HP TC4400 - Manual (Page 110)

Removal and Replacement Procedures
Maintenance and Service Guide 5–27
✎
The thermal paste should be thoroughly cleaned from the
surfaces of the heat sink 1 and processor 2 each time the heat
sink is removed. Thermal paste is included with all heat sink
and processor spare part kits.
Thermal Paste Locations
Reverse the above procedure to install the heat sink.