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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