Soldering 72, The Fundamentals

by Kurt0326 | May 23, 2015 | (14) Posted in How To

Soldering, for some it is a magical craft that is too astronomical to even consider learning.

Well my friends, then this artical is for you. Face it, we in the R/C hobby (especially the electric side) will eventually come across some type of problem that will require you to solder. It is inevitable, so what are you going to do? Throw away your R/C craft because that stupid wire broke? Or do you think the guy at the hobby shop is going to fix it? Well he just might, but most R/C shops now do not solder for the customers anymore due to legal liability. Yes "because they are a business" people will sue the business for aircraft failure even if the failure is unrelated to the soldering job rather taking responcibility themselves.

Why should I solder? This is a good question. After all, all you need is contact metal to metal right? Shoot, with enough current you don't even need contact and the electricity will just arc across the points. You could just simply twist the wires back together. "Maybe I could just get away with using a cheap twist connector thing, electric tape or a crimp connection?" All of this is true. If your just looking to quickly connect wires it will get the job done. I have just one word to offer to you and I will give you three good reasons why it is very important. (Reliability) This is the reason that makes it indispensable, you can't do without it.

An unsoldered connection will be:

  1. susceptible to corrosion and oxidation; very basically meaning the metals get dirty and current can't flow through. Oxidation, will be the most repeated problem with soldering. So you are going to hear a lot about it.
  2. weak against stressors like vibration or pulling and twisting and may lose connection all together.  
  3. susceptible to increased resistance, meaning the current can't move through the connection freely like a traffic jam. Or pouring water out of a glass vs. a bottle.

When you have a wire brake, a properly soldered connection will be stronger than the original wire itself. 

Now if you are ready, you could take this as another step in your R/C life and educate yourself. Become that mister fix-it! Or if you want to start scratch building, that will require this skill.

I know, I have been there with you. I was scared. I thought it was a difficult craft. Well I have some great news. It’s not! If you have the patience to learn how to fly, this could be a piece of cake for you. 

What I am going to build is a series of articles for you all. It this article I will cover the bare basics. Before you ask, no I will not cover actual soldering in this artical. It is best to start from the ground up. If you don't have the foundation, the information and help that people offer can fall through the cracks.

However, if you are in a hurry and can not wait for me to finish the series, I highly recommend that you watch the video Basic Soldering For Electronics. This is the most in dept video I have seen yet, but even this video does not cover some of the basics and you will still need the information covered in these articles. So with any further ado, yet's get in to it shall we?

Soldering 72: The Fundamentals


What are we going to learn:

  • Terms - need to know
  • Gear - ID'n that whatcha call it?
  • Safety - Which end is the hot end?

Terms you need to know:

  • Soldering: is a process in which two or more metal items are joined together by melting and flowing a filler metal (solder) into the joint, the filler metal having a lower melting point then the adjoining metal. Soldering differs from welding in that soldering does not involve melting the work pieces. In brazing, the filler metal melts at a higher temperature, but the work piece metal does not melt. Consider that soldering is more like gluing with molten metal, unlike welding where the base metals are actually melted and combined.
  •  Oxidation: is the loss of electrons or an increase in oxidation state by a molecule, atom, or ion. What does that mean? Okay, when metals (like the copper on PCBs) loose electrons, they attract oxygen molecules that will bond to the surface of the metals forming an insulation barrier like a blanket. In soldering, a barrier just one molecule thick will not allow the wetting action to take place.
  • Wetting: This is the bread and butter that makes soldering so important. Wetting is the way solder bonds to pieces together. Please, watch this video for more information on what wetting is in great depth.

  • Cold joint: This is a contact that has poor wetting. Another way to think about it is if a good energized electric circuit is considered hot, then cold means bad connection.                                               
  • Printed Circuit Boards: Also called PC boards or PCBs are an electronic circuit consisting of thin strips of a conducting material such as copper, which have been etched from a layer fixed to a flat insulating sheet called a printed circuit board, and to which integrated circuits and other components are attached. These are needed for clean builds. Otherwise all of the pieces would be a mess of wires and parts.
  • Tinning: or to pre-tin. This is the action to add solder to the end of the wire that is exposed. This will keep the wire from oxidizing, fraying or to prepare the wire to be soldered.

GEAR - Identifying the tools, specifications and uses.

Solder:  (/ˈsldə/,[1] /ˈsɒldə/[1] or in North America /ˈsɒdər/[2]) is a fusible metal alloy used to join together metal work pieces and having a melting point below that of the work piece(s).




More about solder:

 The Gauge: or SWG (Standard Wire Gauge)

 Solder comes in many different sizes, but 22 or 18 are generally the most common. The bigger the SWG number the smaller the wire. I use 22 for most of my soldering or 26 for surface mounting on PC boards.

 What does the fraction mean?

 So there is a fraction on the spool of solder like 60 over 40 or 60/40. Solder is normally made of two different metals, tin (Sn) and lead (Pb)  (TIN/LEAD). Each type of solder has different characteristics.

