Lead-tin solder obsolescence and lead-free transition

Brief context. Fifteen years of industry/government effort to find a lead-free replacement has not produced anything that wets as well or as fast as lead-tin.

They tried a number of experiments. This is the wetting time in seconds. There are a couple of different wetting tests — I may talk about the different ones later, because wetting time becomes important particularly when you're trying to do a printed circuit board. You put the little solder paste on top of the circuit board — you've screen-printed on a solder paste. This one is pre-tinned: copper with electroplate of tin on the surface. You're going to melt the solder to the surface. This is old, lead-tin solders. Nowadays, for the last fifteen years people have spent a lot of money trying to get the lead out of the solder for environmental reasons, which has been a big problem because nothing wets as well or as fast as lead-tin solder. Hundreds of millions of dollars have been spent by industry and government.