thermal design

Hello all, 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...

I am a student in power electronic filed. When I design PCB and calculate the junction temperature of MOSFET, I am very confused about the thermal design question. My PCB design is here: (in the middle of the figure) : three MOSFETs in parallel, so 12 MOSFETs(Rthj-c=0.4 from datasheet) in one...