Guide to Lapping Your GPU CoreFormer staff writer - April 29, 2003
Category: Cooling, VGA Cooling
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Many of us in the overclocking community love to push every little bit of power out of our components whenever possible. Whether its upgrading equipment or improving on our existing hardware, many find themselves doing hours of work for a small drop in temperature, a gain in clock speeds, or both if possible. Lapping a heat sink is a common way to improve a system's cooling factor, but what about the component the heat sink itself is trying to cool? If that component isn't as flat as the heat sink, then there was probably little-to-no gain in lapping the heat sink to that component. One processor that many have overlooked perfection is one of the more common ones: The Nvidia Geforce 4 GPU itself. Today, I'll show you how to lap your video card processor core.
What you'll need
Lapping the core
First step is getting off your current heat sink (in this guide, it is not the stock heat sink, but the Thermaltake Gf4 Cooler). There are 2 pins to remove. There're a couple ways to get the pins off depending on how the heatsink is attached to your video card. Some heatsinks have pins you pull out or and some require pushing barbs in together on the plastic pins, located on the back side of the card. After that, it may be a little stubborn due to thermal pastes, but a twist and it should come off. If it is epoxy that holds it down, you are at risk of damaging you video card, but you can get it off with a blow dryer or heat gun. Just heat it up and slip something like a credit card between the heat sink and GPU and it should pop off.
As you noticed, the only contact spots were AROUND the center of the GPU, where the center is where cooling is needed the most. This is due to the odd shape of the cpu, but thats why were here, right? To fix this problem.
Should go a little something like this once you clean off all the thermal paste. It wont ever look the same after this, so take a last look.
As we put a strait edge on the GPU processor, we can see it curves slightly inward, which is what is killing our thermal tranfer to the heat sink. You can barely tell from the pic, but you can definatly see light shine through the crack between the strait edge and GPU. If it were even fairly flat, we wouldn't see any light at all. Just set your strait edge (or razor blade) from corner to corner of the GPU to see this for yourself. Our goal: get the GPU as flat as possible. If you havn't already, you may want to lap the heat sink to your video card for best performance and lapping of the GPU (explanation coming up). To lap the heat sink, take a look at this guide and it should get you started in the right direction. I highly recommend doing a heat sink of any sort before doing something as valuable as your graphics processor. After you lap the heat sink, if you have chosen to, it's time to get to business. Lapping will cause small fragments of various, conductive metal pieces to go just about everywhere (as well as water from wet sanding), so we should first protect out other components on the board. To do this, get your plastic bag and lay it down on top of the GPU. In this example, we use a Zip-Lock bag and just put it inside of there.
Trace the outer edge of the GPU on the bag with a marker. Take the card out and cut out a about an inch away from the tracing. This gives room for the tape to stick to the video card and bag. Put a layer of tape around the edges of where you cut out. Then place the video card back in the bag and seal it.
Use electrical tape to hold down the plastic bag and protect the naked areas around the GPU. Layer up the tape until you get around the edge of the GPU. If you can, keep the tape low so you don't sand it. We now have all of our components protected, so here comes the fun part: lapping It's time to choose something flat to lap the GPU with now. Since few can exactly fit a mirror around the capacitors and other high-raised objects on the board, something smaller will have to fit. One reason I highly suggested lapping the heat sink to the video card is because it will make it as flat as it gets, therefore it would make the GPU just about as flat if you choose to use it on sanding your processor (which in this guide, we used the heat sink for the base of the sand paper). So placing the sandpaper on the heat sink, folding the extra paper around the sides of the heat sink, dab a small amount of water on the sand paper and begin lapping the GPU with 400 grit. The best advice would be sanding in a circular pattern. That's what was done here and as long as you apply even pressure (remember, not to really push on it though!) and good circles, it should turn out perfect. If the sand paper starts rubbing against any of your protection (tape or bag), give just an extra layer of tape on there so it wont sand through. One thing that was unclear was the top that you see when you first wipe off all the thermal paste is not the GPU die. The die is much like that of the AMD Athlon XP chips, but buried inside this copper core. So don't think you are actually sanding the top of the die itself, but simply, the copper core around it.
Once we start to see the copper around the GPU, you may want to go to the next grit paper. Just change grit to the finer grain per inch once the ring of chrome disappears around the edges, revealing the copper underneath.
After 800 grit
After 800 grit, its optional to continue to a finer finish, but only if you wanted to get the smoothest of surface (mirror lap). Lap just a little more with the 1200, 1500, or even 2000 grit to get the perfect surface. Its time to wrap things up once you start to see the GPU die though (should start seeing a square develop around the copper. I left a small amount of the silver on top so I didn't start sanding away at the die itself!)
After 1200 grit
1500 grit was all that was available for this guide, but it was a good mirror finish on the copper. And to finish our lapping off, cleaning time! Rubbing alcohol is the best way to clean all the residue off. Clean off all you can, then take out the video card and clean it without the protection. I would use a Q-tip and the rubbing alcohol and get around the sides of the GPU where it was hard to get with the bag and tap on there.
After 1500 grit
There you have it, the final result...
After 400 grit
There was no light visible through the strait edge.
Now, let's find out if lapping actually helped anything. Just simply apply the thermal paste, put the heat sink back on, snap it all in, apply some pressure (to ensure contact), and install the card! If you didn't break it, it should boot.
All stability and full load heat testing was done on Unreal Tournament 2003 with all highest settings and 1600X1200 16bit, played for 20-30 min. All temperatures in celsius and rounded to the nearest .5°.
Defiantly a significant drop in the temperature. A 4� drop on both idle and load.
The drop in temps made it much more stable at higher clock frequencies. I didn't try to adjust the ram anymore, since i didn't think the difference would be that great in the heat to the ram.
Again, we see a good drop in temps on the overclocked side of things. 4.5� difference on idle, with 5� difference on load. Conclusion This game with these settings depends HEAVILY on the video card. This is a good example of the gains in FPS on high detail and resolution settings in the real world of overclocking to improve gaming. Not a huge difference, but still, some is better than none! Whether your looking for stability or more clock speed, this is a cheap modification well worth doing (Especially those planning to do a voltage mod to the card). Hope everybody can benefit from this guide...