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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