I've got the following on my table:
Those are listed in reverse preference order.
ExpressPCB's RoHS process uses 99% silver. It's still copper underneath, but it may make sense to use silver-bearing solder like the common 62-36-2 eutectic blend for such boards.
Tangent speaks the truth.
In industrial process, the boards have very thin copper
on them before they are etched. Saves on copper and time.
Then they are plated back up to whatever thickness is required.
They can be plated in any coating the customer requires; tin,
silver bearing tin, silver, gold, unobtainium (if you can afford it)
or whatever else they have up their sleeve.
Other than the copper layer, most of the more exotic stuff is
plated on after the solder mask is applied so only the exposed
pads are plated with silver, gold or unobtainium.
I have found what I think is the best non-leaded solder as it's almost as easy to work with as leaded solder. It's "blended" and made by Sparkfun and is 96% tin, 3.0% silver, 0.5% copper, and 0.15 antimony. Best silver bearing solder I ever used. I'm not much of an electronics buff compared to the real deal but I do need to solder something once in a while and this solder is GREAT stuff!
Yes, Sparkfun, legendary house of metallurgy.
This is just another of a great number of lead-free solders. One that subs in toxic antimony for toxic lead, by the way.
I find it odd that the product page doesn't say whether the alloy is eutectic. Also, it mentions water-soluble flux as though it is purely a virtue, when in fact it's a warning sign: you must clean that sort of flux off your boards, because it is caustic.
(Reminds me of the "triple organic" sign I passed on the road the other day. Ooooo, that must be better than just double organic!)