Mechanical switches need to be mounted on a pcb. A rubber dome has a membrane instead. Look here:
http://en.wikipedia.org/wiki/Keyboard_technology
Huh? No they don't. Mechanical switches only need to have wires connected to them, and arranged in a solid form. They don't need to be mounted into a pcb. The only reason manufacturer's use pcb, is because it's convenient, and costs less to create a pcb with all the wiring, than having to solder every switch. The siig minitouch 2, the new version is a conductive rubber board over pcb, not rubber dome, which means you can scratch off the junk over the contact points, solder wire to the pcb, then to a mechanical switch. If you then suspend the switch over the pcb, in a plate, it's perfectly good.
Read my steampunk hack page.
chimera15, I thought the Minitouch plate can be used itself.
mounting the keys to the switches sounds like a real pain
* Edit: king of unattentive
You can't use the siig minitouch plate, because it doesn't have one. It has plastic plungers, and it's almost totally impossible to use the plastic even if you cut it out to mount mechanical switches. You need a donor board to create a cut down plate from.