Well maybe because it has slipped through the fuzzy zone into metallurgy?

 

Regards 

 

 <blocked::http://www.linkedin.com/pub/mike-fenner/0/b3a/421> Mike Fenner 

Bonding Services & Products
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From: Inge Hernefjord [mailto:[log in to unmask]] 
Sent: Wednesday, May 29, 2013 4:51 PM
To: Mike Fenner
Cc: TechNet E-Mail Forum
Subject: Re: [TN] Gold Removal

 

Mike,

 

I admire your patience. I absolutely agree with all that you say, classical
school stuff. I still can't see why gold should appear as molecules in a
metal interdiffusion process. I have read lots of reports about gold
migration and diffusion in gold plated semiconductors,  like MESFET, HBT.
Written by TI or NG or others, and gold is never mentioned as molecules in
the mentioned processes. Well, I stop here, let's leave the topic, I risc
fool myself.

Inge

 

On 29 May 2013 13:27, Mike Fenner <[log in to unmask]> wrote:

Inge
Try it this way
A molecule is the smallest chemically stable form a substance can exist in.
The term is usually used to mean combinations of different elements but can
also be used to describe for example an oxygen molecule which is just a pair
of oxygen atoms. A single oxygen atom is not chemically stable and will
react with anything handy if it can, or pair up with another oxygen atom if
it can't. Oxygen is diatomic.
Neon on the other hand doesn't do this so the smallest chemically stable
unit of neon is one atom; it's monatomic in other words. By the definition
above a neon atom is a molecule, but it wouldn't usually be thought of in
that way.
The problem of understanding chemical terms is that though there are laws of
chemistry not all chemicals completely obey they them. The Laws can be more
like Rules. Things can be a bit fuzzy at the margins. At the same time
chemical terms have entered every day use and have grown fuzzy too. So which
term to describe what is also fuzzy, there can be more than one. Chemists
know what they mean because they know the context and there are
linguistic/social conventions as well as scientific on word use. This can be
a bit puzzling for non chemists, especially engineers not familiar with
these conventions and who like everything neat and tidy.
(Comment: This is partially why we get into such back and forth on stuff
like defining fluxes and how they work.)

Nearly all elements are chemically active. They therefore chemically react
to form molecules. Some of these molecules are very simple: carbon dioxide
is CO2 and water is H2O. Some of them are more complex. One of my favourite
molecules is C2H6O which is more normally written C2H5OH or CH2CH3OH which
reflect how the atoms are arranged. Its everyday name is of course ethyl
alcohol, more formally known as ethanol. The chemistry of life is very
complicated and some molecules are very large indeed - DNA for example. The
chemistry of life was originally called organic chemistry, the chemistry of
organisms; because carbon is intrinsic in organisms it also meant the
chemistry of carbon.  The chemical industry has now synthesised some "life
chemicals" ethanol being one, plus thousands of new chemicals and continues
to do so. So organic chemistry now is usually understood to refer to that
part of chemistry. This leaves inorganic to describe the rest of chemistry
not described by any of the terms evolved above.

Some elements don't react at all they are inert, argon neon etc. they are
loners. Monatomic.
Gold is pretty well nearly inert, so stays monatomic, but under certain
circumstances can be made to react. So it's in one the fuzzy zones mentioned
above.
When Brian comes in he may or may not feel motivated to simplify/correct
this explanation, meanwhile I don't know if this helps or not, but as I've
typed it I'm sending it :)




Mike

-----Original Message-----
From: TechNet [mailto:[log in to unmask]] On Behalf Of Inge Hernefjord

Sent: Wednesday, May 29, 2013 7:06 AM
To: [log in to unmask]
Subject: Re: [TN] Gold Removal

Bev,

Alright. Remember that I am a fossil. We talked 'atoms'  for Solid State
Technology and Metallurgy  in general. And molecules belonged to organic
chemistry. Still I don't understand why gold should diffuse as gold atom
pairs in a gold tin interdiffusion process.  But never mind, there are more
important things in daily life...

