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electriciansparadise -- Electrician's Guide to Soldering

Years ago, before the era of wirenuts (solderless connectors), splices were made within enclosures by soldering the wires together. The ends were stripped and twisted together, then fluxed and soldered, finally wrapped in two kinds of tape -- first electrical tape to secure and insulate the joint, then friction tape for protection against abrasion. Wirenuts were a great advance. In new work, you didnÍt have to worry about not having an electrical supply to accomplish the soldering. Moreover, the wirenuts were quick and easy to use and, equally important, to remove for testing or alterations.

But there are still instances when electricians are called upon to solder and it is important to possess the necessary skills. Actually soldering is quite easy but you have to be aware of a few fundamentals in order to do high quality work in this area. Unlike welding which has to penetrate deeply into both metals to be joined, solder just sticks to the surface. Therefore, much less heat is required.

The first step is to consider and evaluate the metals to be soldered. Soldering works good with copper, lead and most brass, but there are many metals that canÍt be joined with soldering, notably aluminum. Most electrical work involves copper to copper joints, and it is here that solder works quite well. If in doubt, try to solder a sample of the metal involved. In the case of aluminum, solder just slides off and wonÍt stick, or if sufficient heat is applied, parts of the aluminum melt and instantly fall away. It doesnÍt work.

The next step is to choose the right tool and the right solder. Generally, for electrical work a torch is not appropriate. The heat is too spread out and by the time there is enough heat to accomplish the soldering, nearby insulation and electrical components are damaged. Anytime insulation has been scorched, it no longer works as insulation and will further deteriorate with time so that it is necessary to replace the whole wire. Similarly, if an electrical component such as a microchip becomes heated at all, it will become nonfunctional and must be replaced. If a lead is cut off or broken too short, it cannot be repaired and the component must be replaced.

One way to deal with the excess heat is to attach one or more heat sinks between where the soldering is to be done and the component. These heat sinks are like heavy alligator clips which clip onto the wire lead. This metal absorbs excess heat and radiates it into the air so that less heat travels down the wire in the direction of the component. If you donÍt have a heat sink, you can improvise by using needle nose pliers. Squeeze the jaws in place and wrap electrical tape around the handles to keep the tool tight.

In order to make solder stick, it is necessary to clean any dirt or oxidation off the wire. Any impurities act as insulation and prevent bringing the metal up to temperature. Gently scrape with a knife until you see shiny new-looking copper, without cutting into the metal and removing any of it. Then apply flux. When the flux gets close to the melting point of solder, it bubbles and cleans away any remaining oxidation.

The tip of the soldering iron also has to be kept clean. If it appears other than shiny silver, it is not clean. It has an oxide coating. You can't solder with a tip like this. Here again the oxide acts as a thermal barrier. If you put solder against a corroded tip that is up to temperature, the solder will just just crumble and fall away. To clean a tip, let it heat up and then wipe it on a slightly damp sponge. Then you can add a little flux and melt some solder onto the tip and you are ready to go. This is called "tinning the tip". Keep the damp sponge handy and whenever you see the oxide is starting to appear, retin the tip as described. When you are done soldering, clean the tip and apply a nice blob of solder as the tip is cooling. The solder coating will prevent the tip from oxidizing and you can start right in when you are ready for your next job.

It is important to choose the right flux. Acid based flux is good for soldering pipes and radiators, but it has no place in electrical work. It is too powerful and any slight residue will corrode and compromise the joint in the future. In an emergency, acid flux can be used but after the soldering is done, the joint has to be swabbed down with water so that the acid is cleaned off. But it is better to use the right flux.

The right flux for soldering electrical joints is resin flux. Any residue remaining after the job is completed will not corrode the joint or adjacent work.

Before starting, choose the right iron. For soldering 14 or 12 AWG copper wire, a 100 watt soldering gun is about right. For finer wires or printed circuits, a pencil point 40 watt iron is needed.

The rule for soldering wires together is that first they should be looped or twisted together so that the joint is mechanically strong, then apply flux and solder. You can increase the conductivity and strength of a crimp-on connection by applying flux and then running in some solder. This is done with three horsepower and over submersible pump motors.

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