stylistic:tone, structural:summarization
Resistance soldering

Resistance soldering is soldering in which the heat required to melt the solder is created by passing an electric current through the parts to be soldered. When electric current is conducted through any metal, heat is generated; when that current is confined to a smaller cross-sectional area, the heat produced in the entire circuit is concentrated in the portion with the reduced cross-sectional area. The current doing the heating is applied by electrodes or tips energized from a low (open-circuit) voltage source, typically 2-7 volts. They can be tweezer-like for general connections or specially-shaped to make contact with parts located closely together.

Resistance soldering is unlike using a conduction iron, where heat is produced within an element and then passed through a thermally conductive tip into the joint area. A cold soldering iron requires time to reach working temperature and must be kept hot between solder joints. Thermal transfer may be inhibited if the tip is not kept properly wetted during use. With resistance soldering an intense heat can be rapidly developed directly within the joint area and in a tightly controlled manner. This allows a faster ramp up to the required solder melt temperature and minimizes thermal travel away from the solder joint, which helps to minimize the potential for thermal damage to materials or components in the surrounding area. Heat is only produced while each joint is being made, making resistance soldering more energy efficient. Because of these advantages, resistance soldering is common in industries which solder in small spaces such as connectors and wire terminals, and where high power is required, such as desoldering automotive parts.

Resistance soldering equipment, unlike conduction irons, can be used for difficult soldering and brazing applications where significantly higher temperatures may be required. This makes resistance comparable to flame soldering in some situations, but the resistance heat is more localized because of direct contact, whereas the flame might heat a larger area.