Hi Guy - I guess I am confused as how the IMC could be unacceptable if there are not industry defined standards and there is no linkage to a failure mode. Seems very very subjective. Dave On Thu, Sep 6, 2018 at 9:15 AM, Guy Ramsey <[log in to unmask]> wrote: > Not linked to a root cause, but observed as unacceptable, too thin and > inconsistent. > soak time (150 to 200) = 150 sec > reflow time (above 217) = 75 sec > peak temp = 250 > Seven thermal couples placed at various places on and in the board all > within 3 degrees delta. The board is heavy, Megtron 6 with 34 copper > layers. Most of the thermal load is the board. There would be very little > difference from pad to pad on any given component. Solder mask defined > pads conform to MFG recommendations. We learned that the DDR packages are > several years old. Maybe the solder spheres are hosed? > > On Thu, Sep 6, 2018 at 9:38 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. > > >