I have seen a few people asking about lapping the Coppermine CPU, and I thought I might have some useful insight into this subject. I work at a factory which makes silicon wafers, the likes of which could be used in the manufacture of processors. I believe the new Coppermine FCPGA actually exposes the back side of the silicon for mounting to the heat sink. Two things about this make lapping sound like a bad idea to me:
First, silicon is a lot like glass in its properties. From my experience it is a bit tougher, but if it is handled roughly it will scratch, chip or crack just the same. I would wager the flip chip would not hold up well to sandpaper.
Second, the wafers used in device manufacturing are very, very flat. I’m talking angstroms here. They get lapped on huge high precision machines and are later polished in a 3-step or more process using felt-like pads and slurry so fine it looks like slightly cloudy water. When they ship to customers they shine like mirrors on the front side and are usually rather dull but smooth on the back. The photolithography process used in device
manufacturing demands precision. I can pretty much guarantee that the little silicon bit on the CPU is much better without our clumsy attempts to make it “better.” The blue coating it is sealed with probably doesn’t do flatness any good, but I don’t know for sure.
I hope this might be useful information to some of your readers. I sure would hate to see someone waste a $250 CPU to find out the hard way.