What is Soldering Flux and How To Use It

In the modern world, it so frustrating to see the building which has cost the owners million get rust. This fact is true because most metal manufacturing companies do not apply soldering flux in their metals at their early stages. Soldering flux is a chemical which is used to prevent oxidation of metals when joining them. This chemical removes oxides from the surface of the metal thus preventing rusting to take place. Fluxes are used to purify metal as well as cleaning agents. The conventional soldering fluxes are hydrochloric acid, borax and ammonium chloride. An adequate temperature for a process of soldering is 60ºC – 450ºC/ 145ºF – 830ºF

How to Use Soldering Flux

To solder your metal, you need to apply a layer of the flux liberally on the surface of the metal which is to be soldered and then heat the metal gently until the soldering iron starts to melt directly. Make sure that the iron is vast and hot enough to perform the task expeditiously. Before you start your work, ensure the tip of the iron is clean and coated with solder paste. Fix the wire soldering into the junction when the metal meets the alloy work and ensures that the solder flows freely. In the case of significant work, you need to rotate the iron a bit around to ensure proper circulation of the soldering paste. When soldering electronics by use of hands, a rosin-core paste is used with flux soldering simultaneously as it only requires thin tip of the small iron.

Iron Fluxing

Credits: Phil Gradwell

Soldering Flux Types

There are different kinds of fluxes such as rosin flux, organic acid flux, solder fumes, and chemical acid flux.

Silver Soldering Flux

Silver soldering is the most common technology which is applied by manufacturing companies. It involves heating an alloy to high temperatures which are above 800ºF and then joining it with a non-ferrous filler metal. These high temperatures are used to ensure that there is a creation of barrier as well as making the metal to be corrosive. The molten filler at its liquid temperature interacts with a layer of the base metals thus cooling down to build exceptionally strong joint due to this grain structure interaction.

Silver soldering process is applied in different heat sources like the torch, resistance, and furnace. This process uses alloys and filter metals such as copper. Silver soldering is a common method for joining and bonding non-ferrous and ferrous base metals such as steel, copper, and brass metals. In high production rates, silver soldering is done by automated machines which are fast and also cost saving. Since fluxes are corrosive and toxic, a lot of care should be taken during this process of soldering.

Rosin Flux

In general, rosin flux is one of the oldest form of flux used, and it works with the principle of refined and purified. Its characteristic is its ability to flow easily when it is hot, removing solid particles from a metal surface which is being soldered and its ability to remove oxides. Rosin fluxes are acidic when liquid form becomes robust and inert when it cools down. A good policy is to ensure that you remove rosin residue from a PCB using alcoholic substances and chemicals since they are nonpolar compounds.

Organic Acid Fluxes

Organic acid fluxes are examples of most common fluxes which are used as water-soluble acidic fluxes. Citric acid, stearic acid, and nitric acid are some common weak acids which are used as the organic acid. These weak acids are commonly combined with solvents such as isopropyl, water, and alcohol. They are usually stronger than rosin fluxes, and this makes them clean the oxides from the metal surface quicker. Also, the nature of water-soluble organic fluff makes it easy to wash PCB without interfering with other components which should not get wet.

It is advisable to clean this organic acid flux regularly since their residues are electrically conductive and this can significantly affect the performance and the operation of the circuit. Failure to do so, it can cause a lot of damage if the circuit is operated before cleaning the flux residual.

Soldering Fume

The solder fume type mostly works with the smoke and fumes which are released during soldering. It involves reactions of several chemicals compounds which reacts with oxide layers on the surfaces of the metals. The most common compound are alcohols, acidic fumes, and formaldehyde. Since acidic gasses are toxic, solder fumes can lead to irritation and nerve insensitivity to those handling it. To avoid this, people should avoid drinking, eating or even smoking in areas with solder. Only a few instances of risk getting cancer are witnessed as the solder fumes have the low boiling point as to when compared with flux and thus before the flux melts the coating will already be removed out.

Inorganic Flux

The final type of flux is inorganic flux. Inorganic flux is a typical blend of stronger acids such as concentrated hydrochloric acid, ammonium chloride, and zinc chloride. This kind of fluxes is targeted towards coating higher metals like copper and stainless steel. Complete cleaning should be done after using inorganic flux to remove the residuals which are corrosive from the surface of metal thus preventing solder joints from weakening or even getting destruction. This type of flux should not be used in electronic gadgets or any electrical works to prevent burst or explosion of this gadgets.

Soldering Flux Alternative

Since most of this fluxes are expensive to buy at the domestic level, there are various alternatives which are relatively cheaper to perform the same task. For instance, individual may consider using vaseline oil instead of rosin flux to remove or prevent oxidation layer on a surface of a metal. Instead of using flux remover you may take into account to rub alcohol over the metal and then wash it gently.

Soldering Paste vs. Soldering Flux

The best soldering flux is less harmful and corrosive because scorching temperatures are relatively small, and thus they can coat metals quickly by eliminating the oxidation layer.

Solder paste is the powder which is used in the manufacture of circuit boards. It holds the particles together but when it is heated it melts up creating a medium for mechanical and electrical connection. Solder flux chemicals are used to remove an oxide layer from the surface of a metal. I will advocate for solder flux since solder paste has a lot of limitation such as powder may melt and connect too many wires together which can lead to short circuit.

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