Rumor has it that Clumpy and Kloumpios have a Nauga wildlife preserve here
in Iowa to protect them.
Dave
From: "Smith, Rick" <[log in to unmask]>
To: <[log in to unmask]>
Date: 04/15/2013 03:48 PM
Subject: Re: [TN] copper nanosolder
Sent by: TechNet <[log in to unmask]>
The folks in Naugatuck, Ct call the little buggers Nauggie's. They're
trapped along the banks of the Naugatuck River although since the demise
of the Naugatuck Chemical they seem to have become scarce.
-----Original Message-----
From: TechNet [mailto:[log in to unmask]] On Behalf Of Stadem, Richard D.
Sent: Thursday, April 11, 2013 10:18 AM
To: [log in to unmask]
Subject: Re: [TN] copper nanosolder
Yes. They are still used in the manufacture of Naugahide. Nanu wire is
what is used to stitch the hides of the individual naugas together. It is
what gives you that unique nu car smell.
-----Original Message-----
From: TechNet [mailto:[log in to unmask]] On Behalf Of Douglas Pauls
Sent: Thursday, April 11, 2013 8:43 AM
To: [log in to unmask]
Subject: Re: [TN] copper nanosolder
Those were nanu particles.....
Doug Pauls
From: "Whittaker, Dewey (EHCOE)" <[log in to unmask]>
To: <[log in to unmask]>
Date: 04/11/2013 08:30 AM
Subject: Re: [TN] copper nanosolder
Sent by: TechNet <[log in to unmask]>
I thought nano-particles were left over from the "Mork and Mindy" show.
Dewey
-----Original Message-----
From: TechNet [mailto:[log in to unmask]] On Behalf Of Mike Fenner
Sent: Thursday, April 11, 2013 2:29 AM
To: [log in to unmask]
Subject: Re: [TN] copper nanosolder
Well I am more technologist than scientist. I am also a pragmatic
scepticist. In other words you can convince me with numbers but not
unsupported assertions. Numbers need to be actual units, not relative to
something else. Relative numbers is marketing, handy for gaining
attention.
So to me nano-particle science is in the same place as very high frequency
circuitry. In high frequency Ohm's Law goes out of the window. Same with
nanos, the ordinary rules governing physical and chemical behaviour no
longer apply.
So I am prepared to accept very low fusion temperatures for normally high
MP metals, if you give me the data and circumstances under which it
happens.
Now there are silver based products on the market with very low processing
temperatures. Similarly there are products using nano structures whose
chemistry produces rather startling outcomes.
Turning to the claims for the invention, I note 200C is at the extreme low
end of claims, but not incredible.
Doing it in copper would be significant. Not just for joining but in all
sorts of areas.
It's all lab based. Doesn't mean it can be industrialised, but clearly if
it can be then its worth a go.
Somebody somewhere thinks it's worth million dollars punt, so development
is being funded.
OTOH As I said in my earlier post, similar claims have been made in good
faith or for funding, for a long time now. In fact we are well in the
payoff time zone for some. Of course not all R&D succeeds, but the huge
effort going into nano, added layer manufacturing, and other new stuff is
unlikely to be completely misplaced.
I think that one day people will look back at how we do stuff now in large
areas of electronics and manufacturing generally, and regard them in the
same way as we do tubes and point to point wiring.
But that's a marketing forecast :)
Some places it's already starting.
Regards
Mike Fenner
Bonding Services & Products
M: +44 [0] 7810 526 317
T: +44 [0] 1865 522 663
-----Original Message-----
From: TechNet [mailto:[log in to unmask]] On Behalf Of Robert Kondner
Sent: Wednesday, April 10, 2013 9:07 PM
To: [log in to unmask]
Subject: Re: [TN] copper nanosolder
Hi,
How does "Welding" fit into these "Sintering / Melting" processes? I
recall that hot plastic iron can be welded by hitting it together with a
hammer.
And there are friction welds and cold welds.
I guess it is all in the resulting grain structures? When I took a short
welding class the motto was "A Weld is Stronger than the Base Items". Not
sure that is always try but that was how my "Welding" was tested! I
recall I at least passed the class. That was stick welding with a Lincoln
welder in "Farm Shop".
Bob K.
-----Original Message-----
From: TechNet [mailto:[log in to unmask]] On Behalf Of Bob Landman
Sent: Wednesday, April 10, 2013 12:20 PM
To: [log in to unmask]
Subject: Re: [TN] copper nanosolder
(posting on behalf of Gordon Davy)
Bob, Denny, or Mike, since you're subscribed to TechNet, feel free to
post this reaction to Zinn's abstract (and bio). Perhaps if he sees it,
he'll be able to respond before his June 12 presentation.
Gordon Davy
Peoria, AZ
I don't want to deprecate Zinn's work. Learning how to make copper
nanoparticles and keep them from oxidizing or agglomerating is difficult.
But I am concerned with his claim that reducing the copper particle size
reduces the melting temperature to 200°C. It is true that surface atoms
are not as tightly bonded to their neighbors as bulk atoms, so reducing a
substance's particle size, by increasing the surface-to-volume ratio,
does reduce the melting temperature somewhat below the bulk value. That
is the basis of sintering, which occurs below the bulk melting
temperature.
