September 4th, 2015

Soldering Tutorial

Soldering Tutorial – How to Solder

If you want to make anything that involves an Arduino, raspberry pi or any kind of circuitry, the odds are that you are going to have to solder something to a circuit board. Don’t worry – it’s much simpler than it looks! Soldering is a key skill to master if you want to work with electronics. It’s a tricky business too: if you want to attach metal wiring or components to a PCB (printed circuit board) a little finesse with a soldering iron goes a long way. Here’s a beginner’s guide to soldering

Soldering Tutorial - How to Solder

Basic Kit

Clockwise from top left:
1. Solder Wire
A 60% tin, 40% lead wire (commonly called a 60/40) is probably the easiest solder wire to work with and is easy and inexpensive to source – 250g will cost in the region of £15.
2. Solder Iron and Stand
A pencil-style 25W will see you right. Don’t skimp on the wattage – longer heating times with cooler irons damage the integrity of your solder joint.
3. Sponge
Most stands should come with a sponge and a place to store it. A 100% cellulose sponge is the most effective. Before you start soldering, make sure that your sponge is dampened with water and wet to the touch.
4. Diagonal Cutters
5. A small pair of diagonal wire cutters will allow you to trim the excess from your newly soldered joints.

Soldering Tutorial - How to Solder

Soldering Tutorial - How to Solder

Once you’ve turned on your iron and heated it to the correct temperature – 370 degrees centigrade should be about right for 60/40 wire – you need to clean the iron and ‘tin the tip’. Wipe the tip of the iron on the damp sponge to prevent any oxidation and then immediately touch a small amount of solder wire to the tip of the iron and wipe it away on the sponge.

Handy Tip: Never use files or abrasives like sandpaper as it will damage the plating and ruin your iron

Soldering Tutorial - How to Solder

Solder Iron A is an example of a dirty tip. If you’re having trouble tipping, you can repair an oxidised tip by treating it with tip-tinning paste. Solder Iron B is what you should be seeing – a thin, shiny layer on the tip of the iron.

Soldering Tutorial - How to Solder

To prepare the PCB, make sure that it’s free from dirt / fingerprints and oxidation by cleaning it with rubbing alcohol. Now, putting your board in a vice if you have access to one, is a very useful way to steady it and leave your hands free to hold the solder wire and iron in the place you want them – it’s really important that the parts being joined do not move, as if they do you end with a faulty ‘cold joint.

Soldering Tutorial - How to Solder

Strip the wire / component you wish to solder free of its plastic casing. Then hold the wire at the point at which you wish to create a joint and heat it with the iron. Once the metal is heating, touch the tip of the solder wire between the iron and the wire / component so that it melts and flows into the hole and on your wire, joining them together. Once enough solder has coated the join (it should only take a few seconds), carefully remove the iron and allow the solder to cool.

Soldering Tutorial - How to Solder

Once your joint has dried, clip the excess wire / component with the diagonal clippers as close as you can to the board. A well-bounded joint will look like a smooth, shiny, slightly rounded pyramid.

Handy Tip: Take care not to inhale the soldering fumes in lead-based solder. Make sure you work with mouth and nose protection in a well-ventilated area.

Soldering Tutorial - How to Solder

Common Issues

(Clockwise from top left)

1. Overheated joint

This blackened mess was caused by the solder not flowing well, which usually happens because of a dirty or under-heated iron. You can fix the problem by cleaning gently with a toothbrush and rubbing alcohol and starting again.

2. Cold Joint

Cold joints are caused by not allowing the solder to melt completely. They make a circuit unreliable and prone to cracks. You can recognise a cold joint by its rough / lumpy surface and can fix one by simply reheating the joint with your iron, being careful to remove any excess solder by drawing it off with the iron’s tip.

3. Disturbed joint

Disturbed joints look very similar to cold joints – crystalline and rough. However, such joints are caused by movement during the solder’s solidifying process. You can simply reheat the area and repair the damage but be sure to keep your tools as still as possible.