How do I properly lap my heatsink/waterblock?

[W1zzard]

Why lap?

If you look at this heatsink:


[PIC of heatsink + ruler with light shining through]

You can see that its surface is not completely even and looks rough.

An extreme magnification of the mating surfaces (heatsink base and CPU die or heatspreader) looks like this:


Without any thermal paste these gaps are filled by air which is an extremely poor thermal conductor (0.021 W/mK). Heat transfer will only take place between the various high points that contact each other. To improve this we use thermal interface materials (TIMs) like Arctic Silver. These compounds will not dry out or harden at temperatures well above the maximum operating temperature of your CPU and fill the the microscopic small gaps with a paste that contains thermally conductive metal oxides. The thermal conductivity of such a paste is roughly 10-100 times better than air (0.4 - 8.0 W/mK). But this is still a factor 50-100 difference to copper's thermal conductivity of 385 W/mK.

What lapping does is reduce the thickness of the TIM layer between your heatsink and your CPU.



There are several criteria that determine how good your heat transfer between two surfaces is:
- Flatness
- Smoothness
- Hardness
- Stiffness
- Interface pressure

How much can I gain by lapping my heatsink?

CPU temperatures that are 0°C to 5°C lower. You decide if that is worth your time and effort.

How can I test if my heatsink is flat?

• Get a glass plate, those are usually VERY flat.
• Put a drop of water on the heatsink base
• Put the glass plate on the base

Here are pictures of a rather bad heatsink base:


These pictures are taken from a very flat hand-lapped waterblock base:

The second image really has water between glass and copper, but it is spread all over the heatsink base. Look near the arrow to see a small water droplet. The suction pressure is so big that when you raise the glass plate, the heatsink sticks to the glass and lifts off.

Do I want a mirror finish?

If you start lapping your surface beyond the 600 grit range your gaps in the heatsink will be very small. Thus you MUST apply a very very small amount of thermal paste for proper thermal transfer. In most cases where you have a mirror finish your final result will be like this:

There's no contact between the two metals because of excess thermal paste. The heat transfer of this is worse than with a surface that is only 600 grit because of the boundary layer of TIM between heatsink and CPU.

Lapping instructions

Buy some wet and dry sandpaper. Good grit ranges are 120, 200, 400, 600 and maybe 800. One sheet of each is enough.
Get a FLAT piece to work on. Recommended here is a slab of glass or marble.
To test whether a heat sink needs to be planed, you'll need a thin knife blade or similar device, such as a wallpaper knife.

Put the coarsest (120 grit) sandpaper on your working surface and make sure it's clean.
Start gently moving the heatsink either in an up direction and then pick it up and move it back down or in a down direction, whatever suits you best. Just dont change the direction. Do not rotate the heatsink while using the same piece of sandpaper.
Do not push too hard on it or you will round the edges. The combined weight of your hand and the heatsink is enough pressure.
Every minute clean the sandpaper and heatsink of excess metal and grit.
You switch to the next finer grit when your heatsink base has lines only in the sanding direction.
[PIC]
Between sandpaper changes rotate your workpiece by 90 degrees. This helps you see when all lines from the previous grit are gone.
Do this till you are at your final grit. Your result should look like the following picture: [PIC]

If you want a finer polish you can wet sand with a lubricant on your paper in a circular motion. This is usually not required.

Cleaning after lapping

Do not use nail polish remover that contains oil or other additives. Pure acetone is good because it evaporates without leaving anything behind. Same goes for cleaning alcohol.[/by]

From Cathar:

Some further tips and tricks from someone who has lapped hundreds of blocks.

I personally recommend the use of "Low Smell" kerosene as a cutting agent/lubricant. I prefer it over water or liquid detergent that some people recommend, purely because it doesn't affect the sandpaper and cause it to "curl up" as it dries.

On your flat surface (I use a marble cutting board) slosh some kerosene over the surface and place the sandpaper on top and push down. The "suction" of the liquid will hold the sandpaper flat on the surface.

The kerosene also makes work MUCH easier and faster. The heatsink/block will glide better over the paper and is far less prone to "sticking" or "catching" on the paper causing the paper to tear.

