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HS Cu/Alu question

  1. Feb 20, 2004 #1
    Hi all
    This is an uncertanty that has been flooding the nett for a long time.

    Heatsink (HS) made of Aluminimum verses Copper.
    Which material gives you the overall best performance?
    A detailed explanation would be appriciated.
     
  2. jcsd
  3. Feb 20, 2004 #2

    Integral

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    There is so much more involved in a heatsink, then simply the material used, that your question is impossible to answer.

    A well designed heatsink will do a better job then a poorly designed heatsink. The real question is, "How much are you willing to pay?".
     
  4. Feb 21, 2004 #3
    Let us keep things simple and asume that the design of the HS is the same.
     
  5. Feb 21, 2004 #4

    Integral

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    Can't do that.

    The material properties of Al and Cu are very different. It is nearly impossible to work Cu to create the thin fins that you commonly see on Al heat sinks.

    Again how much do you want to spend.
     
  6. Feb 21, 2004 #5
    This is a THEORETICAL question
     
  7. Feb 21, 2004 #6

    Integral

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    I disagree, it is a very real question. If you over simplify it the answer is meaningless. It is a very hard question to answer because of the many factors that enter into the proper design of a heat sink. It may well be that the optimal Cu heat sink will look different form an optimal Al heat sink. So what does it mean to compare the same design? You will only be comparing the abilities of those metals for that design, still no answer to the raging question. Which is the best material for heat sinks.


    Actually I think "theoretically" diamond would be a wonderful heat sink material, why did you not include that in your question?
     
  8. Feb 21, 2004 #7
    Hmmhmm
    I would like to remind you that it is I that is asking the question not you.
    I have no intention of bying a new HS.

    It is apparent to me the way you answering that you have no idea at all what you are talking about.

    This is related to thermaldynamics and can be explained using the laws of thermaldynamics.
     
  9. Feb 21, 2004 #8
    keeping things simple

    Assuming that Al and Cu are equally machinable and you don't have to worry about the materials melting temperature, then the one with the higher thermal conductivity ought to take heat out of the system faster, as you'll get more convection out of the fin and into the air and conduction through the fin itself. I'm assuming both Al and Cu have the same radiation characteristics (both emit poorly in the visible but good everywhere else - actually you only have to verify that they're good absorbers at the wavelength a blackbody at the same temperature would emit the most).

    As for diamond, that has the highest thermal conductivity that I know of, but the thing will turn to graphite at elevated temperatures. Actually the thing will combust first. Maybe diamond is used in microchips where the heat isn't all that tremendous.
     
  10. Feb 21, 2004 #9
    Re: keeping things simple

    If I understand you correctly you are saying that the material with the highest thermal conductivity measured in W/m2K (Watt per squaremeter Kelvin) is the best material to use?
     
  11. Feb 21, 2004 #10

    Integral

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    Both thermal conductivity and emissivity of Cu are higher. The emissivity, which is a measure of how the material transfers heat from the surface, may be even more important then the Thermal conductivity. So Cu has great properties, but as I said above there is more to problem then simply material properties. If the question was that easy then there would be no discussion. Clearly there is much discussion over this topic, put nowhere will you find a definite answer. That is the point I have been trying to bring home to you.

    2 things bite you, the expense of Cu and its poor machine-ability as well as difficulties casting it. Unfortunately as I mentioned above, CU is not as machinable as AL. (Do I have to show the chips I have made in the past to prove my knowledge!) Having attempted to machine Cu and having machined and cast lots of AL, I do have some experience at this level. While Cu is castable, the temps required are much higher thus requiring more capable furnaces and perhaps an inert atmosphere. Al is very easy to cast, it has a low melting point and wonderful fluid properties, this is why you see some many Al products.

    The amount of energy required to cool a CPU are still low enough that completely adequate heat sinks can easily and cheaply be made from AL, the extra cost involved in Cu, both material and fabrication, to not result is sufficient improved performance to be warranted.

    One thing you need to learn in life, often, the more eager someone is to claim absolute knowledge, the more likely it is, that they have no clue what they are talking about.
     
  12. Feb 21, 2004 #11

    Integral

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    So you are saying that a CPU in NOT a microchip??? What is it?
     
  13. Feb 22, 2004 #12
    I posted before you said that Al was sufficient for CPUs.

    By microchips I mean computer circuitry. Ignoring the economic and engineering problems, the physical problem I see with diamond is its combustibility. I was thinking that with just 1 diamond you could make a lot of tiny fins to cool computer circuitry.
     
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