The Different Solders for Electrical Vs. Plumbing
Soldering joins copper wires used in electrical circuitry, or copper pipes used in plumbing, by filling small gaps between two hot pieces of copper with a molten metal alloy. Tin, one of the best metals for hot bonding to copper, forms a weak joint if used alone. When tin mixes with other metals, the solder gains strength, and the alloy's melting temperature changes. Different combinations of metals provide the best solders for electrical or plumbing applications.
Solder joins two copper parts by flowing into the spaces between metal crystals like water into a sponge. Solder seals plumbing connections and provides a conductive bridge for electronics. The strength of a solder joint increases if the two pieces being joined fit together neatly and form a strong mechanical connection. Plumbing solder with high tensile strength makes stronger pipe joints, but melts at higher temperatures than softer electronic solder. The extra heat needed to melt plumbing solder can damage electronic components. Using the wrong solder can result in plumbing fixtures that leak and electrical connections that fail.
The layer of oxide on the surface of a copper wire or pipe prevents solder from bonding. Both copper parts need thorough cleaning, down to bright metal, before joining. Chemical flux, either painted onto the copper or contained in the wire solder's core, flows over the hot metal and floats contaminating oxides away. When the solder melts, the molten metal displaces the flux. Resin-core solders used in electronics etch copper slightly when heated but won't corrode circuits when cool. Acid flux in plumbing solder efficiently cleans larger copper surfaces such as copper tubing, but can ruin delicate electronic parts.
The easiest solders to work with contain lead. Lead alloyed with tin and other metals creates a solder that melts at a low temperature and flows smoothly. In 1986, amendments to the Safe Drinking Water Act ended the use of lead solder in drinking-water applications. Concerns about lead exposure in the electronics industry and lead contamination from aging electronic products caused a similar shift to lead-free electronic solder. All types are still sold, so be sure the product says "lead-free" if the solder is intended for household plumbing. To work with lead-free electrical solder, you'll need hotter soldering irons.
The most demanding applications in either plumbing or electrical work require metal alloys that melt at higher temperatures than alloys based on tin. Brazing pipes with silver alloys creates a strong joint capable of withstanding high pressure. Brazing requires a torch fueled either by MAPP gas or acetylene. A propane torch won't generate enough heat for brazing pipes. Unless you're experienced, hire a professional for any plumbing job requiring brazing. Electrical silver solder lowers the resistance of connections, reducing noise in audio circuitry and computer applications, but isn't necessary for ordinary household wiring. Hobbyists often use silver solder for jewelry-making and other art work.