Heat sink grease

I like these:

Peter Wieck Melrose Park, PA

heatsink compound is grese loaded with zinc oxide powder. The ZO provides the thermal conductivity.

If you're stuck for some, toothpaste is surprisingly good. I tried it on a high diss AMD 8 core CPU, it only ran a couple of degrees hotter than the proper stuff.

NT

Are those the gray rubbery ones ? I like them, no goop required. One place I worked told us to use goop with them anyway, they were kind of anal about things.

If you need electrical insulation, petroleum jelly is probably better. The main objective is to fill the air gaps.

Petroleum jelly melts & runs.

NT

The web page says they are pink; probably why Peter likes them!

Mike.

They are a very subtle shade of Dove Grey....

Peter Wieck Melrose Park, PA

The best way to use thermal goo is to have the heat sink and device touch each other with direct metal to metal contact, and with whatever thermal goo you select filling in only the gaps. Making a thermal sandwich with a thick layer of thermal goo which prevents direct contact doesn't work very well. Idea is to grind flat and mirror polish the heat sink and whatever is getting hot to get more metal to metal contact, and use very little thermal goo. Some CPU's and video chips have a mirror finish.

However, if you want to roll your own, diamonds are your best friend. Here's a list of thermal conductivity of various compounds and concoctions. W/m*K Diamond 1000 h-BN 600 (boron nitride) c-BN 740 (boron nitride) Silver 406 Copper 385 Gold 314 AlN 285 (aluminum nitride ceramic) Aluminum 205 Graphite 200 Carbon 150 SiC 120 (silicon carbide) Brass 109 ZnO 50 (zinc oxide) Al2O3 25 (aluminum oxide ceramic) TiO2 10 (titanium dioxide)

The common white thermal grease is zinc oxide, aluminum oxide, or both. The expensive stuff adds boron nitride. The clear stuff is just the grease, which is totally useless for thermal conduction but might be a handy carrier if you want you mix your own using various powders.

Tooth paste is the most common "alternative" thermal goo, although sun screen which contains zinc oxide and perhaps titanium oxide should also work.

If you can used and control a conductive thermal goo, try "liquid metal", and alloy of bismuth and indium:

Good luck.

I have several tubes of the stuff. It works, but I prefer Arctic Silver 5 for CPU overclocking and RF power devices. Actually, I prefer lapping and polishing the device and heatsink, but that's not always an option. A small tube of Arctic Silver 5 lasts me about 20 i7 size CPU's or about $0.25/per CPU because I use very little.

That's not very compatible with my dictum "The less thermal goo you use, the better it works". You want metal to metal as much as possible with the thermal goo just filling in the cracks and gouges.

I've posted my test results in sci.electronics.design. I'll see if I can find the article. You might find it of interest.

Sigh.

At least we agree on that part.

This should work:

A bit on tooth paste:

Using gold leaf:

Plenty more in that thread:

I found a more complete list of thermal conductivity:

W/m*K Diamond 1000 c-BN 740 (Cubic Boron Nitride) h-BN 600 (Hexagonal Boron Nitride) Silver 406 Copper 385 Gold 314 AlN 285 (aluminum nitride ceramic) Aluminum 205 Graphite 200 Carbon 150 SiC 120 Brass 109 Indium 86 ZnO 50 (zinc oxide) Al2O3 25 (aluminum oxide ceramic) Pastes 4.0 SilPad 2000 3.5 Circuit Works 1.84 Dow Corning 340 0.67

Note that most white thermal goo at the low end of the thermal conductivity list with Dow Corning 340 in the really awful category. Don't believe me? See: and look in the box under "properties". Thermal Conductivity = 0.67 Watts per meter K

I use some very fine particle size diamond lapping compounds in my shop. Maybe I should consider using some for heat sink compound next time I want to overclock the crap out of something. In fact, it could first be used for lapping the parts and then just left in place. Eric

Not sure where you disagree Jeff. Not speaking for the other Jeff (jurb), but I agree with him. If you get too much compound out of the sides, you'v e wasted it. If none appears you may not have put enough.

