A: Most solder is an alloy of lead and tin. Lead-free solder often use an alloy of tin and silver, though other metals, such as copper, zinc, and more may be used. In certain cases, you may find that lead-free solder requires a more powerful soldering iron to maintain temperatures. Because of this, take care to heat sink temperature-sensitive components (a good idea in any case). Some types of lead-free solder also require more corrosive flux, which can increase the hazard of harmful fumes when soldering. Be sure to work in a well-ventilated area (also a good idea, in any case).