The main types of fluxes

Flux is a compound used in soldering to improve the quality of parts’ output elements connection between each other or with PCB (printed circuit boards). The correct choice and application of it determine how firmly the electronic components will be connected to each other, as well as their ability to conduct electricity. In this article, we will consider the main types of flux and the criteria of choosing it that you need to pay attention to.

Why is flux required?

In soldering technology, flux performs three main functions:

• Dissolves oxide and sulfide films formed on the metal surfaces of the soldered elements during contacting with air and other reagents;
• Prevents the rapid formation of new oxide and sulfide films, thereby improving the electrical conductivity of the connection;
• Reduces the surface tension of the molten solder and, accordingly, increases the wetting and adhesion of soldering surfaces;

A common flux that almost everyone has encountered is rosin, the resin of conifers (mainly pines), from which all volatile and liquid components have been removed.  However, many other flux compounds are used in the electronics industry.

Flux classification

Nowadays, two main categories of fluxes are used in radio and microelectronics:

• Chemically active. Such fluxes contain acids (hydrochloric, phosphoric) or salts (zinc chloride, ammonium chloride). Due to their activity, they dissolve fatty and oily contaminations, oxide and sulfide films well. Therefore, they are used for soldering on nickel and steel — surfaces with poor solderability. At the same time, their refuse cause corrosion of metal elements and destroy the PCB (printed circuit board) base, so they must be removed immediately after soldering. Chemically active fluxes practically are not used in consumer radio electronics and in those cases when cleaning is difficult.
• Chemically passive. Fluxes of this type contain organic or synthetic ionless activators. They remove oxides worse, but they excellently clean off fat or oil and protect well from re-oxidation. Their main advantage is the absence of corrosive activity, as well as low emission of toxic components and its safety for humans.  Chemically passive fluxes are rosin (a mixture of resin acids), fats, vaseline and some oils.  They are most commonly used for hand soldering, and also can be used in cases where cleaning is impossible or difficult.

Moreover, depending on the consistency, fluxes are divided into liquid, gel and solid.  They also differ in their composition, which can be based on organic or synthetic components, as well as their combination.  Our qualified specialists will help you to choose the right flux in accordance with the features of the production at your enterprise.