flux: A chemical substance that helps and promotes the welding process and protects against oxidation. Flux can be divided into solid, liquid and gas. There are mainly "auxiliary heat conduction", "removal of oxide", "reduce the surface tension of the welded material", "removal of oil on the surface of the welded material, increase the welding area", "prevent reoxidation" and other aspects, in these aspects of the more key roles are two: "removal of oxide" and "reduce the surface tension of the welded material".
Introduction to Materials
Flux is usually a mixture of rosin as the main component, which is an auxiliary material to ensure the smooth progress of the welding process. Welding is the main technological process in electronic assembly. Flux is the auxiliary material used in welding. The main function of flux is to remove the oxide on the surface of solder and welded base metal, so that the metal surface can achieve the necessary cleanliness. It prevents the re-oxidation of the surface during welding, reduces the surface tension of solder, and improves the welding performance. The quality of flux directly affects the quality of electronic products.
Composition of ingredients
In recent decades, in the soldering process of electronic products production, rosin resin is generally used, which is mainly composed of rosin, resin, halide containing active agents, additives and organic solvents. Although this kind of flux has good weldability and low cost, it has high residue after welding. The residue contains halogen ions, which will gradually cause the decline of electrical insulation performance and short circuit and other problems. To solve this problem, it is necessary to clean the residue of rosin resin based flux on electronic printed board. This will not only increase the production cost, but also the cleaning agent for the residual flux of rosin resin system is mainly fluorochlorine compound. This compound is a depleting substance of the atmospheric ozone layer and is among the banned and eliminated. The process still used by many companies is the aforementioned process of using rosin tree finger flux solder and then cleaning with cleaning agent, which has low efficiency and high cost.
The main raw materials of no-wash flux are organic solvent, rosin resin and its derivatives, synthetic resin surface active agent, organic acid activator, anti-corrosion agent, co-solvent, film forming agent. In short, various solid components are dissolved in various liquids to form uniform and transparent mixed solutions, in which the proportion of various components is different and the role is different.
Organic solvent: one or several mixtures of ketones, alcohols and esters, commonly used are ethanol, propanol and 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, so that it forms a uniform solution, which is convenient for the welding components to be evenly coated with the right amount of flux components, and it can also clean light dirt and oil on the metal surface.
Natural resins and their derivatives or synthetic resins
Surfactants: halogenated surfactants have strong activity and high welding aid capacity, but because halogen ions are difficult to clean, high ion residue, halogen elements (mainly chloride) have strong corrosion, so it is not suitable for use as raw materials for unwashed flux, surfactants without halogen, slightly weaker activity, but less ion residue. Surfactants are mainly non-ionic surfactants of fatty acid group or aromatic group. Their main function is to reduce the surface tension generated when solder and lead foot metal contact, enhance the surface wetting force, enhance the permeability of organic acid activator, and also play the role of foaming agent
Organic acid activator: composed of one or more of the organic acid dibasic acid or aromatic acid, such as succinic acid, glutaric acid, itaconic acid, o-hydroxybenzoic acid, quadipic acid, heptanoic acid, malic acid, succinic acid, etc. Its main function is to remove the oxide on the lead foot and the oxide on the molten solder surface, and it is one of the key components of the flux
Anti-corrosion agent: reduce the residual material of solid components such as resin and activator after high temperature decomposition
Cosolvent: prevents the tendency of solid components such as activators to decolorize from the solution and avoids the uneven distribution of poor activators
Film forming agent: in the process of lead foot soldering, the coated flux precipitates and crystallises to form a uniform film. The residue after high temperature decomposition can be quickly cured, hardened and reduced viscosity due to the existence of film forming agent.
