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Soldering - A beginners guide.
I have compiled this guide for those that may not be experienced in the dark and mystifying art of soldering. It is only meant to be basic, and to give you a bit of help to learn the basic techniques of how to solder small electronic components and projects. The skills required to solder say a brass locomotive kit together are slightly different, and a bit beyond this guide. For the purpose of this article, I shall be trying to explain the techniques used to solder electrical and electronic connections. Depending on the type of work you need to do, make sure you are using the correct type of solder and flux.

What is soldering?
Soldering is a way of joining together two or more pieces of metal. In this instance the metal is joined together by melting an alloy, soft solder (usually made up of 40% lead and 60% tin) so that it forms a thin layer between the two surfaces. The temperature at which the solder melts depends on the amount of tin in the alloy, the more tin the lower the melting point.

How to Solder
The average beginner to railway modelling is too scared to try soldering. It is considered to be a black art, and soldering upside down is a real no no. Basic soldering is a skill that is easy to learn and not that hard to master. It just takes practice and with this practice comes confidence. The more soldering you do, the easier it will become. Honest.

Although I will focus on model railway electrical and components, the skills you will learn can be used on many projects.

Good luck, and remember....good soldering takes practice!

Soldering Tools
The only tools that are really essential to enable you to solder are a soldering iron and some fluxed solder. There are however lots of other soldering accessories available which may be useful. Most modellers may have these items in their tool box.

Different soldering jobs will require a range of different tools and equipment. Different soldering projects will also require different temperatures too. For circuit board work you will need a finer tip, a lower temperature and finer grade solder. You may also find that a magnifying glass will be beneficial. Clamps and holders are also handy when soldering cables, as are heat sinks. To wire dropper wires to code 100 track, will require a larger iron as the track will require more heat to allow soldering.

Soldering Irons
There are several things to consider when choosing a soldering iron. I do not recommend soldering guns, even though I use one, as these have no temperature control and can get too hot very quick. This can result in damage to circuit boards, melt cable insulation, and even damaged connectors or track sleepers.

For everyday soldering a 25 or 40 watt iron with a small to medium sized bit is all that will be required. Larger bit sizes and bigger wattage irons have their place, but not for most model railway electrical joints. A larger wattage soldering iron does not mean that it is hotter, it means that it has heat to spare when working.

It is important to remember that a higher wattage iron does not necessarily mean a hotter soldering iron. Higher wattage irons just have more power available to supply heat faster as it is absorbed by the materials being soldered. A low wattage iron may not keep its temperature on a big joint, as it can lose heat faster than it can reheat itself. Hopefully that will make sense. Therefore, smaller joints such as circuit boards require a lesser wattage iron - around 15-30 watts will be fine. Track wire connectors need something bigger - I recommend 40 watts at least.

There are a lot of low cost low wattage soldering irons with no temperature control available on the market today. Most of these will be perfectly fine for basic soldering, and once you find yourself doing more soldering, you may wish to purchase a better soldering iron or soldering station. If you plan on assembling white metal kits, you may also want to buy a low temperature iron specifically for this task. If you plan to assemble brass kits you will require a large soldering iron that can generate heat quickly as the brass will adsorb heat quickly.

Most soldering irons are mains powered. They may operate from 230v or a reduced 12v through a transformer. Also available are battery and gas powered soldering irons and guns. These are great for the toolbox, but you would be better using a plug in model for your work bench.

Most soldering irons will need to plug into the mains. This is fine most of the time, but if there is no mains socket around, you will need another solution. This is where gas and battery powered soldering irons can be used. They are fully portable and can be taken and used almost anywhere. They may not be as efficient at heating as a good high wattage iron, but they can get you out of trouble in an emergency. If you have a bench setup, you should consider using a soldering station. These usually have a soldering iron and de-soldering iron with heatproof stands, variable heat, and a place for a cleaning pad. A good solder station will be reliable, accurate with its temperature, and with a range of tips handy it can perform any soldering task you attempt with it.

For electrical work you should really use a 60/40 rosin core fluxed solder. Avoid solder that contains an acid flux, as this may damage the materials later if not cleaned away correctly. Rosin core solder is available in three main types - 50/50, 60/40 and 63/37. These numbers represent the amount of tin and lead that are present in the solder. A small bit of silver is also available in some solders, which aids soldering. Solder also comes in various gauges. Solder gauge is classified just like wire gauge and awg is used. For smaller jobs finer solder can be used as less solder will be required. In reality any general purpose rosin core solder will be fine for most jobs on your model layout.

Lead-free solder is also available, and works in exactly the same was as normal lead mix solder. It also comes with cores of flux included. It has higher melting temperatures and does not flow so easily which means that you may need a better soldering iron to use it. Most soldering iron tips can be used with both types of solder. Removing lead free solder is a bit more difficult, but can still be done well with practise. Lead-free solder is better for the environment.

Flux is used to help clean the various oxides from the mating surfaces. It also helps the solder to flow more freely along and into the joint. Most solders now contain a flux in its core. It is always handy to have a small quantity of extra flux available. Again make sure this is a non acid based flux for electrical work.

