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AMD FX (Bulldozer) Owners Club! - Page 381

post #3801 of 8112
The post below was posted in the Air Cooling forum to help people but I'll post it here as it relates to FX CPUs as they generate a lot of heat when OC'ed. The link at the bottom will illustrate why smoother surfaces are better as there are fewer and lower high spots and thus more metal-to-metal contact between the HSF base and the CPU heat spreader.

We can debate surface finish forever but the reality is if it were possible - which is is NOT, then 100% metal-to-metal contact would be the best means to transfer heat from the heat spreader to the HSF. By being smooth and FLAT the two surfaces have the least thermal resistance. Technically the smoother the surface while remaining flat, the higher the percentage of metal-to-metal contact. Shiny does not necessarily mean the surfaces are flat nor smooth.

Lapping is intended to make a surface flat. It can actually make the surface smoother or rougher depending on how the work is done and with what grit abrasive. Polishing is typically done for looks, not for better thermal conduction. It's very difficult to polish a surface the size of a CPU heat spreader and keep it flat. Polishing of specimens for microscopic inspection is not concerned with the sample being flat across the entire surface as is required for good thermal transfer in a HSF/CPU. Micro grain polishing is intended to show the grain structure of the metal or whatever you're interested in. This microscopic metallurgical inspection would show you why a smoother surface transfers heat better than a rough surface where the actual metal-to-metal contact is much lower due essentially to micro high spots. (See link at bottom).

The theory that more surface area via a rougher surface or dimples improves thermal transfer is unlikely for a HSF/CPU application because air has poor thermal conduction meaning TIM must be used to FILL the voids from the rougher surface or dimples to improve thermal conduction. Unfortunately TIM is an insulator compared to proper metal-to-metal contact. So while the surface area may increase with roughness or dimples, the thermal conduction may decrease due to LESS metal-to-metal contact and the need for TIM - which is an insulator.

As far as convex HSF bases are concerned, they are not or should not be convex by design but in fact they are often the result of poor machining - regardless of what a HSF mfg. tells you. They is no need nor desire to have an excessive pressure in the center of the HSF. Beyond a moderate pressure, more pressure does NOT = more thermal conduction. Any quality HSF design should have more than enough pressure to provide proper thermal conduction without a convex base. A convex base can reduce proper pressure and surface contact on the rest of the HSF and heat spreader surface, reducing thermal conduction. You will often see poor results from HSFs with a convex base compared to those with a flat base.

The link below shows a side vew of a smooth surface under magnification. As you can see if you had two "smooth" surfaces - a HSF and a CPU heat spreader, one on top of the other, only the high spots would actually touch each other. TIM is used to fill the MICRO PORES or voids ONLY. It's preferred to have 100% metal-to-metal contact but this is impossible. You only want enough TIM to fill the voids, not so much as to prevent true metal-to-metal contact of the HSF base and CPU heat spreader. This is why more TIM is bad for thermal conduction to the HSF.

http://www.google.com/imgres?q=Surface+finish&start=245&hl=en&sa=X&biw=870&bih=616&addh=36&tbm=isch&prmd=imvnsb&tbnid=jUkHqLhvH9csWM:&imgrefurl=http://www.kepcoinc.com/%3Fpage%3Dserviceselectropolishing&docid=jb931ksq7kFeAM&imgurl=http://www.kepcoinc.com/images/uploaded/electropolishing_diagram2.2.gif&w=400&h=289&ei=D55ST-6YFYejgwfJw4jrDQ&zoom=1&iact=hc&vpx=559&vpy=135&dur=982&hovh=191&hovw=264&tx=143&ty=214&sig=114770364959779861631&page=16&tbnh=131&tbnw=192&ndsp=16&ved=1t:429,r:15,s:245
Edited by AMD4ME - 3/3/12 at 7:47pm
post #3802 of 8112
hello,
from what i have ,by skinning the artical,would removing the heat sink after a while and scraping back the thermal paste be a good idea as it would be more metal to metal contact and just a residual thermal paste please?
    
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post #3803 of 8112

Just make sure you have enough paste to fill all the air voids

When the CPU heats up the tension from the mounting device will squeeze out excess paste


Edited by Tweeky - 3/4/12 at 10:12am
    
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post #3804 of 8112
Guys got some real world Bulldozer power consumption readings and made a post.
Check it out and if any one else has some readings please post them.

http://www.overclock.net/t/1224496/bulldozer-power-consumption#post_16625362
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post #3805 of 8112
Quote:
Originally Posted by MrPerforations View Post

hello,
from what i have ,by skinning the artical,would removing the heat sink after a while and scraping back the thermal paste be a good idea as it would be more metal to metal contact and just a residual thermal paste please?

I wouldn't suggest this. It would likely be optimal to "do it right the first time", so to speak, and not have to pull the HSF back off (unless you are removing the CPU for a return\upgrade).

Some of the key tips I can offer are:
- Properly clean and prepare both surfaces
- Apply grease to HSF, not CPU (I still do CPU, but apparently, others have their ways)
- Instead of just dabbing on and installing, use something both clean and inert to evenly spread and press the grease into the face of the surface and do it (if at all possible) against the metal's grain (like a library card, etc..).
- Less is more, you can actually increase temperatures by having too much.

