Hi Joan
... The solder resist is a other possible cause. Do you have control about
the used solder resist, do specify the type (Peters SD 2463), or at least
the class (IPC-SM-840C, class T)? It seems some types of solder resist are
secreting substances which prevents good solderability (and/or good bond of
a conformal coating). Some solder resist could be ok as type itself, but
mis-processed by pcb-shop (for example to less UV-curing for photosensitive
solder resists, has also catastrophal consequences for the Comparative
Tracking Index, CTI).
You see, there is a alchemistic kitchenette it would be fascinating to
analize the development of failure theses in a jungian manner and so, at
least I have to agree to Earl's mail: "... but what's changed? ..."
Regards

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