The PCB has a pulse oximeter mounted on the surface, and it's tolerance is 0.6mm. The problem is the pulse oximeter needs to touch the bottom case at all times. How to best mount the PCB in the case without putting too much stress on the pulse oximeter? Will screws with flexible washers be all right? Sadly separating pulse oximeter from main PCB is not an option.
I would put a machined guard around the pulse oximeter to keep the surface from it at about 0.2-0.3 (if it is and SMD part soldering height tolerance is about 0.2mm) and then simply screw down the resulting assembly.
Otherwise use weak springs to push the p.o. against the case, need to know the allowed stress on the body for that