TO247 insulated heatsink mounting kit - Page 1
Forum section: electronics / general

author: Faringdon
author_rank: Super Contributor
timestamp: June 28, 2022, 09:10:38 am
content: Hi,We need to screw a TO247 NFET to this heatsink (MC33271)...(FET insulated from heatsink)MC33271 heatsinkhttps://uk.farnell.com/multicomp/mc33271/heatsink-to218-220-247-2-7-c-w/dp/1710614Do you know of specific TO247 thermal pads?...all seem to be TO220Theres this at 1.7W/m-k and 0.3mm thickhttps://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)

author: mariush
author_rank: Super Contributor
timestamp: June 28, 2022, 01:41:57 pm
content: You'll probably also want an insulator for the screw... some examples:https://digikey.co.uk/en/products/detail/assmann-wsw-components/V5731/3511414https://digikey.co.uk/en/products/detail/assmann-wsw-components/V5816/3511531https://digikey.co.uk/en/products/detail/assmann-wsw-components/V5359/3511490

author: MarkF
author_rank: Super Contributor
timestamp: June 28, 2022, 01:44:00 pm
content: 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.

author: Faringdon
author_rank: Super Contributor
timestamp: June 28, 2022, 02:14:12 pm
content: 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.

author: langwadt
author_rank: Super Contributor
timestamp: June 28, 2022, 02:33:47 pm
content: Quote from: mariush on June 28, 2022, 01:41:57 pmthe hole in a TO247 is isolated it doesn't need an insulator

author: Faringdon
author_rank: Super Contributor
timestamp: July 20, 2022, 01:09:12 pm
content: Thanks...So I have purchased the attached, 20mm x 20mm TO247 thermal pads…Digikey part no.1168-TG-A482K-20-20-0.1-0-NDIn 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 padhttps://www.digikey.co.uk/en/products/detail/t-global-technology/TG-A482K-20-20-0-1-0/4385400?s=N4IgTCBcDaIC4HMC0BDALADjAayWADHofiALoC%2BQA

author: T3sl4co1l
author_rank: Super Contributor
timestamp: July 20, 2022, 01:35:26 pm
content: Remove all carrier film before application.Tim

author: Jeroen3
author_rank: Super Contributor
timestamp: July 20, 2022, 01:35:50 pm
content: 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 availablehttps://www.tme.eu/en/details/ws_247/heatsinks-equipment/fischer-elektronik/ws-247/

author: Faringdon
author_rank: Super Contributor
timestamp: July 20, 2022, 07:30:58 pm
content: QuoteThere 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.