Question About Heatsink Lapping

[Ruenin]

I purchased the Zalman CNPS9500 and I'm going to attach it to an AMD 9850 Quad Core. I was reading about lapping (the process of further flattening the surface of a heatsink through sanding with an extremely fine grit automotive sandpaper to improve the contact surface) and I'm seeing reports that it can drop temps by up to 10 degrees. Has anyone here had experience in doing this? Does it make the claimed difference?

 

I would put this in the mods section but didn't because in my opinion, it barely qualifies as a mod.

[Puck]

I purchased the Zalman CNPS9500 and I'm going to attach it to an AMD 9850 Quad Core. I was reading about lapping (the process of further flattening the surface of a heatsink through sanding with an extremely fine grit automotive sandpaper to improve the contact surface) and I'm seeing reports that it can drop temps by up to 10 degrees. Has anyone here had experience in doing this? Does it make the claimed difference?

 

I would put this in the mods section but didn't because in my opinion, it barely qualifies as a mod.

You wont get 10c, but it will help. A lapped hs can use less TIM for better contact and lower temps.

[Crazy_Nate]

An ultra shiny surface isn't going to increase the heat transfer drastically (which is what some people consider lapping to be about).

 

What you really are doing, if you're doing it correctly, is getting your heatsink surface as flat as possible (as well as the top of the heatspreader on your CPU if needed...). Good thermal grease takes care of the rest (the thermal resistance is awfully low, because of the moderately good conductivity and thickness of the layer).

 

So...verify if it'll make a difference, use something you know is flat to check if it's concave or convex. Take it from there.

Edited May 15, 2008 by Crazy_Nate

[Verran]

I certainly wouldn't expect 10c. It's not a drastic difference. I've lapped a lot of heatsinks and it's definitely better but it's usually just a couple degrees.

[wevsspot]

You can use a metal engineer's ruler or even a razor blade to check the flatness of both the heatsink and processor IHS.

 

I've never seen a 10F difference between before and after though. The primary thing you are looking for is increasing the surface area contact between the cpu and heatsink. Mirror shiny is nice, but if you properly apply your TIM it will fill in the microscopic valleys and perform just as well as two surfaces that are mirror finished.

 

I know that you will read many website reviews that talk about the quality of the surface finish on a heatsink, unfortunately they use that as a general qualifier about the quality of the machining on the mating surface.

 

You can have a mirror finish on a heatsink, but if it isn't perfectly flat that doesn't mean a hoot.

Edited May 15, 2008 by wevsspot

[Waco]

I lap the heatsinks for any of my desktop rigs. De-lidding the CPU comes next if it has an IHS that's removable.

 

Making them flat is key - you can have a very dull but flat cooler versus a mirror-finish non-flat cooler and the flat one will win by a landslide every time.

 

I use a large 5/8" sheet of glass to lap on...it pretty much guarantees I get a flat surface if I take my time.

[The Smith]

Yeah, check if your CNPS9500 is already flat, but if I remember well, on these HS, a good machining job is already done in factory. So I would not expect much amelioration...

Edited May 15, 2008 by The Smith