Soldering

Soldering is a method of connecting two pieces of metal together by melting another filler metal in between them. There are many kinds of soldering, but this article is designed to teach you the basics of electrical soldering.

Soldering can be dangerous if you don't follow a few basic safety procedures. You are working with tools that are hot, and melted metals. You want to make sure you don't burn yourself. It's a good idea not to wear loose fitting clothing that could get in the way when you are working, as well as tie your hair back if it is long. It is also important to wash your hands after you do any soldering. Some solder contains lead, and you don't want to be eating that.

The four basic safety rules:

1. The iron is hot.
2. The fumes are not fun. Work in a well ventilated area, or use a fume extractor.
3. Always wear safety goggles. Flying molten lead hurts.
4. Wash those lead-y hands after soldering before touching your face or eating.

Soldering only takes a little bit of basic equipment. You need a soldering iron to heat the solder, an iron stand to put the iron on so it doesn't burn the table, and solder. You can add desoldering braid to this to help if you blow it. A good light will also help you with your work.

A soldering iron is a pen shaped tool with a fine tip that heats up. One of the ways soldering irons are measured by is wattage. For most basic soldering, a 25 to 50 Watt soldering iron will work without any problems. Most irons are simple single temperature models, but it is also possible to buy advanced solder stations where you can directly set the tip temperature with a dial or knob. If you have this feature set your temperature to 300°C for leaded solder, and 375°C for lead free solder.

A soldering iron stand is used to keep the hot tip of the soldering iron from burning the table or work surface when you set the iron down. They are often included with higher end soldering irons, but must be purchased separately with most budget models. The one in the photo also incorporates a place to hold a damp sponge as well as a spot for brass wool for cleaning.

There are many different kinds of solder. All solder for electrical/electronic use is flux cored. Lead-free solder has become the go-to type as the toxicity of lead has been further recognized. It is harder to use than solder containing lead, and has a higher melting point. There are a number of alloys that are lead-free. This kind of solder is better for the environment and your health.

A couple of common types of leaded solder are 63/37 and 60/40. This solder is made of tin and lead and both have a flux core. In the case of 63/37 it is 63%. tin and 37% lead. This kind of solder is inexpensive and easy to work with, however it does contain lead, which can be dangerous to work with if you don't follow proper safety procedures. Many professionals use it for repairs.

For someone just starting out and learning how to solder, using leaded solder may be easier, but lead-free solders and fluxes have come a long way.

Now we get to the fun part, actually soldering. The first thing to do is to place the part on the printed circuit board. Make sure that the board and part are clean. Any dirt or debris on the board or the lead will prevent the solder from sticking to everything properly. It can also be helpful to use a small piece of either masking tape or electrical tape to secure the part to the board. You don't need to do this all the time, but if you have trouble with any particular part staying in place, it can help quite a bit. Finally, double check that the part you are soldering is in the right place on your circuit board, and that it is in the right orientation. Some parts, like capacitors, diodes, transistors and integrated circuits will either not work, or be damaged if they aren't put in properly. If you are just joining wire, you may find it helpful to have something to hold the joint. A device called a soldering splint is helpful for this.

Take the iron in one hand, and the solder in the other. When I solder, I hold the iron in my dominant hand, but you should try each way to see what feels best for you. Add a little bit of solder to the tip of the soldering iron. This is called 'tinning' the iron, and it helps protect the tip of the iron, as well as making it transfer heat better.

Touch the iron to the joint that you're soldering, making sure to touch both the copper pad on the board as well as the lead on the part. The idea is to heat up every part of the connection to the same temperature so that the solder flows evenly into all the tiny spaces.

After a one or two seconds, slowly poke the solder into the joint. If the joint is hot enough, the solder should melt and flow into the joint. You only want to add a few millimeters worth of solder, so don't go crazy. Once you add the solder, pull it away, then slowly pull the iron away from the joint. You can then wipe the tip on a damp sponge or in some brass wool to clean it, add another bit of fresh solder and place the soldering iron into its holder.

A properly made solder joint should look like a cone, with the sides of the solder straight. If they curve in a little, that's okay.

Red Box is leaded solder, Orange Box lead-free

If they are more flat to the board than a cone shape or you might have a cone, but there are craters then there isn't enough solder on the joint, and you should add a little bit more. If it bulges out there's a little too much solder. If this happens, the best thing to do is desolder the joint with desoldering braid and try again.

With leaded solder, the joint should also be shiny. If it isn't, then the joint didn't get hot enough when it was melted. The way to fix this problem is to reheat the joint and try again. You might want to add a little flux too if you have to do it again. With lead-free solder it might not be shiny.

Once you have a joint that looks good, that's it! Keep on soldering all of the other parts onto the board and you're on your way to having a working electronics project.

Soldering Glossary of Terms

How to Solder and Desolder Connections

Soldering Iron Not Melting Solder

Soldering Iron Not Heating

Soldering Materials 101

Soldering Iron Tips

Soldering Best Practices