The received wisdom on having Bismuth involved in any lead to lead-free 
assembly transition is that it should be avoided because of the possibility of 
forming a low-melt Sn-Pb-Bi phase within the solder joint, possibily at grain 
boundaries and risks realiability problems. But how likely is it that for example, 
SMT AE caps RoHS-compliant from Panasonic using a SnBi termination finish 
will provide the right Sn/Pb/Bi contributions to create the troublesome alloy?

I found a presentation from NEC which explains their choice of SnBi finish and 
explains research they commissioned that found the low-melt phase will not 
occur.

<http://www.alpha.cooksonelectronics.com/sacxdatalibrary/pdfs/NECSMT.PDF
>

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