Kinds of Solder

Except for special jeweler's solder, solder is usually silver or gray.

Solder joins together two metal pieces or wires, or wires to components in electronics. A soldering gun or torch heats the metal pieces and melts the softer solder against them; these fuse when the solder cools. Available varieties of solders fall into two general types: hard and soft solders. Solder is categorized in gauges, or thicknesses; 22-gauge solder is used for electronics. Smaller-gauge solders are thicker than higher-gauge solders.

Gold Solders

Hard solders, which are usually copper-based, melt at higher temperatures than other solders. When using a mixture of solder types, always begin with the hardest solder and work down to the softest solder, to prevent melting your soldered joint later. Jewelry makers use hard solders, mixing copper with gold or silver and requiring torches to melt the solder. Mixing the precious metal with copper lowers the melting temperature of the solder. Jewelers name these solders according to the amount of copper added to the silver or gold. "Eight" solder has a ratio of seven parts silver to one part copper. Jewelers also use solder of six, four and three. In jewelry making, the color of the solder is as important as the strength of the solder material; jewelers adjust the amount of gold or silver to match the color of the piece being crafted.

Silver Solders

Gold and platinum pieces generally require gold and platinum solders, respectively, but many other metals, such as copper, nickel, steel and silver will accept a silver solder. Silver solders vary by melting temperature; these include, from the highest melting point to the lowest, enamel solders and hard, medium, easy and extra-easy grades. Enameling solder melts at 1,217 C -- only 150 degrees less than the silver itself. The other solders melt at progressively lower temperatures; hard solder melts at 773 C, medium solder at 747 C and easy solder at 711 C. Expert jewelers recommend staying away from lower-melting solders, to prevent the piece from falling apart during repair.

Core Solders

Solders often have an inner core made of a different material. These include flux cores; flux is a material that helps your solder to flow more easily and cleanly into the pores in the metal. Rosin is sometimes added to a core, to hold the solder together until its melting point is reached. For metals that are hard to bond, acid-core solders help the solder bite into the metal. These types of solders are melted with a soldering iron instead of a torch.

Lead Versus Lead-Free

The solders with the lowest melting points contain lead; they are mixtures of lead and tin in varying ratios. With this solder, the first number in the name represents the percentage of tin; the second is the percentage of lead. The most common types are 60/40, 63/37 and 50/50; 60/40 and 63/37 are used in electronics, whereas 50/50 is used for plumbing. The use of lead, a toxic substance, in solders is being phased out in Europe and China. Lead-free solders usually replace the lead with tin; copper, silver and antimony may also be used. Cadmium is another toxic solder component, usually mixed with silver or zinc. Use zinc-aluminum and zinc-tin solders for soldering aluminum.

References

• "A General Dictionary of Commerce, Trade, and Manufacture"; Thomas Mortimer; 1810
• "The Encyclopedia of Jewelry-Making Techniques"; Jinks McGrath; 1995
• AJH Custom Knives: Differences Between Soft Solder and Hard Solder
• eFunda: Solder Types