As is traditional, let me start off with a standard disclaimer. Slug sanding is getting into the "extreme overclocking" range of activities. Be aware that there is a chance of destroying your CPU by doing this. I provide this article for information and entertainment only - if you choose to sand your own CPU slugs, you do so AT YOUR OWN RISK. I can afford to lose a CPU or two in the course of experimentation and I accept that risk - that may not be true for you. Having said that, I have sanded 6 CPU's to full copper (I'll explain that later) and they all work fine still. However, READ THE ENTIRE ARTICLE BEFORE PROCEEDING. I have deliberately not included a "What you need" section to force you to read the whole thing first. Oh, and you are DEFINITELY voiding your warranty.

Right, that's kept the lawyers happy. Now - what the hell is slug sanding anyway? If you follow the overclocking newsgroup (alt.comp.hardware.overclocking) or read hardware sites you will have encountered the term at some point. It's nothing too mystical, basically you sand the top of the CPU's casing so that it's nice and flat, so you get better thermal transfer to the heatsink. This makes your CPU's run cooler, and may help you achieve stability at higher speeds. You will notice the most improvement on CPU's that have very warped slugs - usually the corners are higher than the centre, so they "push" the core of the CPU, the bit that gets the hottest and needs the most cooling, away from the heatsink. Thermal paste can fill the gap, but having a flat slug is better - and a flat slug with paste on it is best of all. You may also want to consider sanding your heatsink - but we'll not be covering that today..

We'll only be looking at PPGA Celerons today. You can sand the Slot1 ones too, but apparently sanding PentiumII's and III's is a bad idea.. we don't have any here, so I'm not sure why that is. Anyway.. here's what the slug looks like before sanding:

The slug is the raised bit of silvery stuff in the middle. There's usually a strange little logo right in the centre of it. This logo also appears on the other side of the chip.. anyone know what it is? :) (UPDATE: It's a 2D barcode which contains all the info on the chip, batch number, S-code etc)

An important thing to keep in mind when sanding your slug is that you don't want to make it any worse than it currently is. So you need to have a very flat surface for sanding on - glass is ideal. I use a sheet of glass with sandpaper taped to the top of it, like so:

The big pile of Gatorade bottles is helpful but not required. :) Some people say you have to use Silicon Carbide sandpaper but when I asked for that at the local hardware store all I got was blank looks. The generic dark-grey wet/dry stuff worked fine for me (in the photos it looks brown because of the copper from the CPU's - when you buy it, it's all the same colour as the corners). I start with grade 280, then change to 600 to get it really flat, then to 1200 to polish to a nice shiny finish. You will still have scratches on the surface - you're never going to get to a true "mirror" finish, but you should be able to see your face reflected in it - it should be nice and shiny, and FLAT, by the time you finish.

Keep in mind that you are scraping little tiny peices of METAL off the cpu when you do this. So don't do it ANYWHERE NEAR your PC or anything else that might be damaged by tiny conductive particles. Do it somewhere where you can properly clean up afterwards, vacuum the whole area etc.

Before you start, you need to protect the CPU. You need to make sure you don't leave metal particles that could short out the pins when you put it back in the socket. The best way to avoid this is to never get them near the pins in the first place. Also, you need to protect it against static and against water if you're going to be wetsanding. You also want to be careful not to bend the pins - this is usually not catastrophic, but it's a pain in the neck to straighten them out properly if you bend them.

The best way to protect against all these things is to seal the CPU inside a static-proof bag while leaving the slug exposed. To do this, drop the CPU into the corner of an antistatic bag. Cut the bag away so you have a little pocket of bag around the chip. Leave about 1.5cm around it - it's better to leave too much than too little. Fold the open sides around and tape them on the bottom (the PIN side). So you now have the CPU completely sealed in a little antistatic pocket:

top (slug side)	bottom (pin side)

Now, to expose the slug so you can sand it. Cut around the slug with a stanley knife or similar - you want to actually expose a fair bit of the area around the slug - I usually leave about a 5mm gap. This is so you can stick the sides of the hole to the chip itself with sticky tape, to maintain the seal, while still exposing the slug. See the next pictures:

cut open, before taping	taped

Now! The CPU is in a mostly static-proof package, which is also waterproof and metal-shavings-proof. Also, there should now be a fair bit of stickytape and folded static bag protecting the pins on the bottom from your clumsy fingers during sanding. Now we're ready to sand. Allow yourself some time for this - you don't want to be rushing it. Say half an hour or so to make sure you do it properly.

