3.6 mm Pentalobe screw is stripped

Stripped heads or stripped threads? ie. does it just turn around and around, or can you not get a screwdriver in there?

If it's stripped head:

1. Get a left hand drill bit. Machinists use these all the time to back out stuck screws. Use it in a drill set to SLOW speed.

2. You can get a product called screwgrab that's a friction gel that helps drivers get a hold of the screws. Works better with phillips screws though.

3. You can glue a bit in there. Use superglue, or even better epoxy. Let it set up. Then back the screw out.

4. Take the iphone and set it on something that vibrates. I've used the top of the washing machine and ran a couple of cycles. The vibrating will work screws loose. The only thing to remember is to check ALL the screws afterwards.

If it's stripped threads you should be able to remove the back anyway. The backs have tabs that the screws go in. They do strip fairly easily, and sometimes they actually get disconnected from the back or crack. So just push the back up and pop it off, then the screws will fall out. To replace you can either replace the back with one from here or use superglue or threadlocker on the threads of the screws when you replace.