Soldering Guide

Introduction

Soldering kit.

Solder is a metallic alloy used when melted 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 repairing, building, and modifying electronic components. The most frequent use of soldering is in attaching electronic components to printed circuit boards (PCB). This guide was written to help beginners and novices with the basics of soldering electronic components together. While the basics of soldering is seemingly straightforward, and simple, only the correct tools, technique, and practice will produce the "perfect" joints.

Safety

Safety glasses.

Before you get started, you must first understand that the rosin in the solder is harmful to your body. Therefore, you must always work in a well ventilated area. Next, be sure to protect your eyes. Safety glasses are a cheap investment for a lifetime of vision. Finally, static electricity can cause problems, especially to integrated circuits and other semiconductor devices. It is a good idea to work in an antistatic area with an antistatic soldering iron. Antistatic mats are available to overcome this.

How to Solder

1. Equipment: Basic Tools

Soldernig iron. Rosin core solder.

The one tool that you will always need is a soldering iron. A soldering iron between 15W and 30W is recommended. The use of a soldering iron with a higher wattage can cause unneccessary damage to electronic components, and is generally not used in basic soldering work. You will also need some solder. A rosin core solder, preferably with a small diameter is recommend. The solder will be composed of 60% lead - 40% tin, 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 accessories page for detailed information regarding tool selection.

2. Surface Preparation: Cleaning

Before you can start soldering, you must make certain that all parts to be soldered are free from grease, oxidation and other contamination, lest you form 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 Prepartion: Tinning

Tinned wire.

Both 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. Rest the iron tip on both the component lead and the PCB. It will only take one or two seconds to heat the components up. Once you have heated up the component and the circuit board, solder can be applied. 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 then, quickly remove the soldering iron. Do not move the newly formed joint for a few seconds until the solder cools down and becomes solid. Moving the joint at this point will cause a formation of a cold joint.

5. Cleaning & Finishing up

Cleaning the soldering iron with a damp sponge.

You should clean the tip after each solder. 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. Additional tips on cleaning and finishing can be found here.