1. Not all process engineer need perform shift, it is really base on your department and your boss. Even in the same fab, may some ppl need do shift while some ppl dunt need, up to your manager's preference.
2. Shift got allowance, night shift allowance > day shift allowance, so if you wanna more money, go for shift.
3. 3/4 day working means: 1st week, work from sunday to wednesday, then rest from thursday until saturday. then 2nd week, work from sunday to tuesday, then rest from wednesday. repeat it. You really got a lot of personal time.
4. If you do shift, normally boss will not ask you for OT unless come on another day since you have work for 12hr per day. But even you do the normal working schedual, actually you will work around 12hr a day as fresh, and lots of time without OT pay.
As a process engineer in FAB, I suggest you do shift.