why is there a notch in radial-finned extruded TO-220 heatsinks

[mhenschel]

At first blush I would have thought that a heatsink would be configured to mate intimately with the heat-generating component for maximum heat transfer.
Yet, many of these heatsinks have a cutout just where you'd figure there should be more contact with the body of the unit... below the tab.
What's the thinking?

 

[Osvaldo de Banfield]

Perhaps the idea is to fill it with thermal paste. But who knows...

 

[Andersonix]

these heatsinks

Did you mean to attach a pic or a link?

 

[EdGr]

I think the notch ensures air flow if one side is blocked by other components.
Ed

 

[mhenschel]

Sorry, I did mean to

Again, it seems to me that the full body length of the device should be against the heatsink.

 

[Michael Bean]

Do you mean like these?



I've wondered the same thing, it seems kind of counter productive to achieving the desired results.

Mike

 

[Andersonix]

Likely to provide access/clearance for these multi-pin chips

 

[Tony Salsich]

I suspect these particular heat sinks are meant for a lesser used package (neither TO-220 nor TO-247) that has a thin metal tab extending out of the middle of the part. I cannot remember the number of it though.

 

[Tony Salsich]

They are likely meant for a TO-202.
https://www.centralsemi.com/docs/PDD/TO-202PD.PDF

 

[Mark Tillotson]

Those heatsinks are tiny and handle a few watts at most, so their thermal impedance to the die isn't very crucial.