Good flux for soldering

Flux for soldering is an auxiliary substance, the use of which helps to clean the surfaces of the metal elements being connected from oxidation. By resorting to soldering without the use of flux, one should not count on high-quality performance of work and reliable fastening of necessary details. Therefore, before you start work on connecting parts with a soldering iron, you need to pick a good, high-quality flux.

Intended use of

Fluxes are primarily used to remove all kinds of contaminants from the metal surface. Moreover, when soldering joints, they protect the heated solder from oxidation. This, in turn, contributes to the spreadability of the solder and, accordingly, to improve the quality of soldering.

flux for soldering

A good flux for soldering can be selected only based on the nature of the metal compounds and alloy solder. Remains of any fluxes, regardless of their type, after the work is to be removed from the joints, as they themselves contaminate the metal and can lead to the development of corro

sion processes.

Types of fluxes for soldering

Conditionally fluxes are divided into two main categories - oxidation and reduction. Also, depending on the need to perform certain tasks, allocate fluxes for melting metal, welding, electrolysis, growing monocrystals, soldering colored and jewelry alloys.

In general, according to the effect that occurs on the metal during soldering, the following fluxes are distinguished:

  • active( acid);
  • are acid-free;
  • anticorrosive;
  • activated;
  • protective.

Active fluxes

Such flux for soldering often contains hydrochloric acid, fluoride and chloride metals. The action of active fluxes involves active dissolution of oxide films on the surface of metal parts. Due to these properties, the maximum mechanical strength of the resulting compounds is ensured.

Despite its wide distribution, active fluxes are not suitable for use in the installation and soldering of electrical equipment, because their residues quickly corrode the place of connection of parts.

Acid-Free Fluxes

An acid-free flux for soldering, commonly known as rosin, is a substance based on alcohol, glycerin and turpentine. When the soldering iron is heated to a temperature of more than 150 oC, the use of such a flux makes it possible to dissolve the oxides of lead, copper, and tin, reliably cleaning the metal surfaces.

flux for soldering aluminum

The main advantage of flux in the form of rosin is the absence of the effect of disconnecting the surfaces to be joined when soldering. This flux is actively used for brazing copper, bronze, and brass.

Activated fluxes

Prepare this type of flux based on phosphoric or hydrochloric acid aniline, diethylamine or salicylic acid. This option is applicable for soldering a number of metals and alloys, for example iron, copper, steel, nickel, zinc, silver, and copper parts without the need for preliminary stripping.

Anticorrosive fluxes

Based on the definition itself, it is easy to guess that an anti-corrosion flux is used for soldering most often when it is necessary to connect parts potentially susceptible to the development of corrosion processes.

The composition of flux for soldering with anti-rust properties includes the use of technical petroleum jelly, salicylic acid, triethanolamine and ethyl alcohol. Despite its main purpose, this type of flux requires careful removal of its residues after completion of soldering by rubbing parts with acetone or alcohol.

Protective fluxes

Since no destructive chemical attack on metals occurs during the application, a protective flux for soldering chips can be used. Like the bulk of other types of flux, these substances protect the previously cleaned metal surfaces from oxidation. To the category of protective fluxes are primarily Vaseline, wax, sugar powder, olive oil, other substances with weak chemical activity.


The most common alcohol-based fluxes usually have a liquid consistency. Therefore, they need to be stored in a carefully sealed, sealed container. Otherwise, there is a loss of their basic properties and even complete evaporation.

flux for brazing copper

Flux solder paste also needs to be stored in a closed container. The optimal conditions for such a flux is a low-level room. Despite the fact that the paste does not absorb moisture from the environment, there is a danger of condensation of moisture on the walls of the container and the surfaces located nearby.

Keep the flux-gel for soldering away from flammable substances, objects and open flame sources, since most of the fluxes in this category are highly flammable. The storage temperature should be at least 10 and not more than 25 degrees Celsius.

Application of

flux When performing soldering, joints are well cleaned, covered with flux and heated with a soldering iron. At the application site the flux begins to foam and smoke. At this point, a small amount of solder should be applied to the tip of the soldering iron, which will subsequently cover the joined surfaces.

soldering flux for soldering

Probably, it is not necessary to talk once again about the properties and advantages of using fluxes during soldering. It is enough just to take a soldering iron and try to connect the parts without flux. In this case, the soldering process will be really long, and the result is frankly substandard, since the solder will be too unreliable to fix on the surface to be soldered.

How to prepare flux for soldering by hand?

The simplest option for self-preparation of flux is the use of a rosin-alcohol base. To begin with, rosin powder is poured into the container, after which it is poured with alcohol solution. After some time, the alcohol evaporates and the flux acquires a moderately thick consistency, convenient for applying the substance to the metal parts during soldering.

flux solder paste

As an independently prepared flux suitable for tinning steel and copper surfaces, acetylsalicylic acid dissolved in a small amount of water, acetone or alcohol can be used. Such a liquid flux is conveniently stored in a container from varnish, using a cap with a brush when applied.

How to choose the right flux?

According to the opinion of avid radio amateurs who are well versed in soldering, the choice of a suitable flux is almost a 100% guarantee of successful work. First of all, it is necessary to focus on the material of the parts to be joined, as well as the nature of the soldering.

flux gel for soldering

For the soldering of radio components, copper parts and wires, it is advisable to use inactive fluxes based on rosin. Such fluxes are a modified version of conventional rosin as a result of the addition of a number of constituents known as activators.

Inactive fluxes have improved antioxidant properties. Due to the pasty or liquid state, such fluxes can be applied directly to the mounting plates or solder joints of metal joints. This flux is ideal for soldering aluminum. In addition, it is worth noting their wide availability and relatively low cost.

With regard to medium-fluxes, it is advisable to use them for soldering the most delicate contacts, for example, when repairing mobile phones and other modern portable devices. For this purpose, fluxes are suitable that do not foam and boil during operation, have minimal corrosivity, and are easily applied to the boards.

flux composition for soldering

Often, medium-fluxes are used by masters of service centers for the repair of digital mobile devices. Usually they are used for soldering the smallest microcircuits. And they are suitable for use not only with lead, but also with lead-free solders.

The most universal are gel-like fluxes. They can be used for almost any type of soldering. Gel-like flux is especially effective for soldering aluminum, copper, other common materials using lead solders.

In conclusion

The correct selection of suitable consumables when performing soldering is a guarantee of a quality work performed. In addition to choosing a good flux, you need to choose the appropriate soldering solder, nozzle for the hair dryer, soldering tip, and other.

Even when using the most advanced soldering stations in the presence of unsuitable flux, solder or stinger, you can ultimately get the wrong result, which was calculated. Much water has flowed under the bridge since the time when specialists actively used classical soldering irons up to 60 W with a homemade, turned-out file with a copper sting, as well as ordinary rosin as a flux. At present, the use of such a material and technical base is extremely inefficient.