Heat sink compound

[Randall]

Who is using what these days? I purchase it so seldom that I don't keep up with the latest. I see different types at a fair price range. I've always just used whatever my local supplier had, but now there is none where I am, so I ask, is the expensive stuff worth it, or is the old stuff good enough?

[Enzo]

I use whatever looks cheap. Fender et al don't use expensive booteek silicone cream. I am sure there are special high performance concoctions, maybe NASA uses them. Maybe CPU cores need them. A pair of 7815s in some device, need basic Kmart stuff.

I used to buy GC products off the hook.

[R.G.]

Heat sink compounds are used to fill the microscopic air voids between the device being cooled and the heat sink. Having **anything other than air or other good inulator ** in those voids is dramatically better than leaving the voids. Accordingly, the first fillers were greases; these promptly thinned and ran out if the joint got too hot. Then there were special oils/greases that helped by not thinning so much.

Then someone decided that greases and oils were not really all that good at conducting heat, and thought to fill the goo with a high percentage of better conducting dusts. Zinc oxide is dramatically more heat conductive than oils and greases, and was nontoxic, cheap and easily worked. Thus began the era of white heat sink goos.

And the era of producing modestly better goos by substituting more thixotropic bases and more conductive fillers, getting more filler in, etc. Mounting power transistors usually needs an electrically non-conductive interface, so nonconductive fillers are the watchword. For things like CPUs, non-conductivity isn't as important, so the computer/CPU goos can be filled with metal power for a little better conductivity, or even the king of thermal conductivity, diamond powder.

But back to your question. There are lot of heat sink goos. Using any heat sink goo is so much better than none that you can continue to use what you have as long as it's still spreadable. The difference between what you have (assuming a white, oxide filled one) and the most heavily advertised firebreathing goop on the market may be two or three to one for just the goo, but that's a small part of the thermal interface, so changing to a different goo won't dramatically change the heat tranfer - unless you're running on the edge of core meltdown, and if you are doing that, you have a whole different set of problems.

Use what you have if it's usable, get some ordinary white goo if you have to buy more. The real problem with goo today is buying a small enough amount to be affordable. The big names want to sell quart cans.

[rjb]

...Zinc oxide is dramatically more heat conductive than oils and greases, and was nontoxic, cheap and easily worked. Thus began the era of white heat sink goos....

...The real problem with goo today is buying a small enough amount to be affordable. The big names want to sell quart cans.

How about this? I guess not, hunh?
https://www.walgreens.com/store/c/wa...c-341e240f4367

[Randall]

Thank you for that comprehensive as usual answer R.G. I will sleep better at night knowing I am not cheating by using the basic white goo!

[tedmich]

pick something that's K value is somewhere to the right of AIR in this picture. Ideally one easier to use than Lead or Diamond...

[R.G.]

How about this? I guess not, hunh?
https://www.walgreens.com/store/c/wa...c-341e240f4367

Actually - if I were in a world of hurt for heat sink compound, I'd go for it. As I noted, ANYTHING is better than air in those voids. There is, as usual, a string of asterisks involved. But you knew that, right?

The finely-ground zinc oxide is good, and will be very finely ground so it seems like a smooth lotion on skin. In this case, the binder goo is the problem. It's almost certain not to be a thixotropic mixture, so it will relax under the pressure of the mounting screws, and squeeze out. It's not likely to be a good inorganic grease or other paste-forming stuff, so it will likely get thinner and run out with heat - and heat is why we're here.

So if I had to repair something and I was doing a show out in West Bum... er, West Buttercup Wyoming, and only had a drugstore available, I'd do it in a second. But I'd count on wiping it all out and replacing it with proper stuff when I got back to my shop. My shop has a 4-oz can of goo that I've been using out of for nearly 20 years now. It's still half full.

I do like the convenience of the little heatsink goo syringes that they put CPU compound in, and the little tear-open plastic packs (like the burger joint ketchup packs, but heatsink goo) but not enough to go buy new stuff until I empty that can.

[xtian]

R.G.! R.G.! R.G.!

The Wikipedia of electronics. Love ya', man.