TO247 insulated heatsink mounting kit

[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]

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

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

[Faringdon]

Thanks...
So I have purchased the attached, 20mm x 20mm TO247 thermal pads…

Digikey part no.
1168-TG-A482K-20-20-0.1-0-ND

In the Digikey photo,  and the datasheet, it just appears to be a red pad, but as the photos show, it actually has like a clear plastic backing. Is the red bit supposed to peel away from this clear plastic backing? ..if so it  wouldnt be easy to peel away.

Digikey page of thermal pad
https://www.digikey.co.uk/en/products/detail/t-global-technology/TG-A482K-20-20-0-1-0/4385400?s=N4IgTCBcDaIC4HMC0BDALADjAayWADHofiALoC%2BQA

[T3sl4co1l]

Remove all carrier film before application.

Tim

[Jeroen3]

Try this pad:

https://www.tme.eu/en/details/wk_247/heatsinks-equipment/fischer-elektronik/wk-247/
It's one sided slightly adhesive for ease of application, comes on roll, hole precut.

or this oxide plate, gives better thermals and insulation at higher cost and thickness:

https://www.tme.eu/nl/details/aos218_247_1/radiatoren-uitrusting/fischer-elektronik/aos-218-247-1/

AAVID thermalloy/Boys sells similar parts, just look it up in their catalogs. For the americans.

Edit: non adhesive also available https://www.tme.eu/en/details/ws_247/heatsinks-equipment/fischer-elektronik/ws-247/

[Faringdon]

Remove all carrier film before application.

There was some film on it, which i removed, but the clear plastic sheet thing appears very strongly adhered to the red bit......it doesnt seem to be removeable at all, i tried "widgering" it with a scalpel blade edge, but i just couldnt get it off the clear bit.