I also personally recommend cloth-backed sand-paper if you can find it. It is sturdier and holds its "grit" (the coarse particles) much better than the paper backed sand-papers. It costs more, but will typically last up to 3 times longer.

I also recommend turning the block/heatsink by 180 degrees every so often when sanding up and down. Despite one's best efforts the pressure applied by the hand is rarely even.

When looking to see if all the "lines" are going in one direction, hold the block up at a shallow angle to a bright light (like you're looking across the base). Look very carefully for patches of "discoloration". Such discoloration is an indication that the base is not flat, despite all of the prior grit's marks being removed from even a careful examination.

I highly recommend that on the final grit you will use (either 600 or 800) that once all the earlier grit's marks have been removed that the block is turned 90 degrees and keep sanding up and down until all of the 600/800 grits opposing marks are also removed. This step is important as a very slight concave bowing of the base can occur if just sanding up and down in one direction only on the same grit.

Follow up with a quick circular lap at your finest grit. Perform about 15 laps, turn 90 degrees, do another 15, and so on until you've turned it 3 times. I find it is very important to use kerosene on this last circular stage, even if you haven't used at all up until this point in time.

[Mussels]

Nice guide, seems a pic or two is missing tho.

"[PIC of heatsink + ruler with light shining through]" but no pic, etc.

[JC316]

I am fixing to test on my stock heatsink before even THINKING about my freezer pro, but I have a question.

Cathar mentions rotating it 180 degrees, do you keep sanding in the same direction, or reverse? Example:

I am sanding in an upward motion and I need to rotate it 180 degrees, do I continue in an upward motion, or do I start in a downward motion? Thanks in advance.

[Ketxxx]

Follow the machine marks for the best possible finish. Dont go against them and just keep sanding until your happy with the finish. Be aware that if your sanding aluminium, depending on the quality of it, it can be difficult to get a mirror finish, in which case aiming for a very smooth feeling, flat finish, is the best option.

[Jonnycat]

I've always just done a "figure eight" pattern, with good (enough?) results.

[JC316]

Well, I laped my stock heatsink and I think it went rather well. It was HORRIBLE, the middle wasn't even touched for my first 5 minutes of sanding. With the water test, it was worse than the HS that was shown here. After I was done, it was perfectly flat and I could squeeze water out from all sides. Tomorrow, I am going to take my northbridge cooler off and lap it. Thanks for the replies and for this article, it really works great.

[Lazzer408]

Does anyone have before/after thermal results? How big IS the benifit? 2deg? 15deg?

[TLH]

Originally Posted by Lazzer408

Does anyone have before/after thermal results? How big IS the benifit? 2deg? 15deg?

Kinda depends on how bad it was in the first place and what it's going to sit on when you're done.
I lapped my Thermaltake Volcano 12 that sat on a xp3200 at the time and saw absolutely no difference whatsoever.It was pretty smooth though already and sitting on an Athlon XP's core is really tiny.
Mostly people report a couple of degrees C I think.

[JC316]

Originally Posted by Lazzer408

Does anyone have before/after thermal results? How big IS the benifit? 2deg? 15deg?

Ok I have some numbers for you. My Northbridge temps were

34*C Idle - 48*C Load. This was before lapping

Now they are 24*C idle - 36*C load after lapping and silver compound.

This was a bad case though. The cooler was visibly lopsided and the "thermal" material was teh consistinsy of frozen bubble gum.

[vipercrazy]

both the xbox 360 HS's could use a major lapping
the gpu specifically, its some crappy metal and it looks like it came strait out of the ground

[Coolyou]

Great article.. I would have written one myself, but never had the time to!

Also take a gander at this article! I had never laughed so much in my life...
http://hubpages.com/hub/How-to-destr...-by-lapping-it

[KBD]

i thought CPUs could be lapped.


silly article though

[sneekypeet]

Originally Posted by KBD

i thought CPUs could be lapped.


silly article though

They can be ...it just goes to show that any ass with an opinion can try to sway the masses. aslo anyone claiming 20*C drop in temps was wrong to begin with. I personally have done many CPU's and got good results with each. Of course the older hardwae is where it mattered most

[KBD]

Originally Posted by sneekypeet

They can be ...it just goes to show that any ass with an opinion can try to sway the masses. aslo anyone claiming 20*C drop in temps was wrong to begin with. I personally have done many CPU's and got good results with each. Of course the older hardwae is where it mattered most

thats why said the article is silly. I did lap my heatsink but i was afraid to touch the CPU, i was worried that the dust may get to the CPU sensitive areas and i didnt see any CPU lapping guides, perhaps its time for one on TPU?

