An amateur tries DDR4 layout with KiCad and has some concerns ...

[homebrew]

Hi everyone

I couldn't resist the challenge to do my first true high speed design. Beforehand, I read a lot, watched probably every Rick Hartley and Robert Feranec video I could find on YouTube. So I though I did my homework but now I don't feel that I get along particularly well...

The board I intend to design is around one of NXPs communication processors (LS10XX) with 8GB of DDR4 RAM. As the DDR4 part seems to be the biggest challenge for me I startet with that part of the design to see if I'm capable of doing this at all.

So here are some considerations and restrictions:
* As I cannot shell out k$ on professional software, I'm practically bound to KiCad.
* The same goes for the the pcb manufacturing. It must be manufacturable in a pooled service. I found the Eurocircuits does 8-layer impedance controlled boards with a 4/4 spacing and 0.125mm anular rings in a reasonable price range. Burried vias, via in pad etc. is out of question for me.

The stackup I use (One of Rick Hartleys suggested stackups 58:04):
1. Signal/Pwr
2. GND
3. Signal/Pwr
4. PWR
5. GND
6. Signal/Pwr
7. GND
8. Signa/Pwr

Using Eurocircuits impedance calculators, it turned out that given their "asymmetric" use of prepreg and core material gives roughly the same impedances for mictrostrips and striplines with this particular stackup - a coincidence?. This was a pivotal moment to me realising this property, because otherwise I would have stoped right there.

NXP has some good design guidelines on the web for DDR4: https://www.nxp.com/files-static/32bit/doc/app_note/AN5097.pdf

Most of their guidelines I think I can match but for some (e.g. suggested trace distances) I can't even imagine anybody matching it. My biggest concern is crosstalk in the Address/Command lines due to a lack of distance between individual signals. Given my impedance calculations I need 0.166mm thick traces. In combination with 0.8mm BGA pitch, it was a challenge to me to get the fly-by-topology routed at all.

So here is the VEREY unfinished/current "piece of art".

What do you think?
Is it even worth continuing?
Any suggestions?