since I’m attempting to port Postmarket OS to Xperia XZ3 phone I used Flex PCB from Aliexpress that acted as adapter to access the UART from the micro SD card pin.
Unfortunately the flex PCB adapter stopped working so I made proper board in Kicad.
I’d ask for review of the layout.
The thing is the SDIO interface is of high speed nature. So the previous idea to make just 2 layer board is not a good design in the end. IMHO the half duplex interface to SIM card does not need such care, right?
So I’m thinkering to make it 4 layers with ground planes and probably try to match the impedances for the SDIO signals.
Also since the footprints for micro SD card and SIM card are missing I’ll shortly upstream them. Also on that note want to make simple adapter for E-SIM package which is also missing.
One additional point I noticed is that the SIM adapters have pins labelled as C# instead just numbers which requires changes to match the signals from schematics to the footprints.
The intention of this forum is to help people with learning how KiCad works. It is not for learning electronics or PCB design, but we do an occasional PCB design review. I had a very brief glance at screenshots of the link above and one of the other designs you requested a review for, and it looks like typical beginners mistakes. Start by learning why you need a proper GND plane, then learn how to achieve that and implement it in your own designs. Searching this forum for older reviews and then read though the thread and think about and implement the recommendations in your own design.
The link below is a review from 2019 and it’s quite extensive.
Thanks @paulvdh for the review. You are right about the question why?
The aim was just to make UART board both then got tedious after measuring all the dimensions and adding the components that to justify the time I added in there the kitchen sink.
There are other wonderful boards that deal with similar complexity such as the SD Mux from Pengutronix (Pengutronix - The USB-SD-Mux is now FAST) that should have been studied first as an example. Also the provided link goes deep enough.
My aim is just to share project that could be useful to someone else who might need something similar. That said the problem is that I’m trying to come up with specs for a device that was not intended to be used in that way and and I’m attempting to extend it at the same time trying to cut corners to make it reasonably complex.
That’s hard to see without external view. So thanks for pointing that out!
Redesigned the board to be simple pass-through out for the SIM and uSD with one feature and that’s selection if the SD card has power or not and the RX pin can then be used.
Started from the ground up as 4 layer board with the stackup selected from the beginning to ensure the traces are impedance matched.