Epoxy filled with micro spheres for thickness control

Yup. More spheres are better, up to the point where they stop sliding past each other into a single layer. You want the fractional areal coverage of spheres to be much greater than the ratio of the Young's moduli of the epoxy and the glass. The epoxy wants to shrink by ~1% when it cures, so the more glass you have, the less the epoxy can squash it.

Cheers

Phil Hobbs

Cataphote. They make retroflector glass spheres, like for STOP signs, with a shot mill process. They also size grade them for spacer applications.

I see worker-guys stencil white paint on the street and then toss on handfulls of the beads. The wind blows the strays around, and the whole neighborhood sparkles for a while.

How about sand? Or monofilament bits?

I found this,

I think I want a solid sphere?

George H.

OK, I was thinking fewer sphere's would be better. I'm mostly worried about thermal expansion type stuff. Maybe with stiff sphere's and squishy epoxy there is some nice mixture.

George H.

Monofilament is interesting... I could get quartz fiber and lay down some sections.

George H.

you never said what the spheres are.

One would presume Silica.

At that point, you could use Stycast as the base for the mix.

Go to the nearest auto-machine shop, and get a handful of their glass beads from their bead blaster. Get them from a new bag of beads. Or get their bead source and buy a bag yourself.

Fiberglass insulation, in small amounts? I have no idea what the diameter might be.

A few small plastic washers?

Epoxy and hollow glass microspheres are used to gap ferrite cores.

I guess if the CTE of the two surfaces you're using is much different you might have problems. PCB material has pretty low CTE in the X-Y directions.

Best regards, Spehro Pefhany

You can get micro spheres from almost any fiberglass supply house, local or online. Tap plastics, US Composites, Fiber Glast, Aircraft Spruce and others. TAP Plastics has a 1/4lb jar for $9.65. 1/4LB will probably last you a long time unless the wind blows it away.

If you are looking for heat transfer you might try Alumina Trihydrate powder. It is used in large castings to help get rid of the heat. I've never used it. US Composites carries it.

There's ceramic-filled epoxy available as a super-zoot heat sink compound. I don't know if the ceramic is large or regular enough to guarantee electrical insulation, though.

Yikes, $300/g? That's like $135,000 per pound.

Cheers

Phil Hobbs

Get the silica. Better thermal, and for sure solid.

Crushed industrial diamond is best.

Cheap. Just use that or garnet grinding grade grit. They filter it so size is consistent.

Ideally, you would want some fine grain media in with your chosen size to make fills.

So, yeah, grinding media is cheapest solution.

Micro balloons?

Yeah I just don't know. A lot of the micro spheres that I find are hollow glass.

George H.

Ohh I remember buying glass wool in the past...

George H.

Yeah, well Si and Germanium look even smaller than G-10. (Metals are bigger.) I'm just going to have to experiment.. If epoxy doesn't work my fall back plan is to use Silicon grease under the sample and hold it in place with a dab or two of rubber cement. Kinda messy looking, but it worked fine in grad school.

George H.

Thanks Joe, The price is a bit better than what I found :^)

george H.

Well the slightly bigger spheres are only ~$150/ gram... but still...

George H.