Presumably, if the particles were small enough, no atom would have the
full number of nearest neighbors - it would be all "surface." But the
melting temperature for bulk copper is just short of 1100°C. That's a
stretch!
The particles of copper in powders sold for sintering are mostly smaller
than 44 µm (-325 mesh). The process requires compacting the powder (plus
lubricant) at 4,000 to 8,000 atmospheres pressure, then and heating at
750-900°C for 5-7 minutes (see copper-powders.com).
Dr. Zinn's copper is in the form of "nano-particles," so they are
presumably smaller than 1 µm. One can contemplate whether that roughly
1½ to 2 orders of magnitude size reduction is sufficient to account for
the differences between the above conditions necessary for sintering and
for conventional reflow soldering. A differential thermal analysis curve
would support the claim that, with or without compaction, his nano-copper
"solder" melts at 200°C.
Consider this analysis taken from everyday observation. When snowflakes,
which may have nano-scale features, fall and land, they sometimes sinter,
and sometimes (when temperatures remain below about -15°C) they do not.
People refer to that latter kind, once it has landed, as "powder" snow.
Similarly, one cannot skate on very cold ice because the surface lacks
the "liquid-like" layer to lubricate the blade. (Pressure melting is a
minor
factor.)
So if dropping the temperature of ice by fifteen degrees below its
melting temperature prevents sintering and skating, is it likely that
copper sintering will occur at a temperature nearly nine hundred degrees
below its melting temperature? As for melting, even if individual
particles were to melt at such a low temperature and join to form a
liquid, what would prevent the liquid, now with dimensions measuring from
micrometers to millimeters, from instantly freezing?
More likely, the copper particles dissolve into the tin or tin-lead
plating on the board lands and component terminations (to form bronze, if
the reaction goes to completion). Even if the nanoparticles are not
melting or sintering, it's a clever idea, but we need to know:
* How well these bronze connections, presumably far stiffer than those
of
a tin-based solder, survive temperature cycling. * The
microstructure,
so we can understand the attachment mechanism. * The width of the
process
window. * Whether the adequacy of the attachment can be judged by its
appearance, and if so, by what criteria. * Whether using Zinn's
solder
at 200°C gives benefits large enough to warrant replacing Pb-free
reflow
soldering (peak local temperature up to 260°C by convection, lower by
condensation). (For those still using SnPb solder, the conditions don't
seem different enough to warrant consideration.) * Whether Zinn has
tried
his "solder" with non-tin land finishes such as immersion silver, ENIG,
and ENEPIG, and NiPdAu termination finish. Since I suspect that the
colloidal copper does not melt or sinter at 200°C, I suspect that
it is not going to perform with Ag or Pd nearly as nicely as with
near-molten Sn, and its reaction with Ni would be even worse.
* If it doesn't make reliable bonds with all the finishes likely
to
be present on an assembly, then it is not a "drop-in replacement"
for solder. (Yes, the designer can specify a compatible finish for the
lands of the board he designs, but not the termination finish of the
components he chooses. He can specify, say, immersion tin instead of
ENIG, but must accept NiPdAu on some components.) * Maybe Zinn can add
enough nanoparticle Sn to the formula to provide the necessary
wetting
to Pd without increasing the reflow temperature and without
introducing
a risk of whiskers from the solder itself. * The risk of short
circuits due to whiskers growing SAC solder appears to be low, from
SnPb solder even lower, and with Zinn's solder it may be zero. But
regardless of the solder used, the overall risk for an assembly
remains
high due to portions of Pb-free Sn termination finish that don't get
solder-coated.
Here are two other ways of dealing with the risk of tin whiskers:
1. Mitigation - speculative For assemblies for which Pb is permitted,
if components with a Pb-free Sn tin finish were dipped in SnPb solder
paste (or perhaps a paste of colloidal Sn and Pb) and heated (before or
during assembly soldering), all of the original finish might be covered
with a layer of SnPb, and the assembly would then have a low risk of
short circuits due to tin whiskers. The paste also might bridge.
2. Prevention - reduced to practice After attaching components by
conventional SnPb or SAC soldering, a thin layer of a
whisker-impenetrable metal such as nickel can be applied to the solder
and the remaining
(uncoated) Pb-free Sn finish by electroless deposition. The process
requires immersing the entire assembly in the bath for a minute or two.
But because electroless deposition occurs only on conducting surfaces,
insulating surfaces remain uncoated, and the performance of the assembly
is unaffected. (Full disclosure: Bob, Denny, and I are the named inventors
on a patent application for this process - see www.ldfcoatings.com.)
A few additional observations:
* Note the irony, given the meaning of Zinn in his mother tongue, of
him developing a tin-free solder. * Note the nine-year gap (between
1995 and 2004) in his bio. * The claim of "10-15x electrical and
thermal conductivity improvements" is irrelevant: what counts is
overall
conductance, and the reduction in a connection's conductance due to use
of conventional solder (compared to copper) is insignificant. * A
substance's melting temperature is a thermodynamic property. Some might
regard the reduction in the melting temperature of colloidal copper as
"significant" or even "dramatic." But it is not "rapid" (a term that
implies a kinetic effect).
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