Hi Wayne - very reassuring to see your experience and mine align. I think
the common theme is poor soldering process - as you detailed, not having
correct reflow parameters impacts the formation of an IMC which means the
solder joint integrity is lost. For the examples you detailed, did the
users not attempt to properly profile the assembly?

Dave

On Thu, Sep 6, 2018 at 8:37 AM, Wayne Showers <[log in to unmask]>
wrote:

> IMC has been the bane of my existence more than once.  So here is my take
> from experience backed up with some lab evidence.
> I have had failures attributable to insufficient IMC.  Almost all of these
> were corrected by either ramp-to-peak or increased time above liquidus /
> intimate contact time / temperature.
> For SAC, the intimate contact temperature I have been able to dial in on
> is time above 208C after liquidus is achieved.
> For SnPb, the intimate contact temperature I have been able to dial in on
> is time above 177C after liquidus is achieved.
> I have found that if I can back end a little more time above these
> temperatures on the profile, I have more consistent joints.  I have not
> devoted a whole lot of 'science' on these numbers just 20+ years of trial
> and error coupled with white papers, IPC BOK, and other research.
>
> I have yet to have a problem or a return tied to excessive IMC.  I am sure
> that at some point excessive IMC may cause or have caused a failure mode, I
> just have not seen it.  The few times where it may have been a contributing
> cause, I also cooked the parts making cross-sectioning of the IMC moot.
>