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Subject:
From:
David Hillman <[log in to unmask]>
Reply To:
TechNet E-Mail Forum <[log in to unmask]>, David Hillman <[log in to unmask]>
Date:
Wed, 23 Nov 2016 12:20:52 -0600
Content-Type:
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Hi Richard - well, we usually agree but not this time. The formation of the
gold/tin IMC happens as the solder joint is molten and being formed. Gold
and tin can form the IMC phase in a solid state condition but it is very
very very slow and only in very rare occasions has been found to be a
failure root cause. Gold will migrate and form gold/tin IMC in the presence
of nickel plating but that is a Gibb's free energy issue and again, rarely
is a failure root cause (think of all the ENIG boards soldered in the
industry). If you don't have a gold embrittlement problem right after
soldering, you have a very high probability of not having a gold
embrittlement problem. The reason for all of the JSTD-001 criteria is an
attempt to get folks to manage this issue proactively and not reactively.

Dave

On Wed, Nov 23, 2016 at 12:03 PM, Stadem, Richard D. <
[log in to unmask]> wrote:

> Just keep in mind that gold nucleation is a time-variable event. It begins
> immediately after a solder joint is formed, but continues for a long time,
> typically for two or three years or until equilibrium is reached. The
> embrittlement due to gold nucleation will seldom be present immediately
> after soldering, but solder joints will typically fail perhaps between 6
> months to two years later.
> That is why the J-STD-001 reads that you must show objective proof, and
> that proof needs to consider the time variable as a factor to test.
>
> -----Original Message-----
> From: TechNet [mailto:[log in to unmask]] On Behalf Of Vladimir
> Sent: Wednesday, November 23, 2016 11:27 AM
> To: [log in to unmask]
> Subject: Re: [TN] Gold embrittlement
>
> Hi Ioan,
>
> Au and Sn form intermetallic platelets and cracking goes at their
> interface with the matrix.
>
> ‎The fact that your product did pass the test doesn't mean there were no
> cracking in solder and the product will last a as long as it supposed to in
> field (it will depend on how good a reliability model was).
>
> I'd definitely suggest you to section ‎joints after the test.
>
> Regards,
>
> Vladimir
>
> SENTEC
>
> Sent from my BlackBerry 10 smartphone on the Rogers network.
>   Original Message
> From: Ioan Tempea
> Sent: Wednesday, November 23, 2016 12:02
> To: [log in to unmask]
> Reply To: TechNet E-Mail Forum
> Subject: [TN] Gold embrittlement
>
> Dear Technos,
>
> I have SnPb37 joints with 4-8% Au that did not fail thermal cycling, no
> cracks, pass electrical tests like a charm. This kinda contradicts
> J-STD-001 and common knowledge, so I would appreciate some insider info
> regarding Au embrittlement, to help me figure this one out.
>
> I know one could write volumes on this, but I'm sure the questions below
> can be answered in a brief manner.
>
>
> * How did Au embrittlement end up being a reliability issue? Real
> catastrophic failures?
>
> * What is the effect on the long term reliability of solder joints?
>
> * What screening method creates catastrophic failure of embrittled joints
> (mechanical shock, thermal cycling, vibration, etc.)?
>
> * It looks like the embrittlement process goes on as long as there's Au to
> combine with Sn. What is the speed of this reaction? Otherwise said, how
> long does it take for a joint with high Au content to become brittle?
>
> * Has anybody screen for embrittlement? Or, anyone tried to maximise
> embrittlement (e.g. 100 hours @ 150 C) and then screened the hardware?
>
> * Anything else I should know?
>
> Thanks,
>
> Ioan Tempea, P. Eng.
> Manufacturing Engineer, Satellite Systems
>
> [cid:[log in to unmask]]
>
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