About strange computation of 120 ohm impedance

[mulfycrowh]

My manufacturer made the computation for both impedances with the stackup I shared.

[goncaloc]

I don't think you will be able to have both 50R and 120R on the same layer
To increase the necessary width of a track you will have to increase the thickness of the prepreg, so when you have 0.12mm for the 120R your 50R will be so wide it won't be practical.

[mulfycrowh]

Seems OK with 50 Ohm impedance but always getting a very small track for 120 Ohm.
I should have something like 0.12 mm.

[goncaloc]

Hi Mulfycrowh

AD19 does no support multiple Dielectric between copper layers, remove one of the prepregs and change de other to 180um
You should have a 300um width for 50R

[mulfycrowh]

I tried to enter the attached stackup from my manufacturer.
Now it is no more possible to reach 50 Ohm impedance...

Any idea maybe?
Thanks a lot.

[WhoKnewKnows]

For controlled impedance, if the built in trace width calculator calculates that the traces need to be incredibly thin, the you need to change something else in the design, like the dielectric material or the dielectric thickness. Perhaps try sharing the entire layer stackup, not just the impedance calculation portion?

[mulfycrowh]

Hi everyone,

I am using AD 19.
My stackup has 4 standard layers.
I would like to add 120 ohm tracks.
Here attached the result.
I am little bit surprised by the result: 0.018 mm is very small.
I guess an error.
Any idea?