How to: soldering for FPV

What is soldering, and why you need it

If you are interested in FPV (first person view) an early skill to learn is soldering. Soldering is the process of joining electronic components by applying heat and melting a conductive metal in between the components to join them together. The conduit is called solder and is most often a mix of tin and lead. The goal of soldering is to bond the electrical components both physically and electrically. The reason soldering is so important if you are interested in FPV is because once learned, it will allow you to build, repair, and modify your own drones. Doing this yourself will save you time, money, and frustration. Trying to ship a broken drone back to a repair service is oftentimes slow and expensive! The ability to repair a drone yourself means that you can keep spare parts on hand and have your drone flying again in just a few minutes, instead of having to wait weeks.

What you’ll need

To get started soldering you will need a few tools. Firstly you will need a soldering iron. The best is a high watt rated electric soldering iron. Neither soldering guns nor butane irons are advised. You will also need some solder. 60/40, or 63/37 rosin core solder is the best. This denotes the percentage of tin/lead that makes up the solder. Lead free solder is cheaper and safer to use, but does not provide as strong of a conduit and bond. Leaded solder is not dangerous as long as you remember to wash your hands after soldering before you eat your next meal.

Flux is an important addition to the tool kit as adding it to the electrical components before applying heat will help the bond strengthen and conduct electricity better. You will want to use tweezers while soldering to keep your hands away from the heat. Lastly, use some isopropyl alcohol and a toothbrush to clean up the circuit board after soldering.

A wet sponge, or brass wool are the two options for keeping your iron clean while using it. You want to clean off old solder that has oxidized, and you want to apply fresh solder to the tip of the iron whenever you start a new solder job. If you are soldering multiple items all at once it is okay to do a few jobs in quick succession before cleaning the iron off and applying fresh solder.

The best configuration for your soldering iron depends on your particular iron and the job you are working on. For small electronics like our FPV drones you typically want to run your iron at a temperature above 300C (575F). You can increase the temperature up to 400C (750F) for larger soldering jobs such as heavy gauge wires like you might find on a battery lead. These thick wires have so much conductive material in them that they absorb heat very quickly. This is where a high watt iron is important, or having patience with the work and allowing both sides of the job to heat up thoroughly.

Using the right iron tip is important as well. For most jobs the tip that your iron comes with, a conical tip, will get the job done, but using a chisel tip, or a bevel tip might come in handy as a backup, especially for those larger wires. Motor wires and battery leads don’t require as much precision, and those wider tips transfer heat really well.

Again, what you will need

  • Soldering Iron
  • Solder
  • A wet sponge
  • Flux pen
  • Tweezers
  • Isopropyl and a toothbrush

How to solder

Get your tools out and prepare your electronics. The best way to prepare is by mounting the electronics you’ll be working on to the frame, then trimming the wires to the appropriate length. It is best to leave a small amount of slack, you can always cut more wire, you can never add it back. After trimming the wire you will need to strip a couple millimeters of wire insulation to expose the wire strands. Wire strippers or just your fingernails will do the trick. Once the wire is stripped you need to pre tin your work surfaces. Most often this will be one wire and one pad. Whether a wire or a pad, the technique is the same. Take your clean hot iron, apply a small amount of solder to the tip to wet it, then touch the tip to the work and allow it to transfer heat. The size of the work determines how much time you need to hold contact. Practice is really the best way to learn the timing, but at 300C you only need about a second for the smallest wires, and two to three seconds for something larger like a motor wire. While you heat up the work, feed more solder onto the work, between where the iron is contacting it. Don’t feed the solder onto the iron itself. Once you have fed enough solder to create a small shiny bubble on the work, remove the iron and allow it to cool.
Do not blow on it to cool it. Once you have pre tinned both sides of the work, you are ready to join them together. In the case of a wire going on a pad, place the tinned wire on the tinned pad and place the iron wet with solder on top of that. Allow the heat to pass through the wire, melting the solder in it and melting the solder on the pad below it. Once all the solder is liquified and the wire is in place, remove the iron and allow the whole job to cool without blowing on it.
The end result should be a wire going into a shiny ball of solder sitting neatly on the pad. If the ball is not shiny it’s called a cold solder joint, which is less durable. It’s caused by too much heat and/or not enough flux. The best way to repair the cold joint is to undo it, add more flux, and redo it, ensuring to be as quick as possible with the heat application. If the end result has a solder ball too large you risk overcrowding nearby pads and creating a short circuit which will damage electronics. If the solder ball is too small you will be able to see the shape of the exposed wire through the solder and it won’t be smooth.

Get to work!

It is really beneficial to take some time to practice soldering before you try your hand at it on expensive electronics. Really getting down the timing and temperatures is important. Diatone and FPVCrate both make soldering practice boards that are great for this. Combine that with some spare wires and your new soldering iron tool kit to really get the habits formed to create the cleanest solder joints. Like with anything practice makes perfect, so get started and practice often until you feel comfortable showing off your finished work to others!

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