CPU As A Heat Sink

We’ve noticed that wireless routers pump out a bunch of heat. [Jernej Kranjec] wanted to make sure that he didn’t fry it once he started adding more load to his router using OpenWRT. What he came up with is the idea of using an old CPU as a passive heat sink. He applied a bit of thermal paste to the center and some super glue to the corners. You can see the finished product is an old AMD chip adhered “dead bug” style to the stock processor. We’d bet it’s not very efficient compared to an aluminum or copper heat sink, but it normally would have no help in shedding those extra degrees.

51 thoughts on “CPU As A Heat Sink

  1. @????
    Well it is hardly the CPU’s intended purpouse. Not only that its a modification of the router also. While it may be dead simple. Even obvious for some. It is stil a hack in my opinion.

    Some of the best innovations are the simplist of innovations.

  2. I don’t think this is a good idea. In fact, it’s not out of the question that this could make the die temperature of the chip he’s trying to cool even hotter.

    I think you’d be better off using an equally-sized square of aluminum.

  3. Might as well just bolt a chunk of glass to the top of the CPU, I don’t see how this is a hack in any way, sense or form. I’ve often used random cutlery to cool sink-less CPUs temporarily, I’d not consider it a hack though!

  4. DSL modems make hell of a more heat especially those cheap dlink craps what isps love to use. How about make haxx for those.
    Got a WRT54G and it hardly makes any heat.

  5. Why didn’t he check if the temperature was actually lower after the “hack”? I don’t think this concept will do much good, and it certainly restricts the airflow inside the box even more.

  6. “We’d bet it’s not very efficient compared to an aluminum or copper heat sink”.

    well said. having designed various “boxes”.
    total thermal dissipation of the devices is
    a significant concern. i’m willing to wager
    that router was designed for x watts of heat
    dissipation (within it’s design constraints).

    like OC’ing a CPU, you need additional ways
    to cool down the box. it would be interesting
    to get quantitative values using an IR non
    contact thermometer before & after the mod,
    and before/after the OpenWRT ‘upgrade’.

    probably a better idea, or perhaps adjunct
    add on mod, would be a small high flow cooling
    fan (of the types seen in blade servers).

    but acquiring actual empirical thermal data
    would probably be a more prudent course of

    i tend to agree with the other poster suggesting
    it may actually cause a temperature rise (vs.
    cooling). since now you have to heat up the mass
    of that old CPU. what does that leave you ? a
    bigger heat radiator !

    ehh, whatever. not my box.

  7. Would be really surprised if this helped the temperature of the processor in the slightest. Like the other commenters, I have a feeling this might even increase temperature slightly, since now there isn’t even air moving around the chip itself.

    I guess his logic was that the pins of the chip would act like the vanes on a regular heatsink, but that just doesn’t make a whole lot of sense in thermal terms. The pins are obviously insulated from each other, and their connection to the die itself is not going to move much heat energy.

    Popping a few more holes in the case and putting in a small fan would have been a lot more effective.

  8. Actually, letting it run hot would make it last longer. It makes the hot carriers less hot by comparison. The think stays on so much that repeated heating and cooling is a non-issue.

    Another think which will shorten the life is just the use, but a heatsink won’t make OpenWRT smash the chip less.

    The only real reason to cool a chip is if it really is too hot, or you’re trying to squeeze more Hz from it. So no, every few C does not count.

  9. Or maybe they posted this to inspire discussion. I hadn’t considered opening up my router and installing a heatsink before but now that you mention it, my linksys does get pretty warm…

  10. dont you get it?
    HAD is full of a bunch of trolls, why do you think they keep posting every turd that comes out the ardruino butt?
    or a ps1 running microsoft windows 94
    holy crap, i just realised the psx is like 15 years old

  11. I agree that an old CPU probably isn’t the best thermal conductor, but the most difficult step is the transfer from the heat-sink to the air.
    Metal pins turn out to be the best way to do this (but expensive to fabricate). The pins leave a lot of space for the air to move around, while causing the most turbulence which increases air-speed very close to the surface of the pins.

  12. @Thesarte

    AMD had 486 processors too you know.

    Not to mention that could be a Cyrix MediaGX for all you know, I have one of those too. Come to think of it I may have a Cyrix Samuel II somewhere around here.

    Check the link before you spread rumors:

    Shame it is only the DX2-66, I have the DX4-100 (although it could be argued that the 25mhz system bus holds it back compared to the 33mhz DX2 bus speed in some cases).

