What Is Solder?
Solder is an alloy, which is a combination of two or more metals. It is heated to its melting point and used to join together other metals. The most common solder is called half-and-half, or "plumber's" solder, and is composed of equal parts of lead and tin. Other metals used in solder are aluminum, cadmium, zinc, nickel, gold, silver, palladium, bismuth, copper, and antimony.
Soldering is an ancient joining method. It is mentioned in the Bible (Isaiah 41:7) and there is evidence of its use in Mesopotamia some 5,000 years ago. (Mesoptamia was an ancient republic located in present-day Iraq.) Solder was later used in Egypt, Greece, and Rome. Solder is frequently used today in the construction of electronic circuitry.
Sources: Brady, George S. Materials Handbook, 13th ed., pp. 768-70; Manko, Howard H. Solders and Soldering, 2nd ed., p. xv.