Originally Posted by Cathar
Well in the hunt for the best die-baseplate thermal "connection" with my waterblock research, I've found the "best" method that I've been able to achieve, and it falls in line with what's accepted and been tried elsewhere. However, me knowing me, I don't believe stuff until I try it for myself.
Basically I've lapped bases with:
150 grit
220 grit
320 grit
600 grit
800 grit
1000 grit
1200 grit
1500 grit
brasso + strong cloth
toothpaste + cloth
fine-cut cleanser
jeweller's rouge
All in incremental steps, to varying degrees of finish from rough, to a copper finish you can shave in.
So what's worked out the best?
Go to Bunnings. Grab a small board of 12mm thick MDF (Medium Density Fibreboard). It's flat as glass and a whole lot cheaper. Should cost about $5. Pick up 1 sheet each 150grit, 320grit, and 600 grit wet'n'dry sandpaper (black colored).
Take your heatsink, and lightly scribble over the base with a black permanent marker. Color the whole base in if you want.
Stick your 150 grit paper onto the MDF.
Take your heatsink/waterblock and scrub lengthways (if the block has a longer length in one direction - otherwise just pick). Move the block up and down the sandpaper while pushing down firmly. Do not move in a circular motion, just straight up and down. You'll need 3 hands. One to hold the block, and two to hold the edges of the sandpaper down so it doesn't "grab" and fold and rip. If nature didn't supply you with 3 hands, sitting on the floor and using a foot works just as well. Keep scrubbing until you can't see ANY of the ink/black. I periodically look at the base to see how it's going, this is how I can tell if a block is initially convex, concave, or whatever. This can take anything from 1 minute to 30 minutes (or more) depending on how flat the base is to start with.
Once the ink is gone, use the 320grit and scrub cross-ways. This time keep doing it until all the cross-lines left by the 150 grit sand-paper are ground away. Just move the block straight up an down - no round motion. This should take about 3-5 minutes.
Then use the 600 grit sandpaper and moving straight up and down lengthways sand the base until the 320-grit cross-ways lines are gone (another 3-5 minutes).
Finally follow up with a circular grind of the base on the 600-grit sandpaper for about 30 seconds. Wipe clean. This should leave the base with a dull reflective surface.
You're done!
Like I said, I've tried anything from 150-grit up to a mirror polish, but the dull 600-grit finish works out the best. Surprisingly, a 220-grit finish, and a mirror finish give about the same results (at least for me), while the dull 600-grit finish gave me about 0.5C better than either of those two for a ~100W CPU load.
I know that the above has been said here before a few times, so consider this as a re-affirmation of the procedure.