[sneekypeet]

Same process of the blocks really!

I use straight tap water and wet/dry sand paper...the biggest issue I had was being careful on the 939's not to kill the pins!

[KBD]

Originally Posted by sneekypeet

Same process of the blocks really!

I use straight tap water and wet/dry sand paper...the biggest issue I had was being careful on the 939's not to kill the pins!

how do you know when to stop lapping, i mean with HSF its obvious, mirror finish, but with CPU i wouldnt want to lap it to death. And does it even make sense with 775/AM2/AM2+ CPUs?

[sneekypeet]

Originally Posted by KBD

how do you know when to stop lapping, i mean with HSF its obvious, mirror finish, but with CPU i wouldnt want to lap it to death. And does it even make sense with 775/AM2/AM2+ CPUs?

its like 2-5*C at most. You will know. the inside is copper and when you start it off it is nickle (IIRC) plated. as you sand you remove the plating and expose the inner metal. you will see as long as the table/piece of glass/ rock countertop is level and flat, that it will come off the edges first usually. I went untill it was all copper at like 800 grit, you may want to start lower, then I just progressed with grits until i reached 2000 and 95% of the scratches were gone. Polishing is up to you, I do use neverdull to shine it up, then just clean with 90% alcohol then install. you can only screw it up if you push to hard while sanding or are using an unlevel surface to sand on.

Pull out a razor blade and cheeck its level-ness in all directions( top to bottom, side to side, and corner to corner) if you dont see light Id leave it, but again its a few hour process if done correctly. so ita a time over gain type of thing.

I lapped all my previous CPU's that stayed in my rig....this E7200 its the first in a while I havent lapped!

[panchoman]

most of the time instinct will tell you when to stop, you want to sand down the nickel plating on top untill you get to the main copper part of the ihs. sand the copper untill its completely flat (a razor blade is a good tool to use for this). also some people like to wet sand with mineral oil in order to minimize the risk of ESD due to friction and frying from using water to wet sand.

lapping causes about a 2-5C difference in temps most of the time btw.

[KBD]

very helpful, thnx guys. I'll definately consider lapping a CPU when upgrade in a month or so.

[panchoman]

http://forums.techpowerup.com/showthread.php?t=32771

thats a good thread to take a look at man.

[KBD]

Originally Posted by panchoman

http://forums.techpowerup.com/showthread.php?t=32771

thats a good thread to take a look at man.

great, nice find

[Coolyou]

Originally Posted by KBD

how do you know when to stop lapping, i mean with HSF its obvious, mirror finish, but with CPU i wouldnt want to lap it to death. And does it even make sense with 775/AM2/AM2+ CPUs?

Just as sneekypeet stated. However, before you begin it's proper run a razorblade along the top to see if it actually needs to be lapped (nickel-copper alloy conducts, a pure copper base isn't necessary). If it does then mark an X over the nickel plating with a permanent marker. You mark the processor each time you sand it down, until perfectly flat (not mirror finish). This helps guide you to a flat finish, lapping is about a FLAT surface (removing those minute dimples on the surface) not how SHINY.

Water and a small amount of detergent (SMALL AMOUNTS!) is used to help with the metal flakes. Typical and safe process would to sand then clean (cleaning residue on the processor with a dry cloth and rubbing alcohol facing down and washing the sandpaper of excess materials), sand and clean, repeating. You don't lap the processor in one stroke.

As for worrying about the base/pins, would be safe to use the plastic shield which came with the CPU.


Edit:
Forgot to mention... the best place to find this Grit of sandpaper is at a AutoPaint dealer (UnitedAuto B&M or http://www.nortonautomotive.com/), normal car parts stores do not carry this fine of grit. 2000 grit isn't necessary.

[KBD]

thanks

after i lapped my heatsink my temps dropped about 5 C load which i suppose was worth the effort. As others said i should expect additional 2-5C drop if i lap the CPU.