propagation delay within packages). While length tuning is a weak proxy for this, it’s not ideal, especially when delays are stated in time, not length, for some packages. Is this a thing that’s possible, or planned at some point? Thanks!

Are you specifically referring to the need to account for different time delay for microstrip / CPW external (outer layer) traces, compared to inner layer stripline traces ?

Yes, as one part of it, along with via and package delays.

yeah. via and package lengths are all in there, not ns though. and it’s not in the correct place IMO.

there is a related post from me probably worth a read:

as far as inner layer delays are concerned, when i had a mix, and there were short distances, delay difference between inner and outer layers was not significant- IE it was less than the rise time of the waveform. (there is soooo much BS about length matching) . I’m talking about total trace lengths < 40mm.

but if you were doing a backplane with long traces well that might be a different story.
you would need to take into account direction of the weave, and for differential traces, ensuring one trace wasnt on a weave and one not… if you were really serious.

Pedantic note: nanoseconds should be abbreviated as ns. nS is nanosiemens.


Sure, there’s a question of how far down the rabbit hole to go. I don’t care about weave overlap / directionality, but I do care about stripline vs. microstrip and delay time, not length. However it seems that isn’t possible yet - I’ll see if any feature requests are in the issue tracker.

Update: this is the ticket tracking this request from a few years ago: Length/skew matching should operate in the time domain rather than distance (lp:#1788715) (#2222) · Issues · KiCad / KiCad Source Code / kicad · GitLab

1 Like