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Heatsink Insulators?

Discussion in 'Electronic Design' started by Tim Williams, Sep 1, 2006.

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  1. Tim Williams

    Tim Williams Guest

    Didn't spot wide insulators on digikey, anyone have a source?

    I need to insulate some heat spreaders from under 1kV, which should be no
    problem. I want to dissipate up to 200W through a 1.5 x 3" spot with
    minimal heat (~20C temp rise?).

    Tim
     
  2. Eeyore

    Eeyore Guest

    Alumina ?

    Graham
     
  3. Well, for the time being, a layer of self adhesive
    tape would do.

    Rene
     
  4. John  Larkin

    John Larkin Guest

    AlN.

    John
     
  5. Tim Williams

    Tim Williams Guest

    If thin enough, and wide enough, and cheap enough, and drillable enough.

    I seem to recall a post that noted the usual thickness of AlN almost
    outweighs the conductivity.

    Tim
     
  6. John  Larkin

    John Larkin Guest

    Depends on how thick. The OP specified a kilovolt, so some thickness
    is reasonable. AlN conducts heat something like 10x as well as
    alumina, and is close to BeO.

    John
     
  7. Guest

    When I need something like that I consider bringing out my 100 ft. roll
    of mica tape.

    greg
     
  8. Genome

    Genome Guest

    If you only want to insulate some..... then fone up Mrs Berquist and ask
    them for a sample of of their whatever does the job..... Ummm ST-1500.

    Tell them that Genome suggested that they should produce some sheets of just
    less than magazine size for people just like ourselves and have an ordering
    system with a selection of 'quality' magazines to slip the sample in before
    putting it in the brown paper envelope for $15 delivered.

    The wife/boyfreud will think your journey down the garden shed has nothing
    at all to do with mounting high powered semiconductors on metallic things.
    Ooooooh,I feel quite dizzy.

    DNA
    DNA
     
  9. Don Foreman

    Don Foreman Guest

    Check out
    http://www.bergquistcompany.com/objects/Thermal_Materials/Sil_Pad/Sil_Pad_Tables/SPComparison2.pdf

    With an .008" thick Sil-Pad you'd need thermal conductivity of 0.7
    watt/m*K. All of these materials are better than that.
     
  10. Friendian slip?
     
  11. John Larkin

    John Larkin Guest


    That stuff is thermally crap. If you compress it a couple of hundred
    PSI, it might get close to half the thermal conductivity they claim,
    and even that's not all that good.

    John
     
  12. Genome

    Genome Guest

    I think they claim it gets down to thrumble blob at 50PSI according to
    ASTM5570 as defined by them because they have a machine that does it.

    Are you saying they are a lying bunch of fuckers?

    DNA
     
  13. Don Foreman

    Don Foreman Guest

    You've measured it?
     
  14. John  Larkin

    John Larkin Guest

    Yes. I've never seen a sil-pad conduct heat anywhere close to the
    advertized value.

    John
     
  15. Don Foreman

    Don Foreman Guest

    OK. I have no data or relevant experience to refute your assertion,
    but I'm still inclined to believe that they can and do deliver
    performance they advertise. They've been around quite a while.

    I'd be inclined to bet that I could demonstrate their claimed
    performance in my lab to within 20% or better. YMMV.
     
  16. John  Larkin

    John Larkin Guest

    If you've got a 7805 that's dissipating a couple of watts, they're
    fine. But if you are pushing semiconductors hard, which you have to do
    to get real performance, sil-pads are going to be a major roadblock.

    And I doubt the 20% claim. This thermal stuff is notoriously difficult
    to get repeatable measurements from. Just check a few references for
    the thermal conductivities of various materials: you'll see numbers
    all over the place.

    John
     
  17. Don Foreman

    Don Foreman Guest

    I don't have any trouble getting repeatable thermal measurements, but
    I don't have any Sil-pad material to play with. I usually use mica,
    seems to work OK. But then, I never push semiconductors very hard.
    Don't have to -- I'm not designing to cost or for production anymore.
    Example: dirt-simple 600-watt PWM voltage reducer for a boatlift
    motor

    http://users.goldengate.net/~dforeman/PWM_50/
     
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