Lapping heat spreaders

[afireinside]

What grit do you guys start with? I tried 400, nothing. Went down to 220 then got bored and did 30 minutes of 100 with lots of pressure before my IHS was finally all copper. Left some nasty gouges though. Spent 15 minutes afterwards with 220 grit and I'l finish it off tomorrow with more 220 grit then 600-800-1200

http://afireinside.evilspork.net/AFI/AM2reloaded/IMG_1081.JPG

[afireinside]

http://afireinside.evilspork.net/AFI/AM2reloaded/800grit.JPG

Probably made it worse trying to get the gashes out. I hate lapping :(

[STEvil]

about 200 for a minute or two. 400+ after. Usually my sandpaper is so loaded by the end i'm using a 600 grit piece thats probably equivalent to 1000 grit. Scratches arent going to hurt performance as its the concave/convex shape that hurts.

[Vapor]

That looks burned....

But yeah, doesn't need to be polished or anything, even scratches aren't a big deal, the flatness is what counts.

[Nanometer]

I stop at 1200grit. I start at about 300grit. Then 500, then 800 then 1200. Polishing is really pointless besides making things look sexy.

[spookz]

Hey guys, whilst we're on topic about "lapping".. i was just wondernig does "lapping" void our cpu's warranty?, like if it dies, and we have to RMA, will it be accepted?? =S

[dab420]

it is the fastest way to void a warranty.

[spookz]

oh ok! thanks! =D

[Millyons]

results?

[afireinside]

Haven't tried it yet. Maybe today. Running my intel setup right now and I need a computer for the weekend so I don't want to switch :lol: Also want to re-lap my CPU block, unless this is ok:

http://img.photobucket.com/albums/v448/zero-IGN/IMG_1057.jpg

[STEvil]

if its on an IHS its fine. wouldnt put it on a bare core, though.

[Zardokk]

How's the lapping coming along? I don't know how experienced/inexperienced you are at lapping, but a few pointers if I may. First of all, you wanna lap in an up and down motion for the best looks. For the best flatness, a circular or figure eight motion is best. Also, I'd lap up to at least 1500 grit. That's about where sandpaper reaches its limits. Beyond 1500 doesn't make much of a difference. Also, when you're done with sandpaper and you have a nice look to your IHS, take a piece of printer paper and "lap" some with that. I find that it gives a very nice shine.

[WeStSiDePLaYa]

the most often overlooked part of lapping is the material its lapped on. you cant get it flat if your surface isnt flat. thick glass works wonders. i find thin glass can bend ever so slightly and cause issues. now i use a sheet of glass a good 1cm thick.

[Zardokk]

I use a piece of glass from a picture frame. I'd say it's only about 1.5mm thick, so it's proabably a little on the thin side, but it seems to work fine for me. You definately need to lap on glass though. A table or something just won't cut it.

[spookz]

hey what about lapping on granite? (ie. granite table top?)

[STEvil]

was the granite lapped, too?

[spookz]

yeh i'd think so? it's my kitchen table bench =) which is polished up granite? it seems very flat to me.

So if i just tape sandpaper onto it, and start sanding away on my cpu's ihs, it should come out flat? =D

[Sneaky]

sheet of plate glass.

[Makubex_GB]

Just so you know you don't need to go any higher than 600 grit. In fact, I remember there was a thread in this forum that had info which explained how lapping up to 600 grit was better than going over.

Oh, here it is:




"Why Heatsink Polishing Might Be A Bad Idea"
Simon Watkins - 5/14/01

I used to be involved in the manufacture of Acousto-Optic devices for use within high power laser cavities. One of the products was called a Q switch. It was basically a piece of quartz with polished ends through which the laser passed, and a piezoelectric transducer fitted on one face parallel and in line with the laser that could cause diffraction in the beam when it was energized.

Anyway to cut a long story short, the quartz block, because of optical losses and heating by the laser, not to mention high levels of RF energy being fed into the transducer would get very hot - we were pumping 50W CW of NdYag energy into the quartz, and the q-switching effect would result in peak powers of several thousand watts - so hot that the quartz would be destroyed in the laser cavity very quickly if it wasn't cooled.

I remember being involved in a number of experiments during the development of the product that investigated means to cool the device efficiently. In the end, water cooling blocks were used to sandwich the quartz. We experimented with improving the interface between the quartz and the aluminum blocks, and used exactly the same techniques people are using today with H/S and CPU. Heatsink compound, lapping etc.

The aluminum water blocks were made optically flat using the same lapping tools used to flatten the quartz. We are talking extreme flatness here - but flatness being key rather more than smoothness.

Anyway, one thing we found was that if we made the mating surface of the aluminum block too smooth, we lost cooling efficiency - similarly if it was too coarse. To the extent that if we polished the surface, we got significantly worse performance than when the heatsink surface was matte after lapping with, say, 400-600 grade carborundum.

Our conclusions were that the micro pits and valleys left behind after finishing with coarser grade carborundum left micro cavities within which the heatsink compound could fill, but the micro peaks of the aluminium would provide good physical contact to the quartz when the whole assembly was squeezed together under pressure; the micro peaks would flatten slightly providing millions of micro plateaus of contact surface.

