How do i lap?

[Sushiman]

How do i lap a heatsink? I have sandpaper and a powersander... what do i do? Thanks for the help.

mark

[herbal'|']

I don't think a powersander will be necessary. In lapping you're going for the 'mirror' finish, so you will need very very fine grit sandpaper. I usually start out at 1000grit and move up to finishing with 2000grit. If the bottom of the heatsink has large dents or is curved, you could start out with something like 600, but I've yet to need it. You can buy this fine grit sandpaper at any auto parts store.

[ButcherUK]

Take a piece of glass and some fine wet or dry sandpaper - I usually start at 400 or so depending on the flatness of the HSF, I had one that I had to take a grinder and 40 grit to, it was massively convex. Then sand on glass in a side to side motion with increasing grits - rotate 90 degrees each grit. At each stage make sure yo remove all scratches from the previous grit (easy to see as the run perpendicular to the current grit). Once you get to 1000 or 1500 you hae probably gone far enough. You want to wet the sandpaper with water while lapping for a smoother finish. Also you want to apply only a light pressure, if you press too much you will make the heatsink convex. On heavier copper heatsinks the weight of the sink is more than adequate.

[Sushiman]

im a little confused at the glass part.... do i place the glass on a table.... place the sandpaper on top of that.... then move the heatsink across the sandpaper?

[ButcherUK]

Yes that's correct. The glass gives a perfectly flat surface for the sandpaper to press against - ensures a flat sink not just a shiny one.