Need tips on Lapping a HeatSink

[Guest]

Just ordered a ThermalRight SK-6 copper heatsink and since i want the best performance out of it i plan to do some Lapping.Can anyone give me some tips and the sand paper grade they used.Basically i know you have to place the sand paper on a flat surface and then rotate the heatsink on it and then you switch to a higher grade.Do you use water or something else or you do it dry.Do i need special sand paper or i can use regular wood sand paper?

 

[Bud]

I place my paper on a glass surface and single stroke the base...first with 600 then move to 1000 for the final.

I'm not in touch with my feeings, and I like it that way!

 

[silverpig]

I do 600 dry, 800 dry, 1500 dry, 1500 with WD-40...

Another computer wanted. Donations accepted. :^)

 

[Guest]

Do you use some special stuff to get rid of the WD-40?

 

[Mordy]

Some guy discovered that too smooth is bad
<A HREF="http://www.overclockers.com/tips458/" target="_new">http://www.overclockers.com/tips458/</A>


-Beer! Good!
-James Hatfield

 

[ejsmith2]

Yeah, it all depends on the situation.

If you're running a heat exchanger at 30 atmospheres and 6000gph to cool an exothermic reactor, then you can have the walls of the piping too smooth (laminar flow). Not enough turbulance can cause pretty decent insulation. But if you're using a heatsink, on that little tiny surface area, what that lapping does is remove the oxidation. Just that little bit of oxidation (which you can't see) can be a significant transfer barrier. But either way, surface area is the key. The guy that is using optical polishing material is getting that little jewel smoother than sandpaper ever will, which can cut down on the surface area considerably.

So these people using 1000+ grit sand paper ($8 a sheet), and getting 2C cooler temps over 600 grit paper, are doing something different on installation (tighter clamps, putting more thermal gel, washing all that oil off their hands first, buffing the residue of isopropyl off the heatsink). Clamping pressure can make a huge impact.

The thing that matters is you're happy with the results......

 

[peach]

<font color=blue>ok, smith answered this, sort of, but here is something widely known to any mechanical engineer. In heat transfer between a fluid (air counts too) and a solid (convection), laminar flow is bad. Reason is semi-obvious - with laminar flow, air than has already been heated continues to flow slowly along the surface. Turbulent flow is better. What is less obvious is tht turbulent flow experiences less friction as well.

Anyway, solid to solid heat transfer (conduction) is exact opposite. Absolutely minimumizing the gap/maximizing direct contact is the goal.

If one is using poor heat conductive adhesives, obtaining a mirror smooth finish is can be really helpful as the Aluminum would have a better coefficient of conductive heat transfer. However, if one is using Artic Silver II, the silver paste has a better thermal conductivity level than the Aluminum. Assuming (remember what happens when you assume) you fill the gaps of the heat sink with the paste well enough, spending 3 hours on seeing yourself with the bottom of you heatsink may not be worth it. Besides, just how perfectly flat is the chip?

Best solution is to Lapp some and then use the paste.

<i><font color=blue>on company time....</i>

 

[Bud]

$8 bucks a sheet??? heh...please tell me where u shop...I want to make sure to avoid that place.

I'm not in touch with my feeings, and I like it that way!

 

[Guest]

Do you guys use regular wood sand paper or do i have to use special sand paper??

 

[ejsmith2]

You can use anything that gets the grit you want. 'Metal' paper usually has a cloth-fiber backing (stronger), and is waterproof.

 

[bw37]

Good source for fine sandpaper is automotive parts supply, especially one that specializes auto body supplies: paint, bondo, etc.

"Wet or Dry" type sandpaper will hold up with WD-40 or other light oil for lapping. Might also work with water as lube (that's called "wet sanding" in auto prep work, and 400 - 600 grit is typical prior to paint application.).

Place paper on a truly flat surface (glass is good) and lap away. Don't overdo as you might do more than flatten. Make sure you've removed all oil and particles w/solvent and soapy water and rinse and then do a final clean/flush with alcohol as recommended by Arctic Silver application, etc.

my $.02

BW

the more I learn, the less I'm sure I know...

 

[ejsmith2]

That's a damn good $.02, too. I second that.

 

[funkdog]

What about my Alpha Pal6035, It's aluminum with a pressed copper heatplate? Same type of situation with lapping? I mean when I put it on the copper was very shiny, and seemed really flat. I've got pretty decent temps and can overclock fairly well, is pulling it out and lapping it really worth the what 2c I'd probably get?

These are my thoughts, your mileage may vary.

 

[bw37]

I guess I'd follow the time honored adage: "If it ain't broke, don't fix it!"

Of course if you're an O/C fanatic, you WILL try to "fix" it until you break it, right ?

BW

the more I learn, the less I'm sure I know...