Fluxes for soldering and welding are auxiliary compounds that ensure wetting, spreading of solder, and protect the soldering/welding area from oxidation. Soldering fluxes: rosin-based (RMA, RA — for electronics), acid-based (ZnCl₂ — for galvanized and tin works), water-soluble (OA — for industrial PCB soldering). Welding fluxes: fused (AN-348A, OSC-45 — for automatic arc welding under flux) and ceramic. Solder pastes: a mixture of Sn-Ag-Cu solder + flux for SMD assembly. Classification according to IPC J-STD-004. Packaging: jars of 100 g–1 kg (soldering), bags of 25–50 kg (welding), syringes of 10–50 g (solder pastes). Solder paste SAC305 (Sn96.5/Ag3.0/Cu0.5) is the standard for RoHS lead-free soldering. Melting temperature 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 at 2–10°C. Shelf life 6 months. Documentation: IPC certification, TDS, MSDS, CoA.