Soldering

Soldering is a useful technique for quickly, securely joining metal wires/contacts/pins together. This is useful in the creation of electronic circuits.

## Relevance

Soldering is important in instrumentation design to create solid contact between wires in circuits. The alternative, using a breadboard alone, is almost as good but has the downside of using frictional contact to maintain electrical contact (which can degrade over time). However, breadboards can be very quickly reconfigured if required. Soldered circuits are more permanent.

### Uses

* Creating permanent electrical circuits
* Joining wires and pins in situations where a breadboard would be cumbersome/excessive (e.g. adding a resistor inline to the leg of an LED

## Technique overview

Here is a general guide to soldering. Components can be anything (LED, resistor, perfboard, transistor...). When I say "pin" here, I refer to the part of the component with exposed metal that you want to solder to another component.

### Soldering

1. Gather materials: components to solder together, solder wire, soldering iron, wet sponge. The sponge is used to clean the soldering iron tip. This is necessary as the hot tip gathers slag and dirt from the oxidised metal components and old solder.
2. Heat up the soldering iron. If using a temperature controlled iron, set it to whatever temperature is recommended by the soldering wire. 350 degrees C is normal.
3. Once the iron is hot, add some solder to the tip, then wipe it off. The new solder adds flux and removes oxide build up. Wiping it off reveals the clean, silver-shiny tip. This step should be repeated periodically to keep the tip clean, especially during long soldering sessions.
4. Re-apply a small amount of solder (less than 1mm of the wire) to "wet" the tip.
5. For each of the components you wish to solder:
	1. Heat the pin with the tip for a few seconds.
	2. Put the solder wire in contact with the pin, not the soldering iron's tip. The wire should melt onto the pin, allow a fair amount of solder onto the pin. The flux from the wire will strip oxides from the pin, resulting in a strong connection between the pin and the solder.
	3. Remove the iron from the pin. Notice the pin can only "hold" so much, the iron takes some solder away. The solder left on the pin will make it very easy to connect tinningto another component. This process is called **tinning**.
6. Once both components have been tinned, you are ready to join them.
7. If you have access to a helping hand, arrange the components so that the connections you wish to join are touching together. Otherwise, with one hand, hold the components so that their tinned pins are touching (this may require some dexterity).
8. Heat the connection with the iron, the solder on the pins should melt and join the pins together. Add more solder if you want a stronger connection.
9. Remove the iron and allow the connection to cool.
10. Done!

### Desoldering

1. Gather materials: joined components to separate, soldering iron, wet sponge, and, optionally, a desoldering pump
2. Prepare the soldering iron as in soldering (steps 2-4 above)
3. Heat the connection you wish to separate, melting the solder.
4. This may be enough, try pulling the components apart. If the component has multiple pins soldered, you may need to sequentially heat each pin and work it out a little at a time.
5. If this is not enough, this is where the pump comes in handy. You will need to remove some solder.
6. If you have a pump:
	1. Prime the pump (push the plunger) and put the nozzle onto a heated connection.
	2. Remove the iron from the connection
	3. Then immediately trigger the pump (press the button on the side)
7. If you don't have a pump:
	1. Use the soldering iron to wick away the solder, cleaning wicked solder onto the sponge.
	2. Repeat until most of the solder is gone.
8. Repeat the above, keep pulling at the components until they separate.
9. Done!

## Resources

* Great Scott! video on how to solder

This channel is great if you're interested in cool electronics projects, this guy knows his stuff, and always has beautifully soldered components.

This video covers how to solder different components to a perfboard.

His technique is to use solder as the connection between components on the reverse side, I favour using wires on the same side as the component joined with solder underneath. This means that we can colour code the connections.

* Collin's lab: soldering

This channel (from Adafruit) is very informative. This video discusses how to join components by sodlering.

* Sollin's lab: desoldering

This Collin's lab video shows how to remove components.

## Issues

### Solder is melted but not sticking things together

This happens when the metal you are trying to join is covered in an oxide layer, which all metal normally is. This can be removed through the use of flux. The solder we use in the lab has a core of flux, so whatever you melt the solder onto it will remove this oxide layer. If you only melt solder onto the iron tip, then the oxide on the pin of the component is still intact and will not adhere to the solder. Follow the steps above to remove oxide from pins (tin pin before use: heat pin, apply solder, remove heat).