What is a good solder?

Answer 1

It depends on what you are soldering. In general, eutectic alloys -- those that have a single well-defined melting point, are better for electronics. Non-eutectic alloys, where one of the metals starts to crystalize out of solution first before the others have the benefit gradual hardening. While hot, they are a runny liquid, and then they thicken and become clay-like before finally hardening. That means that they provide some physical support while the pieces being soldered can still be adjusted. This is useful in sculpture, sheet metal work and similar contexts. Lead-tin solder is the old reliable standby for electrical work but potentially toxic and illegal in some countries. Tin-copper-silver alloys are less toxic but have somewhat higher (but still reasonable) melting points. Model builders and jewelers like having a range of solders with different melting points so that subassemblies may be built with the highest melting-point solder and then combined using lower melting point solders with the final parts added with the lowest melting point solders. Jewelers like solders containing precious metals, so that, for example, the solder used to join two pieces of sterling silver is also legally the same silver percentage. Jewelers also care very much about the color of the solder they use.