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EPE "Basic Soldering Guide"
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The No. 1 online resource for
starting in electronics soldering.
Now referenced by the Edinburgh Engineering Virtual
Library.
Bookmark this site!
The
Basic Electronics
Soldering & Desoldering Guide
by Alan Winstanley
EPE Magazine Online Editor
How to solder -
types of iron -
desoldering -
troubleshooting.
Types of Iron?
The Art of Soldering
"Cold Soldering" - better than a traditional iron? Read our full review.
Maplin PG509 Gas Soldering Iron review
How to De-solder
Desoldering Photo Gallery & Black Museum of Bad Soldering
Electronics Soldering Guide Photo Gallery
  Maplin PG509 Gas Soldering Iron Review: How does Maplin's budget priced Gas Soldering Iron compare with better known brands? Read how gas soldering irons work and see our full online view with photographs. More details.....
 "Cold Soldering" - a review of the Coldheat Classic Iron, tested on a commercial electronic kit. What are the benefits and drawbacks of this new type of iron? More details....
This written guide will help beginners and novices to
obtain effective results when soldering electronic components. If you
have little or no experience of using a soldering iron, then EPE (Everyday Practical Electronics magazine) recommends
that you practice your soldering technique on some fresh surplus components
and clean stripboard (protoboard), before experimenting with a proper constructional
project. This will help you to avoid the risk of disappointment when you start
to assemble your first prototypes. If you've never soldered before, then read
on!
Everyday Practical Electronics magazine contains the widest variety
of interesting projects and information for beginners, trainees, hobbyists and
professionals in electronics. This Basic Soldering Guide was condensed
from our fully-illustrated series Build Your Own Projects, written by
Alan Winstanley and published in Everyday Practical Electronics magazine, from
November 1996 to March 1997. EPE is read in more than sixty countries: to go
to our Subscriptions Page, please click here. For
EPE Back Issue information, please click here.
Please refer to the Copyright
Notice appearing at the end.
Soldering irons
Topics in this section include:
Voltage
Wattage
Temperature Control
Soldering Stations
Anti Static Protection
Bits (Tips)
Spare Parts
Gas-Powered irons
The most fundamental skill needed to assemble any electronic project is
that of soldering. It takes some practice to make the perfect joint, but, like riding
a bicycle, once learned is never forgotten! The idea is simple: to join electrical parts together
to form an electrical connection, using a molten mixture of lead and tin (solder*) with a soldering
iron. A large range of soldering irons is available - which one is suitable for you depends on your
budget and how serious your interest in electronics is.
[*Note: the use of lead in solder is now increasingly prohibited in many countries. "Lead free" solder is now statutory instead.]
Electronics catalogues often include a selection of well-known brands of soldering iron.
Excellent British-made ones include the universally popular Antex, Adcola and Litesold makes. Other
popular brands include those made by Weller and Ungar. A very basic mains electric soldering iron
can cost from under £5 (US$ 8), but expect a reasonable model to be approximately
£10-£12 (US$ 16 - 20) - though it's possible to spend into three figures on a soldering
iron "station" if you're really serious! Check some suppliers' catalogues for some
typical types. Certain factors you need to bear in mind include:-
Voltage: most irons run from the
mains at 240V. However, low voltage types (e.g. 12V or 24V) generally form part of a
"soldering station" and are designed to be used with a special controller made by the
same manufacturer.
Wattage: Typically, they may have
a power rating of between 15-25 watts or so, which is fine for most work. A higher wattage does
not mean that the iron runs hotter - it simply means that there is more power in
reserve for coping with larger joints. This also depends partly on the design of the
"bit" (the tip of the iron). Consider a higher wattage iron simply as being more
"unstoppable" when it comes to heavier-duty work, because it won't cool down so quickly.
