Why is a flux used in PCBA assembly?

In order to give the printed circuit boards a longer life, they must be properly protected against oxidation and contamination adhering to the soldered surface. Those skilled in the art know that even a small point of contamination can result in future damage and breakage of circuits. To avoid this type of situation, special cleaners for electronic components are used when soldering PCBs. We define them professionally as flux and It is used when dealing with the process of soldering components on PCBs.

What exactly is a flux?

Flux is used to facilitate the soldering process, primarily on printed circuit boards. It is used both in the manual assembly process as well as in automatic assembly. Tiny copper marks often appear on PCBs, which can oxidize, which in turn can lead to an unstable solder joint. Damage can also accumulate on these types of surfaces. As a result, an unstable solder joint may develop. As a result, the circuit board is susceptible to damage and interruption of the connection during operation. Therefore, a suitable chemical is required to clean and facilitate the formation of a permanent solder joint. This brings us to the question of what flux is used for. 

The flux removes oxides from the soldered surface and protects them against air and possible contamination. At the same time, flux wets the soldered surfaces, which makes it much easier to connect individual elements on the surface of the printed circuit board. The method of applying flux varies depending on the chosen soldering method.

What are the types of fluxes?

Flux varies in density and comes in three forms: solid, semi-solid, and liquid. One of the oldest and most frequently used fluxes is the so-called rosin flux that activates at high temperatures and is completely safe for unheated circuits. In turn, the organic acid flux perfectly protects the elements against oxidation and is very easy to apply. Taking into account its conductive properties, residues should be carefully removed from the surface of the tile. Organic acid flux can be easily removed with water.

The last type is an inorganic flux used in the case of metal plates made of copper and stainless steel. Usually, it is not used in electronic devices, but in plumbing. Finally, it is worth mentioning the very popular No-Clean fluxes. They are made of resins and their advantage is that there is no need to clean the flux. This type of flux is most often used in industrial PCB assembly.

What are the advantages of flux?

Flux is to provide the target electronic device with longer life. It protects PCB circuits against oxidation, contamination, but also against moisture. As a result, the circuit printed board can perform flawlessly even in a harsh environment. Flux also facilitates the soldering process, ensuring the perfect connection of individual elements. However, manufacturers must remember to remove the flux by cleaning. Even small flux residues will be counterproductive. Resin-based no-clean fluxes that do not require cleaning are very popular.

Potential causes of tombstoning are broad catalog, including faulty PCB track and pad design, oxidation processes, type of solder paste, template design, ...
Bubbles in the protective layers created in the conformal coating process arise when solvents or air become trapped inside and cannot ...
Wave soldering with using hot nitrogen is a relatively young process that was introduced about 20 years ago. Initially, manufacturers rarely used this method. Today,...
In distributed power systems where multiple DC converters are used, the challenge for designers is to keep these components as small as possible to save space on the board.