Dell Inspiron 13z (N311z, Mid 2011) - Manual (Page 65)

Processor Heat Sink 65
3 Follow the instructions from step 3 to step 15 in "Replacing the System
Board" on page 60.
CAUTION: Before turning on the computer, replace all screws and ensure that no
stray screws remain inside the computer. Failure to do so may result in damage to
the computer.