from running a few tin-nickels in the early 1980's at a few of my accounts -
i can give u some info on this process:

1-   sn/ni plating bath deposits an alloy with a 1:1 atomic ratio of tin to
nickel 
      or 65% tin and 35% nickel by weight

2-   excellent corrosion resistance, bright appearance and is extremely hard

3-   difficult or almost impossible to reflow - since it goes thru a metallic
phase change prior to melting

4-   it has a tendency to dull with age and forms a tenacious, chemically
resistant oxide on the surface which is self-healing

5-   high operating temperature - 140 - 160 F - increases resist leaching
into the plating bath

6-  poor deposit shelf life - due to the formation of the oxide film

u may want to conduct some tests prior to using this process in production - 

this data is provided on a process that was in use back in the 80's - someone
may have changed formaulation over the ages and maybe something new on the
market

regards

Richard Fudalewski
Atotech Canada Ltd

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