As mentioned earlier, AMD recommends the use of an etching pattern on the contact surface of the heatsink, and it is even more important for bare die and lidless devices as a means to allow minimal BLT to the die. The thermal modeling of the etching is very difficult and can make meshing and computation time become excessive. For these reasons, when using etching, AMD recommends modeling a flat surface with very low BLT and/or slightly higher thermal conductivity than the TIM material provides by modeling it implicitly.
Tip: For example, through AMDs experimental testing of the etch pattern and using
Laird 780SP thermal interface material, the improvement results in an equivalent of a
BLT of 70 µm and conductivity of 20 W/mK that modeled the etch improvement. This is a
simple way to understand the in-system benefits of the etching without the time and
effort needed to properly model the etching.