Temperature Control: the
simplest and cheapest types don't have any form of temperature regulation. Simply plug them in and
switch them on! Thermal regulation is "designed in" (by physics, not electronics!): they
may be described as "thermally balanced" so that they have some degree of temperature
"matching" but their output will otherwise not be controlled. Unregulated irons form an
ideal general purpose iron for most users, and they generally cope well with printed circuit board
soldering and general interwiring. Most of these "miniature" types of iron will be of
little use when attempting to solder large joints (e.g. very large terminals or very thick wires)
because the component being soldered will "sink" heat away from the tip of the iron,
cooling it down too much. (This is where a higher wattage comes in useful.)
A proper temperature-controlled iron will be quite a lot more expensive - retailing at say
£40 (US$ 60) or more - and will have some form of built-in thermostatic control, to ensure
that the temperature of the bit (the tip of the iron) is maintained at a fixed level (within
limits). This is desirable especially during more frequent use, since it helps to ensure that the
temperature does not "overshoot" in between times, and also guarantees that the output
will be relatively stable. Some irons have a bimetallic strip thermostat built into the handle
which gives an audible "click" in use: other types use all-electronic controllers, and
some may be adjustable using a screwdriver.
Yet more expensive still, soldering
stations cost from £70 (US$ 115) upwards (the iron may be sold separately, so
you can pick the type you prefer), and consist of a complete bench-top control unit into which a
special low-voltage soldering iron is plugged. Some versions might have a built-in digital
temperature readout, and will have a control knob to enable you to vary the setting. The
temperature could be boosted for soldering larger joints, for example, or for using higher
melting-point solders (e.g. silver solder). These are designed for the most discerning users, or
for continuous production line/ professional use. The best stations have irons which are well
balanced, with comfort-grip handles which remain cool all day. A thermocouple will be built into
the tip or shaft, which monitors temperature.
Anti-static protection: if you're
interested in soldering a lot of static-sensitive parts (e.g. CMOS chips or MOSFET transistors),
more advanced and expensive soldering iron stations use static-dissipative materials in their
construction to ensure that static does not build up on the iron itself. You may see these listed
as "ESD safe" (electrostatic discharge proof). The cheapest irons won't
necessarily be ESD-safe but never the less will still probably perform perfectly well in most hobby
or educational applications, if you take the usual anti-static precautions when handling the
components. The tip would need to be well earthed (grounded) in these circumstances.
Bits: it's useful to have a small
selection of manufacturer's bits (soldering iron tips) available with different diameters or
shapes, which can be changed depending on the type of work in hand. You'll probably find that you
become accustomed to, and work best with, a particular shape of tip. Often, tips are
iron-coated to preserve their life, or they may be bright-plated instead. Copper tips are
seldom seen these days.
Spare parts: it's nice to know
that spare parts may be available, so if the element blows, you don't need to replace the entire
iron. This is especially so with expensive irons. Check through some of the larger mail-order
catalogues.
You will occasionally see gas-powered soldering irons which use butane rather than the mains
electrical supply to operate. They have a catalytic element which, once warmed up, continues to
glow hot when gas passes over them. Service engineers use them for working on repairs where there
may be no power available, or where a joint is tricky to reach with a normal iron, so they are
really for occasional "on the spot" use for quick repairs, rather than for mainstream
construction or assembly work. One example is the Maplin PG509, given a full review with photographs here.
Another technique is the proprietary "Coldheat" battery powered soldering iron that we reviewed here. There are a number of reasons why this should only be used with extreme care (if at all) on electronic circuitboards.
A solder gun is a pistol-shaped iron, typically
running at 100W or more, and is completely unsuitable for soldering modern electronic components:
they're too hot, heavy and unwieldy for micro-electronics use. Plumbing, maybe..!
Soldering irons are best used along with a heat-resistant bench-type holder, so
that the hot iron can be safely parked in between use. Soldering stations already have this
feature, otherwise a separate soldering iron stand is essential, preferably one with a holder for
tip-cleaning sponges. Now let's look at how to use soldering irons properly, and how to put things
right when a joint goes wrong.
 Soldering
Guide Photo Gallery
How to solder
Quick Summary Guide
Cleanliness of Components
Temperature
Time
Amount
Turning to the actual techniques of soldering, firstly it's best to
secure the work somehow so that it doesn't move during soldering and affect your accuracy.
