Flux-Cored Wires

Flux-cored wires represent one of the most widespread and versatile formats in soft soldering, especially in electronics. Their main characteristic is the presence of an internal flux core that, when activated during heating, removes metal oxides and facilitates alloy wetting. This format greatly simplifies the operator's work and ensures consistent results, which is why it has become the standard for manual soldering of printed circuits and wiring. A flux-cored wire consists of an outer sheath of soldering alloy that encloses one or more channels filled with flux inside. The most common versions contain 2% to 3% flux by weight, distributed in a single core or in three micro-cores to obtain more uniform delivery. Diameters vary from about 0.3 mm (for precision work on SMD components and microcircuits) up to 2 mm (used in wiring or junctions on larger conductors). Wire quality depends on both alloy purity and flux stability: diameter regularity, absence of voids in the core and progressive melting are the parameters that determine predictable behavior in production. The choice of internal flux is crucial for performance: no-clean fluxes with low residue (ROL0/ROL1) leave amber to transparent, non-conductive and non-corrosive residues, which often do not require washing and are therefore ideal for modern electronics. RMA/RA rosin-based formulations offer superior activity and a wide process window, suitable for through-hole components or less clean PCBs; residues can be left or removed with solvents. For mechanical applications or on oxidized surfaces (enameled copper, brass, sheet metal), high activity fluxes (organic acids and inorganic salts) are used: they guarantee effective deoxidizing action, but require careful post-soldering cleaning to avoid corrosion. Flux-cored wires are mainly produced in lead-free alloys compliant with RoHS. Among the most common: 99.3Sn0.7Cu for general use; SAC305 (96.5Sn3.0Ag0.5Cu) as standard for electronic assembly thanks to the good compromise between mechanical strength, thermal reliability and wettability; 96.5Sn3.5Ag for bright and robust joints; SN100C (99.3Sn0.7Cu with Ni and Ge) to improve fluidity, reduce oxide formation and obtain bright joints. Compared to traditional SnPb alloys (Sn63Pb37, 183°C), lead-free alloys melt at higher temperatures (217–227°C), with a slight increase in soldering temperature that does not compromise flux-cored wire handling. Flux-cored wire is mainly used in manual soldering with stylus for PCB production and repair, in electrical wiring work and prototyping activities. Its practicality also makes it ideal for small soldering robots that require easily dosable material. In consumer electronics it is used daily to solder discrete components, connectors and rework boards; in professional environments it is common in low/medium volume production lines, while in R&D laboratories it is the preferred tool for rapid assembly tests. The main advantage of flux-cored wire is process simplification: alloy and flux are combined in a single product, reducing steps and ensuring correct deoxidizer dosing. This results in better repeatability and lower risk of defects related to incorrect flux dosing. No-clean fluxes reduce times by eliminating the washing phase; differentiated diameters allow adaptation to components of varying sizes; alloys with Ni or Ag improve joint strength under thermal or mechanical stress conditions. Lead-free flux-cored wires comply with RoHS standards and J-STD-004/006 specifications for flux classification and alloy quality. All batches are traced and accompanied by analysis certificates, in compliance with our ISO 9001:2015 quality system.