Werner's reply did not equate with accepted industry wisdom so I went and looked
for a reference.
According to the first thing to hand - the first edition and therfore now
ancient  Solders and Soldering, silver is soluble in tin up to large amounts,
but the actual amount depends on the temperature, thus at around 240C the
solubility of silver in 63/37 is about 3%. So I guess there is a practical
benefit here unless current editions or other learned tomes say different?


Mike Fenner
BSP
------------------------------
To my knowledge it is a myth, that SN62 alloy (with 2% silver) is effective
in reducing silver metallization leaching during reflow. Solder has such high
solubility in tin and silver/tin intermetallics rapidly disperse throughout
the solder joint that a 2% silver content is not likely to any effect in the
leaching--actually dissolution-- process of the silver into tin. That is
really the reason why the nickel barriers came into widespread use. 

Werner Engelmaier

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