SDRAM and RMII lay-out considerations

Is this going to work?

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Thread Starter


Joined Jul 11, 2018
Hello everyone,

I'm new here so first thing is first.
My name is Marcel, I'm from the Netherlands. I own a company where I develop electronics on customer request.
Also a bit of production of pcba's with the use of a reflow oven, but only (very) small series.

Since I'm developping for all kind of customers I am not very specialised in a specific kind of electronics. So thats why I'm here.

I need to lay-out a design with alot of interfaces, including an ethernet interface and SDRAM (those are the "fastest").

Both interfaces are connected to a STM32F429ZIT, the SDRAM using the FMC (Flexible Memory Controller) at 90MHz, and the ethernet using the RMII interface (at ? MHz).

Now my question follows; is there anyone who has experience with these lay-outs and has got advise to keep in mind?
Like how important is the lenght match of those interfaces? And the impedances?

I'm using a 6 layer board with 4 signal layers, 1 ground layer and 1 power layer. On every layer (except power) there is a polygon pour connected to ground and stitched using via's.

I've attached an image where the SDRAM + current routing can be seen. The white square is the SDRAM (BGA). I've used 2 layers, top and bottom.

Thanks for your feedback!SDRAM routing.png