How to Solder

Few safety precautions:

a)    Never touch the element or tip of the soldering iron.

They are very hot (about 400°C) and will give you a nasty burn.

b)       Take great care to avoid touching the mains flex with the tip of the iron.

The iron should have a heatproof flex for extra protection. An ordinary plastic flex will melt immediately if touched by a hot iron and there is a serious risk of burns and electric shock.

c)       Always return the soldering iron to its stand when not in use.

Never put it down on your workbench, even for a moment!

d)       Work in a well-ventilated area.

The smoke formed as you melt solder is mostly from the flux and quite irritating. Avoid breathing it by keeping you head to the side of, not above, your work.

e)       Wash your hands after using solder.

Traditional solder contains lead which is a poisonous metal

Treatment for minor burns

Most burns from soldering are likely to be minor and treatment is simple:

• Immediately cool the affected area under gently running cold water.

Keep the burn in the cold water for at least 5 minutes (15 minutes is recommended). If ice is readily available this can be helpful too, but do not delay the initial cooling with cold water.

• Do not apply any creams or ointments.

The burn will heal better without them. A dry dressing, such as a clean handkerchief, may be applied if you wish to protect the area from dirt.

• Seek medical attention if the burn covers an area bigger than your hand.

 Preparing the soldering iron:

a)       Place the soldering iron in its stand and plug in.

The iron will take a few minutes to reach its operating temperature of about 400°C.

b)       Dampen the sponge in the stand.

The best way to do this is to lift it out the stand and hold it under a cold tap for a moment, then squeeze to remove excess water. It should be damp, not dripping wet.

c)       Wait a few minutes for the soldering iron to warm up.

You can check if it is ready by trying to melt a little solder on the tip.

d)       Wipe the tip of the iron on the damp sponge.

This will clean the tip.

e)       Melt a little solder on the tip of the iron.

This is called 'tinning' and it will help the heat to flow from the iron's tip to the joint. It only needs to be done when you plug in the iron, and occasionally while soldering if you need to wipe the tip clean on the sponge.

 You are now ready to start soldering

 

a)       Hold the soldering iron like a pen, near the base of the handle.

Imagine you are going to write your name! Remember to never touch the hot element or tip.

b)       Touch the soldering iron onto the joint to be made.

Make sure it touches both the component lead and the track. Hold the tip there for a few seconds and...

c)       Feed a little solder onto the joint.

It should flow smoothly onto the lead and track to form a volcano shape as shown in the diagram. Apply the solder to the joint, not the iron.

d)       Remove the solder, then the iron, while keeping the joint still.

Allow the joint a few seconds to cool before you move the circuit board.

e)       Inspect the joint closely.

It should look shiny and have a 'volcano' shape. If not, you will need to reheat it and feed in a little more solder. This time ensure that both the lead and track are heated fully before applying solder. 

 

Using a heat sink

Some components, such as transistors, can be damaged by heat when soldering. It is wise to use a heat sink clipped to the lead between the joint and the component body, as shown in the picture.You can buy a special tool, but a standard crocodile clip works just as well and is cheaper!

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!

a)      Stick all the components onto a sheet of paper using sticky tape.

b)      Identify each component and write its name or value beside it.

c)      Find Resistor values using  below given colour code .

d)     Capacitor values can be difficult to find because there are many types with different labeling systems!

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

  

TABLE

Component	Picture	Reminders and Warnings
IC Holders (DIL sockets)		Connect the correct way round by making sure the notch is at the correct end. Do NOT put the ICs (chips) in yet.
Resistors		No special precautions are needed with resistors.
Small value capacitors (usually less than 1µF)		These may be connected either way round. Take care with polystyrene capacitors because they are easily damaged by heat.
Electrolytic capacitors (1µF and greater)		Connect the correct way round. They will be marked with a + or - near one lead.
Diodes		Connect the correct way round. Take care with germanium diodes (e.g. OA91) because they are easily damaged by heat.
Transistors		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	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.
Wires to parts off the circuit board, including switches, relays, variable resistors and loudspeakers.	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.
ICs (chips)		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.