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Soldering

Soldering the components

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There is a display board in each of the manufacturing rooms and they show the following:

  • The soldering iron.

  • What a dry joint will look like.

  • The tip of the solder tinned.

  • An exploded view of the solder showing that there is flux inside.

  • A picture of all the tools used in this process.

Soldering Safety Rules

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When soldering the components onto the PCB it is essential to follow a set of safety rules:

  • Never touch the element or tip of the soldering iron. They are very hot (about 400°C) and will give you a nasty burn.

  • Always return the soldering iron to its stand when not in use. Never put it down on your workbench!

  • Work in a well-ventilated area. The smoke formed as you melt solder is mostly from the flux and quite irritating.

  • Avoid breathing in fumes by keeping you head to the side of, not above, your work.

  • Wash your hands after using solder. Solder contains lead which is a poisonous metal.

  • Wear safety glasses! These will protect your eyes from any hot metal.

  • 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.

Preparing the Soldering Iron:

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  • 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.

  • 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.

  • 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.

  • Wipe the tip of the iron on the damp sponge. This will clean the tip.

  • 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.

  • Tinning 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.

  • The solder we use in school is always rolled up on a dowel rod, this is to help you use it without burning your fingers.

  • Try to avoid a dry joint similar to the one pictured below, this type of joint will not make good contact with the copper and the circuit will not work.

  • Heat the solder up enough to allow the solder to form into a cone shape. (See picture below)

Solder Wire
Soldering Joints

You are now ready to start soldering:

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  • 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!

  • 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 then 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 picture below.

  • Then apply the solder to the joint, not the iron.

  • 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.

  • Inspect the joint closely.

  • The joint 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.

First Aid for Burns

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

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  • 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.

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