Inge


On 29 May 2013 02:35, Bev Christian <[log in to unmask]> wrote:

> Inge,
> Technically Richard is correct, see first meaning below.
>
> Random House, Dictionary.com & Funk and Wagnalls Encyclo.
> - the smallest physical unit of an element or compound, consisting of one
> or
> more like atoms in an element and two or more different atoms in a
> compound.
>
> - any very small particle.
>
> Personally I prefer this one below, so for many elements I look at them as
> monatomic and would only speak of them as "atoms", not molecules.  I think
> this is where you are coming from.
>
> Collins English Dictionary
> - the simplest unit of a chemical compound that can exist, consisting of
> two
> or more atoms held together by chemical bonds
>
> Regards,
> Bev
>
> -----Original Message-----
> From: TechNet [mailto:[log in to unmask]] On Behalf Of Inge Hernefjord
> Sent: Tuesday, May 28, 2013 5:03 PM
> To: [log in to unmask]
> Subject: Re: [TN] Gold Removal
>
> What is 'Gold molecules' ?
> I should know, but need some updating..
> Inge
>
>
> On 9 May 2013 21:26, Stadem, Richard D. <[log in to unmask]> wrote:
>
> > As an engineer, I understand metal rulers quite well. I work with goops
> > and glues also, and I agree that you have to have somewhat of a
> left-minded
> > brain to understand that part. I agree it is better left to people like
> > Doug and Dewey.
> >
> > From: [log in to unmask] [mailto:[log in to unmask]]
> > Sent: Thursday, May 09, 2013 11:37 AM
> > To: Stadem, Richard D.
> > Cc: TechNet E-Mail Forum
> > Subject: RE: [TN] Gold Removal
> >
> > Hi Dean - yes, the 1% concern is when you have a "segregated zone" where
> > the gold is not uniformly distributed within the solder joint. The JSTD
> 001
> > Handbook goes into fairly good depth on soldering process constraints
> that
> > deal with the gold distribution. Using your 1% rule would keep you out
of
> > trouble without question.
> >
> > Good discussion - better than that "goops and glues" stuff Doug was
> asking
> > about.  Metals rule  (Ok, please don't shoot me for that, its directed
to
> > Doug and Dewey).
> >
> > Dave
> >
> >
> >
> > From:        "Stadem, Richard D." <[log in to unmask]<mailto:
> > [log in to unmask]>>
> > To:        "[log in to unmask]<mailto:
> > [log in to unmask]>" <[log in to unmask]<mailto:
> > [log in to unmask]>>, "TechNet E-Mail Forum" <[log in to unmask]
> > <mailto:[log in to unmask]>>
> > Date:        05/09/2013 09:56 AM
> > Subject:        RE: [TN] Gold Removal
> > ________________________________
> >
> >
> >
> > Thank you, Dave. That is greatly appreciated! And now:
> > The 3-5% gold content is an industry-accepted ballpark figure. Gold
> > embrittlement can also be seen with gold percentage as little as 1%.
Much
> > also depends on the base metal that the SJ is formed with, and the
> > geometrical shape of the solder joint can also contribute heavily to the
> > embrittlement level. For example, gold plated wire cups are notorious
for
> > embrittlement if not pre-tinned properly. So are gold plated terminals,
> > certain types of IC and hybrid leads, and a few other configurations.
>  For
> > very high reliability applications, it is very very important to monitor
> > the gold (and other impurity levels).
> >
> > From my personal experience, a limit of 1% gold works 99.99999999999% of
> > the time. Several times in my career I have seen termination finishes
> that
> > met the 3-5% limit fail in the field later. Believe me, you do not want
> > that to happen to you!
> >
> > And when working with gold-plated parts, especially SMT connectors, it
is
> > always a good idea to perform XrF periodically at receiving inspection
to
> > make sure that the gold thickness is actually remaining within the
> > component SCD limits.
> >
> > From: [log in to unmask]<mailto:[log in to unmask]>
> > [mailto:[log in to unmask]]
> > Sent: Thursday, May 09, 2013 9:13 AM
> > To: TechNet E-Mail Forum; Stadem, Richard D.
> > Subject: Re: [TN] Gold Removal
> >
> > Hi Dean - you may not be a metallurgist but you must have stayed at a
> > Holiday Inn recently. Very very good process details. Let me change your
> > last paragraph just a bit.
> >
> > Gold and tin will form a intermetallic compound (IMC) - AuSn4 - when the
> > solder joint composition contains 3-5 weight % gold. This IMC is very
> > brittle and will crack during vibration, drop shock or thermal cycling
> > causing the solder joint to degrade and fail (not a porosity issue). The
> > good thing is that gold diffuses into solder at a rate of 100
microinches
> > per second so when the procedures Dean listed are followed, there is
very
> > little chance of having a gold embrittlement issue. The process goal is
> to
> > not allow the gold content in the solder to exceed the 3-5% range.   The
> > IPC JSTD 001 Handbook and the IPC AJ 820A Handbook have a very good
> section
> > on this issue.
> >
> > Dave
> >
> >
> >
> > From:        "Stadem, Richard D." <[log in to unmask]<mailto:
