Best Soldering Flux Reviews for Electronics and PCB

Why you need the flux when solder

Kester Flux PenLarge percent of issues with electronic circuits stem from poor solder joints, and learning the proper soldering technique is crucial to mitigating potential issues. While learning how to solder correctly, it is important to pay special attention to the type of flux used. This material is vital to solder joints, as it helps to provide the best possible connection between the circuit board trace and the component lead.

The flux in solder acts as a cleaning agent to ensure a reliable connection, which can be compromised by native oxides on metals, grime, oils, or any other impurities. Solder flux is activated by heating up the solder (please check our top solder review), which is much akin to the role that Borax plays in welding iron at a blacksmith’s shop. This heating process occurs either with a traditional soldering iron or a solder reflow oven for the smaller surface mount components.



How rosin flux works

ruby_fluxRosin flux is the most common of electronic solder fluxes. Many rolls of solder for this purpose already contain rosin flux in the core. This type of roll is referred to as rosin core solder, and it makes soldering relatively easy. It is simply a matter of heating up the two components to be joined with the tip of the soldering iron and then touching the solder to the connection at a point that is not in direct contact with the soldering iron. This is a type of solder joint that can be learned by nearly everyone interested. Rosin flux is also available in a paste form. It is simply applied to the connection with a brush, and then the solder is applied in a manner similar to soldering with rosin core solder. The paste variety is used when the rosin core is not present in the solder or when the greater care is being taken for a clean connection. Flux paste could also be used with solder paste for surface mount components.

When the connection is complete, rosin flux leaves behind a residue which should be cleaned. This flux residue may contain impurities capable of making unwanted connections between circuit board traces, which can lead to shorts or component failure. To avoid this, simply spray flux cleaner in a well ventilated area, as some of these solvents are toxic or unpleasant to inhale.

Other flux types

MG Chemical Rosin FluxWater soluble flux introduces another option for many soldering applications. This flux is comparatively more environmentally friendly, as the cleanup involves water and letting the connection or connections dry completely before testing. This flux is based off of organic acids, such as citric, lactic, or stearic acid, though they are not nearly as strong as the acid flux used by plumbers for soldering.

Plumbers rely on soldering for their work, too. However, their solder flux is an acid flux. This should never be used for any electronic soldering. Acid flux is virtually guaranteed to provide a poor connection. The role of electronic solder flux is to clean the connection and gently remove oxides and impurities, not to introduce a material intended to be corrosive over time. The metal thickness for copper pipes is sufficient to withstand taking away oxidation with an acid. Printed circuit board traces do not have that same luxury of ample metal to sacrifice. The metals used in electronics are conductive elements, and they should not be altered in any way by the flux. So, be sure to use a rosin flux or a water soluble flux for any electronic soldering.

flux paste

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Why fumes comes out when you solder

Whenever soldering, be sure to take some safety precautions into account. Solder fluxes can be unpredictable and spatter when heated. So, it is advisable to always wear eye protection when soldering. Heating solder also produces fumes. These fumes are usually not carcinogenic nor necessarily toxic, though it is not wise to breathe a significant amount of these fumes. However, the flux material in these solders can lead to future health issues like asthma or developing insensitivity to solder fumes if the exposure is prolonged and repeated. A few connections should not be any concern so long as it’s in a well ventilated area. Also, make a conscious effort to not inhale directly over a connection being soldered. Consider investing in a solder fume extractor, which removes solder fumes from the work area. Finally, many solders contain lead, so be sure to wash hands thoroughly with soap and running water before other activities, such as eating, drinking, or smoking. This precaution helps to prevent ingesting lead, which is a toxic metal. Hope you like our review. Thank you.