I've started adapting Framework's "Microcontroller Input Module" reference design to try out potential PCB layouts. Because I want the keys near the bottom of the module as much as possible, next to the arrow keys, I've moved the microcontroller to the top. And I've staggered the keys left and right instead of making a vertical column of them, partly for ease of recognising them by touch, and partly so that I can get PCB tracks between them. There's not much space because the one-key-modules mount to the bottom of the PCB so there needs to be a huge cutout for the keycap to poke through to the top. So I need to make sure I've left enough space for that. It's complicated more by the locating lugs which also eat into space around the modules. This is what I've got so far:

I'm not sure yet if it might be possible to fit in a fifth key. It depends how much the space "below the line" with the contacts needs to be left clear, and whether I can squeeze the MCU in one of the gaps next to the keys (with all its tracks and supporting components...)