November 23, 2016

We have an OEM who failed to remove gold from some mil spec crystal
oscillators even though the part manufacturer website recommended the gold
be removed.  The OEM determined that about 5% gold wound up in the Sn63
solder joints and they also noted some small cracks in some solder joints.

On Wed, Nov 23, 2016 at 12:27 PM, Vladimir <[log in to unmask]>
wrote:

> 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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> Highway, Ste-Anne-de-Bellevue, QC, Canada H9X 3R2
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