Soldering fluxes for microcircuits and other radio components: classification and application

Soldering is the process of connecting elements of an electrical circuit to each other, requiring the use of special tools and filler materials, one of which is a flux. In accordance with generally accepted rules, it should have a low melting point and low specific gravity. Only when these properties are combined, fluxes for soldering radio components will be able to penetrate deeply into the structure of the elements to be connected, thereby ensuring the required quality of the connection.

Basic material requirements

To obtain a high-quality connection of radio components, their surface must be cleaned of oxide film and grease. It is to solve this problem that fluxes are used, to which the following requirements are imposed:

• They must not chemically react with the solder..
• Effective removal of dirt from the surface of the parts to be joined.
• The ability to increase the fluidity of the solder on the surface of the connected elements and their wetting.
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• Flux residues should be easily removed.
• The melting point should be lower in comparison with the similar parameter of the solder.

Today, all fluxes for soldering microcircuits and other radio components are usually divided into two groups: chemically active and neutral.

Active mixtures

They contain acid-based reagents such as hydrochloric or orthophosphoric. Such materials effectively remove oxides and grease, but after the completion of the soldering, the joint must be thoroughly cleaned. Otherwise, rapid metal corrosion is possible. They try to use active fluxes in the radio-electronic industry as rarely as possible, since they also negatively affect the PCB textolite.

When working with them, you must exercise the utmost care, since contact with acidic substances on the skin can cause burns, and the vapors are very toxic. The most popular active fluxes are borax, zinc chloride, ammonia, and phosphoric and brazing acids.

Passive substances

Representatives of this group cope well with grease contamination, but not as effective in the fight against oxide films.. All of them are organic compounds and are not capable of causing corrosion, which protects radioelements from oxidation. Vapors of most passive materials are dangerous to humans, except LTI-120, which contains no harmful components.

Popular soldering fluxes

A large number of fluxes are used in the electronics industry today. Most popular options:

• Rosin - although it belongs to the group of passive materials, it contains acids, and after the soldering is completed, it is recommended to remove the remaining flux. This is one of the most popular and readily available materials. Since solid rosin is quite difficult to use, liquid rosin is most often used in the radio-electronic industry.
• Soldering acid - contains strong substances such as zinc chloride, hydrochloric and orthophosphoric acids. This flux is readily available and inexpensive. It can be used to connect almost all metals, but do not forget about the high toxicity of soldering acid.
• Borax is a boric acid salt and is available in powder form. To prepare the flux, it must be dissolved in water. Since the borax belongs to the active group, after finishing work with it, it is necessary to carefully remove the remnants.
• Brazing fat - depending on the composition, it can be either active or passive. This material perfectly cleans the surface from grease, but the residues evaporate for a long time.
• LTI-120 is an inexpensive and affordable material that is very popular. Among the disadvantages are rapid evaporation and some toxicity.
• SCF is a mixture of pine rosin and ethyl alcohol. A passive flux that you can easily prepare yourself. When working, it practically does not smoke, but evaporates quickly.
• FCS is a passive flux that does not include rosin.

A large number of fluxes are used in radio electronics, but many of them have a high cost and are practically not used by radio enthusiasts. In rare cases, materials at hand are used, but the quality of soldering in such situations leaves much to be desired.

Among the most popular should be noted:

• Aspirin - the vapors are quite toxic, and you need to exercise the utmost care when working.
• Ammonium - Sometimes used as a replacement for fluxes.
• Glycerin - has a residual resistance, and its remains must be removed.

The flux has a huge impact on the quality of soldering. To obtain a high-quality connection, it is extremely important to choose the right type of material.