In the case of a printed circuit board, various holding frames are fairly popular especially with
densely populated boards: the idea is to insert all the parts on one side ("stuffing the
board"), hold them in place with a special foam pad to prevent them falling out, turn the
board over and then snip off the wires with cutters before making the joints. The frame saves an
awful lot of turning the board over and over, especially with large boards. Other parts could be
held firm in a modeller's small vice, for example.
Solder joints may need to possess some degree of mechanical strength in some cases, especially
with wires soldered to, say, potentiometer or switch tags, and this means that the wire should be
looped through the tag and secured before solder is applied. The down side is that it is more
difficult to de-solder the joint (see later) and remove the wire afterwards, if required.
Otherwise, in the case of an ordinary circuit board, components' wires are bent to fit through the
board, inserted flush against the board's surface, splayed outwards a little so that the part grips
the board, and then soldered.
In my view - opinions vary - it's generally better to snip the surplus wires leads off
first, to make the joint more accessible and avoid applying a mechanical shock to the p.c.b.
joint. However, in the case of semiconductors, I often tend to leave the snipping until
after the joint has been made, since the excess wire will help to sink away some of the heat
from the semiconductor junction. Integrated circuits can either be soldered directly into place if
you are confident enough, or better, use a dual-in-line socket to prevent heat damage. The chip can
then be swapped out if needed.
Parts which become hot in operation (e.g. some resistors), are raised above the board slightly
to allow air to circulate. Some components, especially large electrolytic capacitors, may require a
mounting clip to be screwed down to the board first, otherwise the part may eventually break off
due to vibration.
The perfectly soldered joint will be nice and shiny looking, and will prove reliable in service.
I would say that:
cleanliness
temperature
time
adequate solder coverage
are the key factors affecting the quality of the joint. A little effort spent now in soldering
the perfect joint may save you - or somebody else - a considerable amount of time in
troubleshooting a defective joint in the future. The basic principles are as follows.
Really Clean
Firstly, and without exception, all parts - including the iron tip itself - must be clean
and free from contamination. Solder just will not "take" to dirty parts!
Old components or copper board can be notoriously difficult to solder, because of the layer of
oxidation which builds up on the surface of the leads. This repels the molten solder and this will
soon be evident because the solder will "bead" into globules, going everywhere except
where you need it. Dirt is the enemy of a good quality soldered joint!
Hence, it is an absolute necessity to ensure that parts are free from grease, oxidation and
other contamination. In the case of old resistors or capacitors, for example, where the leads have
started to oxidise, use a small hand-held file or perhaps scrape a knife blade or rub a fine emery
cloth over them to reveal fresh metal underneath. Stripboard and copper printed circuit board will
generally oxidise after a few months, especially if it has been fingerprinted, and the copper
strips can be cleaned using an abrasive rubber block, like an aggressive eraser, to reveal fresh
shiny copper underneath.
Also available is a fibre-glass filament brush, which is used propelling-pencil-like to remove
any surface contamination. These tend to produce tiny particles which are highly irritating to
skin, so avoid accidental contact with any debris. Afterwards, a wipe with a rag soaked in cleaning
solvent will remove most grease marks and fingerprints. After preparing the surfaces, avoid
touching the parts afterwards if at all possible.
Another side effect of having dirty surfaces is the tendency for people to want to apply more
heat in an attempt to "force the solder to take". This will often do more harm than
good because it may not be possible to burn off any contaminants anyway, and the component may be
overheated. In the case of semiconductors, temperature is quite critical and they may be harmed by
applying such excessive heat.
Before using the iron to make a joint, it should be "tinned" (coated with solder) by
applying a few millimetres of solder, then wiped on a damp sponge preparing it for use: you should
always do this immediately with a new bit, anyway. Personally, I always re-apply a very small
amount of solder again, mainly to improve the thermal contact between the iron and the joint, so
that the solder will flow more quickly and easily. It's sometimes better to tin larger parts as
well before making the joint itself, but it isn't generally necessary with p.c.b. work. (All
EPE printed circuit boards are "roller-tinned" to preserve their quality and to help
with soldering.) A worthwhile product is Weller's Tip Tinner & Cleaner, a small 15 gram
tinlet of paste onto which you dab a hot iron - the product cleans and tins the iron ready for use.