On the polished blocks, there was nowhere for the heatsink compound to go, other than out the sides of course, but you could never exert sufficient pressure to squeeze ALL the heatsink compound out, so you got poor quality thermal transfer through the HS compound sandwich.

Whereas on the rougher surfaced blocks, given a sensibly thin application of heatsink compound, there would be a very high proportion of aluminium making contact with the quartz and any pits would be taken care of by the HS compound. If we went too coarse, there was too little of the aluminum in direct contact with the quartz and temperatures worsened again.

We found the results hard to believe at first, as we all believed somewhat blindly that the polished surface would be best, yet the flat surfaced, but coarser finished heatsinks outperformed the polished ones significantly.

Basically with a polished sink, you'll never put a thin enough coat of H/S compound on it for it all to be expelled, given the relatively limited pressure you can apply. So what is key to achieving optimum thermal conductivity is a high aluminium to CPU contact - micropeaks and perfect flatness will ensure that you achieve that. Try using only up to 600 paper on your heatsinks, no finer.

The manufacturers are possibly aware of this fact as well. Take an FOP38 heatsink for instance. Its base is very flat (I measured mine with an optical flat), but pretty coarse (too coarse I think). Now GlobalWin is perfectly capable of machining the thing somewhat smoother - the sides of the heatsink are finished to a much finer finish than the base.

I suspect the reason for their reasonably coarse base finish is to accommodate the somewhat viscous phase change material, as recommended by AMD. So lapping the heatsink to a finer degree and using heatsink compound instead will help in reducing temps to a degree (groan).

Additionally, the somewhat more viscous nature of Arctic Silver will also help with a coarsely finished interface, because it has a lower thermal resistance than silicon HS compound - that is, IF they are both applied so they are forming the filling of a sandwich!

In a more professional application of the heatsink compound, ideally you need a less viscous substance so that maximal metal to CPU contact can occur. If you can't achieve that because you are making a compound sandwich, you will never get optimum temps.

Anyway, take that info for what it cost you. I just thought it may be of interest, and provoke some discussion.

Simon Watkins



Source: http://www.overclockers.com/tips458/



Cathar also noticed it:

Originally Posted by Cathar
Well in the hunt for the best die-baseplate thermal "connection" with my waterblock research, I've found the "best" method that I've been able to achieve, and it falls in line with what's accepted and been tried elsewhere. However, me knowing me, I don't believe stuff until I try it for myself.

Basically I've lapped bases with:

150 grit
220 grit
320 grit
600 grit
800 grit
1000 grit
1200 grit
1500 grit
brasso + strong cloth
toothpaste + cloth
fine-cut cleanser
jeweller's rouge

All in incremental steps, to varying degrees of finish from rough, to a copper finish you can shave in.

So what's worked out the best?

Go to Bunnings. Grab a small board of 12mm thick MDF (Medium Density Fibreboard). It's flat as glass and a whole lot cheaper. Should cost about $5. Pick up 1 sheet each 150grit, 320grit, and 600 grit wet'n'dry sandpaper (black colored).

Take your heatsink, and lightly scribble over the base with a black permanent marker. Color the whole base in if you want.

Stick your 150 grit paper onto the MDF.

Take your heatsink/waterblock and scrub lengthways (if the block has a longer length in one direction - otherwise just pick). Move the block up and down the sandpaper while pushing down firmly. Do not move in a circular motion, just straight up and down. You'll need 3 hands. One to hold the block, and two to hold the edges of the sandpaper down so it doesn't "grab" and fold and rip. If nature didn't supply you with 3 hands, sitting on the floor and using a foot works just as well. Keep scrubbing until you can't see ANY of the ink/black. I periodically look at the base to see how it's going, this is how I can tell if a block is initially convex, concave, or whatever. This can take anything from 1 minute to 30 minutes (or more) depending on how flat the base is to start with.

Once the ink is gone, use the 320grit and scrub cross-ways. This time keep doing it until all the cross-lines left by the 150 grit sand-paper are ground away. Just move the block straight up an down - no round motion. This should take about 3-5 minutes.

Then use the 600 grit sandpaper and moving straight up and down lengthways sand the base until the 320-grit cross-ways lines are gone (another 3-5 minutes).

Finally follow up with a circular grind of the base on the 600-grit sandpaper for about 30 seconds. Wipe clean. This should leave the base with a dull reflective surface.

You're done!

Like I said, I've tried anything from 150-grit up to a mirror polish, but the dull 600-grit finish works out the best. Surprisingly, a 220-grit finish, and a mirror finish give about the same results (at least for me), while the dull 600-grit finish gave me about 0.5C better than either of those two for a ~100W CPU load.

I know that the above has been said here before a few times, so consider this as a re-affirmation of the procedure.

[afireinside]

Ah was looking for that post. That's why I stopped at 800 grit.

I lapped on a piece of glass, one of those easyPC kits. My first lapping attempt. CPU is working fine @ 2.9 but I'd like to make the block a little smoother.