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MacBytes
Apr 28, 2006, 11:32 AM
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Category: Opinion/Interviews
Link: Are MacBook Pros running hot due to faulty thermal grease application? (http://www.macbytes.com/link.php?sid=20060428123219)
Description:: A thin, minimal coat of thermal grease is all that's called for. Here be goops.

Posted on MacBytes.com (http://www.macbytes.com)
Approved by Mudbug

excalibur313
Apr 28, 2006, 11:43 AM
I don't understand how a thinner layer can cause it to be cooler. Wouldn't that mean that not as much heat is being diverted away from the processor? To me, that seems like a very bad thing. It's kind of dumb that the fans aren't working, I wouldn't mind a little whirring if it meant that my computer wasn't making me impotent.

DMann
Apr 28, 2006, 11:55 AM
I don't understand how a thinner layer can cause it to be cooler. Wouldn't that mean that not as much heat is being diverted away from the processor? To me, that seems like a very bad thing. It's kind of dumb that the fans aren't working, I wouldn't mind a little whirring if it meant that my computer wasn't making me impotent.

A thicker layer would actually retain heat
rather than dissipate it. However, the difference
would not be dramatic. The problem of overheating
is likely due to the fans not activating.

mmmcheese
Apr 28, 2006, 12:07 PM
If a machine feels hotter than another (of the same type), that's likely a GOOD thing...since it's shedding its heat better...


EDIT: Also, thermal compound application depends on the type of compound as well. Most enthusiasts use a type that needs to be very thing. Back in the day, Tom's Hardware did comparison of thermal compounds and found that the white crap from radio shack did just as well high end enthusiast stuff if you ignored the instructions and put a bunch (twice as much if I recall) of it on the chip. So maybe this is the appropriate amount of compound for the type they are using.

SFVCyclone
Apr 28, 2006, 12:10 PM
That Looks pretty bad, very sloppy. Maybe they run hot because not enough downward pressure is being applied?

CanadaRAM
Apr 28, 2006, 12:11 PM
If a machine feels hotter than another (of the same type), that's likely a GOOD thing...since it's shedding its heat better...
Not necessarily -- if it is designed to move the heat out the heat pipes to the fans where it is being dissipated, but instead the heat is staying concentrated in one hot spot because of a failure to conduct it into the heat pipes and fans, that would be a bad thing.

I don't understand how a thinner layer can cause it to be cooler. W

Thermal grease has a very specific purpose. The thinner the layer the better. Here's why:

Metal to metal contact is the best conductor of heat.
Air space is the worst.
Thermal grease is quite a bit worse than metal-on-metal, but better than air.

If the heat sink and the processor pad were perfectly flat and perfectly polished, then you wouldn't need thermal grease because you'd have 100% metal on metal.

But they are not - there are always irregularities and non-flat areas that cause microscopic grooves and air pockets between the two metal surfaces, which is bad.

The thermal grease is intended to fill those micro air pockets and provide a better conduction of heat between the surfaces because grease > air. To do this takes very little grease. If you have more gease than you need, it starts getting between the metal to metal contact, and reducing conduction, because grease < metal. Worst case scenario would be so much grease that it bubbles or moves, and leaves air voids. This is what may be happening in MBPs.

There isn't much, if any, difference between brands of thermal grease.

The key is to get as thin a layer as possible between two surfaces that are af flat as possible, and then clamp them together with enough pressure to ensure maximum metal contact.

mmmcheese
Apr 28, 2006, 01:14 PM
Not necessarily -- if it is designed to move the heat out the heat pipes to the fans where it is being dissipated, but instead the heat is staying concentrated in one hot spot because of a failure to conduct it into the heat pipes and fans, that would be a bad thing.



Thermal grease has a very specific purpose. The thinner the layer the better. Here's why:

Metal to metal contact is the best conductor of heat.
Air space is the worst.
Thermal grease is quite a bit worse than metal-on-metal, but better than air.

If the heat sink and the processor pad were perfectly flat and perfectly polished, then you wouldn't need thermal grease because you'd have 100% metal on metal.

But they are not - there are always irregularities and non-flat areas that cause microscopic grooves and air pockets between the two metal surfaces, which is bad.

The thermal grease is intended to fill those micro air pockets and provide a better conduction of heat between the surfaces because grease > air. To do this takes very little grease. If you have more gease than you need, it starts getting between the metal to metal contact, and reducing conduction, because grease < metal. Worst case scenario would be so much grease that it bubbles or moves, and leaves air voids. This is what may be happening in MBPs.

