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Best heat sink compound?

Discussion in 'Electronic Repair' started by DaveC, Dec 1, 2003.

  1. DaveC

    DaveC Guest

    White "tooth" paste kind, or clear greasy "hair stuff" kind?
     
  2. Robert Baer

    Robert Baer Guest

    I think the white stuff is better.
    Use a *thin* coat, and move the part around in small circles while
    pressing together, to remove air pockets.
     

  3. Most of the stuff I've seeen recenlty uses neither. They use a piece
    of gray rubbery fabric, which looks like it's pre-cut, with holes etc.
    in it. The T's/FETs/diodes are clamped to it with a springy clamp, so
    that as they heat up, the parts can move somewhat. I like that idea,
    because I've had to replace devices that failed because they were no
    longer making good contact with the heatsink. Some of the worst
    failures were the ones that used nylon screws. Once they get loose,
    the device gets hot and melts the screw, and then it's all over very
    quickly. That's probably why many equipment makers put loktite thread
    sealant on the screws and nuts to prevent the loosening.

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  4. Guy Macon

    Guy Macon Guest

    I would find it easier to believe that it was overhyped crap if
    I wasn't typing this on a quad processor Compaq Proliant that
    has the CPUs runnin 10 degrees C cooler since I replaced the
    OEM heat sink compound.
     
  5. cpemma

    cpemma Guest

    Unless you're on forced-air cooling there isn't a major difference, as the
    junction-package and sink-air thermal resistances are so much more than the
    package-HS figure. Better to make sure the mating surfaces are both flat,
    especially round the mounting holes. I think the white goo creeps less so is
    cleaner long-term than silicone grease, silver types are snake-oil in most
    applications.

    Heatsinks-On Semiconductor AN1040-D:
    https://www.onsemi.com/pub/Collateral/AN1040-D.PDF worth a read
     
  6. Make sure you use all the other over hyped crap so it doesn't get
    lonely.
    --
    24 days!


    Michael A. Terrell
    Central Florida
     
  7. This question is timely for me. I'm about to build my own (first time) and
    have bought an Intel P4 2.4 /heatsink pack. Having researched a fair bit
    before starting the job, I discovered thermal paste. Is it really necessary?
    I don't intend to overclock, so will the thin film already attached to the
    base of the heatsink do the job adequately?
    Miles
     

  8. If there is a thin rubbery film already there on the heatsink surface, then
    you don't need to add anything else, it will work fine. But if the heatsink
    is bare (i.e., a plain metal surface), then it's absolutely necessary to use
    some kind of thermal paste between heatsink and CPU. No matter how smooth
    the surfaces are, there will always be small imperfections and particles
    that will not allow a good thermal path between the two. That's the purpose
    of the paste. But in your case it's not necessary as your heatsink already
    has thermally conductive film on it.

    cheers,
    Costas
    _________________________________________________
    Costas Vlachos Email:
    SPAM-TRAPPED: Please remove "-X-" before replying
     
  9. Asimov

    Asimov Guest

    "DaveC" bravely wrote to "All" (01 Dec 03 00:10:21)
    --- on the heady topic of "Best heat sink compound?"

    Try lard, then when you get that frying bacon smell you know it's too hot!

    Da> From: DaveC <>

    Da> White "tooth" paste kind, or clear greasy "hair stuff" kind?

    .... A couple of volts below threshold.
     
  10. First, if you saw that much difference, then it is *obvious* that
    the initial installation with OEM heat sink compound was flawed.
    10C is *way* too much!

    However, there *are* differences between the different heat sink
    compounds. The question is, what is it worth to have 2 degrees
    lower temperatures? If you have a one shot deal, and the price
    is $10, why not??? That fact that for $6 you can do well enough
    just isn't significant.

    On the other hand, if you might do a dozen or more, it starts adding
    up. Likewise if it ever comes to a question of delaying a project
    until the "good stuff" can be obtained, that might not settle too
    well either.

