HP Apollo 4200 Gen9 User Manual page 106

Remove the thermal interface protective cover from the heatsink.
11.
Install the heatsink:
12.
Position the heatsink on the processor backplate.
a.
Tighten one pair of diagonally opposite screws halfway, and then tighten the other pair of screws.
b.
Finish the installation by completely tightening the screws in the same sequence.
c.
Install the air baffle (on page 32).
13.
Hardware options installation 106