The idea is to squeeze as much out as is possible ensuring that only enough to fill gaps is left, on that we all agree. Forcing the device down by ex ternal pressure helps make sure any excess is forced out without relying on the devices own hardware to accomplish.

The center daub verses the even spread is debatable either way. RCA back i n the late 60s told us to use the center daub and let it spread out on it's own. Their reason was to avoid air pockets. On small devices like transi stors, that's what I do. On larger devices, I don't think enough pressure can be exerted to ensure a large area can force enough compound out of the joint, so I tend to carefully spread as thin a layer as I can accomplish.

What's the grain diameter? If it's larger than the depth of the cracks and crevasses in the aluminum extruded heat sink, then you're taking a step backwards. The bulk of the heat is passed by metal to metal contact.

As I vaguely recall, the typical flatness specs for extruded heat sinks is something like 0.007 in/in. So, if the heat sink is 2 inches wide, it can be warped 0.014" and still be considered usable. Ugh. It will take an awfully large amount of heat sink goo to fill a 0.014" gap.

The lack of flatness also causes problems when one tries to using such a heat sink as a lapping plate. If the CPU can is softer than the aluminum, it will convert the formerly flat can into a warped version of the not very flat heat sink. I did stuff like this in the distant past and found a really flat lapping plat to be a necessity.

If you want to see how bad it can get, take a black felt tip pen and "paint" the top of the CPU or the heatsink black. Find a flat surface (glass is good). Drop a sheet of fine emery cloth (2000 grit) on the flat plate. Move the heat sink very slightly over the sand paper. Inspect the heatsink. Where the heat sink was raised, the sandpaper will remove the ink. Where there was a depression, the paint will remain in place. Extra credit for repeating the test with a hot or cold heat sink. Thermal expansion in an extrusion isn't uniform and you will see bending in the heatsink.

There's also a problem with diamond dust and grease. While the grease is great of keeping the diamond dust in place and making it easy to apply, thermal cycling tends to pump the grease away from hot spots leaving rather voids. You can sometimes see this when disassembling a CPU and heatsink combination that has been running for a few years. If you take it apart immediately after assembly, the thermal goo is uniformly distributed (as long as the heat sink is reasonably flat). However a few hundred thermal cycles later, it will have voids.

Sigh 2.0

That makes three Jeff's. Nobody ever agrees with me, so you must be referring to Jeff 1.0.

As usual, I beg to differ:

1. If you apply enough pressure to make the thermal goo ooooze out from the sandwich, you will either bend the device (as in a TO-3 or RF power xsistor) or simply not be able to apply enough pressure with the mounting screws and springs. I was going to calculate or measure the pressure applied based on the recommended mounting screw torque for various heat sinks, but don't have the time. I might have some time this weekend to sandwich some Dow Corning 340 between two metal slabs in an arbor press with a load cell and see what it really takes to squeeze out the thermal goo. As you mention, I also suspect it will be rather high pressure, far beyond what can be done with small fasteners. Offhand, I would guess that this method was invented by a thermal goo salesman in order to inspire users to consume more of his company's thermal goo.
2. The problem with forming bubbles (voids) in the thermal goo was originally mentioned in the literature in reference to removing the heat sink after the thermal goo was applied. That will certainly create bubbles. Somehow, someone extended that to the initial application of thermal goo, which is not correct. I've never bothered to prove this, so if you have time, try a blob of your favorite thermal goo between two glass plates and look at it under a microscope. If there are any bubbles, they should be obvious. If you want, I can do this Friday as I have the necessary equipment:
3. Thermal goo is fairly cheap. However, it does make a mess when the excess is squeezed out of the heat sink sandwich. I prefer not cleaning up the mess.

