Thanks to everyone who replied to this question.

I'm getting the impression that reflowing at or just over the standard
PbSn profile using regular paste would be the safest way for us to go.
The devices that are lead free have Tin, Silver, Copper (SAC) alloy
balls. The board assembly is very high dollar value and we are only
making a few of them for now. Bare boards are FR4 with an ENIG finish.
I'm using filled and overplated via-in-pad. 
Our loader is using vapour-phase reflow equipment.

regards,

Phil Dutton C.I.D.

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