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Purity of PCB plated copper??

Discussion in 'Electronic Design' started by Spehro Pefhany, Jul 16, 2012.

  1. Anyone have a number, in terms of RRR, for the plated copper purity?

    TIA.
     
  2. Tim Williams

    Tim Williams Guest

    I've never even heard of RRR. It appears to be,
    http://en.wikipedia.org/wiki/Residual-resistance_ratio

    Offhand, plated copper is likely to be >99.9%, with oxygen and hydrogen
    being major impurities (one could guess at metal impurities, like Sn or
    Pb?). This chart shows the difference per %at impurity, which is NOT in
    terms of RRR.
    http://www.copper.org/resources/properties/cryogenic/images/Residual-Resistivity-of-Impurities.gif
    Assuming the ratio (delta rho_293K) / (rho_293K) is relatively independent
    of temperature, if divided by rho_293K, these numbers should be relatively
    representative of RRR change per %at. Copper is rho = 1.545 (x 10^-8 ohm.m,
    same units and exponent), so that the maximum effect of 0.1% should be
    around 1 RRR for titanium, and less for others. (Now, is that in RRR
    points, or RRRR (RRR ratio)? Arrr!)

    Tim
     
  3. m II

    m II Guest


    99 44/100 percent pure.

    No..wait...that's something else...


    mike

















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  4. Tim Williams

    Tim Williams Guest

    This has some lower temp values,
    http://hypertextbook.com/facts/2004/BridgetRitter.shtml

    Evidently, RRR(Cu) ~ 1.712 / 0.002 = 856, presumably for research purity Cu
    (>4N???).

    Tim

    --
    Deep Friar: a very philosophical monk.
    Website: http://webpages.charter.net/dawill/tmoranwms

    No idea, could you stick a piece in LN2 and get some measure?
    (There's a graph for Al in White's Low Temp Phyiscs text... I'm
    trying to remember where I saw one for copper. Kittel?)

    Isn't it likely to change for different sources?

    George H.
     
  5. I'm guessing the number is going to be less than 100. For ordinary
    drawn copper wire it's apparently about 50, and I don't expect plated
    copper will be better than that. It gets up into the tens of thousands
    for really pure metal.


    Best regards,
    Spehro Pefhany
     
  6. Copper _never_ goes superconducting, interestingly. Lots of elements
    do, but not Cu, Au or Ag. Aluminum does weird stuff.
    Sort of. As I think of it, a superconductor has infinite conductivity,
    so you can't get halfway there.
    Interesting idea. Skin effect starts to become important at much lower
    frequencies.


    Best regards,
    Spehro Pefhany
     
  7. Tim Williams

    Tim Williams Guest

    Yes, nonzero, not superconducting -- which will generate interesting side
    effects, like very long L/R time constants, with no Meissner effect.
    Well, 98% *from* copper... Obviously, infinite % from zero! :)
    That too!

    Tim
     
  8. Bret Cannon

    Bret Cannon Guest

    "Spehro Pefhany" wrote in message

    I'm guessing the number is going to be less than 100. For ordinary
    drawn copper wire it's apparently about 50, and I don't expect plated
    copper will be better than that. It gets up into the tens of thousands
    for really pure metal.


    Best regards,
    Spehro Pefhany
    --
    "it's the network..." "The Journey is the reward"
    Info for manufacturers: http://www.trexon.com
    Embedded software/hardware/analog Info for designers: http://www.speff.com

    Electro-depositing copper can produce very high levels of purification.
    Physicists doing very low background counting experiments, for example
    looking for double beta decay in the Homestake gold mine 5000 ft below
    ground make the Dewars to hold high purity germanium crystals using
    electrodeposition of copper. Even starting with technical grade copper
    sulfate, the electroplated copper had orders of magnitude less radioactive
    impurities than most other materials.

    Bret Cannon
     
  9. Isn't the copper that wire is drawn from "electrolytic"?


    Best regards,
    Spehro Pefhany
     
  10. Mike

    Mike Guest

    The result depends on the level on contaminants in the copper anode and
    the electrolyte.

    Electrolytic refining can improve the purity by several orders of
    magnitude, but it is not perfect. A small percentage of contaminants will
    still pass through the process. However, you can use multiple stages
    where the purity increases in each stage.

    Regards

    Mike
     
  11. I just tried it with a really strong magnet and a big copper bus bar
    at room temperature- a noticably softer landing, but a long way from
    levitating.
     
  12. It is VERY pure.

    Cincinnati Milacron made the original machines that 4 x 8 foot sheets
    of single and double sided PCBs were made from way back in the sixties.

    Layers are pretty thin now, but the cladding steps are probably quite
    similar.

    I'd say the purity is very high.

    The thing is though... many folks nowadays are using gold boards and
    copper is no longer a factor to any degree like it was.

    The RoHS ushered in platings that will hold up in the high heat
    environments and still wet well. Copper isn't on the list. At least not
    in pure form. I'm sure there are plating alloys that get used.
     
  13. josephkk

    josephkk Guest

    Not perzactly. Lookup drawn wire to learn why.

    ?-)
     
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