Although the board only requires passive cooling, it still needs a certain amount of airflow. Intel’s documentation also strongly suggests blowing air over the two heatsinks. An 80 mm chassis fan running at 5V is easily up to the task, providing adequate cooling with a low noise level.
With the processor cooled by an 80 mm fan, the CPU temperature reaches 32° C when idle; under load the temperature rises to 68° C.
Without a fan providing airflow, the idle temperature increases to 45° C, reaching 95° C under load and, in our experience, resulting in instability. Providing adequate cooling to the system is essential.