Hi againTNs,
I have not been shouting for a while (you say thank you for that?). I'm eventually closing the matter and am´going to make final reporting, what that be worth. Anyway, I've been ploughing thru kgs of papers from different sources, some of which were given by Dough D, Georg W, Biunni, Amkor, Xilinx, Mota and so on. All specked with wisdom and splendid writing. Finally I've been through the results from a BGA consortium led by Pitarresi and Limaye at Binghamton (which I can't discuss in detail of course). The later is a result from testing samples from dozens of PWB vendors.
My own simple exercises seem, despite I'm not a pro on specific areas, to coincide remarkably with the giants like Werner, Dough, Biunni and all the gurus not mentioned here. And it's a little frustrating to see that one has not come to satifying explanations yet about the mechanisms that transform a good ductile solder joint into a brittle and unpredictable one. (Curios: W has to rethink, in the consortium Ni/Sn IMCs as thick as nearly 50 microns were found after considerable few days of ageing.)
When you try to clean the equation from all irrelevancies, it seems to me as my conclusion about ENIG and BGA soldering will be:
* most of the zero-time-failures are due to factors that the majority of the board makers can not handle satisfactorily. And so it will be...
*because of the above, the user need exorbitant know-how about metallurgy and soldering processes for making solderings that will survive in MIL equipments and like for one or two decades without failures.
* IMCs are not so bad guys although they contribute to severe solder joint degrading. If you managed the two points above, you can certainly make very good and reliable BGA solderings on ENIG boards. That is proved by all millions of ENIG boards that are mounted.
* I will recommend to find another and cheaper way (if there is such a one), with simpler board chemistry and soldering processes that are more forgiving, that can cope with banana BGAs and, that can permit a good process without being a professor, and that can permit buying BGAs and boards in a reasonable mixture.
Useing another TN guy's phrase: "what I express here is not necessarily my company's opinion, but just my own." And if lots of you don't agree, I will not change easily.
Thanks for all help, one or two of you will get a copy of my report. Can be used for the barbeque fire at least. He-he
Ingemar Hernefjord
Ericsson Microwave Systems
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