Smith-Kettlewell Soldering Series Part 3
Table of Contents
Soldering I
Soldering II
Soldering III: Tinning Stranded Wire
Soldering IV: Popular RF Connectors
Soldering V: RCA and Motorola Plugs
Soldering VI: Resistance Soldering
Soldering VII
JA3TBW Solder Guide
Soldering Kinks
Vinther Fingertip Soldering Iron
Soldering Part III: Tinning Stranded Wire
I have learned from experience that neglecting to tin stranded or braided wire before soldering it to a terminal is no shortcut. If the bundle of strands is not soldered together beforehand it is very likely that a few individual strands will not be involved in bonding to the terminal. This weakens the connection, and individual strands may subsequently stray over to an adjacent terminal.
In order for all the strands to be presoldered together, the stripped end of the wire must be bathed in fresh solder. As it is with tinning the iron, there is hardly such a thing as applying too much solder. A generous amount of solder can be wrapped around the end of the wire and heated. I keep a roll of very thin solder on hand for this purpose (about .03 inches in diameter). For small wire (above 22 gauge), I use a length of solder about two times as long as the stripped-back portion of the wire. I double this amount when soldering larger wire such as lamp cord or braid.
Don't be stingy with the length of wire from which you remove the insulation--remember, you will have to find this stripped end with the tip of a hot iron.
Give yourself a good 1/2 inch of bare wire beyond the insulation.
Twist the stripped end of the wire between your fingers to tightly bundle the strands. Using the two-to-one rule, fold the solder back against itself about an inch from the end, thus forming a long skinny hook of solder. Slide the wire all the way into the hook and position the bend of the hook just ahead of the insulation. Wrap the 1 inch long piece of solder in a neat coil around the bundle of strands, progressing towards the end of the wire.
Finding the wire with the tip of the iron is no easy task. Hold the wire in one hand the iron in the other, and rest both hands against a familiar referencing object. While bringing them closer and closer together, gently rock one of them up and down so that they are sure to connect as soon as they cross.
When they have met, put the bundle of strands on top of the tip of the iron and wait for the solder to melt. Melting of the solder will be indicated by the disengagement of the wire from the solder leading back to the spool, and by the usual "squeakiness" of solder-wet surfaces.
At this time slowly slide the iron out from under the end of the wire, allowing the wire to flip downward and shake off its excess solder. (This will tend to splatter solder, so don't do it in the direction of other people or the family pet.)
Tinning braided conductor deserves special mention. Taken together, the many strands in the braid present a large amount of surface metal with which the solder can alloy. In addition, these strands are in firm contact with each other--efficient heat transfer occurs between them. The result is that braid acts like a "wick" in the molten solder; bathing the end of the braid in solder will cause a surprising amount of the braid to become stiffly soldered together.
If you wish to tin merely the end of the braid without impairing its flexibility further back, one or two clip-on heat sinks can be attached just behind the length being tinned; this causes an abrupt decrease in temperature beyond which the solder cannot alloy with the strands of the braid. Remember to reattach a heat sink to the braid when soldering it to a terminal, since this "wicking" of the solder can still occur.