Soldering — What It Is and Why It Matters
Soldering is a joining process that uses a filler metal (solder) with a melting point below 840°F (450°C) to bond metals without melting the base material. The solder flows into the joint by capillary action, creating an electrically conductive and mechanically sound bond.
Soldering is the standard joining method for electronics, circuit board assembly, copper plumbing, stained glass, and jewelry. Common solder compositions include tin-lead (traditional), tin-silver-copper (lead-free, required by RoHS for electronics), and tin-antimony alloys.
Flux is essential for soldering — it cleans the metal surfaces, prevents oxidation during heating, and promotes solder flow. Rosin-core flux is standard for electronics; acid-core flux is used for plumbing but must never be used on electronics as it causes corrosion. While soldering produces weaker joints than brazing or welding, it is perfect for applications where high strength is not the primary requirement.
Frequently Asked Questions
Is soldering considered welding?
Technically no. Welding melts the base metals together; soldering only melts the filler metal. However, soldering falls under the broader umbrella of metal joining processes, and the American Welding Society includes soldering in its standards and educational programs.
Why does solder need flux?
Metal surfaces oxidize when heated, and oxides prevent solder from bonding to the metal. Flux chemically removes these oxides and prevents new ones from forming during the heating process, allowing the solder to wet and flow properly into the joint.