“How to: Solder Electrical Wires”

 By Ron Stultz

28 December 2005

Summary: heat the wire, not the solder. 

The soldering of electrical wires is not difficult but there are several keys to making a good soldered joint:

- Make sure the wires are electrically twisted together. Solder is not a replacement for a strong mechanical connection.

- Use good quality rosin core solder. I prefer small diameter solder as it melts easily and I only rarely solder heavy gauge wires where a larger diameter solder would be more effective.

- Do not use more soldering iron (rated in watts) than you need and do not use less. This means that on integrated circuits, too much heat on chip leads can destroy the chip. On heavy gauge wires, it might take you holding a small soldering iron on the wires a very long time to get solder to melt and flow, whereas a larger iron will heat the wires quicker and thus the solder.

- Hot, excess solder likes to drip so solder on a flat surface. Solder, which drips on a flat surface usually will not burn the surface but if you drip solder on fabric, you have a mess getting it out.

- Allow the soldering iron to get good and hot before you try to use it. One way to test if it is hot enough and also to prepare if for soldering is to "tin" it. This means, taking some solder and applying it directly on the soldering iron tip. If the solder melts easily, then the iron is hot enough and you have also prepared the iron for soldering.

-  Heat the wires, not the solder. By this I mean you start by placing the soldering iron on the wires to be soldered and then place the solder on the wires. Once the wires become hot enough, the solder will melt and once the wire joint is covered with solder, remove the soldering iron and solder.

- If you are doing a lot of soldering, take a sponge and damp it and between solderings, wipe the soldering iron across the sponge to remove excess solder and flux. Keep the tip of the iron clean.

A good soldered joint? One, which is bright and shiny and not dull or flat in appearance, and also one, which clearly, visibly, has solder around and through the electrical, mechanical junction.

What do you do if you do not get a good solder joint the first time? If you are soldering a circuit board component or a circuit chip, it is best to use what is called a solder sucker to remove all excess solder from the joint and then heat the circuit component or chip lead again and touch with solder. If what you are soldering is just wires, reheat the junction and when solder in or on the junction begins to melt, apply new solder and let new solder and old solder melt together.