Soldering is an important aspect of many jobs nowadays, from plumbing, electronics, and metalwork.
It is the process of joining metals together which provides a permanent hold which is also reversible.
In plumbing it is used as a connection between copper pipes, electronics to secure components and connection purposes in jewelry.
Flux is like solering’s sidekick. It is a cleaning agent used to clean surfaces to remove oxidation, to provide a better means of soldering.
But, is it essential? Can you solder without flux?
Yes, you can solder without flux. While it is helpful in the process of soldering as the flux helps break down the oxides on the metal, it is not needed. Also, most solder nowadays come with a rosin core which does the job of flux helping breaking down oxides.
It depends on many variables such as, what the application is, whether the solder you are using already contains flux or not etc. I will also cover the benefits of using flux.
Soldering and Solder
Before we dive into whether you have to use flux when soldering, let us learn the basics of soldering.
Learning the basics behind soldering will help to better understand the importance of flux later on.
Also, I will cover solder and what it is made of, as well as different types of solder.
What is Soldering?
Soldering in its most basic definition is, when two or more items are joined together. These items are commonly metals.
A soldering iron is a piece of equipment used in the process of heating solder (a metal alloy usually made of tin and lead) to join these metals.
The soldering iron is heated to temperatures ranging from 200 – 600 degrees Fahrenheit ( 95-315 degrees Celsius) in order to melt the solder.
Soldering irons come in a range of prices and qualities. When buying a soldering iron, it is best to spend money on high quality ones, as lower quality soldering irons sometimes have trouble melting the solder.
Welding is sometimes confused with soldering. However, these two processes are quite different.
The main difference between them is the melting process. In soldering, the metals involved are heated but never melted. With welding, the base metal is melted.
Types of Soldering
When it comes to soldering, there are three categories or forms of soldering ; Soft soldering, silver soldering, and brazing.
As we advance from one form to the next, the temperatures increase as well as the strength of the joints. The lowest temperatures start with soft soldering, then silver and finally brazing.
The temperatures increase due to the melting point of the filler materials.
Soft soldering uses a tin and lead alloy as a filler. Silver soldering uses an alloy containing silver and brazing uses an alloy that contains brass.
It was common in the past for solder to only be lead based. But, due to environmental and health concerns the use of lead free alloys is more common.
Applications of Soldering
As we saw the soldering and solder are used in order to join metals.
It is utilized in many jobs. The most common of them which you might be more familiar with is in electronics.
Apart from just electronics, soldering is used in plumbing, metalwork, flashing and in industries involving jewelry and musical instruments.
In electronics soldering provides connection between electronic components also allowing the flow of electricity. It is an essential part of electronics.
Plumbing requires a secure, permanent but reversible connection between copper systems. Soldering provides exactly that.
Jewelry and musical instruments use a combination of silver soldering and brazing in their assembly as well as repair.
So you can see soldering plays a crucial role in many areas.
As I briefly mentioned, solder is a filler material used in the process of soldering.
To create permanent but reversible bonds between metal pieces, solder is used. It is a fusible metal alloy. It is a key element in the process of soldering.
Having a great mechanical joint is crucial and having a great electrical joint in electronic applications is a necessity. Without a strong electrical joint, electricity will not be able to flow rendering the circuit and those components useless.
Solder traditionally was used in the electronics industry. It used a blend of Tin and Lead.
Types of Solder
However, as I mentioned the different applications, there also exist different types of solder.
With many things there comes an abundance of choice. The same goes with the choices of solder. So picking the right solder can be confusing.
Fortunately for you and me, there are three main categories that solder falls into.They are Lead based, Lead Free and Flux Core solder.
The first type of solder was the traditional solder used for electronics and contained 60% tin and 40% lead. This type of solder has a low melting point ranging from 356 – 374 degrees fahrenheit (or 180 – 190 degrees celsius). This type of solder is often referred to as soft solder and is commonly used with soft soldering.
Second on the list is a Lead Free Solder. After a while, the health risks and environmental effects of lead in consumer electronics was known to be negative. So having lead based solder was not the ideal situation.
Due to this, a Lead Free solder was created and Lead based solder banned from being sold commercially.
Lead free solder usually contain 99.3% tin and 0.7% copper with higher melting temperatures around 422 degrees Fahrenheit (217 degrees Celsius).
The final solder, and most important to the question at hand (can you solder without flux) is Flux Core solder. This solder has the flux embedded in the solder and does the job of what flux does without needing to apply it externally.
I will cover the benefits of this type of solder later when I discuss whether you can or cannot solder without flux.
I mentioned above about two other techniques of soldering which included silver soldering and brazing.
For silver soldering, silver solder is used which is an alloy that contains silver and another metal ranging from copper, zinc, nickel , manganese, cadmium, tin, silicon and many others.
Brazing uses solder that contains metals including gold, silver, copper, brass and iron.
With different types of solder also comes different solder sizes. The size of the solder is determined by its gauge. The gauge is effectively determined by its diameter.
Different gauges of solder will be beneficial depending on the application.
When it comes to electronics work, the smaller the gauge size the better.
Applications involving plumbing on the other hand would require a larger gauge solder.
So, depending on the application you are using solder for will determine what size solder you will need.
As we saw that soldering plays a vital role in many applications and solder is an essential part in the soldering process. We cannot have one without the other.