  13. This is my Netgeart shitty router, but I added a simple GPU heatsink (I think its GPU? The on-board at least on older Motherboards)

    Anywho, I pasted that over the Original Broadcom cpu and added a small 12v Fan over the heat sink and it works amazingly well!

    :) I did this like a few years ago and it still holds up to this day ;o


    yea the cutting is a little messy >_>

  14. Do you guys EVER proofread? I know this is a hacking website, but it seems like you guys just throw some junk together and hope we wont notice. Don’t you guys get payed for this???

    I’m not claiming to be an English professor, but step your game up.

  15. @moo,

    I can’t remember the version of mine but it does get relatively hot. I know some Net Gear routers have been using the same case in other models. So to say you have the same one I do is not really relevant because they could be completely different models.

    How ever, I added it because yes it does get hot and the place I had it in wasn’t the best for a router, all in all it worked out good.

  16. the plastic on top of the “heatsink” chip is probably insulating preventing heat transfer, if he could de-capsulate the dead cpu and then attach it might work pretty good.

  17. It seems some people need brush-up on their thermodynamics theory. Couple of notes:

    1. When a greater mass is heated, it means the mass stays cooler longer, but it also retains heat longer when the external heat source is removed. That does not imply the mass will have a hotter operating temperature, that entirely depends on the nature of the surface area which is in contact with the air. In short, doesn’t matter what you use as a heat sink (provided you can transfer heat adequately); greater mass == more work to heat it up.

    2. CPU packages are designed to be fairly efficient in drawing heat away from the substrate onto the outer case, onto the pins, and also the metal plate which dumps heat onto a heat sink. The reverse is also true when the heat source is applied externally on the CPU case.

    3. Ceramic materials can be good heat conductors. Not as good as pure copper, but infinitely better than many insulators. It’s one of the reasons why they were used in early CPU packages and why you see them in high power electronics.

  18. thats brilliant! who’d have thought that a cpu would make a good heatsink?

    this gives me an idea, grow some copper “pipes” on a piece of scrap copperclad pcb with holes in the resist (spin coating resist if unavailable) then peel off the copper using applied heat :)

    ought to work and has the added bonus of being flexible and easily glued to a surface.

    might take longer but should work as well if not better than this technique with the added bonus of occupying a larger surface area.

  19. hmmmm…. still alot of argueing here lol … i still say if it needs to be cooled let the AC do it lol .. someday i might post pics but i fear they wil end up with a similar fate .. FAIL .. posted repetedly by people who have never tryd it to see if it actualy works

  20. Here’s a thought: Go find an old CPU that you don’t plan to use again and touch the bottom of the pins. Did they feel colder than the rest of the processor {hint, they should}? I just did this and I still say you’re better off getting a real heatsink but this proves that this hack isn’t completely pointless.

    And I think it looks a lot better than pennies and scrap aluminum.

  21. I have to agree, this is the opposite of cool or effective.

    Judging by the way most folks glop on the heat sink compound nowadays it’s probably double insulated now.

    Seriously, a piece of scrap metal would at least be…metal.

  22. id imagine the die, even though its ceramic, is probably pretty good at conducting heat. I bet they dope it with something to carry heat away better. Id be skeptical about exactly how well the cpu die is transmitting the heat onto the pins. Why not just thermal glue (jb weld mixed with aluminum or copper powder works hella good) an upside down bottle cap too it and throw a small fan anywhere in the case so atleast the air is less stagnant.

  23. Why not just bolt on a small cooling fan that steals power from the AC/DC adapter to the outside/inside of the router? I’m sure that would give enough cooling, better than superglue and an old processor. At least use thermal epoxy……

  24. i like the idea of sticking things in the freezer and running them off the light. you know you need to get a network cable in there though, so you are going to need a drill and some sprayfoam anyway, why not run in the power while you’re at it? although running off the light bulb would only require that you clip off the little peg that switches the light off when the door is closed. i could see someone now,using a big ol’ deep freezer as a computer desk, wires for usb and display coming out, phone line coming in, maybe a wireless antenna or two coming out as well, and using external drives.. except there is no leg room under the deep freeze.
    anyway, i have plenty of old aluminum heatsinks from cpus from around 550mhz down to 33mhz. i could friggin send you one lol.
    i also have a couple old laptops 166 and 133mhz someone might want to hack..
    if i did this hack, it would probably have consisted of: thin glass of water, arctic silver, dremel, caulk/silicone. lol

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