In this tutorial I will show you a few tips about soldering. Getting good at soldering takes some practice, but it’s going to be one of the most useful skills you’ll learn in this hobby. Your soldering quality also determines how reliable your mini quad and RC plane builds are going to be.
Soldering is basically joining two pieces of metals with molten solder, it’s not too different from gluing :) The keys are to have stead hands, use quality gears, practice the techniques a lot, and learn how to not burn yourself :)
I will show you a few common examples you will likely come across during building and repairing a mini quad (racing drone).
Table of Content
- Soldering Tools
- How to Solder
- Soldering Temperature
- Cleaning Solder Joints
Getting some quality soldering equipment is just as important as acquiring good soldering skills. Go check out this post which explains what Soldering Iron, Solder, and Soldering related Tools I recommend.
Preparation Before Soldering
Heat up the iron, and clean the tip to make sure it’s shiny.
Dull grey and black residue can build up on the tip during soldering, which affects your soldering quality. Simply wipe them off with a tip cleaner.
Right after cleaning, add a tiny bit of solder to the tip, this will help heat transfer to the solder joint.
Tiny solder balls can form and shoot all over the place when solder wire is melted. It’s quite a common problem, people drop solder on the flight controller without noticing, and smoke comes out as soon as they plug in the battery.
Consider covering up areas on your flight controller where you are not working on, with some masking tape or electrical tape.
Pro Tip: When I am done with soldering I normally clean the tip, and add a decent amount of solder to the tip before turning soldering iron off. This is like a protection layer to the tip.
Always “tin” the wires and pads first before attempting to solder them together, this will make joining them much easier later on.
Tinning is basically covering the wire or solder pads with an appropriate amount of solder.
If you are not using solder with rosin core, or if the solder isn’t sticking to the wire, then you might want to apply some solder paste (flux) to the wire first.
Pro Tip: It takes a few seconds for the molten solder to cool down – do not move the parts during this time, because it can cause fractures in the joint that might fail due to vibrations and crash impacts!
Soldering Small Wire to Pad
The most common soldering job is soldering a wire to a pad on a PDB or flight controller.
As mentioned, tin the wire and the solder pad first. Heat up the pad and melt the solder on it, and bring the wire to the pad quickly. Once the two joined, gently remove your soldering iron, and hold the wire in place for a few seconds until the solder joint cools down and hardens completely.
Pro Tip: Don’t be afraid to use a bit more solder. When you are not using enough, the joint can come off easily. When a solder joint doesn’t have enough solder, it will look bumpy, and the strands of wire are visible.
The finished joints should look round, shiny, solid and completely covered by solder. Here is another example how it should look.
Remember not to leave the iron on the pad for too long to avoid overheat and damage to the copper pad.
If you let go of the wire too early before the solder completely sets, or didn’t use enough solder, you might end up with a cold solder joint or just an unreliable solder joint.
A cold solder joint looks bumpy and dull, it makes bad contact between the components and is unreliable. If this happens, or if you are just not sure, simply solder it again until you are happy with how it looks.
Soldering Large Wire to Pad
When soldering large wires, for example, a XT60 pigtail (12AWG to 16AWG) to the PDB (power distribution board), make sure you are using high heat on your soldering iron.
When tinning the wires and pads, use slightly more solder.
And apply a decent amount of flux paste on the pad, this will help tremendously!
Use high heat to make it quick. (See my advice on soldering temperature later in this guide)
It’s going to take longer to melt the solder on the PDB because of the large amount of copper in it. When heating up the joint, you shouldn’t have to press too hard on the wire or the wire strands could get flattened.
The resulting solder joints should be round and shiny, the wires should be completely covered in solder.
Header Pin to Through-Hole
When soldering header pins to through-holes, you don’t pre-tin the contacts or you can’t get the header pin through the hole.
- Insert the header pin through the hole, hold it in a desired angle with your hand or blue-tack
- Heat up both the header pin and the ring on the through hole for a couple of seconds
- Bring the solder to the joint and it should make a solid, shiny, “volcano” like bond
Wire to Through-Hole
There are two ways to approach this, you can either treat the through-hole like a solder pad (solder from the top), or do it like soldering a header pin (solder from the bottom). It depends on which side of the board you can access more easily.
