Solder and Rework - A guide to techniques and equipment

Solder and Rework

Soldering is used in every electrical product globally to join electrical parts together, using a mixture of lead and tin (solder/flux), with an electrical soldering iron. Soldering irons are heated by an electrical element with the tip being used to heat the solder. Tips are often removable so they can be changed if damaged or worn out without replacing the entire soldering iron. Usually, the solder is applied in the form of flux covered wire which is available in different materials and compositions intended for different uses. There are a large range of soldering irons available so your choice can be determined by your budget and individual needs.

Robotic soldering units are also available and depending on your requirements can be more beneficial. For high volumes of soldering, automated or robotic soldering stations are more cost effective and much more efficient.

When selecting your manual soldering iron or soldering station you need to be aware of the voltage, wattage and temperature control. A higher wattage model would be better for larger joints as there is more power in reserve meaning it will not lose its heat so quickly. You can expect to pay more for higher wattage soldering irons which are temperature controlled and therefore better suited to heavy duty projects.

A soldering station incorporates a bench top control unit with its own soldering iron. For safety reasons a soldering iron should always be kept in a heat resistant holder whilst switched on but not in use. The soldering station takes care of this problem as it contains this feature. As with all tooling and electrical procedures, health and safety is paramount.

To ensure your soldering project goes without a hitch there are several things you need to consider. Initially you must ensure all parts of the equipment and your work area are extremely clean. This so your solder is effective as any contamination will result in the components not bonding as they should. Older components can be very tricky to solder due to build-up of oxidisation. Between solder, the tip should always be cleaned with a sponge or cloth. All parts should also be the same temperature before administering the solder to assist the flow of the solder over the joint. The tip of the soldering iron needs to be as near to the required area as possible to ensure the heat transfers sufficiently. The duration of the application is another important factor to consider in order to prevent damage to the component. The size of the tip, the wattage and the size of the joint will all contribute to the required duration for each individual project. The final consideration is the quantity of solder to use for a successful bond. Too little solder can result in an unsuccessful joint requiring reworking at a later date. Too much solder may cause shorts circuits.

It is also very important not to attempt to move the part until the solder has cooled down. As the solder is solidifying do not be tempted to touch or rearrange the work area as this will most likely result in a failed joint. When it has cooled the appearance of the solder surface will change from when it was at a much higher temperature.

Desolder pumps and stations are also available for reworking purposes. A braid is used to draw up the solder from the affected area. If the joint is hard to reach or somehow difficult to remove it is sometimes necessary to initially apply more solder before desoldering the entire area.