What is a flux used for| How to Use Flux in Soldering


Flux for Soldering: How does it work? The flux used in soldering is more important for joint formation. In the electronics and wires industry, engineers and technicians often ask these types of questions. Even company purchase departments may ask them.

During the soldering process, fluxes are very important to ensure that the joints are made properly without causing bridged pins or other errors. The cleaning process plays a vital role in the yield of electronic assemblies and the quality of the product.

The purpose of flux in soldering is to remove and other metallic impurities from the soldering surface and prepare a clean, solid joint. Depending on the type of flux used, cleaning may be required following the finish of the soldering process.

What is flux in soldering

At room temperature, all metals except pure gold and platinum oxidize in the air. When humidity and temperature increase, oxidation occurs more quickly. Since metal oxide surfaces are a barrier to the formation of a bond, they must be removed with solder flux before joining by welding or brazing. At soldering temperatures, flux chemically reacts with oxides in order to produce fresh, tarnish-free surfaces.

So that solid inter-metallic bonding can take place. The main function of the solder flux can be broken down into the below parts. Solder flux is used to remove the metal oxide surfaces that, in the joining process, prohibit a bond between the metals. At soldering temperatures, flux chemically reacts with oxides in order to produce fresh, tarnish-free surfaces.

Since metal oxide surfaces are a barrier to the formation of a bond, they must be removed with solder flux before joining by welding or brazing. At soldering temperatures, flux chemically reacts with oxides in order to produce fresh, tarnish-free surfaces. So that solid inter-metallic bonding can take place. The main function of the solder flux can be broken down into the below parts.

Solder flux is used to remove the metal oxide surfaces that, in the joining process, prohibit a bond between the metals. At soldering temperatures, flux chemically reacts with oxides in order to produce fresh, tarnish-free surfaces. So that strong intermetallic bonds can be formed. Here are the main functions of the solder flux: an aqueous solution, a solid solution, and a liquid solution.

  • Cleaning the dirt and oxidized layer on the metallic surface to be soldered.
  • Reducing the surface tension and viscosity of molten solder to improve the wettability.
  • When contact and spread on metal surfaces prevent metal from being re-oxidized at higher temperatures.
  • Allow molten solder paste to form solid long-lasting electrical and mechanical joints

How to Select Soldering Flux Type

Fluxes in general provide activity via the action of halides (chlorides, bromides). Flux with a higher halide content performs better in removing oxides from the soldering surface and enhances the strength of soldered joints. Soldering flux with high activity will leave corrosive by-products behind the board as a result of a high reaction, resulting in reliability problems in the field.

For the electronic assembly of the product, there are mainly two points that need to be considered: The flux needs to be inactive before and after the soldering, but active at soldering temperature so that tarnish and oxides can be easily removed. Ideally, the soldering iron flux should function slightly below the soldering temperature in order to keep the soldering surface ready for soldering. Due to the high residue of fluxes on board, active flux is not recommended due to unwanted product reliability issues.

However, no-clean flux is available to meet these needs, and even at soldering temperatures, it doesn’t perform well. To use it, the user and the supplier must maintain a clean work environment and change their culture. Therefore, soldering flux should provide a balance between activity and cleanability. No-clean fluxes, also known as low residue fluxes, are halide-free and use organic acids to produce flux with solder activity. To ensure this, boards and components must be solderable and just-in-time inventory must also be used. 

To prevent oxidation of the soldering surface during the soldering process, an inert atmosphere such as nitrogen may also be required.

How to Use Flux in Soldering-Step by Step Guide

How to Use Flux in Soldering-Step by Step Guide

In electronics, it is crucial to use flux when soldering in order to make solid and shiny joints. The soldering iron tip must be properly cleaned and the iron must be placed on a stand before starting the activity.

To tin, the tip with solder, apply solder to the tip of the iron when it is hot. Cleaning the tip with a sponge is needed after tinning. The tinning process protects the tip from oxidation, reduces wear, and enhances heat transfer.

Step 1- When soldering two pieces, it is good to use steel wool or scotch brite to remove oxide layers from the surface.

Step 2- Using a brush, apply flux with solder to both pieces of the terminal that need to be connected.

Step 3- To heat the joint without burning away the flux, use adjustable temperature control to set the iron to the right temperature (400°C/752°F). Inhaling fumes or direct skin contact with a flush is dangerous, so always take precautions.

What Type of flux is used in Electronics Soldering?

Rosin Flux

Natural Rosin Fluxes are obtained from the stumps of pine trees. Therefore, these are natural products that are extracted from pine trees. Generally, rosin is composed of C19H19COOH, but the formula varies from batch to batch. The rosin flux is further divided into non-activated (N), mildly activated (RMA), and activated (RA).

Non-activated Rosin Fluxes (R) are not activated and are therefore best suited to use on clean or minimally oxidized soldering surfaces. For other hand soldering jobs, rosin fluxes of type (R) are used for soldering copper wire, printed circuit boards, and semiconductors. The Rosin Mildly Activated (RMA) Fluxes are strong cleaners that are more powerful than their Non-Activated (R) counterparts. For general-use cables, PCBs, and electronic components, these fluxes in soldering are ideal for handling higher-containment leads.

Rosen-activated (RA) fluxes provide the best cleaning performance among all rosin-activated fluxes. Soldering for electrical components with this product is the best choice for soldering hard-to-clean surfaces.

Low Residue or No- clean Flux and Solder Paste:

In current technology, a printed circuit board assembly can be soldered without having to be cleaned. It is common practice in Europe for companies not to clean rosin fluxes (R and RMA) since they don’t cause any reliability issues if not cleaned (especially if they are halide-free). Globally, No-Clean fluxes are becoming more prevalent since the ban on CFCs.

Solder pastes and fluxes don’t require cleaning after use, resulting in significant savings on both cleaning costs and capital expenditure investment.

Organic Acid Fluxes

These fluxes are stronger in soldering than rosin fluxes, but they are less efficient than inorganic fluxes. In addition to organic acids, water-soluble fluxes are also known as organic acid fluxes. For both military and commercial applications, organic acid fluxes are justified for use with mixed assemblies (types II and III).

Once the assembly has been completely dried, the flux residues can be removed using normal water since they are water-soluble.

Inorganic Acid Fluxes

Soldering surfaces that are difficult to bond with inorganic acid fluxes are perfect. These fluxes have a much higher melting point than organic fluxes. Frequently oxidized metallic parts can be removed by these methods. This includes acids and salts such as hydrochlorides, hydrofluoric, stannous chlorides, sodium fluorides, and zinc chlorides.

Solder flux in non-electronic applications is used for brazing copper pipes, which is an inorganic use of flux in soldering. Chemically active residues can cause serious field failures because they leave behind chemically active residues that can cause corrosion

How to use liquid flux when soldering

  • For flux for electrical soldering use rosin-based flux to make solid joints.
  • For plumbing, joints recommended acid flux when soldering pipes because acids are more prone to remove oxide layers.
  • Solder top tining is very important to keep clean when working with electronics.
  • Always keep your soldering iron in a stand while it is on for the safety and reliability of equipment.
  • Use all precautionary wearings during soldering for safety purposes.

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Hello, this is Manoj, A Soldering and DIY Tool expert. Writing is one of my hobbies. With more than 20 years of broad experience. I love researching, discovering, and sharing new products with others, I hope you’ll enjoy the greatest featured products to make life easier, more fun, and more productive.

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