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What is Solder Flux – How to Use Flux in Soldering

Learn What is Solder Flux & How to Use Flux in Soldering.

Here we will learn What is Solder Flux and How to Use Flux in Soldering.

Solder Flux

What is Solder Flux (Soldering Flux)?

Solder flux is a kind of chemical used in Automatic PCB Assembly and Hand Soldering. It is basically used to clean surface of PCB before soldering process. It helps to clean and remove oxides and other impurities and thus helps in wetting.

Rosin Flux is manufactured from a type of Resin obtained from pines and some other plants.

Types of Solder Flux

According to the electronics industry standards, J-STD-004, solder fluxes are classified into 3 major categories based on their flux activity:

1. Rosin Flux

Rosin flux is primarily composed of natural resin extracted from the oleoresin of pine trees and refined. The rosin category is further divided three subcategories:

  • Rosin (R) Flux: It has only rosin and is the least active. This type of flux is mostly used for surfaces that are clean. It leaves virtually no residue after soldering.
  • Rosin Mildly Activated (RMA) Flux: It has sufficient activator to clean the solder-coated or plated lands and component terminations or leads, thereby enabling the molten solder to wet these areas.
  • Rosin Activated (RA) Flux: Type RA is most active of the rosin fluxes, and leaves the most residues after soldering.

2. Water Soluble Flux

Water soluble flux is also known as organic acid (OA) flux. It is is primarily composed of organic materials other than rosin or resin. Water-soluble flux provides good soldering results because they have good flux activity. They have good wetting action (ability to remove oxides and prepare a clean surface for soldering). However, they may be too aggressive, calling for extra precaution during cleaning of the PCB Assemblies to avoid flux contamination.

3. No-Clean Flux

These are flux that doesn’t need any cleaning after soldering process.

Why is Solder Flux Used in Soldering?

The main function or use of flux in any Printed Circuit Board Assembly or rework is to clean and remove any oxide and impurities from the board. These oxides deposited on the board may not permit good solder joints. If the solder joint is poor, there will be poor electrical conduction or poor flow of electricity through the circuit.

Solder flux helps to de-oxidize metals (copper tracks on the PCB and leads of electronic components) and helps better soldering and wetting. The activators in the flux promote wetting of the molten solder to the surface mount lands and component terminations or leads by removing oxides and other surface contaminants.

Read: Lead-Free Soldering: A Safer Approach to PCB Assembly

Availability of Soldering Flux

Solder flux is available in different forms:

  1. Liquid Flux
  2. Flux Pen (Good for Mobile Phone Repairing)
  3. Flux Paste
  4. Solid Flux

Alpha Cookson trusted manufacturer and supplier of all types of solder flux.

Flux Pen

Flux Pen

Choosing the Best Flux for Soldering

Several factors determine the type of flux to be used during soldering:

Soldering Flux Cleaning

After the soldering process is over, it is important to clean the board to remove any unwanted flux residue that can affect the performance of the board and can even cause electrical short circuit. No-clean flux doesn’t need any cleaning. In case of fluxes that need cleaning after soldering, solvent cleaning or aqueous cleaners can be used. Most soldering flux manufacturers and vendors also supply flux cleaners.

FAQs: Soldering Flux

There are three main types of soldering flux: rosin flux, water-soluble flux, and no-clean flux. Rosin flux is organic and common for general soldering. Water-soluble flux is easily cleaned with water. No-clean flux leaves a minimal residue and is suitable for sensitive electronics.

Consider the materials being soldered, workspace environment, and the required cleanliness level. Rosin flux is versatile, while water-soluble flux is suitable for washable applications. No-clean flux requires NO CLEANING after soldering and is preferred for delicate components.

Flux is highly recommended for most soldering jobs. It improves solder joint quality and reliability. However, for certain specific applications like soldering non-oxidized metals, flux might not be required.

Apply a small amount of flux to the joint area before soldering. You can use a flux pen, brush, or flux cored solder wire. Avoid excessive flux as it can lead to messy soldering and residue buildup. Clean excess flux after soldering for a professional finish.

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Santosh Das

Santosh, founder of this Electronics Tutorial Website, is an Electronics Geek, Blogger and Young Entrepreneur. He possesses vast experience in the field of electronics, electronic components, PCB, Soldering, SMT, Telecommunication, ESD Safety, and PCB Assembly Tools, Equipment and Consumables. Keep visiting for daily dose of Tips and Tutorials.

Also Read:

43 Responses

  1. johny radio says:

    “Several factors determine the type of solder flux to be used during soldering”

    But you don’t say which flux is best for each scenario.

  2. Advance Tech says:

    Very Nice! Thanks for sharing this information.

  3. Advance Tech says:

    Great content.Thanks for sharing this fruitful content.

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