PCB Flux Types and Applications

The welding material does not always adhere to the component, which can lead to bad welding joints, pins
that are bridged, or even no welding joints. To overcome these issues, use flux and the correct
temperature.

What Does Flux Mean?

A good bond is dependent on two factors: a welding which is compatible with the metals to be bonded and
a clean metal surface that’s free of dust, oxides, and grime. Cleaning the surface and using good
storage methods will prevent dust and dirt from accumulating. Oxides require a different approach.

Oxides are formed on almost all metals by oxygen reacting with them.Rust is commonly called on iron.
However, oxidation also occurs in tin and aluminum. Oxides can make welding difficult or impossible by
preventing the metallurgical bonds that are formed during welding. Oxidation happens all the time but at
higher temperatures it is much more rapid. For example, when flux is used to wash the metal and reacts
with oxide, a primed metal surface can be left for a successful welding.

Flux is used to protect the metal from further oxidation during welding. Each type of flux has a
specific use and limitations.

Flux Types

The flux that is included in the core of the welding wire is adequate for many applications. There are
applications, however, where additional flux can be beneficial. For example, surface mount welding or
dewelding. The best flux is always the most aggressive (least acidic) flux, which will react with the
oxides of the component and create a strong bond.

Rosin Flux

Rosins (which have been refined and purified) are some of the oldest fluxes. Rosin fluxes are still in
use, but they blend other fluxes together to maximize their properties.

Ideal is a flux that flows easily, removes oxides rapidly, and removes foreign matter from metal
surfaces. Rosin flux, when liquid, is acidic. However, it becomes inert and solid upon cooling. As rosin
is inert and solid, it can be left on the PCB. This will not damage the circuit unless the circuit
becomes too hot. It is always best to remove any rosin residues from the PCB. Alcohol can be used to
remove the flux residue if you’re applying PCB cosmetics or conformal coatings.

Organic Acid Flux

Water-soluble organic acids flux is one of the most common fluxes. Citric acid, lactic acid, and stearic
acids are all weak acids that can be used in organic acid fluxes. Solvents like isopropyl and water are
used to mix weak organic acids.

Organic acid flux can remove oxides more quickly than rosin. Organic acid flux is water-soluble,
allowing the PCBs to be cleaned easily with just plain water. This protects the components that are not
wet. OA residues can be conductive, and affect the performance and operation of the circuit. Remove flux
residues after welding.

Inorganic Acid Flux

Inorganic fluxes work better on stronger metals, such as brass, copper and stainless steel. This mixture
is made up of hydrochloric, zinc chloride and ammonium cyanide. After using inorganic acid flux, it is
important to thoroughly clean the surface. If left uncleaned, corrosive residues can cause welding
joints to weaken or even destroy. It is not recommended to use inorganic flux for electrical or
electronic work.

Welding Fumes

In the fumes that are released during welding, there are several chemical compounds that come from the
reaction of the acid with the oxide layer. In welding fumes, other compounds like formaldehyde and
toluene are also present. These fumes may cause asthma or increase sensitivity to welding gases. Use a
respirator and ensure adequate ventilation.

Orinew Technology: Because the boiling point of welding and melting temperatures of welding are
several times higher, the risks of cancer and lead from welding fumes is very low. Lead is most likely
to be released from welding fumes. To prevent lead from entering your body, you should take extra care
when welding. Wash your hands, avoid smoking, eating and drinking in the vicinity of welding.