The ambient temperature is defined as follows based on the JEDEC standard, assuming that the semiconductor device and the board are in a state of thermal equilibrium.
When there is no wind and the board is horizontal, the temperature is measured 25 mm below the bottom surface of the board, directly under the center of the semiconductor device.
In forced cooling, the board is either horizontal or vertical. The speed of the wind horizontal to the board is at least 2 m/s. The temperature is measured 25 mm below the bottom surface of the board, 100 to 150 mm upwind from the board (diagonally behind the device).
When executing thermal design at the set level, factors such as the temperature distribution, outer casing size, and heat dissipation characteristics must be taken into consideration. Also, since it is difficult to achieve highly accurate thermal design, make sure that your condition settings include sufficient margins.