What is flux and why is it important in electronic soldering?

Flux is essentially a ce made from mixtures of chemicals such as fluorides, borates, borax or boric acid, (in paste, liquid or powder form) designed to prevent the formation of rust in the joints, which acts as an insulator against contact with air during the fusion process.

What are the benefits of flux?

• Acts as a protective barrier especially in tin soldering.

•It makes the metal more workable and ensures good adhesion of the components.

•Improves weld quality

•Improved conductivity.

•It distributes heat evenly and has the ability to promote welds at lower temperatures.

Inconveniences and precautions in the use of flux

•Some chemicals present in the flux can be aggressive and prone to generate corrosion in the elements. Others can create interference with components by acting as insulators.

•There is a possibility of contamination of sensitive parts. In addition, some chemicals present in water-soluble fluxes may adversely affect the dielectric properties of printed circuit layers.

•In high-frequency circuits, it has been observed that in some cases they can cause electromigration of the connections and the formation of whiskers.

•It is essential to use goggles, mask and gloves when handling these products. 

Types of flux.

•Colophony Flux (Type R)

Derived from pine tar resin.

Its effectiveness lies in its ability to dissolve oxide layers, thanks to the addition of acid activators.

•No clean flux (No clean).

They arise to avoid cleaning processes. They can be based on natural rosin or contain synthetic resins, offering advantages by leaving less residues. 

•Flux (aqueous) water-soluble.

Water-soluble fluxes use resins that require post rinsing. This option eliminates the need for solvents.

Flux applications.

- Repair of micro-welds.

•SMD soldering on printed circuit boards (PCBs).

•Reballing processes for BGA (Ball Grid Array Soldering) on electronic components.

•Cleaning of rust remains or residues.

Different flux formats

• Flux paste

Ideal for precise and controlled applications.

It is easily applied with tools such as spatulas.

•Liquid flux

It can be applied by brushes, dispensers or immersion.

Provides uniform coverage on surfaces to be welded.

•Gel Flux

Provides adhesion on vertical or inclined surfaces.

Improved application control.

•Flux in dispenser pen format.

Allows precise and controlled application.

•Flux powder.

It can be mixed with water or other solvents to form a liquid solution.

Suitable for certain specialized applications.

•Flux on spray

It offers a fast and uniform application.

Ideal for covering large areas or complex surfaces.

IPC J Standard Flow Classification: Rigor and Regulations.

The IPC J Standard flux classification system has replaced the military welding standards under QQ-S-571 and MIL-F-14256.

Currently we can find the following classification:

Categories

• RO (rosin)

•OR (organic)

•IN (inorganic)

•RE (resin/synthetic resin)

Classification by flux solution activity

• L (low activity or <0.5% halide)

• M (medium activity or 0 to 2% halide)

• H (high activity or 0 to > 2% halide)

Classification by halide content

•0 (without halides)

•1 (some halides)

How to choose the right flux?

Aspects such as working temperature, material compatibility and cleaning properties, among others, should be considered in order to make a choice that is as close as possible to our projects, needs and preferences.