Surface Mapping Athlons For Fun And Knowledge

ryemax writes: "'Surface Mapped Athlon - Is Lapping Required?' is the title of today's bit of insight from FrostyTech. Basically we took an Athlon and measured to within 0.0005" how out-of-whack the surface of the aluminum plate is. With that knowledge and a few hundred values we made a nifty image map of the surface features. With that done, the picture was overlaid atop an image of the processor so all can see where surface flatness may be a problem. Why, you ask? Because I get really annoyed when expensive heatsinks/cold plates get suck on unflat surfaces - and thermal performance gets kicked in the arse. So, rather then just say "it's unflat", I decided to quantitatively prove it using a dial micrometer. Bottom line -- lap that Althon plate." Wow.

Comments

Re:Uh...

[Anonymous Coward]

The key issue is to make sure you have a *no* air between the surfaces. Air and other gases have extremely poor thermal conductivity compared with solids and liquids. Therefore air acts as a insulator (the same principle behind styrofoam and sleeping bags).

If there is any air between the surfaces, it should be in as thin a film as possible. Better yet, replace the air with a thermal paste. The paste doesn't have as high a thermal conductivity as metal or ceramic, but it will be much better than air.

Thinner films of thermal paste are better, thus (I assume) the concern about flat surfaces. But if I had to pick, I would take a thick film of thermal paste over a thin film of air.

If you want to do a thought experiment on this, the dimensions of thermal conductivity are

Energy/(Time*(Length^2)*(TempDifference/Length))
i.e. BTU/(hour*ft*DegF)

Using these units, thermal conductivity is approximately:

Vacuum = 0.000...
Air = 0.014
Water = 0.36
Steel = 26
Aluminum = 117
Copper = 224

(Source: Perry Chemical Engineering Handbook)

Thermal conductivity does not take convection into account, but convection can be ignored in thin films.

This is just plane silly.

[aardvaark]

1) The stated value of measuring accuracy is bogus. For one thing, if he did it with a micrometer, you are getting thickness of the plate, not flatness of the plate. It could be totally flat on the heat sink side, and unflat on the other. Plus stupid things like if his body heat raised the temperature of the plate, I bet that whacked off the last measurments from the first by a good .001' atleast, etc., etc. If you are going to say something like .0005' accuracy or whatever it was, put error bars on it, or just don't say it. Misleading.

2) After lapping the processor, then letting it run to operating temperatures, I bet the processor warps some due to differential coefficients of expansion and just cranking the processor on to the motherboard, and the heat sink on top of that.

3) I _assume_ that the the little numbers next to their psuedocolor matrix is a color bar, which shows all of about 1.2 mm of difference in surface relief. When you take in to account the crudity of their measurments, the error bars are probably about that big.

4) Do the math. Heat flux is inversely propotional to the distance between the two surfaces and proportional to the thermal conductivity of the medium and the temperature gradient (q = -(k dT)/l). If you change the distance between the heat sink and processor only a little tiny bit, you only change the heat flow a little tiny bit. It's linear. As long as you increase k by putting heat sink compound, and the distance l isn't huge, then dT mostly takes over.

In other words: Use a good heat sink that stays cool and will make a large dt. Use a thin coat of thermal compound. If your processor still gets too hot, turn down the clock speed a little! Geez. Talk about too much time on your hands.

The person who posted this is wrong!

[fastang]

I will forgive you the inaccuracy of the dial micrometer. But I can't forgive the fact that the flatness of a surface can NOT be measured with a micrometer. You need a known flat surface (certified granite plate), and a dial indicator with sturdy, stable stand. Anyone who has worked in a machine shop can verify this for you. The way that you arrived at your measurement; the surface possibly, could be "perfectly" flat.

This knowledge can be applied elsewhere

[jailbrekr2]

As the human head radiates approximately 75% of all our expended body heat, we could use the lessons learned from this site to efficiently cool our pointy noggins, so as to allow us to overclock our craniums to the maximum extent.

At the very least, cranial cooling will reduce the number of times we product erronious errors, or outright crash.

Damn, I forgot to take my medication again.....

Extrem Overclocking

[Alien54]

Of course extreme overclocking requires extreme cooling. If you go here, you can read about an over-clocking experiment involving a 486sx25, a freezer, and unnatural amounts of alcohol.

they tried various options with good results. They had the computer running in the freezer

Towards the end, things got hazy. To quote:

Accounts of the remainder of the experiment (everything after the celebration) are somewhat sketchy at best.

It would appear that after all the motherboard jumpers were removed for storage, someone accidently powered the system up. This caused the whole setup to run uncontrollably fast.

Fortunately, one of the technicians (the one who had destroyed the least of the "coolant") had the presence of mind to check the clock speed...

247MHz!

There was only one thing to do. Halflife.

Completely playable, the game ran fine for 2 minutes and 34 seconds (or 3 minutes 12 seconds, depending on who you listen to...) then crashed horribly.

By this time however, the processor was utterly wrecked. As was the motherboard.

And the power supply, graphics card, soundcard and RAM. Most of the Holy Spirits had boiled too.

some very interesting photos too