comment: >
  
  I think they're slotted into a 3d printed plate and the connections are hand-soldered wires. OP has hidden the wires underneath the plate as you could see a Philips screw head at the top left corner.
context: Looks great! Can the Pi Pico run something like qmk? Or is it custom programmed? >
  
  It can run QMK or even KMK which is written in CircuitPython and can be modified by editing a text file in a virtual drive from the pi. Really nifty.
  Edit: link www.kmkfw.io >
  
  Very cool, thanks! >
  
  A little numpad for my nephew I designed and printed. It is using some keycaps from a previous build and Novelkeys BOX Jade Clickys. 
  His name is printed on the underside. He was very happy to receive this gift. >
  
  Are the switches not on a PCB? I can't seem to understand how this is done, what are the switches attached to?