Introduction to soldering

What is Soldering?
Soldering is the process of using liquid metal to bind, in the case of these balloon projects, electronic parts to a circuit board. It's pronounced like 'sodder' despite the spelling. The metal used to solder is typically a tin or lead alloy that has a high conductivity, so as to allow the electrical signals to pass through the metal and into the part.

Types of Soldering
There are two main kinds of soldering used in this type of situation: through hole and surface mount. Through hole refers to sticking parts with pins on them through premade holes in the PCB and attaching them. Surface mount is what it sounds like: taking a part, setting it on the pre-fabricated pads, and using the solder wire to attach them there. This guide will focus on surface mount.

Preparations
Start by turning on something to clear the air of any fumes. In the Whitworth lab, there is a large fan by the soldering station. Use that. The next step depends on the situation. There are multiple methods to solder, but the two that have been used during the project use solder paste (a series of near-microscopic metal balls of tin, formed into a paste) or standard solder wire. If you are using the solder wire, turn on the solder iron and give it time to heat up (after it is fully heated the green light will start flashing). For solder wire, also get a sponge wet so you can clean off the tip of the soldering iron after each use. If you are using the solder paste, there is a special hot air machine to melt the tiny metal balls into molten metal so they can perform the same function as the wire. Turn that on if you plan to use solder paste, set the temperature and air pressure, and just let it rest until you plan to use it. An essential problem avoidance technique is to simply test the fit of your parts before you attach them. Make sure they fit the pads. Always do this. You don't want to put large quantities (relatively) of solder paste onto your circuit board only to discover your part doesn't fit, and you especially don't want to solder other parts onto the board only to discover one of them doesn't fit the board. Note that while it may seem unlikely, or that your teacher would never make that mistake, sometimes it isn't up to them. Sometimes the company will simply send the wrong part, and if you have the rest of your board already soldered, then it limits your options for fixing the situation significantly.

Procedure with Solder Wire for Surface Mount
First set the piece you wish to mount onto the pads. Make sure if there are specific pins that you line them up correctly. The methods of showing which pin is pin 1 vary, but look for tiny markings by the pads and on the part, anything to distinguish one corner from the rest. Take the wire, making sure to hold it from a distance back from the front to avoid burning yourself, and place it on the pin (which should be neatly on the pad it is designed to be on). Then take the soldering iron and lightly press it to the end of the wire, letting it melt off and onto the pad. Small amounts are best, just ensure that there is enough to form a solid connection. Do this for every pin, then remove the wire and iron both and let it cool.

Procedure with Solder Paste for Surface Mount
First, add tiny amounts of the paste to each pad. If the pad is covered, or the blob of paste is raised very far at all above the pad, you added too much. Then place the part the same way as for solder wire. Finally, grab the hot air blower, position it exactly vertically a little ways above the pads, and move it slowly back and forth to cover the entire area. Keep doing that until you can see the paste melt and get drawn to the pad (it will be clear when this has happened). Once all the pads have the paste melted onto them, remove the hot air blower and let it cool.

Solder Paste Mistakes
If you add too much solder paste, it can sometimes overflow when it melts and stretch into other pads, potentially creating unwanted electrical connections between the pads. The first thing you can try to fix this is using a small, thin object you don't mind getting solder paste on it to clean up excess from around the edges, or to pick up some and transfer it to other pads. If that doesn't work, sometimes the process of the paste melting will fix it for you when it is drawn towards the pads. This option is a last resort, however. If all else fails, try to use the process for cleaning up hardened solder that is outlined in another section.

Solder Wire Mistakes
This method can be harder to use in certain situations, since the metal has to be melted onto the pad directly and there are some parts where the pad is hidden. In situations like that, a common mistake is, after a failed attempt to solder it, to go back and add more solder without clearing up the original first. This leads to the part being raised above the pads, and can make electrical connections difficult to create. Instead, after each failed attempt, try to clean up the failed solder as best as possible, using the method that is outlined in the next section.

Cleaning Up Hardened Solder - Excess or Mistake
To clean up already hardened solder, use a copper braid to press against the solder, then touch the solder iron to it. Try to make it reach between the individual braids to touch the solder directly, as this makes it most efficient. This could take some practice to get the hang of. Also, it is not a cure-all for fixing any mistake. When done right, it can remove significant portions of the solder that is present, but it isn't perfect.

Burning the Board
This mistake is simple. Don't press the solder iron against the solder for too long, or too repeatedly. If you do you risk burning the circuit board itself, which can sometimes stop it from working as it should. Sometimes it is unavoidable, when parts are being particularly difficult or things just aren't working out. But generally it is better to stop, clean up all the excess solder, take a breath, and try again from scratch than it is to continue trying the same failed technique over and over from the most recent possible point.

Getting Distracted
This final mistake seems obvious, but is so easy to fall into. Someone comes over and talks to you, or a loud sound erupts in your area, or if you're the daydreaming type, you get lost in thought. Remember you are holding an EXTREMELY hot tool (no matter which method you're using). You can seriously burn yourself or someone else if you get too distracted. If you have to hold a conversation or focus on something other than the tool in your hand, it should not be in your hand. Put it back in its holder and go do what you need to do. It will keep.