#TIL Apple lays PCB traces under the screw holes of the iPhone motherboards and uses multiple types of screws with ~0.1mm difference in length. If your ever screw the 0.1mm longer screw to the wrong place, the PCB traces under the screw would be damaged, thus instantly kills the entire motherboard.
There is no obvious mechanical or electrical reasons to do it, it sounds almost like a "tamper-detection" mechanism designed to retaliate to anyone who dire to attempt fixing an iPhone.
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