Thermal Insulators.

Glass has relatively poor thermal conductivity (perhaps 30 times worse than alumina), among other things. You can heat a glass rod to incandescence at one end and hold the other end in between your bare fingers (but avoid the 'cold' end of the rod...).

Best regards, Spehro Pefhany

What's the minimum thermal conductivity that'll work for you? What's the maximum electrical conductivity that'll work for you? What's the dielectric strength necessary? If you can answer these three questions then your search should be simpler.

Here's some suggestions for things to look at, but it's your responsibility to see which, if any, are good enough:

1. If you are epoxying things anyway, you may want use the epoxy as your thermal transfer medium as well as your adhesive. Just epoxy hot copper to cold copper, with some beads or something cleverer to space the parts far enough to get the electrical separation you need. This depends on having an epoxy that'll give you the thermal and electrical properties you need in a thickness that you can control, as well as your being able to glue it without significant voids. There are epoxies out there that are made for gluing heat sinks -- look around.
2. The best ratio of thermal conductivity vs. electrical conductivity that I know if is beryllium oxide ceramic. Unfortunately it's dust is pretty toxic, so you would have to use great care if you needed to work it in any way, or if you dropped a piece and broke it. I'd think long and hard before _I_ used it, but it's used in quite a few RF transistors that have high power densities.
3. What about good old mica spacers?

1. Steatite is a fancy name for soapstone. It used to be quite popular as a 'ceramic' material in the '30s. I have no idea how it stacks up for your thermal and electrical properties, but I do know it is very machinable.

2. Check out Small Parts, Inc. -- they may have what you're looking for.

I'll definately avoid glass. Glad you spoke.

If I don't get the alumina I need, might just use the thermal epoxy with spacers. Tiny blass beads about 100um Hmm, wonder if they have ceramic beads.

greg

The material that has extremely high thermal conductivity and is also a good electrical insulator is..... . . . . . . . .....Diamond! One can use black diamond, which is less expensive.

Good idea. I could sprinkle some dust into the epoxy to insure isolation.

greg

Check this out.