Soldering Flux: What Is It and How Do You Use It?


This may be an unfamiliar term for a lot of people. The basic definition of this term is any chemical compound used in soldering to purify the soldered surface, inhibit oxidation and remove impurities from the process. But what does this mean? It can act as a cleaning agent, a deoxidizing agent, an acidic medium, and so on. Having the right flux for your type of project will make soldering easier, quicker, and better for the environment.

Brief Explanation of Soldering Flux

Soldering flux is a substance that aids in the flow of soldering, which is the act of joining metal components by melting and flowing solder into the junction. It inhibits oxidation and improves wetting, helping the solder to adhere to both the linked metal parts and the soldering iron.

Soldering fluxes are often liquids or pastes that are applied to the surface of the metal to be connected before it is heated using a torch or electric soldering iron. Because the flux ensures that nothing on the metal’s surface interferes with its bonding with solder, it’s critical not to use it too late in the process—you want to finish everything else first.

Soldering Flux

Soldering Flux

Why is Flux Necessary in Soldering Electronics?

Soldering electronics is a tricky business. You need to have the right tools, you need to know how to use them, and you need to know how to do it safely.

Flux is made up of chemical compounds that help remove impurities from the surface of the metals being soldered together. It also lowers the melting point of solder on contact with heated metal, allowing it to flow more easily into crevices and around parts of a circuit board.

Types of Soldering Flux

Each has its own benefits and drawbacks, so you should use whichever type fits your needs best. Here are some common types:

Rosin Flux

It’s a mixture of rosin and other chemicals, typically including boric acid and sal ammoniac. Rosin fluxes are usually formulated to be compatible with specific metals, such as copper or nickel. They can also be formulated to be used with specific types of solder, such as lead-free solder or silver-bearing solder.

There are also a few types of Rosin Flux available in the market:

Rosin Flux

Rosin Flux

Rosin Activated or RA Flux

The most commonly used type of soldering flux. It’s a synthetic resin that’s dissolved in alcohol.

When you apply it to your metal surfaces, it acts as a solvent that helps remove oxides and other impurities from the joints of your metal pieces. This allows you to solder them together more easily and with greater success.

RA Flux also helps prevent oxidation during the heating process, which improves your chances of getting a good connection between the two pieces.

Rosin Mildly Activated

A relatively new type of flux, and it’s gaining popularity in the electronics industry because it works well for soldering surface-mount components. It’s made from partially rosin-based compounds that have been treated with oxygen, which helps the solder flow more easily over the joint.

Non-Active Rosin Flux

A type of soldering flux that is not electrically conductive. It’s usually a rosin-based material that helps to remove oxidation from metal surfaces when heated, as well as being a good solvent for other types of fluxes.

It does not require activation by heat or chemical oxidization. It is often used as a cleaner for the surface of metals prior to soldering, and it can be used to prevent oxidation of the metal during soldering.

No-Clean Flux

A type of soldering flux that does not require the use of a cleaning solvent to remove it. It is typically used in electronics applications where a clean surface is required, such as in semiconductor manufacturing. It’s great for people who want to solder in an area where cleanup would be difficult or impossible.

No-Clean Flux

No-Clean Flux

Rosin-Based No-Clean Flux

It’s used in applications where the heat source will be fairly low, like when soldering small components.

Rosin-based no-clean flux has a high melting point and a low evaporation rate, which means that it won’t evaporate as quickly as other types of solder fluxes (which are generally lower in melting point and higher in evaporation rate). This means that the rosin-based no-clean flux will stay on your board longer and give you more time to solder before it dries out or hardens up.

True Synthetic No-Clean Flux

Has no organic solvents. It is used for soldering and brazing electrical and electronic components and assemblies. It is applied in such a way that it enhances the wetting of surfaces, prevents oxidation, and minimizes the need for cleaning.

Water Soluble

It’s used by most people because it’s relatively inexpensive, and it can be used with both lead-free and leaded solder.

Water soluble flux is made up of a combination of ammonium chloride and ammonium bifluoride. The ammonium chloride dissolves in water, while the ammonium bifluoride is insoluble in water but reacts with molten solder to form an acid that helps remove impurities from the surface of the metal being soldered.

Water Soluble

Water Soluble

IPC J Standard for Soldering Flux

The IPC-J-STD-001 series of standards cover a wide range of soldering fluxes, including acid, rosin, water-soluble, and other types. The standard defines the requirements for the classification, evaluation, and testing of soldering fluxes.

Soldering flux is a cleaning agent used during the soldering process. It removes oxidation and prevents new oxidation from forming on the surfaces being soldered.

IPC J-STD-001 is useful when designing products that must be assembled using solders, such as electronics assembly equipment and printed circuit boards.

