Soldering is the joining together of two metals to give physical bonding and good electrical conductivity. Solder is a combination of metals, which are solid at normal room temperatures and become liquid at between 180 and 200ºC. Solder bonds well to various metals, and extremely well to copper.

Soldering has many uses. It is used primarily to assemble electronic components such as resistors, capacitors and ICs onto printed circuit boards. However, it can also be used to join wires, metals, and even manufacture jewellery.

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.



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: -

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 400ºC.

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 will melt if touched by a hot soldering iron. Therefore silicone rubber insulated power leads are extremely popular for long life and electrical safety.

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 schools or for 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. You should always use much safer.

As your soldering skills improve, you may work with temperature sensitive devices such as integrated circuits. For these applications a temperature-controlled soldering iron (TCS) should be used.

For bench work a soldering station may be used. This incorporates temperature selection, optional digital temperature readout, 24V transformer, an iron holder, and a sponge, all within a neat bench unit.





1. Twist lead if multi-stranded and tin the area to be soldered. 2. Bend the lead to fit the position on the PCB. Do not bend too close to the component body as damage to the component may occur. 3. If the component is temperature sensitive use a pair of pliers as a heatsink between the component body and the point to be soldered. 4. Tin the site where the component is to be soldered.