Solder is a metal with a low melting point that is used to create the conductive joints between components and tracks in electrical circuits. There are many types of solder used for different metals, but the most common solder used for electronics is an alloy of tin and lead.

Solder Flux

Flux is essential for making good solder joints. It removes the thin film of surface oxidation that prevents two metals sticking together. It also prevents more oxidation occurring during soldering. Heat causes the flux to change it's chemical structure and become more acidic, allowing it to dissolve this oxidation. There are many types of flux, and the one for tin/lead solder is a mix of ammonium chloride and rosin.

Soldering Irons

The basic soldering iron is a metal rod with a pointed tip, heated by a coil of resistance wire in the handle. Soldering stations have temperature controls which are essential for soldering components that can be damaged by too much heat.

Soldering Machines

Large circuit boards, like those found in computers, can have thousands of solder joins on them. These are done by industrial soldering machines because they are cheaper, quicker, and have fewer errors than manual soldering. Basically, the circuit boards are skimmed over the top of a bath full of molten solder, and the joints pickup just enough solder to form a joint.

Removing Solder

Solder can be removed using a pump or wick. A solder pump can be as simple as a rubber bulb with a nozzle, but the spring-loaded syringe types are better. The joint is heated with a soldering iron, and the liquid solder sucked up into the pump. Wicks are copper braid infused with flux which draw up the molten solder when applied to a joint with a soldering iron.