What is the best aluminum for heat sink?

Aluminum extrusions - may be not much less than that of "poured aluminum", which has heat conductivity of 161 w/m-k.

Die-cast zinc-aluminum alloy - 127 for "ZA-27", 115 for "ZA-8". Die-cast zinc "zamak" - 113 w/m-k Die-cast die-castable aluminum alloy - 96.2 w/m-k Annealed brass - 61 w/m-k

Extruded copper - 300 w/m-k Extruded aluminum - 200 w/m-k

(There are heat-treated versions of 6061 including T4 and T6, which have mildly increased electrical resistivity, and I suspect also slightly decreased thermal conductivity.)

If this spacer has to conduct several 10's of watts or more and every degree matters, I say make it out of copper or silver.

Otherwise, extruded aluminum, poured aluminum and 6061 are close enough to each other for "best aluminum", and I expect ordinary aluminum plate and bar stock (to be machined into shape) to be similar.

- Don Klipstein ( snipped-for-privacy@misty.com)

All of the above.

You'll lose more delta-T at the mating surfaces than in the aluminum, most likely. Matweb

d be

All aluminum alloys have approximately the same conductivity (thermal and electrical). Pure aluminum (1199 is the purest) is maybe 20% higher conductivity than 356, 6061, 7075, etc.

Tim

Addendum: all metallic alloys have higher resistivity (thermal and electrical) than either pure metal. For instance, sterling silver is more resistive than either silver or copper. I suppose aluminum alloys are fairly surprising in that regard, as they are still fairly conductive.

Tim

As small as that is...

A pure Copper block...

Or...

A pure Aluminum block

You could thermally epoxy one side if possible. Fine mating surfaces and compression during the face to face cure. Then build up a small bead of the epoxy around that fixed end, since those finely mated faces won't have much epoxy between them... at all. Silver filled IC chip epoxy is best for that, but many others are also suitable... if you decide to "fix" one side. Other wise, managing the two (four) faces that will be mating is possible, just a tad more difficult sometimes.

Aluminum alloys are poorer thermal conductors than pure Al is. Pure is like 210 W/m-K,and 6061-T6 is like 167 W/m-K.

Looks like the closer to pure, the better, but all searches nowadays point one toward Copper and alloys thereof.

Copper is 385 W/m-K. Much better

Actually, I found it to vary quite a bit. Pure being best.

Copper is the one that I found remains the same, regardless of how wrought, and well into some alloys.

Regular 6061 T6 is 21% lower than pure Al in thermal speak.

Better look again. Even Al suffers a hit, once the lattice, she is split.

copper is better. aluminium is cheaper. pure is better than alloy.

the less gap you get at each join the better, so a flat mirror finish on all surfaces is is ideal.

copper is better. aluminium is cheaper. pure is better than alloy.

the less gap you get at each join the better, so a flat mirror finish on all surfaces is good.

Metal is much much better than heatsink paste so if you can solder or weld the spacer to the heatsink (with the apropriate solder and tools) so much the better.

'Ya know, if you can clamp the assembly quite tightly (or even apply some persuation as a part of assembly), you could use pure aluminum to fill the space, no grease. It's soft stuff, about like lead. Oh, and use springy washers too, I suppose...

Tim

"> Addendum: all metallic alloys have higher resistivity (thermal and

Well except for super conductors where some alloys are better.

George H.

The best aluminum is copper!

After that, check the thermal conductivity of various alloys. They can vary a lot.

And make the spacer big to spread the heat laterally.

John

Yup. A copper heat spreader can work wonders on an aluminum heat sink. Too bad isotopically pure diamond isn't in the McMaster catalog.

John

I don't know the purity of a penny, but I have used a penny for a interface on an rf transistor.

greg

sink.

grease

be

an rf transistor.

It depends on the age. Modern pennies are mostly zinc.

If it were, could anybody afford it? ;-)

Cheers! Rich

Like This?

Cheers! Rich

Instead of a spacer, use a rectangular heat pipe that sticks out far enough to cool aggressively. ;-)

Cheers! Rich

Yup, like this:

ftp://jjlarkin.lmi.net/Amp.jpg

The shiny things are copper heat spreaders, nickel plated. I did one DSRD-based [1] HV pulser that was built on a gold-plated copper block, water cooled; it looked great. You can get a peek of it here:

John