Ryan,

I cannot thank you enough for such an excellent reply. Your comments and
demeanor in this posting are mind and heart felt but I?m still numb compared
with, say, twenty years ago when I ?really? had a handle on solder,
soldering, solderability, and the process management requirements to ensure
high quality/reliability product. The following are my responses to yours:

Ryan: I didn't gather from Werner's comments that thick IMC's are good; rather
that thick IMC's are NOT bad. This is an important difference because the
pervasive industry "myth" is that thick IMC's are bad. Like you, I haven't
seen the lower limit defined.

Me: At first, I thought Werner?s comments clearly implied that the thicker
the IMC, the better the solder joint in terms of initial quality and long
term reliability. After your observation, I?ll focus more on his truly
expert commentary. Still, as you have said, if thick is better, then how low
can you go and/or does it really matter? Of course it does if thicker means
better and that none means no ?wetting? ? pardon the term forever ingrained
in my mind for lack of one better. What, by the way is the best term today?

Ryan: Further, the major failure mechanism contributor is the lead layer. If
this
layer is removed with each rework, then there is no limit to the number of
rework operations provided the pads are solderable. (of course, ignoring
board and pad damage). I have validated this through my own experiments
that compared BGA's seeing no rework on up to BGA's seeing six reworks and
then temp cycled. There was no correlation between joint failures and
rework cycles, but the IMC's did get visibly thicker.

Me: I understand your comments here and find no objections, today, to their
accuracy. My question, now, turns to lead ? free solder medium types ? as
eutectics?.  Can they be judged like lead when whatever metal takes its
place? I too have experimented much with extended rework cycles, especially
with BGA device types and came to the same conclusions but for clearly
understanding lead?s role in all this. Mostly, I found that using ?thick?
flux worked better than solder paste in the rework world and would like to
find a way to use it on their initial soldering processes (few voids, little
solder bridging, etc.) thereby alleviating most need for rework.

Ryan: I hope this answers two of your questions.

Me: It?s a great start and thanks again.

Ryan: BTW, if Manko, Rahn, and Wassink do not agree, remember how the scientific
process works. A hypothesis is formed based on observations made up to that
point. The hypothesis is then tested and based on the observations of that
test, the hypothesis is either validated or invalidated.

Me: My only issues here, though not with your comments, concern the time
soldering has been practiced both as an art form and a scientific or
industrial endeavor. It seems, at this point, there should be clear
scientific evidence (physical laws), beyond hypotheses, dispelling the need
for, at least, many more opinions on the subject. I still, as do we all, see
too many variations on this theme. I mean, how many more books, papers, and
articles are needed until we, at least, have consensus about what
constitutes and contributes to high quality/reliable solder joints ? though
I applaud everyone involved in the experimentation, writing, and implementation.

Ryan: The caveat is that the hypothesis must allow for all previous
observations,
and any subsequent observation that invalidates the hypothesis requires that
the hypothesis be changed to reflect the new observation. The point being,
something that is published will only reflect the current wisdom at the time
of publication; and the scientific process allows for changes in past
wisdom. Meaning, Manko, Rahn, and Wassink reserve the right to change their
minds from whatever they may have published in the past.

Me: I certainly have no problem with our soldering and scientific experts
changing their minds based on new research and the imperial evidence
effected by it. I have read nearly all books, papers, and articles
concerning soldering and all its contributory elements. I applaud continued
research in any such vital field. I thirst constantly for more objective
information in lieu of subjective opinions. Still, I see many, maybe too
many, differing opinions among experts and, especially, among those needing
to put the rubber to the road during solder joint processing. I conclude
from all this that solder joints can be very forgiving little devils. This
must be true even as I have great difficulty even ?seeing? 0201 solder
joints let alone accepting them based on this visual/invisible evidence.

Times were much simpler when ?wetting,? ?smooth,? and ?shiny? were terms
embraced and accepted by everyone in industry. Seems like only twenty or so
years ago ? yesterday to me.

Thanks again to all and especially you Ryan, Werner, Peter, and everyone
else posting and caring about such a serious subject,

MoonMan

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