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In the electronics industry, the quality of solder joints is essential to ensure the proper functioning and reliability of devices. A fundamental component in this process is the flux, which plays a crucial role in creating clean, durable, and electrically reliable connections between electronic components and printed circuit boards (PCBs).

What is a Flux and What is Its Role in Electronic Soldering?

Flux is a chemical substance that facilitates the soldering process by removing oxides and contaminants present on the metallic surfaces to be soldered. This cleaning allows the solder material, such as tin, to properly adhere to the connection points, improving electrical conductivity and the durability of the joints while minimizing the risks of electronic failures.

Key Functions of Fluxes in Electronic Soldering

Oxide Removal: Electronic components and PCBs can oxidize when exposed to air. Flux dissolves these oxides to ensure the molten tin adheres smoothly.

Surface Cleaning: Fluxes also remove impurities like oils, dust, or residues that could interfere with the formation of a solid and electrically sound solder joint.

Protection Against Reoxidation: During the soldering process, heat can cause rapid oxidation of surfaces. Flux creates a protective barrier that prevents this reoxidation, ensuring a strong and secure bond.

Improved Wetting: Flux enhances the ability of molten tin to flow and cover metal surfaces, resulting in a more uniform and robust solder joint.

Methods of Flux Application in Electronic Soldering

There are various methods for applying flux in electronic soldering, depending on the process and equipment used:

Brushing: Primarily used in repairs, flux is applied directly to the soldering area with a brush.

Flux-Core Solder Wire: In manual soldering, tin wire contains flux inside, which is released as the wire melts.

Spraying or Automatic Dispensing: In automated processes, flux can be applied precisely before the deposition of tin, ensuring an even distribution.

Classification of Fluxes According to J-STD-004 and EN 61190 1-3 Standards

It can sometimes be difficult to determine which flux is best suited for a specific soldering process or to identify the type and characteristics of a flux based on the codes found on labels. Here, we aim to clarify this concept by explaining the classification of fluxes according to these standards.

To ensure the proper selection of flux based on the type of application and process, two key standards are used in the electronics industry: J-STD-004 and EN 61190 1-3.

J-STD-004 Standard

The J-STD-004 standard classifies fluxes based on their chemical base, activation level, the corrosiveness of residues, and the need for cleaning. These alphanumeric codes help identify the properties of the flux with precision.

Flux Types by Base:

R (Rosin): Resin-based fluxes, with or without chemical activation. They are common in the industry and used in low-corrosivity applications.

WS (Water-Soluble): Water-soluble fluxes, highly active and effective, but require thorough cleaning due to corrosive residues.

NC (No-Clean): Designed to leave minimal residues that do not require cleaning, widely used in mass production of electronic devices.

Activation Levels:

L (Low activity): Low chemical activity, for applications with minimal oxides.

M (Medium activity): Moderate activity, providing better cleaning for more demanding applications.

H (High activity): High activity, for removing tougher oxides. These fluxes typically require cleaning due to the corrosiveness of residues.

Residue and Cleaning:

Type 0: Non-corrosive residues, no cleaning required.

Type 1: Corrosive residues, must be cleaned to avoid long-term performance issues.

Examples of J-STD-004 classification:

ROL0: Rosin-based flux (R), low activity (L), with non-corrosive residues (0), thus no cleaning is required.

ORM1: Organic-based flux (O), high activity (H), with corrosive residues (1), which require post-soldering cleaning.

EN 61190 1-3 Standard

The EN 61190 1-3 standard classifies fluxes similarly to J-STD-004, providing more detailed coding that includes flux activity and its behavior in terms of cleaning.

Classification by Activity and Composition:

1.1.1: Activated resin flux, with non-corrosive residues, suitable for applications without post-cleaning.

1.1.2: Activated resin flux, with corrosive residues that require cleaning.

2.1.2: Low-activity organic flux, with non-corrosive residues.

2.2.3: Activated organic flux, highly active, requiring thorough cleaning due to corrosive residues.

Cleaning and Corrosivity:

The EN 61190 1-3 standard specifies cleaning requirements based on the corrosiveness of residues and the activation level of the flux, ensuring that the correct products are selected for critical applications where any residue could affect device performance.

Post-Soldering Cleaning in Electronic Soldering

Post-soldering cleaning is critical when using fluxes that leave corrosive or conductive residues. These residues can affect the longevity and performance of the joints, especially in sensitive electronic devices. However, no-clean fluxes leave minimal residues that do not interfere with the functionality of the device, reducing the need for post-soldering cleaning, although it is always important to validate their suitability for each specific application.

Selecting the Right Flux for Electronic Soldering

Choosing the right flux is a crucial factor in ensuring the quality of solder joints. At Broquetas S.L, we offer a wide range of fluxes that comply with both J-STD-004 and EN 61190 1-3 standards, providing specific products to meet the diverse needs of the electronics sector, whether for manual or automated applications.