Lapping Guide


Ever heard about the term "lapping"?  Lapping is the process of making a heatsink flat. We want the metal-to-metal contact between the heatsink and CPU die and/or chip to become one as much as possible. The more contact both have, the better cooling is achieved. Nothing is flat, and lapping is one of the solutions we have to achieve better results. However, lapping doesn’t fully make everything better. That’s where thermal compounds come into play. They will fill in the microscopic valleys of the two metals. By lapping you are reducing the size of the microscopic valleys thus making the thermal compound and metals work more efficiently. Lapping works and every heatsink you lap will give you experience to know just how flat those heatsinks really are.

This guide is going to be straight forward telling you how to lap a heatsink of any kind.  So listen will ya?

Before you do anything, you need the following materials...

  • 800 grit wet or dry sandpaper
  • 1500 grit wet or dry sandpaper
  • A piece of glass
  • Metal polish with soft cloth
  • Your heatsink (CPU, NB, etc)

Metal Polish on the left...MOTHERS brand

This was before lapping...Since then the thermal compound is spread evenly

Step 1: Lay out everything you need at your fingertips.
Step 2: Place your 800 grit sandpaper on the piece of glass.

See how concave the heatsink is?  It looks ugly

Step 3: Pour a small amount of warm water on your sandpaper. From there get hold of your heatsink, keep the same amount of pressure, and start sanding in a number "eight" motion.  Do this repeatedly or make up a way that is easiest for you. It doesn’t really matter how or which way you do it.

During lapping, make sure you rinse the paper and the heatsink regularly. You will start to see that the base of your heatsink is concave and paint will come off from different ends. This means that it is not flat. Use your judgment when you want to finish using the 800grit sandpaper.

Finished with 800grit, bring on the 1500grit baby!

Step 4: Repeat the earlier steps above and sand the heatsink down with 1500 grit sandpaper until you feel that the bottom is completely flat. You can now rinse the heatsink with water and at the same time, dry it.  Do not touch the bottom of the heatsink with your finger, as you will transfer oils from your finger into the heatsink thus degrading performance.

After 1500grit

Step 5: This step is really not required. Our goal is to get the heatsink flat. It’s that simple. However, if you want to enjoy a mirror finish, rub some metal polish on it.

Congratulations!   You have successfully completed Modsynergy’s lapping guide.  Enjoy better performance from temperature decreases of your CPU, or whatever you have chosen to do.

Here are some images of the mirror finish of my northbridge heatsink:

Say cheese!

Meet the top of my monitor.

When you have finished lapping, depending on how well you did, you will get anywhere from 1-5c temperature drop.  It varies from board to board and equipment.  Oh by the way, you still need to place thermal compound between chip and heatsink. 

A note that if you touch the heatsink and it feels warm, you know that the heatsink is making a difference.  For example, my SB didn't have a heatsink on and when I would touch it with my finger, it would burn after a few seconds.  Now with a lapped heatsink and thermal compound pad, the heatsink feels warm.  The heatsink and the thermal pad is absorbing the heat and dissipating it away.  If I used a bigger heatsink, which I cannot, the area of dissipated heat would become greater because you have a bigger surface area to move away heat.  Lapping works, there is no reason why it wouldn't.  Lapping, while a bit tiring, is well worth the effort to get every last ounce of performance and cooling off your product.