Steps to a Good Solder Joint
by Jerry Kelly
The metal to be soldered should be clean, free of oxidation and bright. Generally, wire on electronic parts needs no cleaning, but brass, copper and especially music wire should be cleaned with fine sandpaper at the point to be soldered.
The tip of the soldering iron must be properly tinned. If you have a new Iron it probably has an untinned copper tip. Clean the tip, apply the proper flux and heat it until it melts solder. Apply enough solder to cover the business end of the tip. The best solder for this is Stay-Brite since it has no lead. When the tip begins to look black in spots, heat it enough to melt the solder and wipe the tip with a thick, damp cloth. If the black spots are still, there remove them with a file or sand paper and re-tin the tip.
Flux should be used on every joint to prevent oxide forming in the period between cleaning and applying the solder. The two types of flux are rosin and acid. Rosin must be used on electronic connections. The best “radio solder” is 60/40 lead/ tin with a core of rosin flux. Rosin flux is available in paste form from radio supply houses. Excess rosin flux can upset radio circuits by creating high resistance connections between components. Use alcohol to remove excess flux.
For music wire and any joint where strength is important Stay-Brite and its liquid flux should be used. It is 95% tin and 5% silver, which makes a much stronger joint than radio solder. For added strength (such as needed for landing gear) wrap joints with either soft copper or steel wire.
For any joint the metal must reach the proper temperature in order for the solder to flow. If the metal is too cold the solder balls up – a “cold joint” – and has very little strength. Too much heat and the flux burns making an ugly mess.
Finally – let’s solder! Bring the hot soldering tip in contact with the area you want to solder. At the same time bring the solder in so that it is touching both the hot tip and the joint. When the solder starts to melt it will help to conduct the heat to the work. At first the solder will “ball up”, then when the work reaches the correct temperature the solder will flow to the area that has been fluxed. It’s O. K. to move the tip around a little to help spread the solder. If you have applied more solder than needed you can re-heat and wipe the joint with a thick rag or an acid brush.
Acid flux spatters when heated so be sure that you protect the area around the joint with paper towels or rags. When new, music wire has a protective coat to reduce rusting. This coating is what you have to remove to get a good solder joint. Clean the joint with water, then use WD-40 or 3in1 oil to reduce the chance of rusting .