Solder

Solder is a fusible metal alloy melted to join metal parts without melting the parts themselves. It forms an electrical and mechanical connection, especially between electronic components and circuit boards.

Wetting: Wetting is the spreading of a liquid across a solid surface when adhesive forces overcome cohesive forces. Molten solder must wet clean metal surfaces to form a reliable bond.
Alloy: An alloy is a material made from two or more elements, at least one of which is a metal. Solder’s properties come from combining metals in controlled proportions.
Printed circuit board: A printed circuit board is an insulating board carrying conductive pathways that mechanically support and electrically connect components. Solder joins component terminals to conductive pads and plated holes on the board.
Lead-free solder: Lead-free solder is solder formulated without intentionally added lead, commonly using tin with metals such as silver or copper. It replaces traditional lead-bearing alloys in many electronics applications.
Flux (metallurgy): A flux is a substance that removes or prevents oxides during metal joining and other high-temperature processes. Flux clears surface oxides that would stop molten solder from wetting a joint.
Eutectic system: A eutectic system has a composition that melts and solidifies at a lower temperature than neighboring compositions. Eutectic solder can change directly between solid and liquid at a single temperature.
Reflow soldering: Reflow soldering joins surface-mount components by heating solder paste until it melts and then solidifies. It is the standard high-volume method for soldering surface-mount assemblies.
Tin-lead solder: Tin-lead solder is an alloy, commonly near 63 percent tin and 37 percent lead, used for joining metals. Its low melting point and predictable behavior made it a longstanding electronics standard.
Soldering: Soldering is a metal-joining process that uses a filler alloy melted below the melting points of the joined parts. Solder is the filler material at the center of this joining process.
Phase diagram: A phase diagram maps the stable phases of a material as temperature, pressure, or composition changes. Phase diagrams show how solder composition affects its melting and solidification.

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