An equivalent is Adcola Tip-Save.
Normal electronics grade solder is now "lead free" and typically contains Sn 97 Ag 2.5 Cu 0.5 (i.e. 97% tin, 2.5% silver and 0.5% copper). It already contains cores of "flux" which helps the molten
solder to flow more easily over the joint. Flux removes oxides which arise during
heating, and is seen as a brown fluid bubbling away on the joint. The use of separate acid flux paste
(e.g. as used by plumbers) should NEVER be necessary in normal electronics applications because electronics-grade solder already contains the correct grade of flux! Other solders are available for specialist work, including aluminium and silver-solder.
Different solder diameters are produced, too; 20-22 SWG (19-21 AWG) is 0.91-0.71mm
diameter and is fine for most work. Choose 18 SWG (16 AWG) for larger joints
requiring more solder.
Temperature
Another step to successful soldering is to ensure that the temperature of all the
parts is raised to roughly the same level before applying solder. Imagine, for instance, trying to
solder a resistor into place on a printed circuit board: it's far better to heat both the
copper p.c.b. and the resistor lead at the same time before applying solder, so that the
solder will flow much more readily over the joint. Heating one part but not the other is far less
satisfactory joint, so strive to ensure that the iron is in contact with all the components
first, before touching the solder to it. The melting point of most solder is in the region of
188°C (370°F) and the iron tip temperature is typically 330-350°C
(626°-662°F). The latest lead-free solders typically require a higher temperature.
Now is the time
Next, the joint should be heated with the bit for just the right amount of time - during
which a short length of solder is applied to the joint. Do not use the iron to carry molten
solder over to the joint! Excessive time will damage the component and perhaps the circuit board
copper foil too! Heat the joint with the tip of the iron, then continue heating whilst applying
solder, then remove the iron and allow the joint to cool. This should take only a few seconds, with
experience. The heating period depends on the temperature of your iron and size of the joint - and
larger parts need more heat than smaller ones - but some parts (semiconductor diodes, transistors
and i.c.s), are sensitive to heat and should not be heated for more than a few seconds. Novices
sometimes buy a small clip-on heat-shunt, which resembles a pair of aluminium tweezers. In the case
of, say, a transistor, the shunt is attached to one of the leads near to the transistor's body. Any
excess heat then diverts up the heat shunt instead of into the transistor junction, thereby saving
the device from over-heating. Beginners find them reassuring until they've gained more experience.
Solder Coverage
The final key to a successful solder joint is to apply an appropriate amount of solder. Too
much solder is an unnecessary waste and may cause short circuits with adjacent joints. Too
little and it may not support the component properly, or may not fully form a working joint.
How much to apply, only really comes with practice. A few millimetres only, is enough for an
"average" p.c.b. joint, (if there is such a thing).
Desoldering methods
A soldered joint which is improperly made will be electrically
"noisy", unreliable and is likely to get worse in time. It may even not have made any
electrical connection at all, or could work initially and then cause the equipment to fail at a
later date! It can be hard to judge the quality of a solder joint purely by appearances, because
you cannot say how the joint actually formed on the inside, but by following the guidelines
there is no reason why you should not obtain perfect results.
A joint which is poorly formed is often called a "dry joint". Usually it results from
dirt or grease preventing the solder from melting onto the parts properly, and is often noticeable
because of the tendency of the solder not to "spread" but to form beads or globules
instead, perhaps partially. Alternatively, if it seems to take an inordinately long time for the
solder to spread, this is another sign of possible dirt and that the joint may potentially be a dry
one.
There will undoubtedly come a time when you need to remove the solder from a joint:
possibly to replace a faulty component or fix a dry joint. The usual way is to use a
desoldering pump or vacuum pump which works like a small spring-loaded bicycle pump, only in
reverse! (More demanding users using CMOS devices might need a pump which is ESD safe.) A
spring-loaded plunger is released at the push of a button and the molten solder is then drawn up
into the pump. It may take one or two attempts to clean up a joint this way, but a small
desoldering pump is an invaluable tool especially for p.c.b. work.