TIM is the lesser of two (really three) evils. It's just taking space to not let air or moisture in. It conducts better than air, but, still worse than metal, so, it's purpose is to fill micro imperfections, not be a perfectly flat layer of material to sit completely evenly across for the CPU.
post #3806 of 8112
I should mention that it's good to check the HSF base and CPU heat spreader with a razor blade or machinist straight edge or similar to be sure they are reasonably flat before you start.

Scraping off the excess with a straight edge before you install the HSF is fine but the layer should really not be anywhere close to thick and you need to be careful not to remove all the TIM. The best way I can describe how thin you want the TIM is almost a translucent film. That's all you want.

IME it's best to apply the TIM to the CPU, not the HSF base as some bases are larger than the CPU heat spreader and the TIM not in contact with the CPU heat spreader could run down the side of the CPU when it gets hot.

Keep in mind this is the ideal situation and it may get you a couple degrees over the pea or grain of rice method. It's not going to lower your load temps. a lot, but some folks find it worth the effort.
Edited by AMD4ME - 3/4/12 at 1:31pm
post #3807 of 8112
Can you guys please link me to some overclocked 4100 benchmarks. I know its kinda lacking at stock clock but, for the grace of god I can't find it myself. I will have mine by mid week and just want to have something to shoot for/compare aginst.
post #3808 of 8112
Quote:
Originally Posted by AMD4ME View Post

I should mention that it's good to check the HSF base and CPU heat spreader with a razor blade or machinist straight edge or similar to be sure they are reasonably flat before you start.
Scraping off the excess with a straight edge before you install the HSF is fine but the layer should really not be anywhere close to thick and you need to be careful not to remove all the TIM. The best way I can describe how thin you want the TIM is almost a translucent film. That's all you want.
IME it's best to apply the TIM to the CPU, not the HSF base as some bases are larger than the CPU heat spreader and the TIM not in contact with the CPU heat spreader could run down the side of the CPU when it gets hot.
Keep in mind this is the ideal situation and it may get you a couple degrees over the pea or grain of rice method. It's not going to lower your load temps. a lot, but some folks find it worth the effort.

I was actually thinking about bringing my CNPS9000 into school to check it with a straight-edge and feeler gauges (I think the smallest I'll have handy is 0.0005"). It has a smooth, polished surface unlike the stock HSF I installed.

I always used to put my TIM on the CPU and spread it there (the Zalman brush-in-cap makes for a really easy application process). What I had gathered from the article I linked to and the fact that the stock HSF had paste on it and not the CPU lead me to believe that perhaps applying it to the HSF was the way to go. I prefer the CPU and if you're saying CPU as well, that's good enough for me to keep doing it that way.

I'm now amused by a time I was nearly out of Zalman TIM and was installing a processor that night to finish a school project or some other time sensitive task and needed the PC for it. I had it spread on so thin that I could read the text on the surface of the processor and was scared *****less that I was going to burn up a processor as a result.

I wonder how many people RMA'd cooling products over time when all they needed to do was reinstall them with less TIM. It still sounds weird in my head: "less TIM, less Temps"... may never get used to that.

Oh yeah, one other thing before I hop off here. I wouldn't use a razor blade. This is one area where my automotive experience is definitely going to help. Many people use razors on gasket surfaces and while in some situations its an acceptable practice, many times the person ends up knicking and altering the surface they are preparing for a new gasket, liquid gasket, or another flat mating surface. This generally causes leaks and other associated problems with this condition.

To combat the issue, someone along the line came up with what are essentially plastic razor blades specifically intended for use on metallic surfaces like HSF bottoms and tops of CPUs to name only two. The plastic blades posses sufficient hardness to apply pressure to them and successfully remove existing material (old gasket material, dirt, contaminants and the like) without breaking all that often. Dragging one of these across the surface, applying even pressure across the implement, could prove as an effective method of leveling TIM and removing its excess during processor and HSF installation. It could possibly prove useful in "dry" removal of old material, saving us from using cleaning products that some TIM manufacturers sell, or, like I use, isopropyl rubbing alcohol.

Those blades can be easily purchased through the internet and are not expensive. I will see if I can obtain one from class, use it and post the results for anyone who is curios. We may need to call up someone like Artic Silver and see if we can't get them to start including one with each unit of their TIM to ease the application process and help guarantee the highest level of performance possible.

One item I've used for situations like this rather successfully is an ice scraper. Plastic, hard, flat and attached to a handle that provides more than adequate leverage, they're an easy and relatively available (also inexpensive) solution for this sort of thing.
post #3809 of 8112
The only reason for mentioning the razor blade was to check flatness, not for scraping excess TIM off the CPU. If you're going to drag something over the CPU to scape excess TIM off make sure it's straight or it defeats the whole point. A plastic credit card or scaper may or may not actually be flat and straight but a machinists straight edge is. Exercise great care so you don't create burrs or scratches.

This kind of work requires dexterity and care or you can FUBAR your CPU. It's not for those who think a hammer is a precision tool for making round pegs fit in square holes. wink.gif
Edited by AMD4ME - 3/4/12 at 4:32pm
post #3810 of 8112
The thin film method is best suited for lapped cpus and heatsinks.

Have you seen the state of the IHS recently? Its simply astounding how badly they are made, and you usually need quite a bit of TIM to fill the voids in them.

You would think that they could simply do a quick and dirty lapping on them before and after plating.
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