What is Solder?

Solder is a metallic alloy used to join two metallic surfaces into one. Joining metal parts together, by allowing a molten metal alloy to flow around them is called soldering. When the solder cools and solidifies, it provides a good electrical connection between the parts, along with a little mechanical strength. It is a skill that should be honed by both professionals and hobbyists alike, and is essential in building, repairing, and modifying electronic components.

Safety

You should always work in a well ventilated area. Avoid breathing in the fumes, as prolonged exposure to solder can cause health problems. While some "experts" disagree, we advise that you always protect your eyes. Safety glasses are a minor discomfort and an inexpensive investment for a lifetime of normal vision.

How to Solder: Overview

1. Equipment: Basic Tools

The one tool that you will always need is a soldering iron. A soldering iron between 25W and 30W is recommended for minor electronics work. Higher wattage soldering irons are generally not used for soldering small electronic components. You will also need some solder. A rosin core solder, preferably with a small diameter is recommend. The solder will be composed of 60% tin - 40% lead, and cores of rosin "flux" which helps the molten solder to flow more easily over the joint. A thin solder with a small diameter makes tinning the exact amount of solder that you will need much easier. It is always a good idea to have a small wet sponge to clean and cool the soldering iron tip. Most soldering iron holders come with a sponge attached to its base. Refer to the soldering tools page for detailed information regarding tool selection.

2. Component Preparation

Before you can start soldering, you must make certain that all parts to be soldered are free from grease, oxidation and other contamination, otherwise you will find yourself battling with globules of molten soldering flowing around where you don't want them to. An unclean surface can also cause the solder to not bind well to the surface, and novices can make the mistake of overheating the components as they try to force the solder to stick. This will usually result in irreversible damage and force you to replace the components. It is very important to understand how to properly prepare the components to be soldered.

3. Component Tinning

Both soldering contacts must be tinned before you attempt to solder them. This coats or fills the wires or connector contacts with solder so that you can melt them together. For example, if you are soldering a piece of insulated wire, use a wire stripper to strip away the tip of the insulation to expose the copper wire within, and then lightly coat it with solder. You must also tin the tip of the iron to help conduct heat to the components.

4. Applying Heat and Solder

With the tinned soldering iron in hand, you are now ready to heat the components to be soldered. The purpose of the soldering iron is not to transfer a glob of solder, but to provide heat. Many novices wrongly attempt to use the soldering iron to shape the joint. Solder will naturally flow to the parts that are heated, and do not require you to shape the joint with the soldering iron tip.

Rest the iron tip on both the component lead and the circuit board. It will only take a few seconds to heat the components up depending on the surface area. Once you have heated up the component and the circuit board, solder will naturally flow towards the heat. Touch the tip of the strand of solder to the heated component lead and the solder pad on the circuit board, but not to the tip of the iron. At this point, the solder will flow freely around the component lead and the pad. Once the surface of the pad has been completely coated, you must stop adding solder and quickly remove the soldering iron. Do not move the newly formed joint for a few seconds until the solder cools down and becomes solid.

5. Cleaning and Finishing up

You should clean the soldering iron tip after each soldering session. There are solutions specifically designed for this but a damp sponge works just as well. The idea is to rub the soldering iron tip each and every time you finish a solder joint. That is to say, you will be cleaning the tip several times per session if your project requires you to form multiple solder joints. To clean the solder off a circuit board, you should use a solder wick. First place the wick on the joint or track you want to clean up, and apply your soldering iron on top. The solder will melt and be drawn into the wick. The wick will fill up, so gently pull the wick through the joint and your iron, and the solder will flow into it as it passes.