Asus Z9PH-D16 - Manual (Page 30)

2-12 Chapter 2: Hardware information
The Thermal Interface Material is toxic and inedible. DO NOT eat it. If it
gets into your eyes or touches your skin, wash it off immediately, and seek
professional medical help.
Some heatsinks come with pre-
applied thermal paste. If so, skip
this step.
11. Apply some Thermal Interface
Material to the exposed area of
the CPU that the heatsink will be
in contact with, ensuring that it is
spread in an even thin layer.