Hi Ioan - the IPC JSTD 001 specification is not in error, gold
embrittlement does and can cause solder joint integrity issues. Not
everyone on the committee is on the same page in terms of exact details but
gold embrittlement is something that you should be addressing (long story
for a later date). Gold embrittlement occurs when the gold content exceeds
3%-5% in the solder joint. Gold and tin form an intermetallic phases that
is very brittle and does not deal with thermal cycle and/or vibration
stresses very well. The IPC JSTD 001 Handbook and the IPC-AJ-830 standard
both have good information on gold embrittlement if you want to get
additional knowledge. Two big questions need answered when dealing with
gold embrittlment; (1) is the volume of solder sufficient to avoid reaching
3%-5% gold levels?; (2) Is the soldering process hot enough, long enough to
allow the gold to distribute uniformly across the volume of solder present?
If you can't answer "Yes" to both of these questions, then  you probably
have an issues. Generally, gold embrittlement solder joints fail very
quickly when exposed to thermal cycle, vibration or drop shock
conditioning. However, in some cases such as yours, a gold embrittled
solder joint is not subjected to enough stress to cause failure in its
configuration in the product use environment. I have seen three cases were
gold embrittled solder joints did not result in product failure. Gold
embrittlement is best controlled by managing your component finishes and
soldering processes. The gold/tin IMC is created at the time of soldering
so the phenomenon isn't a "happens over time" type of failure mode.  A
third reference with good information on gold embrittlement is the AWS
Soldering Handbook, ISBN 0-87171-618-6.

Hope this helps, let me know if you have additional questions.

Dave Hillman
Rockwell Collins
[log in to unmask]


On Wed, Nov 23, 2016 at 11:01 AM, Ioan Tempea <
[log in to unmask]> wrote:

> 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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