Deflux

Deflux is the process of removing flux residues from soldered joints and assemblies after soldering. Flux is a chemical additive used to improve wetting and oxide removal during soldering; residues may remain and, in some cases, be corrosive or electrically conductive. Defluxing is typically performed when cleanliness requirements are strict, such as in medical devices, aerospace, automotive, and high-reliability electronics, or when a no-clean flux is not used or when residues are likely to affect performance.

Methods of defluxing include solvent-based cleaning, water-based cleaners, or semi-aqueous formulations. Cleaning can be done by immersion, spray, or manual wiping, often with ultrasonic agitation to enhance residue removal, followed by thorough drying. The choice of cleaner depends on flux type (rosin-based, water-soluble, or no-clean), board materials, and component sensitivity. Common solvents include isopropyl alcohol and professional flux removers. After cleaning, boards should be dried completely to avoid moisture-related damage.

Quality and safety considerations include post-cleaning inspection and ionic contamination testing in some industries to verify residue removal. Cleaning procedures should comply with safety data sheets, provide adequate ventilation, and use appropriate protective equipment. Some flux residues are designed to be harmless and may be left on no-clean designs, while others are corrosive or conductive and require removal.

Alternative practices include using no-clean flux to reduce the need for defluxing, though certain assemblies or environments may still require cleaning. Defluxing practices are influenced by industry standards such as IPC guidelines and the cleanliness requirements of the final product.