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TPS1663: Calculation conditions of thermal resistance

Part Number: TPS1663

Hi team members.

I want to know calculation conditions of thermal resistance of TPS1663.

the datasheet (7.4 Thermal Information)says 

RθJA (Junction-to-ambient thermal resistance) 31.4 /32.2 °C/W
RθJB Junction-to-board thermal resistance 10.2/10℃/W

What is the board condition when calculating the above thermal resistance?