Hi Genny,
Nothing at this point, short of bombing the EU-parliament--and most likely 
not even that--and not even taking my workshops, would explain everything and 
make the sun shine again in your world. Confusion and uncertainty reins supreme.
First, yes, the Engelmaier-Wild model is mine.
Second, MIL-HDBK-217 is utterly useless as far as solder joint reliability is 
concerned.
Third, ATC [accelerated temperature cycling] of actual product is rather time 
consuming because you may not know when failures have occurred—remember, 
solder joint failures show up as very short-duration intermittents.
Fourth, when you pick a temperature range, e.g., TC2 and a performance level, 
e.g., NTC-C [1,000 cycles], that means you need to pass the 1,000 cycles witho
ut failures of any of the 32 samples on test—6 boards is statistically 
non-robust, but since we are mostly guessing, what the hell.
Fifth, all the above is for SnPb-solders, but applies to LF-solders as well. 
In addition, for LF-solders we do not as yet know how many cycles at what 
temperature range correspond to what kind of product SJ reliability. My best 
recommendation—with the understanding that we [the whole industry] are desperate, 
is to use the Engelmaier-Wild model and apply a safety/uncertainty factor the 
the number of cycles of perhaps about 5 or so [no guarantees—and yeah, that is 
not what you want to hear, we should have all been screaming 5 years age, well 
actually, some of us did].
By the way, you may want to attend my LF-Soldering Reliability Issues 
workshop at the IPC/JEDEC conference in Santa Clara on March 7, and perhaps the first 
3 SJ Reliability Series parts on March 6 as well.

Werner

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