An Introduction to Soldering

What is Soldering ? Soldering is the joining together of two metals to give physical bonding and good electrical conductivity. It is used primarily in electrical and electronic circuitry. Solder is a combination of metals, which are solid at normal room temperatures and become liquid at between 180 and 200°C. Solder bonds well to various metals, and extremely well to copper. In electronics a 60/40 fluxed core solder is used. This consists of 60% Lead and 40% Tin, with flux cores added through the length of the solder. Flux is an aggressive chemical that removes oxides and impurities from the parts to be soldered. This ensures a good physical and electrical joint is made. Fluxes enable good "wetting" or "tinning". Wetting is a term that describes good adhesion of the solder to the components being soldered. Tinning is a term that describes the application of solder to the soldering iron tip, or to a component being prepared for soldering. Soldering Irons These are the tools, which heat the solder from room temperature to its melting point. A modern basic electrical soldering iron consists of the following: - * heating element * soldering bit (often called the tip) * handle * power cord The heating element can be either a resistance wire wound around a ceramic tube, or a thick film resistance element printed onto a ceramic base. The element is then insulated and placed into a metal tube for strength and protection. This is then thermally insulated from the handle. The element reaches temperatures of around 370 to 400°C. i.e. approximately 200 degrees higher than the melting point of the solder. The soldering bit is a specially shaped piece of copper plated with iron and then usually plated with chrome. Copper is used for good thermal conductivity. Iron is very resistant to aggressive solders and fluxes. The bit then fits over or inside the heating element dependant on the design of the soldering iron. The handle and power cord completes the soldering iron. Various handle styles are available. The power cord is often insulated with PVC. but, this can be damaged and melt if touched by a hot soldering iron. Therefore silicone rubber insulated power leads are extremely popular for long life and electrical safety. Soldering Iron Selection The strength or power of a soldering iron is usually expressed in Watts. Irons generally used in electronics are typically in the range 12 to 25 Watts. The most popular irons for use in hobbyist electronics are the 18 and 25 Watt versions. It must be remembered that a 25 Watt iron will not run hotter than a 12 Watt iron, but it will have more power available to quickly replace heat drained from the iron during soldering. Therefore, the bigger the component being soldered, the greater the need for "quantity of heat", the higher the power needed. Most irons are available in a variety of voltages, 12V, 24V, 115V, and 230V are the most popular. Today most laboratories and repair shops have a wired 24V supply. You should always use this low voltage where possible, as it is much safer. If you would like 24 volts in the home, use an Antex Plug-in power supply unit. As your soldering skills improve, you may work with temperature sensitive devices such as integrated circuits and smaller more delicate components like surface mount. For these applications temperature controlled soldering (TCS) is essential. The lowest cost TCS iron has a temperature sensor in the tip of the element and control circuitry in the handle. The temperature may be set between 200 degC and 450 degC. For bench work a soldering station may be used. This incorporates temperature selection, optional digital readout, anti-static lead connection, 24V transformer, an iron holder, and a sponge, all within a neat bench unit. Care & Maintenance In common with all tools, the soldering iron will last longer with proper care: a) Before and during use wipe the bit on a damp sponge. Most bench stands incorporate a sponge for this purpose. b) When using a new bit, apply solder to it as it heats up. This will ensure good tinning of the bit. c) Always keep a hot iron in a bench stand, or suspended by the hook, when not in use. d) Regularly check the mains lead for burns or other damage. Consider replacing with silicone rubber if necessary. e) If broken or damaged, all component parts are available from Antex as spares. f) Never put a soldering iron into any liquid. g) Periodically remove the bit and clear away any oxide build up. This will prevent the bit from seizing and also will ensure that a low earth continuity is maintained (vital in electrostatic controlled areas). Further information on the craft of soldering can be found in the Basic Soldering Guide of EPE magazine at : www.epemag.wimborne.co.uk/solderfaq.htm Date 8/4/00