    The most hilarious part of the whole thing though, is that the
    difference between any of those silver based compounds that you
    pay an arm and a leg for, is too small to be significant in most
    cases compared to what you can find in virtually *any* automotive
    shop.

    NAPA Item# 765-2569
    Copper Anti-Seize Lubriant

    A 4 ounce bottle will last forwever unless you are in the business
    of turning out multiple systems per day.
     
  11. Guy Macon

    Guy Macon Guest

    Point well taken. The OEM heat sink compound was applied at a
    Compaq factory in 1996, and I replaced it in 2003, so age is
    almost certainly a factor.
     
  12. Tim Wescott

    Tim Wescott Guest

    Define "best".

    Do you mean best thermal conductivity? Best price? Best assembled
    equipment cost? Best reliability? Each "best" will get you a different
    answer. As "cpemma" pointed out, unless your thermal goo is the limiting
    factor in your thermal path you're better off going to something easier to
    assemble than the highest thermal conductivity. On the other hand, if
    you're designing a circuit with 100W transistors that have a 1/2 square inch
    thermal contact area, you'd better use the best thermally conductive
    material that you can find.

    The last place I worked either used thermally conductive glue to attach the
    heatsinks to chips or used the heat conductive elastomer (the brand name was
    Sil-Pad, I think). This was done for ease of manufacture, to bring the
    assembled equipment cost down. The only place where we used thermal goo was
    to cool an electromechanical part who's case temperature couldn't exceed 85C
    without internal damage.
     
  13. Tim Wescott

    Tim Wescott Guest

    -- snip --
    According to one of the mechanical designers at my old work, nylon screws
    contract with cold and stretch. Then when it gets warm again they're loose
    (and presumably about to melt). We designed systems for close to the
    military temperature range, so we simply didn't use nylon screws -- usually
    we used thermally conductive glue, or a stainless-steel screw with a nylon
    shoulder washer if necessary.
     
  14. Jim Weir

    Jim Weir Guest

    You will get many answers to this, and as usual, "best" is a function of several
    variables.

    However, if you are out in East Undershirt hicksville some day and just HAVE to
    get the job done, go down to the drugstore and get a small tube of that white
    stuff you rub on your nose in the summertime (zinc oxide). It isn't the BEST
    thermal conductor you can find, but it will do a fine job in most instances.

    BTW, the "thin rubber fiber" that some other folks are talking about are from a
    company called Bergquist if I'm not mistaken. Expensive, but damned good
    thermal conductivity.

    Jim
     
  15. DaveC

    DaveC Guest

    and you recommend this as a head-sink compound for semiconductors?
     
  16. Considering the question, and the large cross-posting, I kind of
    expected a computer newsgroup to be included. And the threads over
    there about heatskink compound can be somewhat amusing. They range
    from "Do I really need heatsink compound" to debate over the brand name
    of the compound.

    It strikes me that it's right up there with the audio consumers
    and gold plated cables and ten dollar capacitors.

    Michael
     
  17. John Larkin

    John Larkin Guest

    The white thermal compound stuff is better. For serious heat sinking,

    both surfaces must be flat; *very* flat. Most extruded heat
    sinks aren't unless they are machined after extrusion.

    don't use an insulator. If you must, use 0.5 mil
    hard anodize on the heat sink.

    *don't* use a silicone sil-pad or phase-change stuff.
    They are both awful thermally.

    Apply high, uniform mounting pressure. Belleville washers
    and clamps are good.

    Make sure the heatsink baseplate is thick enough to spread
    the heat laterally; otherwise there will be a hot spot under
    the device and all this effort is mostly wasted. Use a copper
    heat spreader if needed.

    If this is for a CPU, forget the whole thing.

    John
     
  18. Depends. Low voltage and mechanically attached, yes.

    I use for cpu's, such as the AMD Athlon series that runs so hot.
     
  19. John Larkin

    John Larkin Guest


    The 'thin' rubber films are typically 5-10 mils thick, which is huge
    in this game. They are rotten thermal conductors, even if you believe
    their published specs. They dominate thermal resistance except for the
    wimpiest of heat sinks.

    John


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