What Is Soldering? – An In-depth Guide [Definition, Types, and Meaning]

what-is-soldering

Soldering in an intricate craft that’s appreciated by geeks who know how much patience and precision it needs to produce a good-looking solder connection. Soldering is essential in most electronic devices, even with the development of microchips. No wonder people are still interested to know about it!

What is soldering? Soldering is a process of joining two or more different types of metals together by melting solder. The solder or filler metal is an alloy which is melted using a hot iron at a temperature higher than 600 degrees Fahrenheit.

Soldering is mainly used in making PCBs, in plumbing, and in roofing. Today, we’ll be learning all about soldering. What is it? What are its applications? How does the process go?

All that will be covered in this in-depth soldering guide.

What Is Soldering?

At its simplest form, soldering is the process of joining two metal pieces with a third type of metal, whose melting point is lower than them. This bonding metal is called “solder.”

Think of an electric circuit, that classic look of a connective tissue on the PCB that links the circuit components together. This “connective tissue” you see is solder.

Soldering is an indispensable part of the electronics industry, where it’s the primary way to join electrical components together. It’s as equally important in making jewelry, joining pipes, air conditioning, stained glass work, sheet metal work, and the list goes on.

One essential distinction to be made here is that soldering is different from welding and brazing.

Related reading: What´s The Difference Between Soldering Brazing and Welding?

While all three processes have the same goal, which is joining metal pieces together, they do it differently.

According to the American Welding Society, soldering is joining metal pieces together in a temperature that’s below 840 Fahrenheit degrees. On the other hand, brazing and welding use higher temperatures and produce stronger bonds.

The main pitfall of soldering, though is the difficulty of correcting its flaws. It’s like ink on paper, what’s done is done, and there is no way to fix it. That’s why it requires loads of practice to master soldering.

The Backstory – Who Invented Soldering?

The art of gluing metals together can be traced back to our ancestors. It’s been used by goldsmiths in Egypt and Troy. Four thousand years ago, they discovered tin, which developed later into the solder alloy.

Back then, they used a metal piece that was heated by fire flames or burning coal to solder.

In the year 1896, Richard Schneider and August Tinnerhol of the American Heater Company developed the first soldering iron, and they received a patent for the “First Electric Heating Apparatus.”

Later on, some improvements were introduced to the tool. General Electric produced a new soldering iron with a latch held to it. They also added a rack that’s connected to a radiator to dissipate the heat of the iron.

It was Ernst Sachs who took the step to manufacture a soldering iron, especially for the industry. The German engineer patented his hammer iron in 1921.

He then founded Ersa, his own company that takes its name from his initials to mass-produce and distribute industry soldering irons all over the globe.

The first use of soldering in electronics was courtesy of William Alferink, in 1926, when he introduced the first soldering station. He was granted a patent for a “Combined Holder and Automatic Circuit Breaker for Electric Soldering Irons” two years later.

The soldering iron started to take the shape of a gun. It was initiated by Supreme Instruments company, in Mississippi, where they invented a soldering pistol for radio repairs. This was in the late thirties.

Then, a generic soldering gun came to life in 1946. Thanks to Carl Weller of Pennsylvania, who received a patent for the “First Solder Gun.” He went on to found his own manufacturing company.

This is considered to be the first instant heat soldering iron. Until then, people had to heat the iron using fire or wait for electricity to heat it.

American Beauty jumped back to the game in 1949. They developed “Temperature Regulating Stands” to control the temperature of their soldering irons, in an attempt to keep up with Weller’s innovative instant irons.

In 1960, Weller received another patent for the “Magnastat Soldering Iron,” which is pretty similar to our welding irons today, and it controls temperature via a magnetic tip.

How Does Soldering Work?

To start with how the soldering process goes, you need to get acquainted with two pieces of equipment: the soldering iron and the soldering station. In addition to the solder itself, of course!

Soldering Iron

A soldering iron is an electrical tool that gets hot when plugged into a 120v outlet. It can heat up to 800°F, where it transfers this heat to electric components like PCB boards and circuits. Then, solder is applied to connect these components together.

High voltage irons don’t produce higher temperatures. They only can heat bigger components. It’s a common misconception among beginners.

A soldering iron can take the shape of a pen or a gun. Both forms are available to this day. The pen is easier to use and control. You can change its tip as well, giving you more versatile options. Hence, we recommend this option for beginners.

The simplest form of soldering irons is that with no temperature control, which still needs a minimum level of mastery to use.