> > [log in to unmask]>>
> > To:        <[log in to unmask]<mailto:[log in to unmask]>>
> > Date:        05/09/2013 08:30 AM
> > Subject:        Re: [TN] Gold Removal
> > Sent by:        TechNet <[log in to unmask]<mailto:[log in to unmask]>>
> >
> > ________________________________
> >
> >
> >
> >
> > Good question, Bob.
> > Gold does not "melt" at soldering temperatures. A dissolution process
> > takes place, and because gold plating on component leads is so thin, the
> > dissolution is typically enough to absorb all of the gold into the
solder
> > bath upon contact with the molten solder. This is also how a solder
joint
> > is formed with copper and certain other metals. Copper, gold, silver,
and
> > nickel do not melt at normal solder temperatures, a small amount is
> > dissolved to form the bond with the solder, called the intermetallic
> > formation.
> >
> > A double tinning method utilizes the first tin pot to dissolve and
absorb
> > the gold into the molten solder, and the second pot is required to
ensure
> > the remaining solder is relatively free of gold (the first pot has gold
> > levels increasing over time as the tinning is performed, so the second
> pot
> > is used to make sure no gold remains). The dual pot method is used where
> > only a small amount of solder is used for tinning, and is thus more
> easily
> > filled with unwanted "impurities" (other alloys and elements other than
> > Sn63Pb37 or whatever the desired alloy is). The dynamic wave is simply
> > another option for obtaining the same results, where a larger volume of
> > solder is pumped to provide a laminar flow that will ensure the gold is
> > removed and replaced with the target alloy, Sn63Pb37 as an example.
> Because
> > of the larger solder volume in the dynamic wave method, the gold content
> is
> > diluted such that it does not go above the limits listed in J-STD-006.
> >
> > When using a double pot method, the gold content must be monitored in
> both
> > pots. This is done with a regular pot analysis, and the data is used to
> > determine the frequency of solder replenishment to dilute the gold and
> > other alloys to an acceptable level. The solder test is relatively
> > inexpensive and can be performed by solder companies such as Alpha,
> Kester,
> > etc. With the laminar flow method, you still need to test at regular
> > intervals, but because of the larger volume of solder it takes longer
for
> > the gold and other impurities to go above the specified limits.
> >
> > Tinning data should be kept to determine the frequency of sampling for
> > test, as well as how often the solder should be refreshed with new
solder
> > to dilute the impurities to an acceptable level. A simple tinning log is
> > valuable in determining the history (number of components tinned, what
> > type, and when) to quantify the amount of tinning over time in order to
> > help determine the safe frequency for adding solder that will ensure the
> > alloy will remain within spec, the spec being J-STD-006, including
> Appendix
> > A and B, which list the allowable levels of "impurities" (it's hard to
> > consider how gold and silver can be considered "impurities", but it's
all
> > relevant to the goal of Sn63Pb37 for leaded solder, and nothing else).
> > J-STD-006 also lists the test methods used to determine the impurities.
> >
> > The concern with having gold levels above the limits in the J-Standard
is
> > that gold in the solder joint will nucleate through the hardened solder
> > joint towards the junction of the component lead and the solder, and/or
> the
> > pad and the solder (the intermetallic junction). Gold wants to return to
> > this intermetallic boundary, like many other elements seeking
> equilibrium.
> > So the gold molecules will actually travel through the solder joint over
> > time (nucleation), leaving behind a more porous solder joint, which is
> > called embrittlement, which leads to solder joint fractures and
> potentially
> > catastrophic electrical failure.
> >
> > I am not a metallurgist by training, so this explanation may be somewhat
> > crude to those who are, but I think it will serve the purpose of
> > explanation. For all of you metallurgists out there, feel free to expand
> on
> > this or correct me.
> >
> > Hope this helps you,
> > R. Dean Stadem
> >
> >
> > -----Original Message-----
> > From: TechNet [mailto:[log in to unmask]] On Behalf Of Robert DeQuattro
> > Sent: Thursday, May 09, 2013 7:28 AM
> > To: [log in to unmask]<mailto:[log in to unmask]>
> > Subject: [TN] Gold Removal
> >
> > Hello Fellow Technetter's,
> >
> > I have a question on J-Std-001E 4.5.1 Gold removal which states a double
> > tinning process  or dynamic solder wave may be used.  Can any of you
> > describe this process.  How is the gold actually removed?  Or is it just
> > being tinned?  Gold melts at over 1000 C so I am a little confused.
> >
> > Thanks,
> >
> > Bob
> >
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