silpad or mica for to247 in F1

If any one has a source for mica insulators TO247 Please let me know..


I am hopeful that the sheets of mica sold by McMaster Carr are the right type for this service.

Part number 8802K16 is a 3x5 sheet of muscovite mica, .004 thick, for a measly $2.17.

I have a roll of thermally conductive kapton film that I will be trying first, though, obtained from the same supplier.



Paid Member
2004-02-24 8:46 pm
The sheet of Mica you are referring to works fine. Just cut a piece the size you need and off you go.

If you want to go crazy and reduce the thermal resistance further, with an xacto knife you can actually "slice" the sheet of mica into thinner sheets. It is easier to do than it sounds.

For class A amplfiers it's not such a big deal to have the extra thermal resistance of a silpad so long as you hit your particular desired junction (channel) temp after warmup... because there's not much dynamic about dissipation.. Far as cycling, you know, are you going to turn the thing on and off 500,000 times, or not? Not. A little rubber just means a bit more sink and you're good to go.
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mica comes in a wide range of thicknesses. The thinner, the less the thermal resistance.
"silpads" and similar come in an even wider range of thermal resistances. Choose a thermal resistance that suits your $ and your device temperature.

There are very few "silpad" types that can better a 2thou (= 2mil = 0.002inch) thick mica for thermal resistance.