"When several devices on a circuit board generate the heat, a solution could be to use a
fan to blow air across the circuit board. Cooler air from outside the equipment can be
blown over warm components to reduce their temperature. Airflow will reduce the
effective thermal resistance of the air interface.
Careful placing of cooling fans can make a big difference to the performance. Large
objects like electrolytic capacitors will tend to block the flow and may steer the cooling air
away from areas of the PCB. If the air flows in the direction of heatsink fins, it will be more
effective. Air flowing across the fins will only cool the front and rear fins, see Figure 14.7.
14.7 - Copy (2).png
If mounting a fan at the top of equipment make sure that the air flows upwards,
with the fan blowing air outwards, so that the fan aids the natural buoyancy of the
hot air. Fans mounted in the side of equipment are much more effective if two
fans are used, one on either side of the enclosure. In a wide enclosure, both fans
could be mounted on the rear panel; one fan should blow in and the other should
blow out so that air circulates around the components inside.
Fans do have a reliability issue, so consider adding a fail-safe mechanism in case the
fan fails to operate. A fail-safe mechanism should monitor the temperature of
sensitive components on the circuit board. Driving the LEDs at a lower power or
turning them off when the temperature rises too high may be a solution."
Until someone convinces me otherwise that's how I'm looking at fans and cooling right now .