Rosin-based soldering flux – TK83 or RF800?

Rosin-based soldering flux – what are liquid fluxes?

Liquid soldering fluxes are chemical agents used in the soldering process whose primary purpose is to improve the wettability of soldered surfaces and facilitate the flow of solder. Thanks to their use, it is possible to obtain durable, aesthetically pleasing, and electrically conductive joints – even when working with oxidized surfaces or difficult-to-solder materials.

In practice, liquid flux removes oxides from metal surfaces, reduces the surface tension of molten solder, and – by ensuring proper spreading – significantly affects the quality of the solder joints produced. For this reason, a properly selected flux not only makes the work easier but also substantially improves the quality and reliability of the connections.

A particularly popular choice is rosin-based soldering flux, i.e. flux formulated on the basis of rosin – a natural resin with very good soldering properties. This group includes both TK83 and RF800, which makes their comparison fully justified.

TK83 Soldering Flux

TK83 soldering flux is a medium-activity, liquid rosin-based soldering flux dissolved in alcohol and enhanced with organic activators. Its formulation has been designed to ensure good solder flow while simultaneously improving the overall efficiency of the soldering process.

TK83 is characterized by very good wetting properties, resulting in even solder distribution and stable, repeatable results. In practice, this means that the flux significantly improves joint quality, particularly in more demanding applications.

Its higher viscosity (approx. 25 cP) allows it to adhere better to the surface, facilitating precise application and improved process control.

Its composition is also noteworthy – TK83 contains a higher rosin content, which is reflected in its characteristic amber color. As a result, it evaporates more slowly and leaves a more stable active layer, which can be advantageous at more challenging soldering points.

Applications of TK83 flux:

assembly of SMD components and multi‑lead packages,

BGA soldering,

soldering of passivated and oxidized surfaces,
machine soldering,
manual tinning and restoration of solderability.

After completing soldering using TK83 flux, attention should be paid to surface cleanliness. Although the No Clean formulation does not require washing, in practice the soldered area can be cleaned with an alcohol-based PCB Cleaner or Kontakt PCB Plus to remove any possible flux residues. This results in an aesthetically pleasing and clean finish of the joints.

What is solderability restoration?

It is the process of restoring a metal’s ability to properly accept solder. For example, burnt or long‑stored wires often undergo oxidation, which makes soldering difficult. An appropriate flux removes the oxide layer and restores the ability to form a durable joint.

TK83 performs particularly well in this application, which makes it a practical choice for service and repair work.

An additional advantage is the No Clean formulation and availability in an 8 ml pen version, which allows for quick and very precise flux application.

Liquid Flux RF800

Liquid Flux RF800 is a popular solution used in both precision and standard soldering operations, especially for SMD components. It is a medium‑activity rosin‑based flux which – similarly to TK83 – does not require cleaning after use.

RF800 is characterized by good surface wetting capability, ensuring proper solder flow under typical soldering conditions. As a result, it improves the aesthetics of solder joints and supports process stability, although its performance is best suited to less demanding applications.

Its lower viscosity (approx. 15.8 cP) makes it more fluid and easy to spread.

soldering of SMD components,
machine soldering,
tinning of wire ends,
soldering of passivated surfaces,
mixed-technology assembly.

RF flux contains less rosin and more alcohol, which causes it to evaporate much faster – especially when heated with a soldering iron. In practice, this means it is “faster” and more dynamic to work with.

RF800 is a solution that performs well where simplicity and process repeatability are key.

In the event of pauses in the operation of flux dispensing equipment, we recommend periodic flushing of the system using an alcohol‑based PCB Cleaner. This product removes dried flux residues more effectively than isopropyl alcohol, helping to prevent nozzle clogging and maintain process stability.

Comparison of soldering fluxes TK83 and RF800

Both products are rosin-based fluxes; however, they differ in properties and practical applications.

Key difference – viscosity:

TK83: approx. 25 cP – better control and precision
RF800: approx. 15.8 cP – higher fluidity and easy spreading

The higher viscosity of TK83 allows it to remain on the surface more effectively, which is important for precise work and repair applications.

Differences in practice:

TK83 performs better in restoring solderability,
TK83 more often improves joint quality in more demanding conditions,
RF800 is suitable for standard applications,
TK83 offers greater application control (e.g. in pen form).

Summary

Both rosin-based flux TK83 and RF800 dry completely after use, leaving no sticky layer or adhesive residues.

Both TK83 and Liquid flux RF800 are effective solutions used in soldering processes.

RF800 performs well in everyday applications, where simplicity and predictable performance are key.

TK83, on the other hand, due to its higher viscosity and effectiveness on more difficult surfaces, is more often used where precision and quality are critical — especially when the goal is a durable joint and greater control over the soldering process.