Besides, this makes it not the best option to solder electronic components, where there’s a big margin of error that we can’t tolerate with such sensitive high priced components.

Soldering Station

The next level is a soldering station. It’s more of an all-in-one device that includes a soldering gun, a hot air gun, and desoldering tools. Its greatest asset is that it allows the user to adjust its temperature precisely. This loosely translates into “a wider range of projects.”

It’s also considered safer to use a soldering station, as it isolates the heating part from the electrical device, providing you with an integrated soldering environment. Moreover, they have alerts, sensors, and fuses. So you don’t need to be bothered with safety measures. Well, relatively, at least!

Solder

Traditional solder is an alloy made of tin and lead. It is the actual connective material that joins the electric components together. There is lead-free solder that has a higher melting point than a regular solder. While it’s not as efficient as lead solder, there’s a direction to shift towards it to reduce the use of lead in electronic equipment.

Usually, solder comes in the form of thin tubes rolled in spools. The inside of these tubes is a flux that prevents oxidation and cleans the surfaces of pieces to be soldered.

Soldering Process Step By Step

How Does Soldering Work? Here’s a basic step by step guide on how to solder electronic components:

1.    Prepare

We’ll start off by prepping. Place the soldering iron on its stand if it comes with one, and plug it in. Make sure that the area you’re working in is well ventilated.

While you’re waiting for the iron to heat, you can get a damp sponge to clean the tip of the iron. Moist the sponge and wipe the tip clean. Be careful when you’re doing this step.

2.    Melt

Start to melt a little part of the solder on the tip of the iron. This will help get the flow going from the iron to the joint. If the solder doesn’t flow, clean it with your damp sponge.

Once your iron’s tip is shining bright silver from molten solder, you’re ready to go.

No need to repeat this step every time you solder a component. Only on the first component, or when the iron’s tip is dull and needs some solder to flow.

3.    Clean

You need to prep the surface you’ll be soldering on. Clean the board that you’ll be working on with a woolen cloth, and remove any residue on it.

4.    Solder

To solder, you need to heat the target connection for a few seconds. Be cautious, and don’t wait for something to melt or change its appearance. Then, apply the solder.

You need to hold the soldering iron like you hold a pen. To ensure a robust connection, make sure that both parts to be connected are hot.

While you’re applying solder, keep the tip of the iron on the target place. Don’t remove it. If you find solder not flowing, it means that the target pieces aren’t heated enough.

If all is well, the solder shall flow smoothly to the heated areas in the connection.

5.    Cool

Just when you feel like it formed a strong connection. Remove the tip and the solder. Finally, take away the iron.

Leave everything to cool down. Don’t move the connection while it’s cooling down. Don’t try to test it at this point. It should take a few seconds.

6.    Inspect

Look at the joint and make sure it’s stable, and it looks shiny or a bit dull in case of lead-free solder. If the connection doesn’t look and feel solid, reheat the iron and redo it.

7.    Finish

When you finish up, unplug the iron and wipe its tip clean, when it starts to cool down, of course!

Basic Soldering Technique >> Check out the video below:

3 Main Types of Soldering

There are three types of soldering: soft soldering, hard soldering, and brazing.

1.   Soft Soldering (90 °C – 450 °C)

This is the most commonly used type of soldering. The one that uses a mixture of tin and lead to join electronic components. It’s also commonly used by plumbers.

In soft soldering, workers use a soldering iron that’s powered by electricity or gas.

The bond produced by soft soldering is a bit weaker than other types. It’s logical, given the fact that it works on delicate material that won’t tolerate high levels of heat.

Other solders used are zinc-aluminum to bond aluminum pieces, in addition to lead-silver and cadmium-silver for applications with higher temperatures. Sometimes tin-bismuth is used as well.

2.   Hard Soldering (>450 °C)

To create a stronger bond, go for hard soldering. This technique is often referred to as “Silver Soldering,” where silver or brass are used as solder here.

As you might’ve guessed, we’re talking about materials that require a higher temperature to heat. This results in stronger bonds.

It’s usually used when the base metals are silver, brass, or glass.

3.   Brazing  (>450 °C)

Brazing is quite similar to hard soldering, where two base metals are heated to a high temperature, then you insert solder to fill in the connection part. It’s also known as capillary action.

Somehow, brazing is considered a type of hard soldering.