 60/40: So this is made from 60% tin and 40% lead. It has a melting point around 190°C. Iron is recommended to be at 300°C to work. It is also very soft, meaning that cracks do not form so readily if the joint moves during cooling.

 63/37: This is made of 63% tin and 37% lead. It's melting point is around 183°C. The primary advantage of this solder is not the lower melting point, but its eutectic property. Non-eutectic solders, like the 60/40 solder, have a semi-solid state between solid and liquid. If a joint is moved during this stage, it can result in what is called a cold solder joint. Eutectic solders, like the 63/37, do not have this semi-solid state and are thus considered easier to work with as it produces fewer bad joints. However, these solders typically cost more than their non-eutectic counterparts. It is most commonly what I use.

 Do not use 50/50 solder. That is used in plumbing and will fail you.

 As well as lead free solder, stay away from it. I know there was a movement in the past to leave the lead solder behind and some people stand by it. Lead-free has a higher melting point (230°C) which means your hobby iron will not be enough to work it. So that means a new "lead-free iron" to get the higher temps. not only that but the Lead-free stuff is around 50% more expensive.


Flux and Rosin:

Flux: In metallurgy, a flux (derived from Latin fluxus meaning “flow”), is a chemical cleaning agent. Fluxes may have more than one function at a time. They are used in both extractive metallurgy and metal joining.

What can it do?

  • It chemically removes oxidation from the surfaces being soldered.

  • It prevents air from oxidizing the surfaces once they have been cleaned.

  • It increases the "wetting" of the surface when the solder is applied.

Rosin core solder has a hollow middle core, like a pencil. Where the pencil is wood with a lead center, the solder is holding a resin flux. When the solder is heated the flux, with the lower melting point, flows out from the center of the solder first to clean and prepare the surface. This melting flux is what the fumes are coming from. Rosin core solder can be both lead and lead-free. Whichever you choose rosin core should be the first choice you should use when soldering electronics. 

Do not use acid core solder. That is for plumbing only. You will harm the delicate electronics with the acid. The acid will also remain active even after the joint cools, while flux is harmless after it cools.

Please again, watch this video on Flux as it goes in to great depth about the subject.


Pencil Iron: A pencil iron is a hand tool used in soldering. It supplies heat to melt solder so that it can flow into the joint between two work pieces.

A soldering iron is composed of a heated metal tip and an insulated handle. Heating is often achieved electrically, by passing an electric current (supplied through an electrical cord or battery cables) through a resistive heating element. Cordless irons can be heated by combustion of gas stored in a small tank, often using a catalytic heater rather than a flame. Simple irons less commonly used than in the past were simply a large copper bit on a handle, heated in a flame.

Pencil irons are measured by watts. The smaller irons start at 30w and are suitable for lite wires and small jobs. Then irons go to 100w or more for bigger jobs. Choosing the right size iron will be covered in my next article.

Now it's important to get the right tool for the job. If you hardly solder wires larger then 16 Gauge you can stick with a small 30w iron. Also important to get an iron with a changeable tip. There will be many differant tip styles to choose from and each have an intended purpose. If you splurge get an iron with temperature control. 

Soldering gun: is an approximately pistol-shaped, electrically powered tool for soldering. The tool has a trigger-style switch so it can be easily operated with one hand. The body of the tool contains a transformer with a primary winding connected to mains electricity when the trigger is pressed, and a single-turn secondary winding of thick copper with very low resistance. A soldering tip, made of a loop of thinner copper wire, is secured to the end of the transformer secondary by screws, completing the secondary circuit. When the primary of the transformer is energized, several hundred amperes of current flow through the secondary and very rapidly heat the copper tip. Since the tip has a much higher resistance than the rest of the tubular copper winding, the tip gets very hot while the remainder of the secondary warms much less. A tap on the primary winding is often used to light a pilot lamp which also lights the work piece.

The soldering gun is useful when soldered joints must be made intermittently. A constant-heat device has to be set in a safe place when powered but not actually in use, to prevent damage or injury. The fast-switching gun cools quickly enough to be set down a few seconds after use.

The soldering gun is also useful for large jobs because of its ability to produce large amounts of heat. So if you are working big wires and large connectors, you could use the gun. Not good for delicate work like PCBs.

Iron Stand: This is a simple soldering iron stand composed of a heavy-duty metal base and a reinforced spring designed to hold your hot iron.

Helping Hands: Also known as a third hand or extra hands, is a type of extremely adjustable jig used in soldering and craftwork to hold materials near each other so that the user can work on them. These are most useful when you not have enough hands to hold everything in place.

Pliers: Pincers with parallel, flat, and typically serrated surfaces, used chiefly for gripping small objects or bending wire. Mostly more holding small objects that you hands are too large for. Plus they hold hot stuff without complaints.

Wire Strippers: A small, hand-held device used to strip the electrical insulation from electric wires. No, do not use your teeth or knife. Use the right tool for the right job.

Multi-meter: An instrument designed to measure electric current, voltage, and usually resistance, typically over several ranges of value. This will come in handy. We are dealing with electricity here. It is nice to be able to measure what we are doing.

