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Soldering Guide

How to Solder | Advice for Components | What is Solder? | Desoldering | Burns

For information about soldering irons and other tools please see the Tools Required page.

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How to Solder

First a few safety precautions:

If you are unlucky (or careless!) enough to burn yourself please read the First Aid section.

Preparing the soldering iron:

You are now ready to start soldering:

Good and bad soldered joints If you are unlucky (or careless!) enough to burn yourself please read the First Aid section.

Crocodile clip, photograph © Rapid Electronics
Crocodile clip
Photograph © Rapid Electronics

Using a heat sink

Some components, such as transistors, can be damaged by heat when soldering so if you are not an expert it is wise to use a heat sink clipped to the lead between the joint and the component body. You can buy a special tool, but a standard crocodile clip works just as well and is cheaper.

Further information

For a much more detailed guide to soldering, including troubleshooting, please see the Basic Soldering Guide on the Everyday Practical Electronics Magazine website.

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Soldering Advice for Components

It is very tempting to start soldering components onto the circuit board straight away, but please take time to identify all the parts first. You are much less likely to make a mistake if you do this!
    Components stuck onto paper
  1. Stick all the components onto a sheet of paper using sticky tape.
  2. Identify each component and write its name or value beside it.
  3. Add the code (R1, R2, C1 etc.) if necessary.
    Many projects from books and magazines label the components with codes (R1, R2, C1, D1 etc.) and you should use the project's parts list to find these codes if they are given.
  4. Resistor values can be found using the resistor colour code which is explained on our Resistors page. You can print out and make your own Resistor Colour Code Calculator to help you.
  5. Capacitor values can be difficult to find because there are many types with different labelling systems! The various systems are explained on our Capacitors page.
Some components require special care when soldering. Many must be placed the correct way round and a few are easily damaged by the heat from soldering. Appropriate warnings are given in the table below, together with other advice which may be useful when soldering.

For more detail on specific components please see the Components page or click on the component name in the table.

For most projects it is best to put the components onto the board in the order given below:

Reminders and Warnings
Chip Holders
(DIL sockets)
chip holder
Connect the correct way round by making sure the notch is at the correct end.
Do NOT put the ICs (chips) in yet.
No special precautions are needed with resistors.
Small value capacitors
(usually less than 1µF)
small value capacitors
These may be connected either way round.
Take care with polystyrene capacitors because they are easily damaged by heat.
Electrolytic capacitors
(1µF and greater)
electrolytic capacitor
Connect the correct way round. They will be marked with a + or - near one lead.
Connect the correct way round.
Take care with germanium diodes (e.g. OA91) because they are easily damaged by heat.
Connect the correct way round.
The diagram may be labelled a or + for anode and k or - for cathode; yes, it really is k, not c, for cathode! The cathode is the short lead and there may be a slight flat on the body of round LEDs.
Connect the correct way round.
Transistors have 3 'legs' (leads) so extra care is needed to ensure the connections are correct.
Easily damaged by heat.
Wire Links between points on the circuit board.
single core wire
single core wire
Use single core wire, this is one solid wire which is plastic-coated.
If there is no danger of touching other parts you can use tinned copper wire, this has no plastic coating and looks just like solder but it is stiffer.
Battery clips, buzzers and other parts with their own wires   Connect the correct way round.
10 Wires to parts off the circuit board, including switches, relays, variable resistors and loudspeakers.
stranded wire
stranded wire
You should use stranded wire which is flexible and plastic-coated.
Do not use single core wire because this will break when it is repeatedly flexed.
11 ICs (chips)
555 timer IC
Connect the correct way round.
Many ICs are static sensitive.
Leave ICs in their antistatic packaging until you need them, then earth your hands by touching a metal water pipe or window frame before touching the ICs.

Carefully insert ICs in their holders: make sure all the pins are lined up with the socket then push down firmly with your thumb.

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What is solder?

Reels of solder
Photograph © Rapid Electronics
Solder is an alloy (mixture) of tin and lead, typically 60% tin and 40% lead. It melts at a temperature of about 200°C. Coating a surface with solder is called 'tinning' because of the tin content of solder. Lead is poisonous and you should always wash your hands after using solder.

Solder for electronics use contains tiny cores of flux, like the wires inside a mains flex. The flux is corrosive, like an acid, and it cleans the metal surfaces as the solder melts. This is why you must melt the solder actually on the joint, not on the iron tip. Without flux most joints would fail because metals quickly oxidise and the solder itself will not flow properly onto a dirty, oxidised, metal surface.

The best size of solder for electronics is 22swg (swg = standard wire gauge).

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At some stage you will probably need to desolder a joint to remove or re-position a wire or component. There are two ways to remove the solder:

Using a desoldering pump (solder sucker)
1.  With a desoldering pump (solder sucker)

Solder remover wick
Photograph © Rapid Electronics
2.  With solder remover wick (copper braid)

After removing most of the solder from the joint(s) you may be able to remove the wire or component lead straight away (allow a few seconds for it to cool). If the joint will not come apart easily apply your soldering iron to melt the remaining traces of solder at the same time as pulling the joint apart, taking care to avoid burning yourself.

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First Aid for Burns

Most burns from soldering are likely to be minor and treatment is simple: To reduce the risk of burns:

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© John Hewes 2007, The Electronics Club, www.kpsec.freeuk.com
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