plastic film is between components and heatsink

[TheBrick]

Hi, taking apart a motor drive board and the is a thin layer of plastic between the power transistors and the heatsink. What plastic is this? I guess it is for electrical isolation but it must also need to have good thermal conductivity? It almost looks like ohp material. What can I use to replace it? (I've lost one of them).

[KJDS]

That sounds like mica.

You can probably replace it with a sil-pad

[TimFox]

Mica was the traditional material, but thin plastic spacers are now common.
One used to be able to buy them at Radio Shack as part of a mounting kit with a small tube of grease.
The spacer must be an electrical insulator, coated with thermal grease on both sides to ensure good thermal contact.
Without grease, there will be small local gaps/bubbles at the interface which will not conduct heat well.
Sil-pads combine those two functions.

[TheBrick]

Yep I can see the thermal paste, thanks. I'm UK based so it looks p like eBay may be the easiest. Nothing listed on maplins and that is the only high street shop around here.

[JamesHowlett]

Is it a solid plastic or a gray rubber-like thin sheet?

[Prime73]

most likely it is a mica insulator. search it on ebay.

[Tac Eht Xilef]

Yep I can see the thermal paste, thanks. I'm UK based so it looks p like eBay may be the easiest. Nothing listed on maplins and that is the only high street shop around here.

http://www.maplin.co.uk/search?text=insulating+washer&x=0&y=0

[TheBrick]

Whoo . strong google skills. I was searching for sill pads thanks!

[TheBrick]

Is it a solid plastic or a gray rubber-like thin sheet?

Thin and clear. Google say 1250 deg c melting point so I might try melting it with my iorn and a wrap tip. If I can't that would suggest mica, I think it would is more likely to be mica due to the age.