thick wiring or thin wiring

Hi guys.

When I check transition time on some sink, I find the thick wire and thin wire will have a very different value.
For some short net, I find the transition time is much smaller when using thinner wire.
For some long net, I finkd the transition time is much small when using thicker
wire.
Can you tell me why ?

This is a very interesting topic, although I'm not sure how you come to your conclusion. Did you manually change the width of wire, while keep all the other nets or cell untouched?

I will try to explain based on my assumption that your conclusion is correct.

First of all, if you use NLDM (non-linear delay model) libraries, then the transition time of the net is calculated based on the driving cell input transtion and the total capacitance on this very net including the net decoupling cap. and other load pins (input pins of other cells) cap. maybe cross-coupling capacitance as well. so if you manually modified the width of the net while keep all other factors unchanged, the thinner wire it is, the smaller net cap it would be (my guess), so you reduced the net cap which cause the first conclusion.

As for the second one, I think as the wire is much longer now, the transition time is no longer based on factors I said before, but also include the resistance of the wire (another guess), this may be true if you use CCS model libraries, so the wider the wire is, the lower the resistance will be, and the resistance factor is so dominating that it makes the transition much faster.