But how did this saga begin? My guess is that it's a combination of politicians not knowing what they're doing and pressure on them to "take action".
To elaborate, these are the problems with lead-free solders:
- The finish of soldered joints is different, complicating inspection.
- The melting point is usually higher by a substantial margin, requiring higher soldering temperatures which are more likely to damage components.
- Most lead-free solders can't take as much mechanical stress as leaded (with SnCu being especially poor).
- Lead-free solders have poorer "wetting" (the spread of the melted solder to cover the soldered surface).
- Mixing different alloys can cause severe reliability problems, especially in BGAs.
- There is an increased risk of voids in soldered joints.
- Tin is susceptible to growing "whiskers" which can cause short circuits at low power levels and plasma arcing at higher ones. Lead is the only element that provides good protection from whisker growth.
- Tin in cold environments (<13.2°C) slowly changes from its normal beta-phase to its nasty, brittle alpha-phase, and cannot be restored to normal. There are three elements that prevent that problem - lead, antimony (also toxic) and bismuth (catastrophically incompatible with lead). The latter two have both been used in solders, but you cannot count on their use; still, I'd guess SnSb might just be the least bad lead-free solder.
To be honest, I wouldn't count on them ever finding a good replacement for leaded solder. It's probably just the one best material for the application, just as copper is best for durable, highly conductive wiring and gold is excellent for highly corrosion-resistant contacts.
