What is solder?

• A. A fusible metal alloy used to create a permanent bond between metal work pieces.
• B. A dry adhesive used to hold components.
• C. A flux used to promote wetting.
• D. A soldering iron accessory.

Answer: (A)

Solder is a filler metal alloy that melts at a relatively low temperature and is used to join metal parts by flowing into the joint and then cooling to form a solid bond. It creates a metallurgical connection, not an adhesive glue, because the bond comes from the melted metal filling the gap and then solidifying. Flux is used in the process to clean surfaces and improve wetting, but the solder itself is the metal that actually forms the joint. Common electronics solders are tin–lead alloys (like 60/40 or 63/37) or lead-free variants such as tin–silver–copper.