1.Flux and flux selection
(1) The function of flux
The rosin resin and the active agent in the flux generate an activation reaction at a certain temperature, and the oxide film on the surface of the weld metal can be removed, and the rosin resin can protect the metal surface from oxidation at a high temperature.
Flux can reduce the surface tension of the molten solder and facilitate the wetting and diffusion of the solder.
(2) Characteristics of flux
1 Melting point is lower than solder, the expansion rate is greater than 85%.
2 Viscosity and density are smaller than molten solder, easy to be replaced, and no toxic gas is produced. The density of the flux can be diluted with a solvent, generally controlled at 0.8 to 0.84 g/c m³; the density of the no-clean flux is about 0.8 g/cm3.
3 no-clean flux requires less than 2.0% solid content, no halide, less residue after welding, no corrosion, good insulation performance, insulation resistance greater than 1×10″ Ω.
4 Water cleaning, semi-aqueous cleaning and solvent cleaning flux require easy cleaning after welding.
5 Storage is stable at room temperature.
(3) Selection of flux
According to the cleaning requirements, the flux is divided into four types: no-clean, water-washing, semi-aqueous cleaning and solvent cleaning. According to the activity of rosin, it is divided into R (inactive), RMA (medium active) and RA (full active). Selecting accord to the specific requirements of the product for cleanliness and electrical performance.
Under normal circumstances, military and life support categories such as satellites, aircraft instruments, submarine communications, life-saving medical devices, weak signal testing instruments and other electronic products must use cleaning flux; others such as communications, industrial equipment, office equipment For electronic products such as computers , no-clean or clean flux can be used; general household appliances can use no-clean flux or RMA (medium active) rosin flux, which can be free of cleaned.
When the density of the flux exceeds the required value, the corresponding diluent can be used for dilution.
Antioxidants are excipients added to reduce the oxidation of solder at high temperatures, which saves solder and improves solder quality.
4.Tin slag reducer
The tin slag reducer separates the molten solder from the dross, thereby saving solder
5.Solder resist or high temperature solder mask tape
It is used to prevent the components attached to the wave soldering from being clogged with solder, and soldering places where soldering is not required, such as gold fingers.
Except for the solder, the above materials should be stored away from light for a period of six months.
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