Polishing HSF Base?

[elpolloloco]

I'm about to install a new HSF on my CPU and I wonder if there would be any benefit to polishing the bottom of the HSF?

I've heard that "lapping" can make for improved cooling efficiency but it seems to me that the thermal paste negates the need for polishing and a rougher surface might actually have more surface area that would increase the cooling potential.

Does anyone have any experiences they could share on this subject or know of a study they can point me to?

Thanks

 

[imported_Kensai]

Lapping is to make the HSF as smooth as possible, thus redusing the distance that the heat has to travel between the CPU and the HSF.

 

[Tiamat]

you want to surface area on all surfaces that are NOT the contact surface. You want the contact surface to touch as much as you can to the heat source. Thus, a smooth surface can do that. Thermal goop is only good for filling the microscopic pores so that air doesnt get in between the sink and the source. Thermal goop sucks for thermal conductivity, but is much better than air is.

 

[pelikan]

For maximum contact between the heatsink and cpu, its not about a smooth surface, its about a flat surface. Lapping can help if the heatsink isn't flat and if it is done properly. Usually lapping up to 600 grit is enough to get the most results from the job. Most heatsinks will not benefit noticeably from lapping.

Polishing may make the heatsink base look nice, but it serves no practical purpose, and leaves rubbing compound on the heatsink which is hard to remove completely.

 

[iwantanewcomputer]

not worth the time if you are using air cooling

 

[NokiaDude]

Originally posted by: iwantanewcomputer
not worth the time if you are using air cooling

 

[Jeff7]

Originally posted by: iwantanewcomputer
not worth the time if you are using air cooling

It need not take much time. My lapping consists of two passes - once with either 320 or 600 grit, depending on how bad the base is, and a final one with 1500 grit. Both are done on a flat countertop, with some water or rubbing alcohol as a lubricant. It produces pretty good results, and really doesn't take very long at all.

 

[gwag]

toothpaste and cloth will smooth it out good, you can get it shiny in aout 10 min.

 

[LED]

Originally posted by: Jeff7

Originally posted by: iwantanewcomputer
not worth the time if you are using air cooling

It need not take much time. My lapping consists of two passes - once with either 320 or 600 grit, depending on how bad the base is, and a final one with 1500 grit. Both are done on a flat countertop, with some water or rubbing alcohol as a lubricant. It produces pretty good results, and really doesn't take very long at all.

Exactly...about 1/2 an hour and you get these kind of results:

PIC 1


PIC 2 Spire

 

[Leper Messiah]

If you feel like doing it, its worth it, but unless your HSFU is really rough, it wont have earth shattering effects, maybe 1-2C at the most.

The theory is, the best way to convey the excess thermal energy is a straight metal-to-metal contact. Since most HSFU are milled to a some what straight surface, microscopic grooves are left on the contact plate, which doesn't allow as much metal-to metal contact. Air is one of the more inefficent thermal conductors, so thermal goop is used to increase the conductivity by filling the little grooves. Lapping the HSFU gets rid of the grooves, giving the maximum metal to metal contact, and reducing the need for TIM.


That being said, since the best way to get rid of heat is straight metal to metal, you want the cleanest surface possible. Things like toothpaste, or jeweler's rouge, and other polishers contain chemicals that contaminates the surface, and destroy's the benefits of lapping. You want a clean, sterile surface, so use 90% rubbing alcohol, which will evaporate without leaving anything behind. Always use wet sand paper too, and use even, vertical strokes, and make sure you're not applying too much pressure to certain areas, to maintain a flat surface.

 

[imported_BadKarma]

Originally posted by: LED

Originally posted by: Jeff7

Originally posted by: iwantanewcomputer
not worth the time if you are using air cooling

It need not take much time. My lapping consists of two passes - once with either 320 or 600 grit, depending on how bad the base is, and a final one with 1500 grit. Both are done on a flat countertop, with some water or rubbing alcohol as a lubricant. It produces pretty good results, and really doesn't take very long at all.

Exactly...about 1/2 an hour and you get these kind of results:

PIC 1


PIC 2 Spire

:shocked:
Wow, that's shiny. I like shiny things.
But seriously, what kind of equipments does one needs to get that kind of result?
:thumbsup:

 

[Leper Messiah]

^^ some 1500grit sandpaper will give you a mirror finish.

 

[Jeff7]

Originally posted by: LED

Originally posted by: Jeff7

Originally posted by: iwantanewcomputer
not worth the time if you are using air cooling

It need not take much time. My lapping consists of two passes - once with either 320 or 600 grit, depending on how bad the base is, and a final one with 1500 grit. Both are done on a flat countertop, with some water or rubbing alcohol as a lubricant. It produces pretty good results, and really doesn't take very long at all.

Exactly...about 1/2 an hour and you get these kind of results:

PIC 1


PIC 2 Spire

Psh, half hour? Try less than 10 minutes for a quick job.
Doing it that quick won't get that kind of a mirror finish though.

 

[sxr7171]

The thing is that flat is far more important shiny as pelikan already mentioned. When you polish you actually introduce some of the polishing compound into the metal interface. IMHO, it is far better to have a perfectly flat surface with the microscopic imperfections filled with thermal paste. But whatever floats your boat people.


Some of you go to engineering schools, ask a professor about it.

 

[Kogan]

You can get lapping kits that come with 300-2000 grit paper for around $5. I got one a few months back and tried it out on my slk-900 heatsink (had some deep machine marks and dents from lots of removals and re-installs). Got it to a near mirror finish (you can only get a true mirror finish if you use polish), and had absolutely no improvement in how well it cooled.

If you've got nothing better to do, go ahead and try it out. Otherwise, I'd take the money you'd spend on sandpaper and put it towards buying a bigger heatsink.

 

[LED]

Wow, that's shiny. I like shiny things.
But seriously, what kind of equipments does one needs to get that kind of result?

Other than the Wet n Dry Sand paper reported, I used a flat mirror tile...Both of the HS's had a ruff finish on the bottom and the cooling increased over 3 C's