in addition, Ioan need to answer  few questions: pass thermal cycle,  
not thermal shock. how many cycles? 500?  no wonder... temperature  
range? -10 to 55?  or -20 to 85?  or -55 to 125?  if you do thermal  
shock liquid to liquid 30 - 50 cycles  at -55 to 125 without failure  
(sufficient  dwell of course), follow by electrical test (no drift at  
full function), you might feel ok to raise issue to check prior  
spec.... The std lowered great deal in last  10 years... temp range,  
cycle number, dwell time, and don't forget electrical testing: use to  
be functional check for delta R change...some way down to the line,  
few changed to open/short (beep or no beep)... however, the physics  
does not  change... you still got some drop it, shock it... few got  
curve that related field data to the test with convincing  
acceleration  factor nowadays... simulation  without spell  out the   
boundary condition or assumption data are scary to the least...
On Nov 23, 2016, at 1:05 PM, David Hillman wrote:

> 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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