I had recently received my new Raspberry Pi in the mail from Newark/Element 14, and like many others, I immediately downloaded Raspbmc and tried out XBMC on the RasPi. Also, like others, I have found that the RasPi can get a little toasty. While this shouldn't be too much of a problem on its own, if it were to be confined in an enclosure, or used in a car, or any other heat intensive application, problems can occur. Since I don't like to waste money, the Raspberry Pi is impossible to get, and I love a good project, I decided it was due time to do something about this heat issue.
Author Remy from Geektopia used a thermal camera in order to measure the heat output of the RasPi under several conditions(The full, translated article can be read here). In the Image below, it can be seen that there are three major heat sources: The SoC(center), the USB/Ethernet controller(right), and the voltage regulator(left).
As you can see in this photo, the average temperature for the SoC while streaming video over network is about 56.1 degrees C. Not melting hot, but hot enough to cause some concern for me. I went digging around in my parts shelves, and grabbed an old aluminum heatsink. I believe it was a chipset heatsink off an old Pentium IV based Dell box.
Luckily, it happened to be just short enough that the overall height of the RasPi is about the same. Using a digital caliper, I measured the three chips I will be covering. The SoC is 12 x 12 mm, the USB/Ethernet chip is 8.6 x 8.6 mm, and the voltage regulator is 6.5 x 5.5 mm.
Using this, I measured out on the heatsink for each chip, rounding up to the next closest fin. Using a band saw, each piece was cut, and sanded down to size.
After getting them down to the right size, I used some thermal compound to attach them to each of the chips.
Now I have heard on the internet about using a common adhesive such as JB weld, and while silver thermal compound is about 12 times better for heat transfer, but in reality, with such a small amount of heat dissipation, the difference in temperatures will be negligible although both the JB weld and thermal compound are magnitudes better than just plain contact(air gaps, even the smallest ones, are excellent insulators). It just depends on whether or not you would want these heatsinks to be removable without destroying the RasPi.
Lastly, it is time for a test. I fired up the RasPi and XBMC, and started streaming a 1080p movie from a Samba share. I took temperature readings a half hour into the movie to test performance.
As seen above, the infrared thermometer shows a temperature of 38.8 degrees Celcius. That's a difference of 17.3 degrees from the average temperature during network video playback! That much improvement will go a long way towards overall system efficiency and stability. Further implementation can be done with a 5v low profile brushless fan that came from a dead netbook. The fan could be powered directly from the GPIO pins. If it is possible to read core temperature with the SoC, then it could even be possible to utilize the GPIO with the fan in order to have the fan be intelligently controlled based on the SoC temperature, all with a simple python script.