Electronics > Manufacturing & Assembly

TO247 insulated heatsink mounting kit

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Faringdon:
Hi,
We need to  screw a TO247 NFET to this heatsink (MC33271)...(FET insulated from heatsink)

MC33271 heatsink
https://uk.farnell.com/multicomp/mc33271/heatsink-to218-220-247-2-7-c-w/dp/1710614

Do you know of specific TO247 thermal pads?...all seem to be TO220

Theres this at 1.7W/m-k and 0.3mm thick
https://www.digikey.co.uk/en/products/detail/t-global-technology/TG-AL373-20-20-0-3-0/3042275

...most offerings have (unwanted) adhesive on one or both sides, are too thick, with way too much voltage isolation, and are all the wrong size for a TO247....~14mm x 14mm. (however, we dont mind a bit of overhang, and can trim them down)



mariush:
You'll probably also want an insulator for the screw... some examples:

https://digikey.co.uk/en/products/detail/assmann-wsw-components/V5731/3511414
https://digikey.co.uk/en/products/detail/assmann-wsw-components/V5816/3511531
https://digikey.co.uk/en/products/detail/assmann-wsw-components/V5359/3511490

MarkF:
I don't use them.
I isolate the whole heatsink instead by placing unconnected pads for the heatsink posts to provide structural support.
And don't run any traces under the heatsink on the top side.

It's probably a bad idea for high frequency stuff. 
But, it gives a slightly better heat transfer without the insulator in power applications.

Faringdon:
Thanks, we will try and get away without  shoulder washers, and hope the TO247 "insulated hole philosophy" will help us.
Good idea about just leaving the heatsinks floating....the fear of noise worries me , but i bet it would have been fine. Too late now, board is layed with HS to local ground.

langwadt:

--- Quote from: mariush on June 28, 2022, 01:41:57 pm ---You'll probably also want an insulator for the screw... some examples:

https://digikey.co.uk/en/products/detail/assmann-wsw-components/V5731/3511414
https://digikey.co.uk/en/products/detail/assmann-wsw-components/V5816/3511531
https://digikey.co.uk/en/products/detail/assmann-wsw-components/V5359/3511490

--- End quote ---

the hole in a TO247 is isolated it doesn't need an insulator

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