Here is how to solder a wire directly on top of a through-hole:
Here is how to insert a wire though the hole, and solder from the bottom just like a header pin.
Joining Two Wires
It’s easier to use a “solder helping hand” for this job.
For small wires and quick jobs, you could simply solder one wire directly next to the other. You could also twist them before soldering to increase mechanical strength.
When joining 2 larger gauge multi-strand wires together, I normally spread the strands first, and push the 2 wires together head to head, then twist them so they don’t come off easily. Now apply some solder flux, and solder them together.
This way maximizes the contact area of the metal and the benefits are the overall smaller and stronger solder joint. Either way works just fine as long as the joint is solid.
Header Pin on a Pad
You don’t tin the header pin nor the solder pad in this job.
- Bring the header pin to the pad and hold it there with a Third Hand or blue tack
- Heat up both the pin and pad for a couple of seconds, and bring solder to the joint
- Remove solder iron and let it cool down
When soldering multiple header pins, it gets easier after the first pin, because the whole thing is secured in place firmly by the first pin.
- Secure the XT60 connector with a helping hand or bench clamp
- Very slightly tin the inside of the XT60 connector. Do not apply too much solder otherwise you might have difficulty inserting the wire into the holes
- Tin the electrical wire, insert the wire into the hole, and heat up both the wire and the connector
- Bring solder to the joint, until the wire is buried in solder
- Remove solder iron, and allow 10+ seconds for it to cool down
Pro Tip: you can connect the female XT60 connector to a male connector during soldering, this can prevent the gold connectors move around when heated up.
Adjust soldering iron temperature for what you are dealing with. DO NOT leave the iron on the soldering pad for too long, overheating can cause the following issues:
- Heat can build up and damage components on the board
- Copper pads can fall off due to over-heat (possible fix)
You want to get your iron on the solder pad in and out FAST! To do that, I personally prefer using slightly higher temperature, as it melt solder more quickly so I can get the job done faster.
Just remember, high heat, SHORT TIME!
Using low heat can actually be more likely to overheat, as it struggles to melt the solder and you have to keep the iron on the pad for longer and eventually damage the pad.
This is the soldering temperatures guidelines I personally follow using good quality 60/40 solder:
- 300C° (580°F) – extremely delicate jobs
- 350C° to 390C° (662-734°F) – soldering signals wires on a flight controller or ESC’s
- 400C° to 450C° (752-842°F) – large connectors, ESC’s power and XT60 pigtail to PDB
Since 63/37 solder has lower melting point, you can use 10-15C° lower temp.
If you are having difficulty soldering large connectors or wires, do not blindly keep increasing temperature. You should check:
- the quality and type of solder you are using. You should really try the solder we recommend in this guide
- your soldering setup, maybe use a bigger tip which can help transfer heat more efficiently
- And use flux!
Temperature vs. Power
Higher temperature and bigger tip can help transfer heat faster and make soldering a bit easier. The power of a soldering iron can also make a difference.
When the iron is making contact with the joint, the temperature is going to drop as heat is being dissipated through the metal, which is effectively a heatsink.
Soldering iron with higher power can put out heat at a faster rate, and minimize temperature drop. For a low power iron, the temperature can drop momentarily and take longer to recover.
Cleaning Up Solder Joints
You might find residue around solder joints after soldering, this is burnt flux. While it’s not conductive, nor have any impact on the performance of your solder joints normally, it’s a good idea to clean it nonetheless.
Simply wipe the residue off with a cotton swab dipped in alcohol.
Some Other Resources
- How NOT to solder by IntoFPV – http://intofpv.com/t-how-not-to-solder
- General soldering by Adafuit – https://learn.adafruit.com/adafruit-guide-excellent-soldering
- Sep 2017 – tutorial created
- Dec 2018 – Added more pro tips and uploaded more example images
- Mar 2019 – Added “cleaning up solder joints”, and some more tools