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How to Lap a Heatsink Guide

Former staff writer    -   November 2, 2002
Category: Cooling
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Introduction

Most overclockers strive to push their equipment just a little bit faster; a 400 MHz overclock just isn't good enough, we want 401 MHz, and then 402 MHz... As we push our equipment faster and faster it produces more heat, this heat of course can take it’s toll on the electronics within the computer. Just as we endeavor for that extra 1 MHz, we attempt to battle the force of heat. 1° C could be the difference between life and death for our PC. To battle heat, we'll buy the best Aluminum case, the best heat sink with a 185 cfm fan, a dozen case fans, and even go as far as to use a pelter or water cooling setup. Even with the best, there is still more that can be done to help cool your CPU, GPU, system chip, and other components. It's a process known as "lapping."

Why Lap?


Due to the machining process, just about every heat sink will have a rough surface. To the naked eye it may look flat or even feel smooth, but there are microscopic groves in the surface. These groves will trap air between the heat sink and the CPU, and cause a poor transfer of heat.

Thermal compound (Artic Silver, Nanotherm, etc.) is used to fill these groves and help transfer the heat from the CPU to the heat sink. Just like air, thermal compound is something else that the heat has to pass through to get from the CPU to the heat sink.

We lap the heat sink to make it smooth, allowing us to get the best possible contact between the CPU and heat sink. Even after lapping, there will still be grooves for the air to be trapped in, but the grooves will be much smaller, and cause less of a problem.

Lapping can be done on any heat sink, pelt, or water block, regardless of its material. Just keep in mind that a softer metal will sand away faster than a hard metal.

Equipment Needed

Heat sink
Sandpaper
o 400 Grit Super Fine Wet/Dry
o 600 Grit Ultra Fine Wet/Dry
o 800 Grit Ultra Fine Wet/Dry
o 1000 Grit Ultra Fine Wet/Dry
o 1500 Grit Mirror Fine Wet/Dry
o 2000 Grit Mirror Fine Wet/Dry
Flat surface
Water
Hand Dishwashing Liquid
Time
Beverage of choice – Beer, Bawls, Coke, or whatever :)

The sandpaper was more difficult to find that I thought it would be. In the end, I managed to find it at Napa Auto Parts and Wall-Mart. It comes in pack of four or five and cost about $3.00.

For a flat surface, most people suggest using a piece of glass or a glass top table. I didn’t happen to have any extra sheets of glass lying around, so I ended up using a sink counter top. This worked well for me, as two other needed items were close at hand: water and hand dishwashing liquid.

Time is also a very important item in the lapping process. Lapping can be done in as little as 30 minutes, but for better results it tends to take close to two hours. You will want to work slow and steady to make sure you do it correctly; otherwise you may end up with a heat sink that is worse off than when you started.

The cold beverage is a must. At least for me. I’ve yet to do a mod or build a computer without something cold to drink. :)

The Process


You will start out with the most coarse grit first (400 Grit), and repeat the process for each higher grit.

Completely soak the sandpaper under some running water, and then place it on your flat surface. I left a bit of standing water on my sandpaper. You can use hot water or cold water, it doesn’t matter. I used cool, as I didn’t want warm water on my hands to defrost my icy mug. :)

Next place a drop of the dishwashing liquid onto the heat sink's base. You only need to do this on the part that we will be lapping. Now, spread the dishwashing liquid around so it covers the base, again, you only need to worry about the part that we will be lapping.

Place the heat sink on the wet sandpaper. Hold the heat sink by the side, and slowly move the heat sink up and down the paper. Be careful not to apply any pressure to the heat sink, we want its own weight to do the work for us.

After about ten passes across the sandpaper, rotate the heat sink 90° (that's a quarter of a turn) and continue to sand until you've made a complete rotation. I continue to do this until I've made 10 complete rotations, stopping every couple of rotations to rewet the sand paper, and reapply the soap.

Repeat the process using the 600, 800, 1000, 1500, and 2000 grit sand paper. In the end, you will have a nice, mirror like reflection on the heat sink base.

Congratulations, you've just lapped your heat sink and created a better surface for heat transfer. You should notice close to a 5°C drop in CPU temperature, though results may vary.

Before
After

After using the 400 grit
After using the 600 grit
After using the 800 grit
After using the 1000 grit
After using the 1500 grit
After using the 2000 grit



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