Soldering Accessories and tools
There are many other tools that can be useful to aid good soldering available from a wide range of suppliers. You do not need them all. We have listed the main ones below.

Soldering Iron Tips
It is useful to have a small selection of manufacturers soldering iron tips available with different diameters or shapes, which can be changed depending on the type of work you intend to do. You will probably find that you become accustomed to, and work best with, a particular shape of tip.

The actual size of your soldering iron tip will make a difference to the job you are trying to do. Using a big tip on a small job will make it harder. Try to use the right size tip whenever you can. You can also get different shaped tips for different jobs. Pointed tips can be used for fine work, and blade or flat tips for more general soldering.

Soldering Iron Stands
Iron stands are handy to use if you are doing several or more joints and wish to put the iron down whilst keeping it hot. It is much safer to use a correct stand than it is to leave a hot iron lying around where it can move and be knocked. Your partner also will not appreciate a burn mark on the dining table. Most stands consist of a heat resistant cradle for your iron to sit in, and also a space for a small sponge or tip cleaner. It really is essential if you are planning to do a lot of bench soldering as it is only a matter of time before you burn something (probably your elbow resting on the hot tip) if you do not use one.

Some stands also combine a helping hands type arrangement which aids holding and supporting your work when soldering.

I strongly recommend clamps of some sort. Trying to hold your soldering iron, the solder, and the wire is tricky enough, but when you have to hold the connector as well it is almost impossible. There are however adjustable clamp devices, or helping hands, that can be manipulated to hold both the connector and the wire in place so you still have two free hands to apply the heat and the solder. These are cheap items and I know mine have paid for them selves many times over. Many also include a magnifying glass.

Magnifying glass
If you are doing work on PCBs (printed circuit boards) you may need to get a magnifying glass. This will help you see the tracks on the PCB, and unless you have exceptional sight, small chip resistors are pretty difficult to solder on well without a magnifying glass. They are not expensive, and some helping hands type devices come with a good magnifying glass attached..

Solder Wick
Solder wick is a fine mesh that you lie on a joint and heat. As the solder melts it is drawn out of the joint into the wick. It is usually used for cleaning up solder from tracks on a circuit board, but you will need a solder sucker to clean out the holes in the circuit board. Place the wick on the solder you want to remove then put your soldering iron on top of the wick. The wick will heat up, then the solder will melt and flow away from the joint and into wick.

Solder Suckers
If you work on PCB's, you are going to need one of these before too long. They are a spring loaded device designed to suck the melted solder out of a joint. They are a bit tricky to use, as you have to melt the solder with your iron, then quickly position the solder sucker over the melted solder and release the spring to suck up the solder. Better quality ones come with a metal tip rather than plastic and these should be bought as a preference.

Fume Extractors
Most solders and fluxes will give off poisonous fumes which can be harmful to skin, eyes and lungs. A fume extractor will suck the fumes (smoke) into itself and filter it. An absolute must for your health if you are setting up a soldering bench. If you do not have the luxury of a fume extractor, ensure you solder in a well ventilated space. If you start to feel any effects of fumes please seek help.

As an example I will now go through the actual process required to make a simple soldered wire to wire connection. I am going to explain how to join one end of wire to another. This is one of the simplest solder joints and will be essential when building a model railway layout.

Step 1: Preparation
This may sound daft but ensure you have everything that you are going to need close at hand. You will need your soldering iron, solder, flux, wire strippers, and something to insulate the joint with after completion. I use heat shrink tube for this.

Once you are ready to begin, you will need to strip your cable. This means removing the insulation from the end of the wire and exposing the copper core. You can either use a wire stripper, side cutters, or a knife to do this. There are many types of wire stripper, and most of them work the same. You simply put the wire in, and squeeze it and pull the end bit off.

Remove about 12mm (1/2 inch) of the cable insulation from the end of the wire, and then twist the fine wire strands together. This will prevent a loose wire strand from causing a short if it is left out of the bundle. Do this to both ends of the wire needing to be joined.

Step 2: Tinning
Whatever it is you are soldering, you should tin both contacts before you attempt to solder them. This coats or fills the wires or connector contacts with solder so you can easily melt them together. If the connection is dirty clean it first using files, wire wool or scrapers. A clean surface is required for good soldering.

To tin a wire, apply the tip of your iron to the wire for a second or two then apply the solder to the wire. Do not put the solder on the iron tip as the tip will be hotter than the wire and the solder may not flow into the wire. The solder should flow freely into the wire and coat it. You may need to snip the end off afterwards, particularly if you have put a little too much solder on and it has formed a little ball at the end of the wire.

Be careful not to overheat the wire, as the insulation will start to melt. On cheaper cable the insulation can shrink back if heated too much, and expose more copper core that you intended. You can cut the wire back after you have tinned it, but it Is best simply not to over heat it.

The larger the copper core, the longer it will take to heat up enough to draw the solder in, so use a higher temperature soldering iron for larger cables if you can.

Once you have tinned both parts, you are ready to solder them together.

As I use heat shrink to protect and insulate the joint it would be best that you slide the heat shrink onto one of the wires if they have cooled. Remember its called heat shrink for a reason , and it will shrink if the wire is too hot.

