Are you looking for a sturdier keyboard case or were you looking for a stiffer keystroke feeling?
If it's the first option you need to reinforce the case or add a plate (depending on how the pcb/plate mounts to the case). If it's option #2 you need to add a plate, people normally go PCB mount for a softer keystroke feeling because a PCB has more give than a metal or plastic plate does.
If you just have a PCB without any sort of case, adding a case will make the board stiffer and change the keystroke feeling a bit.
I hope that answers your question, I'm not totally sure what you're asking