I just finished my initial cut at a PCB for the CHESSmate. This first PCB is an IO board only holding the buttons, 7-segment displays, and LEDs in the precise positions so that they line up perfectly with the membrane.  I also threw in a piezo speaker circuit.

I ended up having to make my first 4-layer PCB primarily because the components were in fixed positions and could not be altered to obtain a more favorable layout for putting down the traces.

Having IO separate from compute will make it easier to test. In addition this configuration will support multiple "back-ends". For instance an emulation implementation that I am leaning towards and/or a "pure" solution replicating the original hardware.

I still have a lot of testing to do before I commit to fabrication. I discovered that 4-layer PCBs are quite a bit more expensive than 2-layer so I want to be sure of a good result.