heatsink "silpad" rolls or strips

Certainly.

Bob

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There's a serious hazard of the bar pressing unevenly on the tops of the transistors, canting them against the heatsink and making poor thermal contact on one side. Some sort of rubber or silicone pucks or buttons on each transistor might center the down force and also equalize it between transistors.

Or use clips:

ftp://66.117.156.8/Amp.jpg

John

Don't use them - they suck. They have crappy thermal resistance, and it's almost impossible to put enough clamping force to get good contact.

Use mica insulators and silicone heat goo.

And, as someone else mentioned, using a bar is a bad idea because you'll get uneven clamping force, unless it's a MONGO bar (probably with a bow shape), which would probably defeat the purpose of what you're trying to accomplish.

Good Luck! Rich

Better yet, have the heatsink milled to about RMS 8 and hard-anodized (which makes the insulator), but still use silicone heat goo.

Good Luck! Rich

Its nice to avoid silicone goo if possible as its messy, some of these silpads in this chart seem to have pretty low thermal resistance:

"

"

2degrees celcius per watt or so for Sil-pad 800, could always be better, but how does mica/silicone goo compare to this?

Also I don't know if hard-anodizing is good enough for my isolation requirements of 500VDC (at least for UL specs). I guess aluminum electrolytic caps prove that anodizing can withstand HV though, I think they have the same internal coating on their rolled sheets.

cheers, Jamie

Hey, if you do not like those products go see Chomerics. They make (or did) some Kapton film stuff that is interesting, with or without goo.