Acer AR380 F1 - Manual (Page 66)

3 System upgrades 48
2 Do not apply any thermal grease to the heatsink or the CPU die;
the required amount has already been applied.
3 Place the heatsink on top of the CPU so that the four mounting
holes are aligned with those on the (preinstalled) heatsink
retention mechanism.
4 Screw in two diagonal screws (i.e. the #1 and the #2 screws) until
just snug. Do not fully tighten the screws or you may damage the
CPU.)
5 Add the two remaining screws then finish the installation by fully
tightening all four screws.
6 Install the air duct. See page 43.
7 Observe the post-installation instructions on page 27.