Soldering Gun

Soldering is a quick, efficient method of joining metals permanently. Everyone who has the occasion to make electrical repairs should know how to solder. Electrical connections that are soldered are far less likely to come apart and will conduct electricity far better than connections that are only "pig-tailed" together.

The most popular (and preferred) method of soldering is with an electric soldering gun. Soldering irons are available in many sizes and wattage ratings. Irons with high wattage ratings deliver higher temperatures and recover lost heat faster. A small soldering iron rated for no more than 40 watts is recommended for home use, especially on electrical projects where excess heat can damage the components being soldered.

There are three ingredients necessary for successful soldering--proper flux, good solder and sufficient heat.

Flux

A soldering flux is necessary to clean the metal of tarnish, prepare it for soldering and to enable the solder to spread into tiny crevices. When soldering electrical work, always use a resin flux or resin core solder, which is non-corrosive and will not attract moisture once the job is finished. Other types of flux (acid-core) will leave a residue that will attract moisture, causing the wires to corrode.

Good Solder

Tin is a unique metal with a low melting point. In a molten state, it dissolves and alloys easily with many metals. Solder is made by mixing tin (which is very expensive) with lead (which is very inexpensive). The most common proportions are 40/60, 50/50 and 60/40, the percentage of tin always being listed first. Low-priced solders often contain less tin, making them very difficult for a beginner to use because more heat is required to melt the solder. A common solder is 40/60 which is well suited for all-around general use, but 60/40 melts easier, has more tin for a better joint and is preferred for electrical work.

Sufficient Heat

Successful soldering requires that the metals to be joined be heated to a temperature that will melt the solder, usually somewhere around 360-460°F (182-237°C), depending on the tin content of the solder. Contrary to popular belief, the purpose of the soldering iron is not to melt the solder itself, but to heat the parts being soldered to a temperature high enough to melt solder when it is touched to the work. Melting flux-cored solder on the soldering iron will usually destroy the effectiveness of the flux.

How to Solder

1. Soldering tips are made of copper for good heat conductance, but must be "tinned" regularly for quick transference of heat to the project and to prevent the solder from sticking to the iron. To "tin" the iron, simply heat it and touch flux-cored solder to the tip; the solder will flow over the tip. Wipe the excess off with a rag.
2. After some use, the tip may become pitted. If so, dress the tip smooth with a fine file and "tin" the tip again.
3. An old saying holds that "metals well-cleaned are half soldered." Flux-cored solder will remove oxides, but rust, bits of insulation and oil or grease must be removed with a wire brush or emery cloth.
4. For maximum strength in soldered parts, the joint must start off clean and tight. Weak joints will result in gaps too wide for the solder to bridge.
5. If a separate soldering flux is used, it should be brushed or swabbed on only those areas that are to be soldered. Most solder contains a core of flux and separate fluxing is unnecessary.
6. Hold the work to be soldered firmly. It is best to solder on a wooden board, because a metal vise will only rob the piece to be soldered of heat and make it difficult to melt solder. Hold the soldering tip with the broadest face against the work to be soldered. Apply solder under the tip close to the work. Apply enough solder to give a heavy film between the iron and piece being soldered, moving slowly and making sure the solder melts properly. Keep the work level or the solder will run to the lowest part, and favor the thicker parts, because these require more heat to melt the solder. If the soldering tip overheats, (the solder coating on the face of the tip burns up). The tip should be re-tinned.
7. Once the soldering is completed, let the soldered joint stand until cool.

   Fig. 2: If necessary, dress a pitted tip with a fine file

   Fig. 3: Tinning the soldering iron

   Fig. 4: Wipe the excess solder from the iron while hot

   Fig. 5: The correct method of soldering. Let the heat transferred to the work melt the solder