Why some components have to hang above PCB?

[Sunsun22]

I am curious to know why some components have to hang above PCB like this one as shown other than reasons of heat: -

[tbr]

Interference with tracks on the pcb below, isolation issues at hv units, positioning space of the robot somewhat limited (but seldom),...

Thomas

[peranders]

I would claim that in 99% of the cases it's about hot parts. Better cooling simply. I can also be that you don't want some other sensitive parts to get hot.

It can also has something to do in the soldering process. Those parts maybe _not_ be able to handle the heat from the wave soldering.

[Sunsun22]

Thank you for the input. Would like to know what are the criteria to determine which component should hang above PCB to prevent interference from tracks in PCB?

Sunny

[anatech]

Hi Sunsun22,
peranders is right. Hot parts are stood off the pcb so the pcb doesn't get damaged. If the part is this hot, you don't want the pcb to be used as a heatsink. High voltage parts are stood off to cut down leakage currents, you may find the pcb cut at right angles below the part depending on voltage or leakage sensitivity. The other reason to stand a part off is one that may burn in a fault, again so the pcb is not damaged.
The ceramic standoffs in your picture normally would indicate a hot part.
-Chris