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.
Before we get started lets think about safety. Soldering has lots of risks,
but you can minimise those risks by following a few safety rules. Hopefully over
time these rules will become common practice every time you solder.
Soldering irons are hot and can make other things hot. Always ensure that
your soldering iron is safely stood on a heat-proof stand when warming up, in
use, or cooling down. If you leave the room, or if you're working on something
else, then switch it off. Never leave a hot iron unattended. Even if a soldering
iron is switched off then it can retain heat for quite a while.
You should always solder on a heat proof surface, I use a cutting mat for a
work surface when carrying out general soldering. Also make sure there is
nothing near that could be harmed by touching anything hot. Never touch the hot
bits of your soldering iron with your bare skin, trust me that get hot.
Some soldering fluxes or pastes can spit and
spray. Be aware of this and if necessary use additional protection to hands and
eyes. They can also give of poisonous fumes and gases. Try not to breath in
these fumes. If necessary buy a cheap fume extractor or filter to keep the
working area healthy.
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!
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
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
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
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
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 tin/lead rosin core fluxed solder.
Avoid solder that contains an acid flux, as this may damage the materials later if
not cleaned away correctly.
Rosin, which is a naturally occuring product which comes from pine trees, 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.
As everyone knows, tin/lead soldering alloys use of lead. Lead has a very high toxicity,
As a result, lead-based solders are among the hazardous materials identified for
restriction or banning by the European Unions Restriction of Hazardous Substances
Directive (RoHS) and Waste Electrical and Electronic Equipment Directive (WEEE), which
took effect in July 2006
The health risks associated with the use of lead and meant that a new solder material
was required. This lead to the developement of 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. Lead-free solder wires should contain at least 2% flux by weight. It
typically requires 15-25% higher melting temperatures that lead/timn mix alloys, 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 and your health.
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. Specialist fluxes are available for lead free solder.
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 Tip Cleanerss
There are several ways to keep soldering iron tips clean and in good condition. Clean
tips solder better, so keeping tips clean is important.
Sponges work very well to clean tips, but they must be kept wet.
The wet sponge can dissipate quite a bit of heart so always let youe soldering iron
reheat before trying to solder again. I read somewhere that you should not use water
to clean a tip if you are using lead free solder, but I cannot find the article at
the moment to find the reasons why.
Brass wire balls
These little brass wire balls work really well and
will not only clean the tip, but will remove the excess solder.
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
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.
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
hands type devices come with a good
magnifying glass attached.
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
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.
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
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
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
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
- Melted solder flows towards heat.
- Most beginners tend to use too much solder and heat the joint for too
- Do not move the joint until the solder has cooled.
- Keep your soldering iron tip clean.
- 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
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 tin/lead 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:-
- Clean all surfaces to be soldered
- Keep your iron clean
- Keep your sponge damp
- Use the correct flux
- Use the correct solder
At all times think safety. Do not get complacent.
All of our soldering tools can be found by