Please note this article first appeared in the August 1995 edition of MARA NEWS


There is only one way to learn how to solder and that is by practice. Failures in "home constructed" projects are caused, most often, by poor soldering, yet it is a skill which can be very easily learned.

Solder is a funny metal; when heated it will become very much like plastic (at lower temperatures). It can be spread or piled up rather like butter but if it is made just a bit hotter, it flows very freely. This is what must happen when a soldered joint is being made. Solder for use in electronic circuits is made from about 60% tin and 40% lead and has one or more cores, containing rosin, running through the complete length. When the solder is heated the rosin melts and keeps the surfaces to be soldered clean.

Now the materials you will need: a small soldering iron, a suitable stand for the iron, a small damp sponge if there isn't one with the stand, and some resin cored solder. The easiest to use is very thin--#22 SWG (Standard Wire Gauge)--and costs about 50 cents for 10 meters, which will last quite a long time. Now practice a few soldered joints.

DON'T attempt a project until you are sure that you can make good soldered joints every time. You will recognize a good joint-the solder will be bright and shiny and you should be able to see the outline of the wire under the solder. If the solder is dull grey, the wire probably moved before the solder set. If it looks like a miniature mountain range, the solder didn't get hot enough. The secret is to use the soldering iron to get everything to the temperature at which the solder flows easily. The tip of the iron must touch both parts and the solder at the same time!

To practice, you will need a couple of metal tags (or a piece of Veroboard) and a length of copper wire. Switch on the iron and when the tip is hot, touch the tip with the resin cored solder and wipe it off on the damp sponge. Now hold the iron so that the bit is touching the wire and the top of the tag, then touch both with the solder at the same time. The solder will melt almost immediately. It should take less than two seconds for this to happen. If after five seconds it hasn't worked remove the iron and allow the board to cool down, then try again. If you are using Veroboard and the solder flows along the track or even worse, fills the gap between tracks, you are using too much solder. You must avoid this because in an actual circuit the solder would connect the tracks and the circuit would not work. Repeat the exercise as many times as you can, using a fresh position on the tag each time. You will soon find that the joints begin to look good. If you get too much solder around a joint, touch it with the hot iron, wipe the bit on the sponge and keep repeating (allowing time for the board to cool) until the amount of solder is reduced. Later, if you do a lot of work on Veroboard and printed circuit boards (PCB), you will find it worthwhile getting a 'solder sucker' which is a kind of pump which sucks up the solder melted by the soldering iron. Keep practicing and aim for that one and a half second joint. A HOT SOLDERING IRON, INCORRECTLY USED, IS DANGEROUS!

Don't burn yourself-never touch the bit and DO put the iron in a position where it will not be touched by accident. DO make sure that younger brothers and sisters can't get their fingers on it! DON'T burn your clothes-wear old ones and better still, an apron or overalls. DON'T burn the furniture. DO cover your work surface with an odd piece of hardboard or similar.

DON'T leave a hot iron unattended, not even for a very short time; always switch off before you leave it.

DON'T lay the iron on your work surface.

DO use a stand-this has the advantage of making the tip of your iron (and the iron) last longer.

DO switch off if there is to be more than five minutes between making one joint and the next (unless you are lucky enough to have a temperature controlled type of iron). This will also make the iron last longer. DON'T shake the iron to remove the solder which collects on the bit. You never know where the hot solder is going to end up-it could damage your eyes or someone else's.

DO wipe the tip on the damp sponge to remove the excess solder. DON'T let the work get too hot-remember, a joint should be complete in less than two seconds. Allow at least ten seconds for the board to cool before you touch it.

DON'T keep the tip of the iron on the work longer than five seconds, even if the solder does not melt.

How to solder a lead to a tag.

(a) Bend the wire round the tag and squeeze it gently with a pair of pliers so it stays put.

(b) Heat the wire and tag with the soldering iron, with the solder ready.

(c) Quickly apply the solder to the joint, and the metal should flow over both the wire and tag.

The National Amateur Radio Association has been granted permission to reproduce material from "D-I-Y Radio," an excellent publication from the Radio Society of Great Britian. If you see their logo, it means the material first appeared in "D-I-Y Radio" and is reproduced with permission.

For more information on the many excellent RSGB publications, write
Radio Society of Great Britian,
Lambda House, Cranborne Road,
Potters Bar, Herts. EN6 3JE ENGLAND

Transmitted: 95-02-16 17:22:46 EST