Step 3: Soldering
Before creating the soldered joint it is first necessary to create a secure strong mechanical joint. By this I mean to basically twist the wires together. As I want a straight join I want to twist the wires together without forming a raised section in the wire. See images below.

As the joint should be no larger than the wires I will be using the method in the centre image. Twist the wires together and trim the end on the tinned wire if its longer than the insulation. Place the hot tip of your iron under the wire twist for a few seconds, then carefully try melting the solder on the top of the join. Once the solder melts remove the iron from below the wire and allow the solder to run into the joint and then cool. Hold the wire steady until this has happened. You will see the solder set as it goes hard. This should all take around 1-3 seconds.

Remember that a good soldered joint will be smooth and shiny. If the joint is dull and crinkly, the wire probably moved during soldering. If you have taken too long it will have solder spikes. If it does not go so well, you may find the insulation has melted, or there is too much stripped wire showing. If this is the case, you should de-solder the joint and start again.

Once everything has cooled it should be possible to slide the heat shrink tube to cover the soldered joint. Once its in place use the body of your soldering iron to heat the shrink material. You can also use a hot are blower, hair dryer or even a naked flame to do this. Once the tubing has shrunk, leave it cool.

You should now have a proper soldered wire connection. It may sound easier to write than to do, but with practice it really will be this simple.

Soldering wires to the bottom or outside of your rail is a very similar principle to joining two wires together. The real difference is that the two items to be soldered are of a vastly different size. Here I find pre tinning both the stripped end of the wire and the pre cleaned place on the rail where the wire is to connect the best method. Pre clean the rail with the aid of a fibre pencil or other means. Tin with a little solder, both the place on the rail and the wires stripped end.

To Tin - apply a small amount of solder to the cleaned irons tip, then touch the iron onto the previously cleaned area to be tinned. Solder will flow from the tip onto the area. If insufficient solder flows, keep the soldering iron tip in position, and feed more of the cored solder into the area.

Once every item has been tinned, place the wire end, which has been bent to a small L shape, up to the solder on the rail. Apply a little solder to the irons tip and place the iron on top of the wire and lightly press down towards the rail. The hot solder on the irons tip will cause both the wires solder and the rails solder to melt into one. If necessary apply a little more cored solder onto the wire with the iron still in place should there not be enough on the rail to make a solid connection. Carefully remove the iron and ensure the wire maintains in contact with the rail and does not move, waiting for 5 to 10 seconds to allow the soldered joint to cool.

The use of crocodile clips or any similar metal sprung clamps fixed onto the rails just either side of the soldering work area are advisable, as these act as mini heat sinks and help prevent the rail being overheated away from the soldering area which can, if the heat is allowed to be transmitted along the rail, subsequently causing the plastic sleeper fixings to melt.

Clean Your Soldering Iron
Whilst soldering you should keep your soldering iron tip clean. If you get a burned looking substance on the end, you should wipe this off. This is a residue from the flux burning. You can wipe it using a special tip sponge, or a piece of tissue paper. Just remember that the tip is hot.

You should really clean your soldering irons tip after use. There are many cleaning solutions and the cheapest (and some say best) is a damp sponge. Just rub the soldering iron tip on it after each solder. Another option is to use tip cleaner. This comes in a little pot that you push the tip into. This works well if your tip has not been cleaned for a while. It does create a lot of smoke, so it is better not to let the tip get so dirty that you need to use tip cleaner.

Some solder stations and holders come with a little pad at the base of the holder. If you have one of these, you should get into the habit of wiping the tip on the pad each time you apply solder with it.

Tips and Tricks
  1. Melted solder flows towards heat.
  2. Most beginners tend to use too much solder and heat the joint for too long.
  3. Do not move the joint until the solder has cooled.
  4. Keep your soldering iron tip clean.
  5. Use the proper type of iron and tip size.
If either of the parts you are soldering is dirty or greasy, the solder will not take or stick to it. De-solder the joint and clean the parts before trying again.

Another reason the solder will not take is that it may not be the right sort of metal. For example you cannot solder aluminium with lead/tin solder.

If the joint has been moved during soldering, it may look grainy or dull. It may also look like this if the joint was not heated properly while soldering.

If the joint was overheated the solder will have formed a spike and there will be burnt flux residue.

In this article I have tried to show how simple it is to solder. When I first started all those years ago I made mistakes and still do. Try using your own methods, as I say these are only my working procedures, yours could be better who knows. All I know is that I get good results from them.

Remember the golden rules:-
  1. Clean all surfaces to be soldered
  2. Keep your iron clean
  3. Keep your sponge damp
  4. Use the correct flux
  5. Use the correct solder

Some of the metals used in solder, the chemicals used in flux and the fumes that they produce can be very harmful. Always read any instructions before use, and always wash your hands after handling or using them. Always store them in a safe place, keep them out of reach of children and clean up any spillages.

All soldering irons regardless of their type will generate heat and get hot. Be aware of where you place your iron, and keep hands and fingers away from the heat. A soldering iron is designed to melt metal, it will not think much of burning a finger, or melting what it is placed near.

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Happy soldering!