My method of applying thermal go is fairly simple. Find the direction on the heat sink in which the machining marks and gouges run. Apply a tiny amount of thermal goo to the heat sink. Use a plastic razor blade: to smear the thermal goo in the direction of ACROSS the machine marks. The idea is to push the thermal goo into the grooves, crevasses, and gouges in the heat sink. If the mating part of the sandwich also has machine marks, do the same thing. The initial blob of thermal goo is intentionally insufficient to cover the entire heat sink. Add small blobs and continue to smear until the surface is covered. You will see quite a bit of metal. That's good as you want metal to metal contact. If there's any excess, wipe it off with the plastic razor. When done, clamp it together and DON'T take it apart for "inspection". If you do, start over by wiping the heat sink clean with alcohol, let dry, and do the blob thing again. Thermal goo tends to harden as the carrier evaporates. It will not flow into the cracks easily and will resist compression. Best to start from scratch.

cracks and crevasses in the aluminum extruded heat sink, then you're taking a step backwards."

Now you're getting into the RMS finish left by the machines. In mass produc tion I doubt it is very good. It is likely the grain is fine enough, in fac t I have seen the results of machining on the surface and it looks like man ufacturers are derating enough or just don't care.

metal contact. "

Which is why I apply as much pressure as possible before tightening any scr ews. The strip, some devices are mounted by clips and the pressure depends on its modulus of elasticity. One advantage is that over time it presses co ntinually and closes the gap, if any.

There is this pink shit out there that has such a high viscosity that I con sider it unacceptable. It is hard to squeeze out of the damn tube, as such it would take so much force to actually get the high spots down to metal to metal contact that it would probably damage the device.

I have used tools to compress these, and I know when to stop. When you tigh ten the vise grips or whatever a little bit more and get no more goop then it is pretty much done. In the case of a large STK IC for example, I will t ake the old part and put it on top of the new part so it spreads the force and isn't likely to break the case. Squeeze the whole shebang until no more comes out.

As far as the compound and its additives, diamond dust is probably the best . Copper beats aluminum or zinc oxide, but diamond blows their doors off. I t also has a very good dielectric strength except for blue diamond. Apparen tly whatever "impurity" is in there causes it. I don' t feel like looking u p what that is, feldspar or some shit ? Doesn't matter. Diamond does have a cost though, just how much is that semiconductor worth ?

heat sink as a lapping plate. "

I wouldn't do that with a computer CPU. I have done it a few times with oth er devices and that was only so mush, I did not really remove any significa nt material. Truth is I was low on the "birdshit" so I thinned it out a bit . Beats nothing and the guy didn't want to wait.

Actually I have cleaned a bunch of them with coffee filters. They do remove some metal. In fact the did it to VCR heads as well, seeing that black on it was not dirt, it was aluminum. It is time to stop, but the heads were ab out as clean as they'll ever get, and it may have enhanced head to tape con tact a bit. Just don't take off too much or there will be a bunch of wear a nd there goes your gap and azimuth offset sooner.

nt" the top of the CPU or the heatsink black. Find a flat surface (glass i s good). Drop a sheet of fine emery cloth (2000 grit) on the flat plate. "

Actually the coffee filter should work.

That sounds like scraping. you know you have machines, and the ways are str aight. Well those are cut on machine with straight ways so they are straigh t. And the ways for that machine are cut on a... this could go on forever. What is the FIRST reference ?

Scraped on plates. People actually scrape them by hand. they have a special surface on which the high spots are perfectly flat to withing a millionth of an inch, but there are valleys for oil. A roller will roll perfectly str aight, or any guide that does not damage the plate. How to achieve this ?

They take two plates that are somewhat flat and blue them and put them toge ther, where the bluing is not is a high spot so they take that down with th e scraping tool. The two plates eventually seem flat, but they might not be . One could be perfectly concave and the other convex to the exact same deg ree so they mate, but are not straight. So they have to use a third plate. you can't have a concave and a convex plate math another plate, it is simpl y impossible. And with hand tools they get them within millionths of an inc h. I have watched them, and watched them sell them. Most companies do not n eed that accuracy but some do. they cannot tolerate a copy of a copy of a c opy of a copy of flatness, they want the original. My friend makes the orig inals.

