Soldering is a process in which two or more metal items are joined together by melting and flowing a filler metal (solder) into the joint, the filler metal having a lower melting point than the adjoining metal. Soldering differs from welding in that soldering does not involve melting the work pieces. In brazing, the filler metal melts at a higher temperature, but the work piece metal does not melt. In the past, nearly all solders contained lead, but environmental concerns have increasingly dictated use of lead-free alloys for electronics and plumbing purposes.
There is evidence that soldering was employed as early as 5000 years ago in Mesopotamia. Soldering and brazing are thought to have arisen very early in the history of metal-working, probably before 4000 BC. Sumerian swords from ~3000 BC were assembled using hard soldering.
Soldering was historically used to make jewelry items, cooking ware and tools, as well as other uses such as in assembling stained glass.
- Reflow Soldering - Solder paste is applied to the PCB's solder pads before components are put in place. Hot air is then used to melt the solder paste, fusing components to the board.
- Wave Soldering - PCB is moved via conveyor above a pool of molten solder. A pump creates waves in the pool, which rise to meet the bottom of PCB and subsequently solder the joints in place.
- Solder wick - After being heated with a soldering iron, solder wick draws molten solder away from solder pads.
- Desoldering Pump - Uses suction to remove molten solder from a PCB.
- Hot Air Gun - Heats a solder joint with a stream of hot air inorder to melt a joint without making direct physical contact.