I've had something bugging me for a while.
Take these two scenarios, which would cool better?
Lets say I have an IC (or in my case, a Transmitter amplifier)
- The chip is free to air
- Has forced air-flow over the top of the IC.
- The chip is covered in thermal paste, or ceramic (so it sets).
- The thermal paste has forced air flow over it.
I'm thinking in scenario 2, there's more thermal mass, so better cooling.... however.....
Where is the changeover?
Lets say, I had an IC, and I dunked it into a bucket of non-flowing thermal paste.
And I had a second identical IC, which I put a fan on, and it's exposed.
Where is the changeover point where 'Thick thermal paste' is more insulating, than it is aiding with cooling?
Or is this likely to never be met, because the thermal conductivity of Thermal paste is always better than air?
So as long as the paste had air flow, it's always better?
Risk of getting a 'hot spot' in the paste, with no flow? Or is thermal conductivity just too good in brand name paste.
Real world application?
The reason I ask, is because an RC hobby of mine is using some 5.8ghz video transmitters.
These things get hot.
Now, most of them are hiding behind anti-interference shields (metal plates).
I know an Air-Gap is the worst possible thing, as air itself insulates;
So in the case of VTX modules that are layered PCB > Transmitter IC > AirGap > EMF Shield
I'm best to pop that shield off, fill the entire gap with non conductive thermal paste, and re-apply the shield.
But the question is, should I be shimming that gap, or can I just use 1mm thick of paste, and call it a day?