Flux
Flux
Flux is one of the most important materials in tin welding. The melting point of the coal flux is lower than that of the solder, and its relative density drilling degree is smaller than that of the solder. The use of welding aid can improve the quality of coal joint and protect the welded surface from damage.
1. Role of flux
The reaction between the crystalline structure of the molten solder and the crystal structure of the base metal. Most of the welding operations are carried out in the atmosphere. The base metal surface and the solder surface will come into contact with various components in the atmosphere and react with each other to produce oxides, most of which have thermal stability and chemical stability. This prevents solder and base metal from becoming alloys. Fluxes are used to remove oxides, sulfides, oils and other contaminants from metal surfaces to prevent the continued oxidation of solders during heating.
In welding, the flux melts before the solder and soon flows over the surface of the solder and the metal being welded, thereby isolating air and preventing oxidation on the metal surface. Reduce the surface tension of solder itself and the metal being welded, and increase the wetting ability of solder.
In addition, the flux can react with the oxide film on the solder and the welded metal surface at high temperature to dissolve it and reduce the pure metal surface, so that the surface of the liquid solder can reflect its surface tension and wettability. The diffusion of metals takes place.
To sum up, the role of flux in welding is to dissolve the oxide and prevent the oxidation of metal surface. 2. Types of flux
There are many types of fluxes, which are usually divided into three categories: organic flux, inorganic flux and resin flux.
The organic flux consists of organic acids, organic halides and so on. This kind of flux has higher acidity and has the advantages of mild chemical action, better weldability and solderability; the drawback is that it is corrosive, the residue is not easy to remove, and the amine substances decomposed in the welding will pollute the air. Can have a negative impact on the operator. Therefore, organic flux is not used alone, but only as activator and rosin.
The main composition of inorganic flux is a mixture of zinc oxide, oxidation discouragement, etc., the melting point of which is less than 1800.
Function of non-oxidation corrosion
Rosin is non-polluting, non-corrosive, good insulation, easy to clean after welding, widely used. But because of its activity,
Poor. Therefore, in immersion welding and wave soldering. Usually in rosin to add active agents.
In addition, the common solder paste, hydrochloric acid and other fluxes. Due to solder paste hydrochloric acid on printed circuit boards and soldering iron heads
It is very corrosive and produces a bad smell during the welding process. This kind of flux can weld the components,
If the residual flux is not cleaned up in time, the printed circuit board will be damaged by corrosion after a period of time
Left behind the trouble.
Therefore, it is best to use rosin as the flux has no corrosive effect on the components, circuit boards, etc.
On the iron head can also play a certain protective role insulation is better. In addition, rosin can also be used as base material
Make a variety of fluxes for use.
3. Selection of flux
The pins of electronic components are mostly made of tin enamel or gold, silver, nickel and other metals, different metal selection flux requirements
Matters needing attention
We should pay attention to the following two points when choosing the flux correctly and reasonably.
When the surface condition of the lead is not very good and the most effective cleaning method is inconvenient, the flux with strong activation and strong ability to remove oxide can be selected.
In the final assembly, the welding parts are basically in a better state of solderability, flux performance is not strong, less corrosive, cleaner flux.
