Sorry, not related directly to the topic, but I wanted to point out that my P4 1.8A IHS was horribly unflat as well. It was very high in the center (which is better than being low in the center, anyway.)
This first picture was after several minutes using 30 micron Al2O3 lapping film and ethanol (about 320 grit equivalent). You can see how horribly high centered it was, because I am all the way into the copper and haven't even come close to lapping out to the edge yet.
This next picture was taken when I decided not to remove much more of the IHS material since I had taken off so much and you can see the irregularities of the IHS substructure. I don't think there was much left of the center section. At this point I was using 9 micron Al2O3 lapping film and ethanol (about 900 grit equivalent).
I then did a final polish with 1 micron Al2O3 lapping film and ethanol. I can't remember the conversion grit size, but probably is around equivalent to 2000 grit. I was going for the no TIM interface bond with the water block, but it kept galling when it would twist slightly when closing the stock Intel heatsink retention levers (I made a water block adaptor that could use the stock Intel mobo bracket). Anyway, just wanted to show that my P4 IHS was NOT flat at all.