But, where does flux come in? What is its role? And is it really needed when you solder?
Let’s learn a little about flux.
What is flux?
Flux is a water based solution that contains a cleaning agent, activator and wetting agent.
It has many functions that are used when soldering. It has to spread on the metals being soldered, it has to clean the surfaces and help spread the solder.
For a flux to be effective it has to satisfy all these three criteria.
The first being a spreading on metals is known as wetting. Fluxes contain a wetting agent that allows the flux to flow better. The flatter the wetting the better as this will cover more surface area.
Consequently, the better the wetting agent will result in the flux being more efficient. The more efficient a flux results in less solder having to be used and thus less cost (because you will have to buy less solder).
Next is cleaning of the surface.
Most metal surfaces have a lot of build up of oxides, oil and dirt. Trying to solder metals that are dirty will not create a secure long lasting bond.
So, fluxes also have the added benefit of cleaning these metal surfaces. The activator package of a flux is a specific chemical designed to remove oxides, oil and dirt.
The flux is acidic in nature because acids are great at removing oxides by converting them to soluble salts.
A great analogy here is the use of detergent in removing grease and grime from your dirty dishes.
Detergent’s were created to do a job that water by itself would not be able to do. Imagine having to wash your dishes with just water alone. It does not have the chemical attributes of a detergent to remove all that dirt.
Dissolved oxides and dirt are then moved away by the flux leaving the metal surfaces clean.
Another important role a flux plays during the cleaning phase is to protect the metal from re-oxidizing. After the metals are cleaned they are exposed to oxygen in the air.
The activator package (which is rosin based) stays active throughout the entire process thus protecting the metal from re-oxidizing.
Finally, flux should promote a good flow of solder. You will know if you have ever tried soldering how annoying it is when the solder just does not stick or flow well and create good joints.
A good flux allows the solder to flow well by lowering the surface tension between the metal and melted solder.
Different types of flux
The flux you use will depend on the application. There are two main applications which include Industrial, and Electronics.
Industrial Applications include plumbing, roofing, automobile, where metals like copper, brass, steel, stainless steel, Aluminum and Aluminium alloys are used.
Electronics Applications use three standards of flux ; rosin, water soluble and no clean fluxes.
Rosin Flux is a natural based resin that is derived from the pine tree. There are three types of rosin flux. They are divided up based on how active they are (resulting in a cleaner surface and more residue).
Rosin (R) is the least active followed by Rosin Mildly Active (RMA) and finally Rosin activated (RA) being the most active.
Water Soluble fluxes are composed of organic materials and are also sometimes referred to as an organic acid flux. It has good flux activity and a great wetting agent.
A No Clean flux has its description in its name. It does not require any cleaning after soldering.
Can you solder without flux?
So, we have covered the process of soldering as well as solder (filler materials) used to bond metals together.
Knowing how the soldering process works will give you a better understanding of whether you need flux or not when soldering.
So can you solder without flux? The best way to approach this question is to give you all of the advantages of soldering with flux.
Also, different applications will demand the use of flux more than others.
The first and most important advantage is, better solder joints. As you saw in the section about flux, its main purpose is to clean and remove oxide as well as any other impurities from the metals being joined.
If you have weak solder joints, the metals being soldered are prone to damage overtime.With electronic soldering having a weak solder joint results in poor electrical conduction.
Next is a better flow of solder. Flux enables a better flow of solder. This has many advantages. Having a better flow of solder means having to use less solder. Using less solder has the added benefit of lowering your cost as you will be using and buying less solder.
Also, soldering at lower temperatures, solder does not melt, flow and adhere well. Using flux will help promote a better flow and alleviate your frustrations.
Lastly, allow for desoldering. If you have ever had the misfortune of having to desolder a solder joint without flux, you know how hard it is. Desoldering a solder joint that has oxidation is near impossible. Since flux removes this oxidation, desoldering will be much easier.
Also using a lead-free solder without flux is quite a challenging task. It is best practice to use flux here.
Like I mentioned above, the application will dictate if you really need flux.
If you are a hobbyist dealing with soldering electronic circuits, it will not really be much of an issue if you solder without flux.
Industrial applications involving electronics, plumbing, automobiles, or construction and repair of jewelry will need better and more secure bonds. These can only be achieved with the use of the right flux.
If you are using a flux, make sure it is matched to the solder you are using.
Solder that contains flux
The good news is, there is a solder out there that has flux embedded in its core. This is known as Rosin Core Solder. As you saw before, Rosin Flux is a widely used natural flux.
The Kester Rosin Core Solder is a great solder which contains flux. It is the difference between good and great soldering joints.
So, for smaller electronic applications you can use this solder without having to externally apply flux and still get the same benefits.
Plumbing solder however, does not contain flux. So, flux will have to be applied externally.
Using flux has many benefits and will only make your life easier during the soldering and desoldering process.
However, if you are not wanting to use flux and are soldering electronic components and circuit boards you have the fortune of having a solder that contains flux.
Soldering Flux Alternatives
Flux in its simplest definition is a cleaning agent. It’s earliest form was carbonate of soda, charcoal, borax, lime etc.
There are many options of cleaning agents you can use with common everyday house items.
If you ever want to make your own flux check this tutorial out. It’s great for the environment too!