I chose this heatsink ( OMNI-UNI-18-50 ) to be used for each 2 SiC MOSFETs out of 6, I calculated the largest permissible thermal impedance between the junction and ambient air to be 4 C/W and the total power to be dissipated for every 2 MOSFETs is 36W.

The MOSFET junction-to-case thermal resistance is 0.5 C/W and the case-to-sink = 0.25 C/W (from datasheet).

Now I need the heatsink thermal resistance to be less than (4-0.5-0.25=3.25 C/W) ...

The problem is I couldn't figure out how to extract the thermal resistance of the heatsink from the graph in the datasheet!

If someone could point out how I could do that? and also check if my calculation is right.

Thank you in advance.