Solder is a metal alloy, meaning that two or more metals have been combined to create a single metal. Solder has been in use for many years as a joining method, as its primary use is to join together other types of metal by heating it to its melting point to create a liquid bond before cooling it to its former hardness. The different types of solder include lead and tin, aluminium, gold, silver, zinc, nickel and rosin-core solder.
Rosin-core solder is a tubular or hollow form of solder. The inner space of the solder is filled with a non-corrosive rosin flux. There are a number of different rosin flux categories, such as pure rosin, mild activation rosin, super-activated rosin and activated synthetic resin. The flux helps to keep the work piece clean during the soldering process and facilitates the bond between the metals and the solder.
Rosin-core solder is the most common type of solder and is a multipurpose solder. Rosin-core solder is the recommended solder when working with electrical wiring and certain metals, including copper and tin. This type of solder is available in different diameters for different purposes. Precise work with electronics is typically best suited for solder with thinner diameter.
There are three main types of rosin-core solder: 50/50 is 50 per cent tin and 50 per cent lead and has a melting temperature of 218 degrees Celsius; 60/40 is 60 per cent tin and 40 per cent lead and has a melting temperature of 188 degrees Celsius; and 63/37 is 63 per cent tin and 37 per cent lead and has a melting temperature of 183 degrees Celsius.
For most soldering applications, 60/40 is recommended.
There are alternative types of solder, but each offers a caveat that you must consider. Solid-core solder does not offer a flux core, so you must apply flux directly to the work piece. Acid-core solder offers a flux core, but it requires frequent cleaning of the work piece to prevent acid wear and is trickier to work with in general. Unless you are well-experienced in soldering, rosin-core solder is typically the best type of solder for most metal-joining applications.
When you are soldering electronics, which is one of the most common uses for this joining process, rosin-core solder is the most effective type to use. You may use solid-core solder for most electronic soldering applications, but should never use acid-core solder, as it can seriously damage the electronic components in your work piece.