Moisten the roughest sandpaper (the lowest grade number, in my case 280). You can dry-sand if you like, but I find wetsanding to be better because it keeps the chip cooler, it makes it a little easier on the arm and it keeps the metal dust and shavings together. I usually do the 280 wet and then the 600 wet, then use the 1200 dry to finish off. I keep a glass of water nearby so I can dip my fingers into it and sprinkle water onto the sandpaper from them. Smooth the drops around on the paper - you don't want to be running your chip through huge puddles of water, you just want very moist sandpaper.

Hold the cpu slug-down (derr) with your thumb and middle finger each on a side. Press down on the middle of the bottom of the CPU with your index finger (between the pins):

I might just take a moment to remind you that you are doing this at your own risk. If you think you're going to be really pissed off (to the point of, say, suing webmasters) if you wreck your chip in the next 20 minutes, stop now. Be happy with whatever speed you're currently stable at. Otherwise..

Remember to keep the slug flat against the sandpaper. Some people say you should do alternating circles, some people say do figure-8's, some people say only do straight lines. What I normally do is do 20 circles, then rotate the cpu 90 degrees, 20 more, rotate 90, 20 more, etc etc etc. I figure that way if there's any bias in the way I'm sanding it should even out over the course of the process. What you really want to avoid is letting the cpu tilt while you sand, so that you end up rounding the corners off. Check it regularly with a flat surface such as the heatsink, or better yet a razor blade edge or steel ruler or similar. I use a little 6-inch steel ruler I bought from the hardware shop for about $6.00.

Now, the primary goal here is to get the slug FLAT. You may reach a flat slug in no time at all. Mine were all not very warped, so what I was really trying to do was get as much of the material off the top of the slug as possible, while keeping it flat. Underneath the silvery stuff there is coppery stuff. Very scientific, I know, but nobody has actually confirmed what the metals we're dealing with here are, as far as I know. But I'll call the coppery stuff copper because it probably is. Sometimes you will get to a completely flat CPU and still have lots of silver on the slug. Sometimes you will have a pattern of part-copper, part-silver. I always sand to full copper, ie, the whole slug is coppery coloured, because I want to get the best thermal transfer I can. Now, warning time: if you sand too far down onto the slug, you will kill your cpu. Under the slug is the silicon bed that is the real heart of the chip. It's actually on the back of the slug. If you expose that your chip is screwed. So be careful how far down you go. Also, even if you don't go all the way through to the silicon, you may weaken the slug to the point where it collapses when you mount a heatsink on it. This is also a chip-killer. So be careful!

copper showing on all 4 sides	almost finished

Is your arm tired yet? :) You may find your stickytape and static bag are being sanded away a bit. This is not that unusual but try not to break the seal - and definitely don't sand away much of the ceramic package (the dark outer bit that the pins are sticking out of).

When you have a lovely polished flat surface, carefully blow or vacuum away all the dust and metal shavings and cut the tape and staticbag away from the cpu. It's easiest if you cut along the sides of the cpu casing and pull the bag apart that way. Vacuum and clean the cpu properly with a tissue, clean your hands thoroughly and clean up your work area. You may want to rinse the sandpaper off so you can use it again - I use wet/dry sandpaper so I just take the whole glass sheet into the shower and rub it almost clean. Now stand back and admire your masterpeice!

mirror mirror on the slug

Now - was it all worth it? In my experience yes - every one of the 6 C366's I've sanded to full copper have shown a drop in temperature - usually 1 or 2 degrees C. This can be all the difference between stability and crashes when you're on the edge. It makes a much more marked difference if you're looking into active cooling - my 2 best C366's would lock up just after loading W98 at 616MHz with a 40W peltier on them - they run well enough to install Sandra and run a few benchmarks now. They'll even let me play about 10 minutes of Sports Car GT! Click here for the full Peltier experiment story.

So don't expect miracles - but do expect a difference. If you're right on the edge and you think heat is the problem, sanding might pay off. Of course, as I keep saying, you are taking something of a risk with the CPU - not a big risk in my experience, but as with all things when overclocking - nothing's guaranteed. :)