Fluxes are broadly categorized based on their chemical composition and the residue they leave behind. Understanding these types is crucial for selecting the appropriate flux for a given application and for managing post-soldering cleaning requirements.
Rosin Flux (R, RMA, RA): This is one of the oldest and most traditional types of flux, derived from pine trees.Rosin (R): Non-activated rosin, very mild, primarily for easily solderable surfaces.Rosin Mildly Activated (RMA): Contains a small amount of activator for slightly more aggressive cleaning. It leaves a non-corrosive, non-conductive residue that often does not require cleaning, though cleaning can improve aesthetics.Rosin Activated (RA): Contains more aggressive activators for heavily oxidized surfaces. It leaves a more corrosive residue that generally requires cleaning to prevent long-term reliability issues.Water-Soluble Flux: These fluxes are typically organic acid-based and are very aggressive in cleaning oxidized surfaces.They are highly active and provide excellent wetting.The residue left by water-soluble fluxes is corrosive and must be cleaned thoroughly with deionized water after soldering. Failure to clean can lead to short circuits and corrosion over time.Often used in high-volume production environments due to their effectiveness and ease of post-solder cleaning in automated wash systems.No-Clean Flux: Designed to leave minimal, non-tacky, non-corrosive, and non-conductive residues that do not require post-soldering cleaning.These fluxes contain very low solids content and are formulated to decompose or volatilize almost completely during the soldering process.They are popular in many electronics assembly processes due to cost savings from eliminating cleaning steps.However, the residue, while benign, can sometimes affect test probe contact or conformal coating adhesion, depending on the specific formulation.Synthetic Activated Flux (SA): These are often halogen-free, synthetic formulations that mimic the performance of rosin or water-soluble fluxes. They are designed for specific applications and can offer various residue characteristics.
