Purity of PCB plated copper??

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

TIA.

Reply to
Spehro Pefhany
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I've never even heard of RRR. It appears to be,

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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.

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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

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Reply to
Tim Williams

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99 44/100 percent pure.

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

mike

Reply to
m II

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.

Reply to
George Herold

This has some lower temp values,

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

Tim

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Reply to
Tim Williams

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

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Reply to
Spehro Pefhany

Fascinating. Regular copper at room temperature is already pretty conductive. It must be scary at ~absolute zero, especially when very pure (and, I might guess, single crystal as well?).

Heck, even if regular stuff is about 50, that's only 98% of the way to a superconductor. If a bar of copper at STP can hold a magnet with a ~seconds time constant, really cold, pure copper must do a pretty good magnetic levitation trick all its own!

Tim

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Reply to
Tim Williams

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

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Reply to
Spehro Pefhany

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

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Reply to
Tim Williams

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

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Reply to
Bret Cannon

Isn't the copper that wire is drawn from "electrolytic"?

Best regards, Spehro Pefhany

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Reply to
Spehro Pefhany

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

Reply to
Mike

ure

conds

I think I saw a plot where really pure aluminum had a resistivity lower than copper at LN2 temperatures. So a neat demo is to drop a magnetic onto a plate of aluminum in a LN2 bath. A nice soft landing!

George H.

ity

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Reply to
George Herold

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.

Reply to
Spehro Pefhany

ure

a

conds

Oh you can't levitate it. But it's similar to a demo where you drop a magnet down a copper tube. It'd be 'cool' to get the tube at 77K and see the difference. Trying to get an idea of the optimal thickness (skin depth) and rate of change in the B field gives me a brain ache.

(According to the tables in the back of White's book, Al and Cu have about the same resistivity at 77K... so my above statement appears to be wrong.)

George H.

Reply to
George Herold

I've used conductivity at 80% of pure and been close to measurements.

Don't know if that is from purity, or porosity.

Reply to
Robert Macy

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.

Reply to
Chieftain of the Carpet Crawlers

=20

=20

radioactive=20

Not perzactly. Lookup drawn wire to learn why.

?-)

Reply to
josephkk

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