If you are a hardcore overclocker, or a temperature junkie, you may have considered lapping your heatsink, but how many of you have considered that your IHS* may have just as many imperfections as your heatsink?
Now for those of you that don't have a clue what I'm talking about when I say lapping, let me give you a little lesson. The process (or art) of lapping is to sand down imperfections in the smoothness of your heatsink or IHS to give the flattest surface possible. One of the side effects of making a metal as flat as possible is that it gets shiny (As totally flat things reflect light better), and if you continue the lapping process far enough you will end up with a mirror finish. The reason we need the surface as flat as possible is so that the heatsink and processor can make more contact and more efficiently conduct the heat away.
Now you may be thinking why aren't all processors and heatsinks made to a mirror shine from the factory if it is so good, but the reality is that improving the already fairly flat surface of most heatsink/IHS's to mirror shine will only realise an average 2-3oC drop in temperatures. So with such little to gain from so much work, why would anyone do it? Well for the same reasons that people overclock their system as much as it physically will go. And as all overclockers will, or should know, cooler temperatures allow processors to be pushed further. So that is why I want to lap my processor!
Before I detail the lapping process, I have to give a warning. This is something that can me messed up very easily, so don't try this if you cannot afford to replace what you could break. It is a long and tedious venture, so if you have no patience then this is probably not for you. Be prepared to get messy, water with grit/filings is hard to get out of clothes/furniture so work somewhere that you can clean up easily, and/or put down some newspaper on your work surface.
OK, for those of you still with me, lets get down to the good stuff!
*(IHS is short for Integrated Heat Spreader, and its job is to spread the heat from the processor core so that it can be more efficiently removed to keep the processor cooler. Its secondary function serves to protect the core from damage from too much pressure from heatsinks etc.).
What you will need is:
- A flat work surface, and/or piece of glass;
Somewhere that is smooth so we don't get bumps under the sandpaper meaning we would be sanding unevenly
Wet and dry sandpaper, ranging from 400 grit to 2500 grit;
(If you can only find up to 1500 grit that should be OK, it will just mean that your finished project will not be as mirror finished as something done with 2500 grit, but it will still be flat, which is what we need here)
To use as lubricant for the sanding and to rinse off filings, so a sink near by is proffered
Heatsink/Processor to lap;
Now I thought that it would be fairly easy to find sandpaper to at least 1500 grit at my local hardware store, so I made a journey out to a B&Q warehouse to see what they had in. Unfortunately the grades of sandpaper I would need were to prove to be more elusive than I originally thought as B&Q only had wet and dry that went up to 600grit, much lower than what I needed. So I bought a pack of 200, 400, 600 in the hopes of finding some finer stuff elsewhere. But I could not. I have since learnt that I was looking in the wrong places and would have probably had more luck in somewhere that is specialised in cars!
So still wanting to lap my processor I had to search elsewhere for the needed grade papers. So I turned to KustomPCs.co.uk and purchased a lapping kit, complete with glass to sand on. There are a total of three kits to choose from and I chose the premium kit at Â£12. If you don't think you'll need the glass, or aren't fussed about getting the best mirror shine possible, then one of the basic kits would be better suited for you. These kits are available internationally from various resellers. The kit I chose has 400, 600, 800, 1000, 1200, 1500, 2000 and 2500 grit. (If you choose to purchase your sandpaper individually you could probably get away with skipping 1200 and maybe 800 if you can't find it).
So kit in hand I set about to join the hardcore enthusiast and lap my processor.
The kit comes with some handy hints and tips to a successful lap. The technique is to wet the sandpaper, so that it sticks to the glass, and also lubricates the processor while lapping. And with minimal force pressing down move the processor backwards and forwards across the sandpaper. Add more water if you feel it dragging too much and alternate the direction of sanding evenly. Slow and steady wins the race in this game, so don't go too fast when sanding.
Some people suggest sanding in a figure of 8, but for best mirror results it is best to only sand perpendicular strokes.
My victim. Start with your CPU cleaned of any TIM and ready to lap.
While researching peoples techniques to lapping I came across this method of drawing a grid with a Sharpie (or CD/DVD type pen) all across the surface. This allows you to more easily see which areas of the surface are getting lapped, and also allows you to check that you are applying even pressure.
Straight away you can see the irregularities on my processor IHS, it seems to be convex in the middle with a lip round the edge. I suspect that the lip round the edge is higher than the middle and as such limits its conductivity.
After a while with the 400 grit, you can start to see it becoming reflective already. You should continue with this layer until you can not see any more marker on the top.
I tried the 600 grit for a while, but some stray material got on the sheet and put a nice scratch along the bottom here. See what I mean about it being easy to mess up? Back to 400 grit I go to remove the scratch.
This is after the 400 grit again. Once the initial flattening has been completed (aka 400 grit), the other layers should only take 5-10 minutes each, as their only purpose is to remove the scratches created by the previous sandpaper.
Now the 600 grit.
After the 800 Grit, a nice mirror effect is starting to appear.
1000 grit also done; notice that the top layer of nickel is mostly gone and the copper underneath is showing. There is still plenty of material left, so don't worry that you are sanding too far through the copper. To remove all the copper would take days at the rate of sanding we are going.
1200 grit finished, over halfway done now
1500 grit, at this point I was beginning to get bored, so probably rushed the next few levels of sandpaper
After 2000 grit, the end is now in sight, with only one level left to go
And my finished product, after 2500 grit.
Look at that for mirror effect. Now that I've done all that hard work, lets go put the stock thermal pad back on and see what a difference its made*.
*Artic Silver 5 was used as the thermal interface material (If you do lap a heatsink or CPU then use a thermal pad I will personally come round and confiscate your system. Make sure that you have a high quality TIM after you have put in all this effort)
The test setup was as follows:
- Core2Duo E6600 @ 2448Mhz,
XFX 7900GS XT,
WD Caviar 160GB x2 in RAID-0,
2GB Crucial Ballistix PC6400 DDR2 (4-4-4-12),
Core Temp 0.95
Even without the needed burn in time to get optimal performance from the Artic silver, we can see that there is already a 2oC difference in idle temps. With proper time for the thermal paste to cure this temperature will only get better.
However, the load temperatures are not quite as impressive, and it shows that the paste still needs further curing to leave behind the temperatures from the original tests. However, given time to fully burn in, this performance should surpass the unlapped temperatures even more.
Artic silver needs to be given a cure time of several days for it to perform to the best of its abilities. It needs several cycles of full load and complete cool down (i.e. System powered off) to be able to perform at its best. Without letting the Artic silver cure properly (it had less than 24 hours and only a few power cycles) it is naturally not performing the best it can. But if initial results are anything to go by then I should be able to look forward too even cooler temperatures yet.
When lapping my processor I was unsure of how much material the finishing layers would take off after the 400 grit, so I did not remove as much as the nickel top layer as I could have done. So as a result there are still a small amount of 'unfinished' bits on my IHS (where there is nickel covering the IHS still), however these 'imperfections' are at the edges of the processor and the hot core is in the middle. So this should not really impact performance, but for aesthetics sake, I may choose to start this whole process over and make my processor completely flat and mirror like at some point in the near future.
If you don't have patience then lapping is definitely not for you. But if you are looking to push your system as far as you can, or you long to have it run a degree or two cooler, then lapping is definitely something you should consider.