Oh Why Do They Paint the Heatsink?

[Cuttlefish]

So, a few weeks ago, after downloading a program to monitor my video card's core temperatures, I realized that the stuttering I would commonly get during games, occurred when my graphics core went above 100^oC. I replaced the cheap thermal gunk between my cores and the heatsink (which actually flaked off), and it definitely helped, but the core still went above 100^oC. Propping my laptop up would make my maximum temperature a few degrees above 90^oC, which meant that I no longer stuttered during games. However, while the heatsink and fan were removed, I remarked at how most of its surface appeared to be painted with black paint! What is particularly disturbing is that this heatsink and fan are shared by both the video core, and the main processor of the computer. Indeed, using a program to monitor my processor's temperature, it was not uncommon for it to go above 85^oC.

Last week, I ordered a replacement heatsink/fan for my laptop model for a little project I had in mind. It arrived this week, and yesterday morning, I began my project of stripping the paint from the heatsink/fan. I gathered my materials: Oven cleaner, 99% Isopropyl Alcohol, and cotton swabs (lots and lots of cotton swabs). Basically I sprayed the oven cleaner into a disposable container (in my case, the bottom of a dismembered bottle of water), and dipped the cotton swabs in it, which I used to apply the oven cleaner to the painted areas of the heatsink. Just like cleaning an oven, you let it sit for a while to loosen what you would like to remove. After a few hours of elbow grease (and cotton swabs), the heatsink/fan was stripped of paint!

Here is a picture which shows the old heatsink/fan in the top two panels, and the bottom panels display the replacement heatsink/fan after it was stripped of its paint and stickers and whatnot. I ended up stripping the top of the fan of paint as well, for aesthetic purposes mainly, because, while stripping the paint from the copper heatpipes, the paint from the nearby fan housing flaked off as well. Knowing there was a flakey fan inside of my laptop would have bothered me immensely.

So the moment of truth had arrived. I reinstalled the heatsink/fan (having to remove and replace the thermal gunk once again), and I turned on my laptop. Well, it turned on! I loaded my graphics core temperature monitoring program, and I felt disheartened because the idle temperature was the same as before. I dove into my game of choice, and the temperature began to climb, until it hit 76^oC, after 45 minutes of gaming or so. The temperature never rose above that point. I also realized that I was not even propping up my laptop, as I had to do to maintain temperatures above 90^oC before! Success!

So now I ask: Why the hell were the majority of the copper and the aluminum parts of my heatsink/fan painted?! When "Tuxedo Black" was ordered, I really would have been satisfied with the outside of the laptop being tuxedo black. You really don't have to paint the heatsink to keep my attention. The fact that it added around 30^oC to my graphics card under load really doesn't help the case of having it look nice either. Maybe it's the geek in me, but I really like being greeted by the chrome surface of my stripped fan when looking into the holes at the bottom of my laptop. I also like seeing the bare aluminum fins peering out of the vent in the back. I know sometimes beauty is chosen over some functionality, but this seems to be taking it to an extreme!

As an aside, I think I would rather enjoy a career in building or dissembling laptops!

[beetle]

The only explanation I have for painting them is maybe to prevent corrosion. But how much do you have to worry about that in a laptop? And there are other things in there that can corrode so... I don't really know. I used to work in electronics and handled black heat sinks all the time and ones that looked like bare aluminum. I thought the black ones were anodized or something. They didn't seem like they were painted. So what you discovered sounds strange. Who knows why they did it.

[Cuttlefish]

The only explanation I have for painting them is maybe to prevent corrosion. But how much do you have to worry about that in a laptop? And there are other things in there that can corrode so... I don't really know. I used to work in electronics and handled black heat sinks all the time and ones that looked like bare aluminum. I thought the black ones were anodized or something. They didn't seem like they were painted. So what you discovered sounds strange. Who knows why they did it.

I thought it could possibly be anodized as well when I pulled it out the first time. But I was curious because, why wasn't all of it anodized if that was the case? I suspected it was paint, and my suspicions were confirmed the first time I removed it because rubbing the painted copper heatpipe sections with a cotton swab dipped in alcohol resulted with some paint being removed, and becoming visible on the swab. Ugh, there was even black tape on it, all along the bottom of the aluminum fins!

The design of the heatsink/fan is obviously to transfer the heat from the cores through the copper heatpipes to the aluminum fins in the back, which are cooled by the fan. It just blows my mind that this laptop company (I believe it is the most popular laptop brand at the moment), would cover virtually half of the heatpipes, and virtually all of the aluminum fins, with black paint, an insulator. They could have at least used metallic paint. It would still suck, but it would show that they were trying not to suck.

I've definitely lost faith in laptop companies after this. You know what they say, if you want something done right, you've got to do it yourself.

[nalgas]

Paint? That's just silly. I've seen plenty of bare metal ones and some anodized ones (my motherboard has pretty blue ones), but painting them is ridiculous. Nice way to transfer heat, jackasses.

