MAX31790 is currently only available in TQFN package (MAX31790ATI+). The themal data can be found below:
Single-Layer board:
Theta Jc - 3°C/W
Theta Ja - 48°C/W
Theta Ja - 48°C/W
Multi-Layer board:
Theta Jc - 3°C/W
Theta Ja - 35°C/W
Theta Ja - 35°C/W