In the welding process, it can help and promote the welding process, and at the same time has a protective effect and prevents oxidation reactions. The flux can be divided into solid, liquid and gas. The main functions include "assisting heat conduction", "removing oxides", "reducing the surface tension of the material being welded", "removing oil stains on the surface of the material being welded and increasing the welding area", and "preventing re-oxidation". Among these aspects, the two most critical functions are: "removing oxides" and "reducing the surface tension of the material being welded".
Flux [1] is usually a mixture with rosin as the main component. It is an auxiliary material to ensure the smooth progress of the soldering process. Soldering is the main process in electronic assembly. Flux is an auxiliary material used in soldering. The main function of flux is to remove oxides on the surface of solder and the base material to be soldered, so that the metal surface reaches the necessary cleanliness. It prevents the surface from re-oxidation during soldering, reduces the surface tension of solder, and improves soldering performance. The quality of flux performance directly affects the quality of electronic products.
In recent decades, in the soldering process of electronic product production, rosin resin-based flux, which is mainly composed of rosin, resin, halide-containing activator, additives and organic solvents, is generally used. Although this type of flux has good solderability and low cost, it has high post-soldering residue. Its residue contains halogen ions, which will gradually cause problems such as reduced electrical insulation performance and short circuit. To solve this problem, the rosin resin-based flux residue on the electronic printed circuit board must be cleaned. This will not only increase production costs, but also the cleaning agent for cleaning the rosin resin-based flux residue is mainly fluorine and chlorine compounds. This compound is a substance that depletes the atmospheric ozone layer and is banned and eliminated. There are still many companies that use the aforementioned process of using rosin resin-based flux solder and then cleaning it with a cleaning agent, which is inefficient and costly.
The main raw materials of no-clean flux are organic solvents, rosin resin and its derivatives, synthetic resin surfactants, organic acid activators, anticorrosive agents, cosolvents, and film-forming agents. Simply put, various solid components are dissolved in various liquids to form a uniform and transparent mixed solution, in which the proportions of various components are different and the functions they play are different.
Organic solvent: one or a mixture of ketones, alcohols, and esters, commonly used are ethanol, propanol, butanol; acetone, toluene isobutyl ketone; ethyl acetate, butyl acetate, etc. As a liquid component, its main function is to dissolve the solid components in the flux to form a uniform solution, so that the components to be soldered can be evenly coated with an appropriate amount of flux components. At the same time, it can also clean light dirt and oil stains on the metal surface.
Natural resin and its derivatives or synthetic resins
Surfactant: Halogen-containing surfactants are highly active and have high soldering ability, but because halogen ions are difficult to clean, the ion residue is high, and halogen elements (mainly chlorides) are highly corrosive, they are not suitable for use as raw materials for no-clean flux. Halogen-free surfaces Surfactant, slightly weaker in activity, but less ion residue. Surfactants are mainly fatty acid family or aromatic non-ionic surfactants. Their main function is to reduce the surface tension generated when the solder and the lead pin metal come into contact, enhance the surface wetting force, enhance the penetration of organic acid activators, and can also act as a foaming agent.
Organic acid activator: composed of one or more organic acid dibasic acids or aromatic acids, such as succinic acid, glutaric acid, itaconic acid, o-hydroxybenzoic acid, sebacic acid, pimelic acid, malic acid, succinic acid, etc. Its main function is to remove oxides on the lead pins and oxides on the surface of molten solder, and it is one of the key components of flux.
Corrosion inhibitor: reduces the residual substances of solid components such as resins and activators after high-temperature decomposition.
Cosolvent: prevents the tendency of solid components such as activators to dissolve from the solution, and avoids the poor non-uniform distribution of activators.
Film-forming agent: during the soldering process of the lead pins, the applied flux precipitates and crystallizes to form a uniform film. The residue after high-temperature decomposition can be quickly solidified, hardened, and reduced in viscosity due to the presence of film-forming agent.