That said, anything remotely near 90°C is terrifying, not to mention 100. Even 70 is kind of sketchy for a lot of things. Less so for video cards these days, since some of the high end ones seem to be rated for it, but that kind of distresses me when it comes to CPUs and to laptop parts in general (including video cards), considering the lack of space/airflow/cooling in there and how close together everything is. Hooray for drastically shortened component lifetimes.

I think I'll stick to my desktop for games, which idles at room temperature (well, 27/40 CPU/GPU right now, but the air coming out the back is not noticeably warmer than coming in the front) and can't be pushed over 65 even if I try (for the video card; the CPU's usually at least 15° cooler). Yay.

[AirMarshall]

The primary purpose of paint is typically to prevent corrosion. So, for this purpose, it is not unreasonable to paint your heat pipe and sink. Of course the engineering designer must make decision of cost; paint vs. conversion coating (e.g. Alodyne) vs. anodizing; performance of each of those materials both protective and thermodynamically; and marketing considerations.

Paint, if not applied too thickly can aid in heat dissipation in both radiant, and convective (air driven) systems. In a convective system such as this, the paint (color doesn't matter) penetrates into the microscopic crannies and pits of the metal providing a continuous thermal mass for the heat to flow to the surface for convection.

In a radiant heat system, such as used in space craft, the heat sink is painted black with as thin a paint as possible. The black color approximates an ideal 'blackbody" which theoretically radiates energy equally well at all wavelengths.

This information is derived from 'The Sacramento Skyranch Engineering Manual, 1998". If necessary, I can provide sample performance curve graphs of painted vs. unpainted convective heatsink performance.

So, from an engineering perspective it is reasonable to paint the heat pipes and sink. I do not think the paint on the original was keeping it from performing well, nor did removing it from the new sink improve it markedly. I think that you have not performed methodical and complete testing of the two heat sinks.

a.m.

[Cuttlefish]

The primary purpose of paint is typically to prevent corrosion. So, for this purpose, it is not unreasonable to paint your heat pipe and sink. Of course the engineering designer must make decision of cost; paint vs. conversion coating (e.g. Alodyne) vs. anodizing; performance of each of those materials both protective and thermodynamically; and marketing considerations.

Paint, if not applied too thickly can aid in heat dissipation in both radiant, and convective (air driven) systems. In a convective system such as this, the paint (color doesn't matter) penetrates into the microscopic crannies and pits of the metal providing a continuous thermal mass for the heat to flow to the surface for convection.

In a radiant heat system, such as used in space craft, the heat sink is painted black with as thin a paint as possible. The black color approximates an ideal 'blackbody" which theoretically radiates energy equally well at all wavelengths.

This information is derived from 'The Sacramento Skyranch Engineering Manual, 1998". If necessary, I can provide sample performance curve graphs of painted vs. unpainted convective heatsink performance.

So, from an engineering perspective it is reasonable to paint the heat pipes and sink. I do not think the paint on the original was keeping it from performing well, nor did removing it from the new sink improve it markedly. I think that you have not performed methodical and complete testing of the two heat sinks.

a.m.

The main reason I ordered a second heatsink, as opposed to stripping my original one, was because I stripped two screws on the first one, and it was bothering me. I felt that removing it once again would damage the stripped screws beyond any usefulness. This time, no screws were damaged in the process of replacing the heatsink. My decision to strip the paint was made after reading anecdotal reports of others who have reduced their temperatures by doing so.

Your response made me research specific reasons why a heatsink would be painted black. I did find some interesting results, and we are referring to radiation versus convection.

Painting the heatsink black does increase the ability of the heatsink to remove heat by radiation dramatically, but it lowers its ability to remove its heat by convection. The design of my heatsink is ambiguous. If it was going to be a heatsink designed for radiation, then why is it dependent on a fan? The paint on the aluminum heatsink makes it so that it cannot release the heat to the air from the fan easily. Also, the microscopic imperfections in the metal are actually good in the use of a convection-based cooling system: They mean a greater surface area exposed to the air.

If the heatsink was going to be a successful radiation-based cooling system, the fan should probably be scrapped for more aluminum fins, also painted black, to create a larger black body. This is the case with the heatsinks on the back of refrigerators: They are extremely large, as well as black, so that they radiate heat easier.

Even a thin coat of paint will hinder the performance in a convection based cooling system. Paint simply cannot release heat to the air as well as bare metals, namely aluminum, can. You are right though: If paint is to be used, a thin coat is preferred over a thicker one. My laptop's manufacturer released a BIOS update, in response to the high failure rates of the graphics processors in their systems. The BIOS update simply increased the amount of time that the fan would spend at higher RPM's. Increasing the fan speed, in a system based on radiation, would not impact performance very much at all.

It's possible that switching the heatsink/fan itself did the trick, but I believe that the heatsink/fan is more successful as a convection-based, as opposed to a radiation-based, system. The original design of the heatsink/fan, with most of it painted black with a small area of aluminum, appears as if it's trying to be both kinds of systems at once, but being neither well.

EDIT: I overlooked your mentioning of both radiation and convection-based heat transfer. My mistake!