Heat Gun: A device used to emit a stream of hot air, usually at temperatures between 100 °C and 550 °C (200-1000 °F), with some hotter models running around 760 °C (1400 °F), which can be held by hand. For our application to shrink heat shrink.

Heat Shrink: A shrinkable plastic tube used to insulate wires, providing abrasion resistance and environmental protection for stranded and solid wire conductors, connections, joints, terminals, organize wires grouping and separating wires esc. It can also extremely useful in other hobbies not limited to electronics and comes in a huge selection of sizes and colors. The most color used is black and quickly followed by red of course. But think about decorating your project with different colors.

Electrical Tape (or insulating tape) is a type of pressure-sensitive tape used to insulate electrical wires and other materials that conduct electricity. It can be made of many plastics, but vinyl is most popular, as it stretches well and gives an effective and long lasting insulation.

Liquid Electrical Tape Is a liquid paint on version, with many different applications.

Safety Glasses: Toughened glasses or goggles for protecting the eyes when using power tools or industrial or laboratory equipment. Remember safety first. Couldn't you imagine that hot molten solder flung straight in to your bare eye? Unless you don't mind searing pain, emergency room visits and believe eye patches are sexy.

Gloves: Solder, at least the good stuff, is made of led. Your body doesn’t like lead, so it's downright bad for your health. Always use gloves. Likewise, you shouldn't eat or drink during or after handling solder.

Fume Extractor: Designed to filter harmful fumes from soldering. Success is variable widely on the quality. I.E. You pay for what you get.


Soldering Wick: This is one tool for rework or de-soldering. The idea is that the heated liquid solder will wick in to the strand and remove the targeted solder from say a circuit board.

Solder Sucker: Another de-soldering tool. The idea of this is to suck-up the liquid solder. You just push the top plunger down until it locks and heat the target solder, press the button and it's spring loaded vacuum sucks the solder up.

Brass/Copper Wool: Very simply a ball of wool made of brass or copper. Why do we need this? To clean the iron tip. Some use steel wool and claim it is good. Well I've used it. It's not that good for your iron.  The steel wool will clean your iron tip and strip away that thin tin lair that makes soldering possible. Then the bare iron will oxidize, completely rendering your iron useless. Brass or copper will leave your all important tin lair intact.

Sponge: A damp sponge, not saturated. This has been the standard method of cleaning the iron tip for many years. Some shy away from using the sponge because it cools the iron tip. Much like a blacksmith working metal, it will squelch the hot iron and could crack the thin coat of tin. If left to cool and store it will damage the iron tip. Just remember to add a lair of clean solder to the tip after.



  • Only handle the Iron by the handle, treat it like it is hot at all times.
  • Always wear PPE, Personal Protective Equipment. At minimum Safety Glasses and gloves
  • Do not eat or drink before washing hands. That is just general common since but defiantly not after soldering.
  • Keep a clean work area, dispose of all used solder. So it won’t get in to places it shouldn’t be, like childern's mouths.
  • Do not solder in places with combustibles. Let’s not start any fires.
  • Solder in a safe place, best NOT to be in an area children might around unsupervised.
  • Best not to solder in areas with carpet where solder can fall in to.
  • Solder in a well ventilated area or use a good fume extractor.

That is all for this article. Congratulations for making it this far! This was the worst part, just getting the basics. Next I will move in to tool Selection, tool maintenace, basic soldering guide and trouble tips. For those that like to move a bit faster I have found a video that I think will help accelerate your learning called:

Basic Soldering For Electronics

This is the best basic soldering video I have ever watched and I highly recommend watching it. Copy Right 1980! Yes, it's old but there is nearly no change in the soldering techniques today. It covers in great detail the basics so most of us can understand.

Thank you for taking the first step in to soldering. Some times the first step is the hardest, so good for you. Just keep going and we'll make a solderer out of you. Please leave comments and suggestions or any burning questions you have wanted to ask and I will try to answer them or at least point you in the right direction.


Willsonman on May 20, 2016
Good stuff! While there is no real mention of cleanup post-soldering, I use household KETCHUP to clean. The slightly acidic nature of it will take off the flux and help dissolve any blackened areas that have developed. Apply a little to an old toothbrush and clean away. Rinse with water when done and you are left with a beautiful finish. While this may not be necessary for joints, it is very useful when soldering struts or landing gear legs.The cleaner finish will look much better.

Also, a lair is a place where an evil scientist dwells, a layer is a sheet which can be singular or in multiples covering or coating something. :p Love ya Kurt!
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Kurt0326 on May 20, 2016
Thanks for the approval.
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Kurt0326 on May 20, 2016
Now remember this is only the first of a series. If I have not covered a subject yet, that won't mean I will not be covering it in a later article. I had a lot of topics to cover before we actually get into real soldering. So please hang in there folks.
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AERODROME on May 20, 2016
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Kurt0326 on May 22, 2016
Good ideas, I will consider adding these two in. My main focus right now is completing the second article.
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Soldering 72, The Fundamentals