Purity of PCB plated copper??

[Spehro Pefhany]

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

TIA.

 

[Tim Williams]

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

 

[m II]

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

99 44/100 percent pure.

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


mike

















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[Tim Williams]

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

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

TIA.

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.

 

[Spehro Pefhany]

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

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

 

[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?).

Copper _never_ goes superconducting, interestingly. Lots of elements
do, but not Cu, Au or Ag. Aluminum does weird stuff.

Heck, even if regular stuff is about 50, that's only 98% of the way to a
superconductor.

Sort of. As I think of it, a superconductor has infinite conductivity,
so you can't get halfway there.

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

Interesting idea. Skin effect starts to become important at much lower
frequencies.


Best regards,
Spehro Pefhany

 

[Tim Williams]

Copper _never_ goes superconducting, interestingly. Lots of elements
do, but not Cu, Au or Ag. Aluminum does weird stuff.

Yes, nonzero, not superconducting -- which will generate interesting side
effects, like very long L/R time constants, with no Meissner effect.

Sort of. As I think of it, a superconductor has infinite conductivity,
so you can't get halfway there.

Well, 98% *from* copper... Obviously, infinite % from zero!

Interesting idea. Skin effect starts to become important at much lower
frequencies.

That too!

Tim

 

[Bret Cannon]

"Spehro Pefhany" wrote in message

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

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"
[email protected] 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

 

[Spehro Pefhany]

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

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


Best regards,
Spehro Pefhany

 

[Mike]

On Tue, 17 Jul 2012 22:27:58 -0700, the renowned "Bret Cannon"

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

Best regards,
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

 

[Spehro Pefhany]

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.

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.

 

[Chieftain of the Carpet Crawlers]

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

TIA.

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.

 

[josephkk]

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


Best regards,
Spehro Pefhany

Not perzactly. Lookup drawn wire to learn why.

?-)