Soldering and welding fluxes are auxiliary compositions that ensure wetting, solder spreading, and protection of the soldering/welding zone from oxidation. Soldering fluxes: rosin-based (RMA, RA — for electronics), acid-based (ZnCl₂ — for galvanized steel, tinplate work), water-washable (OA — for industrial PCB soldering). Welding fluxes: fused (AN-348A, OTsS-45 — for automatic submerged arc welding) and ceramic. Solder pastes: mixture of Sn-Ag-Cu solder + flux for SMD mounting. Classification according to IPC J-STD-004. Packaging: jars 100 g–1 kg (soldering), bags 25–50 kg (welding), syringes 10–50 g (solder pastes). SAC305 solder paste (Sn96.5/Ag3.0/Cu0.5) — RoHS lead-free soldering standard. Melting point 217–220°C. Particle size: Type 3 (25–45 μm) for standard SMD, Type 4/5 (20–38 / 15–25 μm) for fine-pitch <0.4 mm. Storage: refrigerator 2–10°C. Shelf life 6 months. Documentation: IPC certification, TDS, MSDS, CoA.