Related reading: Aluminum Brazing: Complete Guide – Advantages Over Welding

Soldering by Core Types

Some people prefer to categorize soldering types according to their core types. In this case, there are also three types: solid core solder, acid core solder, and rosin core solder.

Solid Core Solder

These are solders with no flux -we’ll be talking about what flux is in the next section, but for now, let’s say it’s a chemical agent that prevents oxidation-.

In a solid core solder, the solder is hollow from the inside, so it requires an external flux to do the oxidation prevention part. This technique is commonly used by plumbers.

Acid Core Solder

An acid core solder is one whose hollow core is filled with flux. An acid-based flux, as the name suggests. The acid flux is considered the strongest among flux types and hence, provides better “cleaning action.”

This technique is usually used with metals and steel. It results in a lot of flux residue that requires cleaning to avoid corrosion afterward.

Rosin Core Solder

This one is pretty similar to the acid core solder, where the hollow solder has flux inside, but one of rosin instead of acid. Rosin is milder than acid, and it’s not as corrosive as acid.

This type is the most used in electronics because of its minimal residue. Because cleaning up residue is nearly impossible in electrical applications.

Which Flux Can Be Used for Soldering?

Flux is an acidic mixture that helps prevent oxidation of the surface of the components you’ll be soldering.

If you’ve seen a soldering gun before, you might recognize the flux as a brown liquid that drips when you heat the gun. Usually, a flux is a mix of boric acid and alcohol.

In electronics, the flux is embedded inside the solder itself, and it’s called a rosin-core or rosin-flux solder. On the other hand, when you use soldering in plumbing, you need a different type of solder with a separate flux.

A rosin-core solder is one whose melting point is lower than the metals it’s trying to join together. So that when you heat it, the solder melts, but the metals don’t.

The flux doesn’t only provide oxidation, but it also improves the solder’s ability to wet the surfaces it’s joining.

The flux also helps eliminate rust from electronic components, which serves well during soldering.

One of the most distinctive properties of solder flux is its pungent odor. Thus, it’s always advised to solder in a place with good ventilation.

What Is a Soldering Gun Used For?

What is a soldering gun used for? A soldering gun is used in a variety of applications where precision and accuracy are required to join pieces together.

It’s commonly used by jewelers, electricians, and electronics technicians.

In general, a soldering gun is used in applications that a soldering iron would be too big or too hot for. Applications that require precision, as we said.

Here are some applications that require a soldering gun:

Circuits

The most common application for soldering is electronic circuit boards. Soldering is a favorable option here for plenty of reasons; the most important among them is that the solder allows for smooth electrical conductivity.

Besides, it keeps the connections on the surface of the board, so they look neat.

Roofing

Another well-known application for soldering guns is fusing elements when roofing. Soldering is used in flashing roofs to fuse galvanized metals. It’s also used in copper roofs.

Jewelry

Jewelers need something to fuse elements with the highest precision degree possible. What’s better than a soldering gun?

In this case, solders usually have high percentages of silver, for value and aesthetic reasons. Soldering jewelry requires a high level of skill from workers as they always change tips according to the piece they’re working on.

Plumbing

As we mentioned before, plumbers use soldering to join pipes. In some cases, they use welders, but in other cases where they’re working in tight corners, they’ll probably opt for a soldering gun.

What Metals Are Used in Soldering?

Solder comes from the Latin word “solidare,” which means “to make something solid.”

The most common solder is the infamous tin-lead solder, which is used in electronic components. However, there’s a wide variety of alloys that are used in soldering.

Some of them don’t even include tin. Particular elements can be added to the mix to introduce certain properties.

For example, lead-free solder has been trending lately for environmental reasons. Especially when the EU started to restrict the use of lead in electronics. The industry shifted to use some alternatives to mix with tin, like nickel.

It’s important to note that lead-free solder has higher melting points than its counterparts, which poses an inconvenience to the electronic equipment industry.

To lower the melting point of solder, copper is thrown to the mix sometimes. Bismuth does the same, in addition to enhancing the wettability.

On the other hand, silver is used when higher melting points and mechanical strength are required.

What Is Leaded Solder? – Advantages and Disadvantages

You’ve probably heard about leaded solder if you’ve worked in electronics manufacturing before. It’s one of the most sought-after substances in that field and has been for many years.

Leaded solder is a combination of lead and tin, with 40% and 60% percentages, respectively. It melts at 185 °C approximately, and it’s known for its low price.

The lead, in particular, caused concern among health professionals due to its known risks on the human body. Nevertheless, leaded solders are still used to bond metal workpieces. People even thought that creating a 50-50 blend was safer, but it didn’t make a difference.