Things to Consider When Choosing Flux for Soldering

A lot of people have questions about what flux is and how it works, but once you’ve got the basics down, you’ll be able to choose the right kind for your needs. The following are some things to consider on choosing flux:

PCB Type

One of the first things you’ll want to consider is what type of PCB you’re using. Different types of boards have different requirements for soldering, so it’s important to know which one you’re using before you go ahead and start soldering.

If you’re using an FR-4 board, for example, then you’ll need a flux that is designed specifically for such PCBs. If you use the wrong kind of flux on an FR-4 board, it can actually cause damage to the board by making it brittle and difficult to work with.

PCB Type

PCB Type

Electronic Components Type

When choosing flux when soldering, you should consider the type of electronic components that you are working with. For example, if the parts are small and intricate, a low viscosity flux is recommended. The low viscosity flux will not clog up the solder connection points and interfere with the process of soldering.

Electronic Components Type

Electronic Components Type

Soldering Process Type

If you’re new to soldering, it can be hard to know where to start. There are a few different types of soldering processes, and they each have their own strengths and weaknesses. Each type of process has its own advantages and disadvantages. This is why it is important for you to consider which method best suits your needs.

Soldering Process Type

Soldering Process Type

Hand Soldering

When you’re hand-soldering, you want to choose a flux that’s easy to apply and dries quickly. It’s important to make sure your flux is applied evenly across the surface of your part. This will ensure that the soldering process goes smoothly.

Wave Soldering

A process that uses a high-powered infrared lamp to pass over the surface of a circuit board. The heat from the lamp causes solder to wick through the interconnects, fusing them together and creating a strong, reliable connection.

Reflow Soldering

Reflow Soldering is the best type of soldering to use when you want to solder a large amount of components at once. It’s also great for soldering large boards that are difficult to reach.

Metal Type Solderability

The most important thing to consider when choosing a solder is the metal type. There are several factors that determine whether a particular alloy will solder or not, such as its melting point, fluidity, and flux content. For example, copper has a high melting point and requires higher temperatures to melt than aluminum does. Also, aluminum melts at a lower temperature than iron does. When choosing solder for your project, consider the type of metals you are working with and how easily they solder together.

Metal Type Solderability

Metal Type Solderability

Steps in Using Soldering Flux in your PCB

There are several steps you can take to ensure that your soldering flux is working properly.

Step 1 – Clean the Metal Surface

Before soldering, you need to clean both the copper surface and the solder to make them as free of contaminants as possible. You can use a solvent such as rubbing alcohol or lacquer thinner, though some people prefer to use a commercial flux cleaning solution. Be sure not to get any of these solvents on your hands or in other areas where they could cause an accident later on. After cleaning, you should wipe off any residue, which will help prevent corrosion from occurring in the future.

Step 2- Smear the Flux

Apply a thin layer of flux to the surface you are soldering. Be careful not to get any on the parts or any other areas where it won’t be helpful. The more flux you apply, the better it will work at removing any oxides from your board and base material. Too much flux can make it difficult for you to solder things together.

Step 3 – Melt the Flux with the Hot Soldering Gun

The third step in using soldering flux is to melt the flux with the hot soldering gun.

To do this, place the tip of your hot soldering gun against the PCB. Let it heat up for several seconds. Then move quickly to apply solder to the joint you are working on.

Using a little bit of solder at a time. Move your iron to cover all of the areas that need to be soldered. If your iron is too hot and you apply too much solder at once, it will flow out around your joint. It will create an ugly mess that will have to be cleaned later.

Step 4 – Introduce the Soldering Wire

After you have placed the soldering wire in the flux and heated it to a temperature that is appropriate for your wiring. You can then introduce it to your PCB. Your board may have a few components on it, which will require you to apply more solder than just one wire. If you are using a multimeter, this is when you can use it to figure out how much solder to add.


Why Should you Avoid Using Too Much Soldering Flux?

Flux is a necessary part of the soldering process. It’s also important to know when you’re using too much of it, and when you’re using too little.

Using too much flux can lead to a few problems:

Rosin Exposure Cause Irritation

Exposure to rosin flux can cause irritation to the skin, eyes, mucous membranes, and respiratory tract. If you are using rosin flux, make sure you keep it away from these areas.

Causes Electronic Failure

When too much soldering flux is used, it can cause failure. This happens because the excess flux will flow through the circuit board and create a short circuit. The result is that electrical current cannot flow from one component to another correctly and your device stops working.


Soldering flux is a critical part of the soldering process. Without it, your solder will not flow across a joint smoothly. The solder will not adhere properly to the individual components in the circuit board. High-quality flux is necessary to produce a good solder joint. But we should also remember that too much will leave a residue that can be a short circuit to your component’s functionality. Understanding how soldering flux works and what a good solder joint looks like makes all the difference when turning your project into something functional.

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