This is more accurate than polishing granite plates or even countertops. us ually those are done with optical flats and/or light at an oblique angle, a long with a good eye. I got a few sample from my late friend who did those granite and marble tops at his day job, other times he was a sculptor. I co mmissioned him to do one but he died so it is not done. i use those samples to process food, meat usually because we buy in bulk. not easy lugging a p iece into the kitchen but it is worth the trouble, and I like to use on the occasions when I make a real pizza. All the pizza places around here just get worse and worse. They mostly suck or charge an arm and a leg.

leaving rather voids"

Hopefully those voids are where metal to metal contact was actually achieve d. They are usually under spring pressure.

you will see bending in the heatsink. "

Mass production. I am surprised things work as well as they do. but all the mid fi audio amps are junk. Of course they want things to last two days pa st the warranty. One day is pushing it a bit too much.

For power transistors, there is no metal to metal contact at all, if there is a mica insulator in between the transistor and the heat sink. Somehow that thermal paste transfers the heat thru that mica.

Going way back, I think my first encounter with power transistors were the audio power output transistor in car radios. I remember working on one and got that grease on my hands and I had to ask the teacher what that was. He handed me a tube of it and told me to make sure the mica is not cracked and make sure to apply enough of that grease so it oozes out when I tighten the screws. Then he explained the purpose of it. That was in the 1960s.

Since then, I've probably used more on CPUs than I ever did on transistors. But the CPUs dont have an insulator on between.

I dont know how this got into discussing Antifreeze, but you are supposed to mix it 50-50. They claim that 100% antifreeze can freeze. (Personally I have never seen it freeze). But I usually mix around 60% AF and 40% water. I dont buy that premixed AF. The price is usually about the same per gallon, so you're paying for water. That stuff is made for people who are too lazy or stupid to mix it themselves...

I mentioned it, but that was in another thread.

freeze."

Whoever claimed that is an idiot. Don't listen to them. Actually anytihng c an freeze, but that is not what they meant. The statement indicates they're totally unfamiliar with chemistry and physics.

and 40% water. I dont buy that premixed AF. The price is usually about the same per gallon, so you're paying for water. That stuff is made for people who are too lazy or stupid to mix it themselves... "

It used to be that sex sells, now it is easy sells. This country and half t he world is into easy, the easy way out. It has its costs.

As for antifreeze, if there is no water at all in there it is much less lik ely to form corrosive components. There is a difference in how it cools tho ugh, thus :

At the cylinder walls the heat gets intense enough to boil the antifreeze m ixture and there will be a vapor pocket in between the coolant and the heat . It does cool by evaporation some, but that also decomposes the ethylene g lycol to some extent.

Though water has better thermal conductivity than ethylene glycol, that is offset by the higher boiling point which means that more of the coolant wil l be in contact with the heat. Conduction of the heat causes more even cool ing than evaporation.

Also, the overall pressure in the cooling system is lower, resulting in les s stress on all the sealing components as well as the hoses.

Since I started using pure antifreeze with no water I have never had a cool ing system problem. Periodic flushes are unnecessary, look at it years late r and it is still green, it never turns brown. It will never freeze in any environment in which you can survive, about 8.9F. It does not boil until 38

There is a car maker that uses pure polypropylene glycol as coolant in some models, don't recall which. It is highly hydrophilic so it is in a sealed system with no overflow or return. It boils at 381F and freezes at -74F. An other uses oil, though I am pretty sure it is not regular engine oil. the t hermal conductivity is low so while it would not boil much, it would not re move as much heat and the localized pockets of it hot would probably cause breakdown. It may be a synthetic, I am not sure right now.

Another thing abut the lazy consumer, soem of them don't even read. First o f all if they read the ingredients of the shit they buy to eat they wouldn' t. But I think stores put the mixed coolant right with the pure antifreeze and people who don't pay attentyion just buy it because they see a slightly lower price. Lkke im a grocery store, you got "tastes like BUTTER", "can't beleive it's not BUTTER". Even paint, want oil based primer ? Look at the label carefully, many of them say "for OIL BASE", "to be used with OIL BASE " etc.

The money game. It keeps the stupidity contest on and people are winning al l the time.

Smallest grain size is 1 micron. Or .0000039 Inches. My best surface plate is flat within 30 millionths of an inch. My best set of gauge blocks, the ceramic ones, are +1 to + 3 millionths in size except for the 4 inch block which is +4 millionths. Eric