Advantages

This type of solder isn’t popular for nothing; it has impressive flowing properties. The reason is that it needs a lower temperature to get heated than lead-free solder. Also, leaded solder shines brighter, giving it a more attractive appearance.

It also works well for spotting the otherwise hard to spot issues, such as oxidation. Oxidation can cause a toned-down shine, which will mess with the product’s appearance.

Furthermore, the most prominent advantage of leaded solders is that they cost much less than lead-free ones. This is the main reason for its wide popularity. Not to mention that it’s much easier to use, which drives a lot of users to go for it.

Disadvantages

Leaded solders have many economic and manufacturing advantages. However, there are still some downsides to using them.

Lead is a popular chemical element that has multiple uses in manufacturing car batteries and cable sheathing. Despite that, there have been growing concerns about its effect on human health for a long time.

It’s a potent neurotoxin, which means it has direct toxic effects on the user. On top of that, it contains small amounts of radioisotope impurities, which are bad news when undergoing alpha-decay.

As a result, people use silver instead to overcome the health issues that come with lead.

What Is the Difference Between Silver Solder and Regular Solder?

While silver solder isn’t the best choice electrically, it has many advantages that earned it a place among the top solders in manufacturing. It’s also the reason for its constant comparison with other solders.

Silver solder has a higher melting point than regular solders, thereby making it stronger. This also makes it less susceptible to mechanical exhaustion. Besides, it improves its resistance against thermal cycles and high temperatures, as opposed to other types of solders.

Blending silver with tin significantly reduces the chance of tin whiskers forming, which are a common occurrence in regular solder. They’re electrically conductive structures that result from tin surfaces. Additionally, they grow in length and cause short circuits, which attribute to many system failures later on.

Using silver also has its drawbacks compared to regular solder. It’s among many metals that cause grittiness, which is the formation of little bumps on the solder surface. This won’t happen with regular solder. Also, there’s the biggest obstacle of them all: the high price.

What Is the Strongest Solder?

The way it is with electronics manufacturing, strength is the most vital feature to look for. This is mainly to avoid seeing any mechanical exhaustion or fabrication problems.

That being said, the most effective solder isn’t necessarily the better one. There are many aspects to look for when choosing.

What is the strongest solder? The strongest solder known to date is the silver/tin solder, due to its high melting point, along with the impressive brittleness of silver. When it comes to strength, this solder is hard to match.

Nevertheless, silver/tin solders aren’t suitable for all types of electronics. Lead is still the most versatile material.

For example, when manufacturing medical or aerospace electronics, leaded solders are the obvious choice. They are more reliable than silver-based ones in this case.

If there are certain health or environmental demands, lead-free solders become the favored choice. That’s because of the lead’s absence, which serves as a major risk of health.

Solders are often made of alloys, which means you’re free to choose the right mixture for the electronic in hand. It’s all about identifying the demands for the manufacturing process and optimizing it to get a lower cost.

Soldering Safety – Tips and Tricks

The extremely high temperature of a soldering iron can be really dangerous, so safety precautions are not to be taken lightly here. Soldering irons can literally start fires.

Here are some tips you can -and should- follow when soldering.

  • Make sure to wear loose clothes.
  • Tie your hair back.
  • It’s favorable to wear safety glasses.
  • Always unplug the soldering iron or station when not in use.
  • Don’t work in a closed space. Choose a well-ventilated area to protect yourself from the flux.
  • Never ever try to touch the iron’s tip when it’s plugged in, even when it’s off, even when it’s not “hot” enough.
  • Try not to inhale the fumes of the flux. These can be highly irritating to your eyes and nose.
  • Using protective gloves is a plus.
  • Keep the cleaning sponge wet during use.
  • Always use hand soap and water to wash your hands after soldering.
  • Cover your skin if you’re used solder that contains lead.
  • Keep a cleaning solution in a dispensible bottle in your workplace.

Conclusion

We hope we’ve covered everything you needed to know about soldering, the quintessential skill in the field of electronics!

One of the things we love about soldering is that you can easily learn even as a hobby! Somehow it’s a staple in every maker’s skill set, and all you need is an iron, and you’re good to go.

What Is Soldering? >> Check out the video below:

David Harper

David is the Co-Founder and Senior Editor at weldingtroop.com. David's an experienced fitter and tuner/welder who's passionate about helping others develop in life through new skills and opportunities.

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