Soldering Basics

With RC models it is inevitable that at least a small amount of soldering will be required, unless you rely on someone else to do it for you. RC modellers use soldering for bonding metals together to make strong joints in the structure of their models and, much more commonly, to attach electrical components and battery connections.

If you've never tried soldering before it can be quite a daunting task, especially when there's a lot of it to do if, for example, you've bought a multi-rotor in kit form. Mikrokopter products require a lot of soldering, more than most, and their company, and others, make a lot of money from selling Ready to Fly kits because people are afraid of doing the soldering themselves. In fact, if you can afford it, it's worth buying a Mikrokopter in kit form because you will learn a great deal about how multi-rotor platform work and gain a lot of soldering experience by the time you've finished.

Soldering is a process that uses a low temperature metal (solder) that melts and bonds with the metal it comes in contact with. Parts that are joined together using this method are stronger than those using CA glues.

What you need to solder

• Soldering iron
• Solder
• Flux
• Holders
• Heat-tolerant Work Surface
• Wet paper towel or sponge
• Solder wick

Soldering Iron:

This tool heats up by passing electric current through a metal rod. They are rated by Watts, and something with a variable wattage is usally better - these types are usually called Solder Stations and are a little more expensive than a simple soldering iron, though you can use one of these if you are short on funds. Don't get the "trigger" types; they are more expensive and don't heat up until the trigger is pulled. The tips of the iron will reach surface temperatures of 320º C (600º F) or more! If possible, get one with a tip that is tapered to a chisel shape. Keep the tip clean and bright by using sand paper or steel wool. It should also be "tinned", which will be discussed later. Have some type of holder available, whether a bought one or homemade. Laying one down on a table surface is bad news.

Solder:

This is a metal alloy, mostly lead, that melts easily to a liquid form and bonds to the surface (if clean...we'll get to that later). Find solder that is rated for low temperatures and has a small diameter. Find some that is intended for electronic use. Don't get solder with a "rosin core". It's redundant and won't provide you with any advantage over flux.

Flux:

The third ingredient in this formula is a paste that cleans and prepares the metal surfaces to receive the solder. This is critical to success in soldering. Without it, the solder will just bead up and won't flow. There are liquid types of flux available, but I haven't tried them.

You will find all of these items in electronics supply and hardware stores.

Holders:

Naturally, dealing with high temperatures and molten metal implies that you won't want your hands anywhere nearby. Aside from that, using holders makes soldering much easier, because you can align and anchor the parts properly to ensure a successful bond.

Alligator clips make good holders. X-acto makes a double clip apparatus with a heavy base and positionable arms. You can make your own jigs out of balsa wood, but or just use CA glue and a piece of glass or ceramic. As long as the parts can be laid down flat, it it will work well. The parts are laid down in position and stuck to the glass with a tiny bit of CA glue. The glue holds them through the soldering step, and is scraped off later. CA glue can be scraped off of glass pretty easily. You can use old picture frame glass, but tempered would is better. This is assuming your soldering two bits of metal, extending electrical wire etc. For attaching a connector to a lipo battery I find using a pair of pliers with an elastic band around the handles is good for holding a Deans plug, for example, while you solder the wire to it.

Work Surface:

As just mentioned above, ceramic, marble, or glass work surfaces are heat resistant and can be used to hold the parts during soldering.

Method:

It's a good idea to wear safety goggles.

1. Clean parts that are to be soldered with lacquer thinner, sandpaper, steel wool, or Scotch-Brite pads. Clean the cool soldering iron tip also.

2. Assemble the parts jig, if necessary.

3. Plug in the soldering iron and wait about five minutes for it to reach the right temperature, or watch the digital readout if you have a nice solderting station.

4. Squirt some flux out onto your work surface. Use an old paintbrush to "paint" the flux wherever you want the melted solder to go. Be thorough, as any spot missed will not bond with the melted solder as good as it could.

5. When the soldering iron is ready, dip the tip into some flux. It will sizzle a little, so always keep your face away.

6. Touch the solder to the tip, and let just a little melt and remain on the tip. This is called "tinning".

7. Touch the tip with solder "bubble" to the joint, and hold until you see the solder wick away from the tip and onto the part joint. This can be instantaneous or take a second or two. Take the tip away as soon as the solder has coated the joint.

Notes:

If more solder is needed, start at step six again.

The solder will harden in seconds after the heat is taken away. The joint can be sanded if needed to eliminate too much solder buildup.

If a part has several joints that need soldering, use a "heat sink" to absorb the heat and keep it from melting a previously soldered joint and vulnerable components. Crocodile clip work good for this. Put them between the already soldered joint and the one that will be soldered next.

When finished soldering, unplug the iron and wipe the tip quickly onto a wet towel or sponge. There should be a thin film of solder left on the tip. This is good; it keeps the tip from being oxidized between uses. Let it cool thoroughly and you might want to polish it a little before storing. Remember to polish it the next time it is brought out for use.

Difficult joints (especially small ones) are best handled by "tinning" each part separately. That is to say, coat each part with melted solder, assemble, and then apply heat.