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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