DISCLAIMER: The following information WILL void your warranty. Tom's Hardware, Bestofmedia Group and the author of this guide will not be held liable for any damage or loss caused by using the information in this guide.
Note: Your results may vary. No guarantee is made that your cooling performance will improve, nor that it won't decrease, by following this guide.
Heat Sink Lapping Guide
When I received my Thermalright Ultra-120 Extreme I have to say I was a little puzzled. The base where it should contact the heat spreader is not smooth at all, it's actually grooved! You can see a scratch which is where I gently ran my thumb nail over the surface; I could feel the rough edges.
Have a look for yourself:
Anyway, others encouraged me to lap it which I've never done before. After wrestling with the idea for a couple of days as well as reading many articles/guides, I decided to give it a go. $20 worth of sandpaper, a $2 piece of flat glass, and 4 hours of careful work (and sweat) later, I was left with a pretty darn flat HS. You can see by the pictures that this particular one was quite concave instead of being flat which isn't good for keeping contact between the HS and IHS of the CPU.
Did it work you're probably wondering. The temp data as measured in speedfan.exe for a ~1 h x264 encode (uses all 4 cores with a CPU load of >99 %). I had speedfan log the temps (which it does every 3-4 seconds) and I averaged the whole data set per core for the 2nd pass of the 2-pass encode (the 2nd pass is the most CPU intensive). Room temp for both experiments was ~23 °C. By the way, I added a constant of 15 to each core in speedfan since it incorrectly displays temps for quads by 15 °C.
System specs: Q6600 @ 9x333=3.01 GHz (stock voltage), P5B-Deluxe in an Antec p182 case.
A) A VERY flat surface to work upon. As mentioned, a counter top or solid (i.e. hard wood) desk.
B) A large enough pane of glass (8x10 picture frames are almost perfect)
C) High quality wet-or-dry sandpaper. [Note: For the early stages of my lap job, I used regular 110 and 220 wood sandpaper, which stood up to water amazingly well. However, for the finer grains (600 and up) you will want automotive sandpaper.]
Don't think that lapping is for the faint of heart. If your going to do this, plan on spending a weekend (at least) doing it. It is recommended that you lap both the heatsink and the CPU heatspreader for optimal results. While it is certainly not always the case, if you don't lap both surfaces you may not see worthwhile improvements. Results depend on how well the two surfaces fit together.
Also beware that lapping your CPU is inherently risky. So long as your careful to keep yourself grounded, you shouldn't have problems, but keep in mind that you are generating huge amounts of friction and placing your CPU near water, both generally not recommended.