Here's a PCB I'm designing for a custom keyboard controller! It will support up to 16 columns and 5 rows of keys. I'm designing this for my own build, but I'm curious
Keyboard controller - Deskthority wiki
Keyboard PCBs: How to Build Custom Mechanical Keyboards
Wireless Das Keyboard Modification - Build log — ivanyu
China High Quality Computer Keyboard PCB, Keyboard Controller PCB - China Fr4 Pcb, Multilayer Pcb
AVR Programmer built from a USB Keyboard [steve-m.de wiki]
40% Keyboards: Raspberry Pi 400 keyboard controller