Lead-free solder alloys have been around for as long ... At higher temperatures and currents, this process accelerates. Preventing electromigration involves regulating temperature and current ...

For most of the history of industrial electronics, solder has been pretty boring. Mix some lead with a little tin, figure out how to wrap it around a thread of rosin, and that’s pretty much it.

The images show a lead solder pellet, in red ... out that the pellets are part of an industry-standard manufacturing process.