Question in regards to lapping

I've lurked here a few times, and this is now my first post as a registered member, so before I begin . . . hello everyone! *ahem*

I'm currently gathering parts for a new build and am giving serious consideration to lapping both my cpu and heatsink (just have to overcome the fear ). I've done all my research and feel confident in my ability to do it well, but there's some information I've come across that made me curious.

This is the website in question:
http://www.techpowerup.com/articles/cooling/39

I sure do like the look of having a couple mirror copper finishes to place together, but if what I gather from this article is correct (and it seems logical to me), having such a fine finish on both pieces can be more harmful than beneficial due to the decrease in actual metal contact, leaving only the layer of TIM to conduct the heat. Would it be better to lap only one piece, and increase the copper contact area? Perhaps lapping them both to a shine and being gentle in the amount of TIM used would decrease the chance of there being a solid layer of TIM preventing the copper from contacting each other?

What do you think of this, and should it be of concern?

For the record, I intend to lap an e8400 and a Tuniq Tower 120.

Welcome

First of to the forums.

Second, you can do both the CPU and the heatsink if you like. But remember, it is not a mirror finish you are going for, the key word is flatness. A mirror shine is "just" a cosmetic bonus. Not saying that it dose not help to some extend. And I don't think that you have to worry about what the article said, about there not being any metal to metal contact between the two components. It is mostly about the amount of thermal grease that is applied between the two surfaces. Too much has all been bad for thermal conductivity, no matter the surface finish.

Good luck mate.

Thanks for the welcome and the reply!

Here's a bit more about what I'm getting at.

I imagine the best possible scenario for placing a heatsink on a CPU would be if both of the connecting surfaces were 100% completely and totally flat (like Kansas). Copper conducts much better than any compound placed between them, so ideally, a 100% copper-to-copper contact surface area would be the optimal solution. Is this correct to assume?

However, since this is impossible to achieve, the idea in lapping is to get each surface as flat as is possible, and fill in the remaining areas with a thermal compound. I understand this to be the reason you are only supposed to use the tiniest possible amount of any TIM, since it's meant to fill in those little gaps. So if you had a completely flat surface and applied a compound to it, it would create a tiny layer of compound between the two pieces instead of letting the metal pieces touch each other (with each other's legal consent).

So, if you had two not-mirror shined semi-rough contact surfaces with a fair amount of metal contact filled in with TIM, would this make for a superior heat transfer solution than extremely flat, mirror-like surfaces with less possible contact surface?

Or am I way off on all this? I'm probably going to lap these things either way, I just like to best understand the process in order to make sure I'm doing it the best possible way.

White Elephant said:

So, if you had two not-mirror shined semi-rough contact surfaces with a fair amount of metal contact filled in with TIM, would this make for a superior heat transfer solution than extremely flat, mirror-like surfaces with less possible contact surface?

Click to expand...

That's bang on, from what I know/have experienced.

White Elephant said:

So, if you had two not-mirror shined semi-rough contact surfaces with a fair amount of metal contact filled in with TIM, would this make for a superior heat transfer solution than extremely flat, mirror-like surfaces with less possible contact surface?

Click to expand...

i would say yes if you can somehow make all the rough surfaces line up neatly, but since you can't then i would opt for a flat surface. doesn't have to be mirror like but at the very least flat. that will ensure that there is as little tim in between the 2 surfaces as possible. metal to metal will transfer better than if there was a second substance in between.

To add a little to the story. Thermalright introduced last summer the "ultimate" cooler called the IFX-14; it included even a heat pump for the back of the CPU. It turned out to be one of the worst cooler made .The reason: the surface was quite convex, most likely because they soldered the pipes in after machining the surface. So flatness of the surface is over 90% of good heat transfer. It is not easy to lvl a convex surface, because by lapping by hand we tend to sand the edges more then the center. Just visualize holding the piece so that all edges are in the air and putting pressure on the piece to lap it and never touching with the edges the sandpaper. On the other hand a concave surface it a piece of cake. So use a razor blade to check the surface often and in all directions!!
A trick is: seat the cooler with thermal paste then take it off and color the blank metal surface with an ink pen. Remove paste carefully, and then sand the colored surface off. Repeat till nearly all surface shows up. Have fun

Thanks all for your answers.

I think I'll be going for a rather smooth finish, but might stop at around the 600-800 grit level, so nothing too shiny for me.