Sometimes, it's effective to actually add more solder and then desolder the whole lot
with a pump, if the solder is particularly awkward to remove. Care is needed, though, to ensure
that the boards and parts are not damaged by excessive heat; the pumps themselves have a P.T.F.E.
nozzle which is heat proof but may need replacing occasionally.
An excellent alternative to a pump is to use desoldering braid, including the famous
American "Soder-Wick" (sic) or Adcola "TISA-Wick" which are packaged in small
dispenser reels. This product is a specially treated fine copper braid which draws molten solder up
into the braid where it solidifies. The best way is to use the tip of the hot iron to press a short
length of braid down onto the joint to be de-soldered. The iron will subsequently melt the solder,
which will be drawn up into the braid. Take extreme care to ensure that you don't allow the solder
to cool with the braid adhering to the work, or you run the risk of damaging p.c.b. copper tracks
when you attempt to pull the braid off the joint. See my photo gallery for more details.
I recommend buying a small reel of de-soldering braid, especially for larger or difficult joints
which would take several attempts with a pump. It is surprisingly effective, especially on
difficult joints where a desoldering pump may prove a struggle.
Here's a summary of how to make the perfect solder joint.
All parts must be clean and free from dirt and grease.
Try to secure the work firmly.
"Tin" the iron tip with a small amount of solder. Do this immediately, with new tips
being used for the first time.
Clean the tip of the hot soldering iron on a damp sponge.
Many people then add a tiny amount of fresh solder to the cleansed tip.
Heat all parts of the joint with the iron for under a second or so.
Continue heating, then apply sufficient solder only, to form an adequate joint.
Remove and return the iron safely to its stand.
It only takes two or three seconds at most, to solder the average p.c.b. joint.
Do not move parts until the solder has cooled.
Troubleshooting Guide
Solder won't "take" - grease or dirt present - desolder and clean
up the parts. Or, material may not be suitable for soldering with lead/tin
solder (eg aluminium).
Joint is crystalline or grainy-looking - has been moved before being allowed to cool, or joint
was not heated adequately - too small an iron/ too large a joint.
Solder joint forms a "spike" - probably overheated, burning away the flux.
First Aid
If you are unlucky enough to receive burns which require treatment, here's what to do :-
Immediately cool the affected area with cold running water for several minutes.
Remove any rings etc. before swelling starts.
Apply a sterile dressing to protect against infection.
Do not apply lotions, ointments etc., nor prick any blisters which form later.
Seek professional medical advice where necessary.
Maplin PG509 Gas Soldering Iron Review: How does Maplin's budget priced Gas Soldering Iron compare with better known brands? Read how gas soldering irons work, and see our full online view with photographs. More details.....
"Cold Soldering" - a review of the Coldheat Classic Iron, tested on a commercial electronic kit. What are the benefits and drawbacks of this new type of iron? More details....
How to contact the author
Written by Alan Winstanley Email to alan@epemag.demon.co.uk.
Soldering Guide Photo Gallery
Bookmark this site!
Copyright Notice
Text © 1996-2006 Wimborne Publishing Limited, Wimborne, Dorset, England. Everyday Practical Electronics Magazine has provided this document as a free web resource to help constructors, trainees and students. You are welcome to download it, print it and distribute it for personal or educational use. It may not be used in any commercial publication, mirrored on any commercial site nor may it be appended to or amended, or used or distributed for any commercial reason, without the prior permission of the Publishers.
Photographs © 1996-2006 Alan Winstanley WORLD COPYRIGHT RESERVED
Every care has been taken to ensure that the information and guidance given is accurate and reliable, but since conditions of use are beyond our control no legal liability or consequential claims will be accepted for any errors herein.
The British mains voltage supply is 230V a.c. and you should amend ratings for local conditions.
Please check the Everyday Practical Electronics Web Site for details of the current issue, subscription rates, Back issue availability and contact information.
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