Via Length Consideration For Length Matching

I am doing single rank ddr3 routing in a 6 layer board with the following stackup:-
Signal(L1) -> Gnd(L2) -> Signal(L3) -> Pwr(L4) -> Gnd(L5) -> Sig(L6)

(I am using Saturn PCB Toolkit for calculations)


I am confused which parameter to consider for length matching. Physical length or the Timing(step response):roll:

Lets say i have a 1.4 in trace in inner layer(L3) with two vias of lenght 12 mils from Top layer to L3.

Signal Propagation Speed
Top/Bottom 145 ps/in
Inner Layer 175 ps/in


Total Length = Trace Length + 2 * Via Length
(I am not including Fan out Stub here)

(Timing = length * propagation delay => 1.4*175 = 245)
Layer 1-3
Layer 1-6

Trace on top layer without any Via


So in all the above cases the difference in Physical Length is 10 mils only while the timing difference is 44 ps. I am curious to know which factor to take into account if going for much higher speed than the DDR3.

I already read a lot of datasheets, and i didn't find any answers that's why i post it here. Thank you.

Peace

Basically you want your signals to arrive at the same time (with some margin), and the propagation speed on L1, L3 and L6 will be different.
So the only way to go will be time matching.


However, if all of your signals are on the same layer, you can do length matching as they all have the same propagation speed.
Most (advanced) layout systems will allow you to either one. For really high speed signals you also have to consider the timing inside the device. (Die to Pin).


As an Expedition user i can set the delay for my via's and the system will use those delays for timing calculations. I assume that this option is also available
in other (advanced) layout systems

Make it a habit to use time, That is what you really interested in.

Since i don't have access to the advanced software i am doing it manually.
Can you have a look at the attached image of the calculation according to the Timing. Signal flight time is matched.
Am i on the right track or am i missing something?

Thank you so much for the help.
regards