Larry,

Thanks for your reply.  These units are field returns (~ 7 yrs old) from a
consumer electronics (shelf) application.  The manufacturing history is not
going to be easy to resurect.

The key here is that the original solder joints appear to have been "good" and
that the failure is at the interface between the copper pad and the Cu3Sn IMC.
I believe thermal shock could potentially cause this type of failure.  However,
poor solderability of the copper e would have caused large yield loss at HASL or
CCA reflow (I would hope the product would be rejected at that point ;)).
Furthermore, the IMC layer thickness appears "normal" i.e. ~ 1-2 microns.  Would
the IMC even form over contaminated copper?

Best regards,
Ed

[log in to unmask] wrote:

> In a message dated 12/16/99 6:25:35 PM Central Standard Time,
> [log in to unmask] writes:
>
> << Hi everyone ... I have been looking at solder joint failures for quite a
>  while and have stumbled on something new to me.  I hope someone has seen
>  this and can give me some insights.  Here it is ...
>   >>
> Ed,
>
> I have seen this failure many times in the past.  It is normally related to
> two conditions. One being a high thermal excursion and the second being poor
> solderability of the copper.  What you did not mention was what the thermal
> excursions were and how many cycles to failure.  You may also have
> unrealistic expectations of the system in general.
>
> Larry Tawyea

--

               SEM Lab, Inc.
Scanning Electron Microscopy and Failure Analysis
               Snohomish, WA
               (425)335-4400
           http://www.sem-lab.com

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