There isn't much, if any, difference between brands of thermal grease.

The key is to get as thin a layer as possible between two surfaces that are af flat as possible, and then clamp them together with enough pressure to ensure maximum metal contact.

I know the purpose, I'm just saying that even though that's the theory, there is evidence that this is not always the case. They can't explain why this is the case, but for some reason, some of the heatsink compound worked better with a thicker layer.

From those photos, it just looks like messy manufacturing (which is why many companies use thermal pads instead), but I haven't ripped apart my machine and tried all sorts of combinations of compounds and applications...maybe they know something we don't, and this is how it should be applied.

montex
Apr 29, 2006, 02:29 AM
So much bull. The application of thermal paste has little to do with how conductive the heat seal is. The paste fills microscopic holes and scratches between the processor and the heat sink - all excess gets squeezed out between them when the sink is bolted down. The amount of paste actually involved in heat transfer is positively miniscule.

When the seal is broken, and a heat sink is removed, the paste no longer fills the scratches and will form new voids between the sink and the chip if it's re-used. That's why the paste has to be removed and re-applied every time the heat sink is taken off and the previous seal broken.

I think this article is yet another paid-for FUD about the MacBook Pro to scare off potential windows switchers. Now who would want to do a thing like that?

Could it be...

generik
Apr 29, 2006, 04:41 AM
I know the purpose, I'm just saying that even though that's the theory, there is evidence that this is not always the case. They can't explain why this is the case, but for some reason, some of the heatsink compound worked better with a thicker layer.


That's not possible. The only purpose of thermal grease is to serve as a thermal interface between the heat source (ie: the CPU) and the heat vent (heat sink?). Imagine it as a pipe with water flowing through it if you will. Now, will water take a longer time to transverse through a longer pipe as compared to a shorter one?

Likewise the same reasoning applies here, with a thicker glob, the glob itself does have its own specific heat capacity, and hence heat is trapped closer to the CPU for longer instead of passing through the paste and getting vented through the heat sink, as such the air within your MBP gets heated up for that ball toasting experience :rolleyes:

excalibur313
Apr 29, 2006, 10:19 AM
The point you are all are making is in terms of the processor. Yes tons of thermal past will make the processor hotter but a hotter macbook on my lap means that more heat is getting to my legs. I agree that the heat you feel on your legs is probably because the fans aren't turning on to blow heat somewhere else.

pincho
Apr 29, 2006, 10:46 AM
just curious, is there any software app to make the fans spin faster? i would trade more noise for less heat :P

CanadaRAM
Apr 29, 2006, 11:02 AM
So much bull. The application of thermal paste has little to do with how conductive the heat seal is. The paste fills microscopic holes and scratches between the processor and the heat sink - all excess gets squeezed out between them when the sink is bolted down.
Question: How does all the excess get removed?
That assumes there is sufficient pressure to do the squeezing, that the thermal grease is perfectly flowable, and that the two surfaces permit the grease to escape to somewhere.

Harryc
Apr 29, 2006, 02:44 PM
Just thought I'd chime into this thread to say that I did remove my MBP's logic board and reapplied a very thin layer of Arctic Silver to all three surfaces in question. As a result my MBP does not run any cooler, but it wasn't really hot to begin with. Why did I do this then you might ask?. Well, for (2) reasons. First I wanted to know how to take it apart and put it back together again so that I can do my own repairs and upgrades. That might seem a bit strange to some of you , but computer hardware and operating systems are my hobbies and passion. Secondly, I have built dozens of computers over the years (last 25 or so) and I don't like shoddy engineering. The mess of thermal compound that I found on that logic board was not a good example of quality engineering/manufacturing, so I fixed it. I agree with those saying thin is better with regard to thermal compound ... it's been proven over and over.

backspinner
Apr 30, 2006, 03:00 PM
the thermal grease is defenitly not applied correctly, since not the whole surface is covered. The normal way to apply the grease is to put some evenly onto the processor and then squeeze and turn forward and backwards until all grease between the processor and heatsink has been moved to the outside. After this the grease only fills the voids and scratches and the thermal transfer is at optimum. Do not remove the pressure after this process though.

Looking to the pictures, it will be difficult to use this method with a heatpipe with three heatspots mounted to it.