TECHNET Archives

April 2013

TechNet@IPC.ORG

Options: Use Monospaced Font
Show Text Part by Default
Show All Mail Headers

Message: [<< First] [< Prev] [Next >] [Last >>]
Topic: [<< First] [< Prev] [Next >] [Last >>]
Author: [<< First] [< Prev] [Next >] [Last >>]

Print Reply
Subject:
From:
"Whittaker, Dewey (EHCOE)" <[log in to unmask]>
Reply To:
TechNet E-Mail Forum <[log in to unmask]>, Whittaker, Dewey (EHCOE)
Date:
Thu, 11 Apr 2013 13:29:07 +0000
Content-Type:
text/plain
Parts/Attachments:
text/plain (141 lines)
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).

______________________________________________________________________
This email has been scanned by the Symantec Email Security.cloud service.
For more information please contact helpdesk at x2960 or [log in to unmask] ______________________________________________________________________

______________________________________________________________________
This email has been scanned by the Symantec Email Security.cloud service.
For more information please contact helpdesk at x2960 or [log in to unmask] ______________________________________________________________________


______________________________________________________________________
This email has been scanned by the Symantec Email Security.cloud service.
For more information please contact helpdesk at x2960 or [log in to unmask] 
______________________________________________________________________

______________________________________________________________________
This email has been scanned by the Symantec Email Security.cloud service.
For more information please contact helpdesk at x2960 or [log in to unmask] 
______________________________________________________________________

ATOM RSS1 RSS2