Soldering.

What is solder?
Solder is a soft metal, designed to make permanent connections between electronic components. As it forms part of the electrical circuit, correct soldering is extremely important.
For many years, the solder for electronic work has been 60/40, which refers to the materials used in the solder - around 60% tin and 40% lead. Due to recent laws regarding use of lead in electronic products, new products usually use lead free solder.

Which solder to use.
As a general rule of thumb, products which were available before February 2006 will usually use 60/40 solder while products designed after that date will be lead free. There are exemptions from the RoHS rules, and exempt products may continue to use lead in the solder.
When designing or building a new product, unless it is specifically exempted, it should use lead free solder to comply with the law.
When repairing a circuit, you should use the same solder as the manufacturer used. The use of leaded solder for repair of equipment designed for leaded solder is allowed under the UK rules.

Soldering iron.
The choice of soldering iron is also important. The iron must be hot enough to melt the solder, but not so hot that it will damage the tracks on a circuit board.
A suitable iron will be between 12 and 15 Watts. Higher power irons should not be used on circuit boards, but may be useful for soldering on external cases, where used.
For those who are intending to get more involved in repairs and electronics and are willing to spend more, temperature controlled irons are also available.
Also important, is the type of tip used. A good iron will have a tip that can be removed, and several different tips will be available. The iron shown above is a good choice, the tips and heating elements are easily removed and changed.
The tip for circuit board use should be a small one, not too wide... and not one of those that looks like a big screwdriver tip! Special tips are available for surface mount components, and even greater care should be taken with soldering on such circuits.

A new iron.
When you get a new soldering iron, the first thing you MUST do, is tin the tip. If you do not do this, the tip will oxidise and will not solder correctly.
To tin the tip, you plug in the iron, and apply solder as soon as the tip is warm enough to melt it. Do not let the iron reach full temperature before tinning the tip.

Using the soldering iron.
Before using the iron, be sure that the tip and joint are clean and the tip is tinned.
To solder a joint, first heat the joint, then melt the solder on the heated joint. Do NOT melt the solder on the tip, then "stick" it on the joint... it is not glue, it is part of the circuit.
Do not overheat the joint, as this may damage the board or components. Also, heating the solder for too long will burn away all the flux, and the joint will be poor.

Removing components.
Components should only be removed if really necessary. Whenever possible, components should be tested while in circuit.
When removing components, a special tool should be used to suck the solder from the joint. Care should be taken not to overheat the board or components so, if the solder is not all removed in the first try, let the joint cool before re-trying.

Maintaining the soldering iron.
Always keep the tip clean and tinned. To clean the iron, you can get an iron stand which holds a small sponge. This sponge should be kept damp, so the tip can be wiped on it.