The reaction is one of oxidation, resulting in peroxides, hydroxy and keto compounds. The conjugated double bonds of the abietic type acids are particularly susceptible to oxidation by atmospheric oxygen because of the unsaturation. Oxidation of the rosin during heating involves the double bonds of the resin acids. Wood and tall ail rosin are similar to gum rosin but contain a different mixture of Tall oil rosin is a byproduct of the paper pulping process. Wood rosin is obtained by boiling aged tree stumps. Gun rosin essentially is pine tree sap that has had approximately 20% turpentine distilled off. ![]() The problem arises when it is required to remove the residue either because the assembly will operate hot (above 65̊C) where the rosin becomes tacky, or the rosin might flake off and get between electrical contacts or just for aesthetics (not a good reason for cleaning). Typically rosin fluxes, including mostĪctivated types, have insulation resistances in the 1010 ohms or higher. Rosin fluxes are active enough to solder electronic assemblies and the residue has a very good insulation resistance. If rosin fluxes appear to be such a problem, why continue to use them? The answer is simple. Rosin Flux more often has been used for electronic assemblies when the white residue problem arises. Halide (chloride and bromide) salts help reduce oxidation and improve activity but may result in heat of soldering may also no be removed with water. The organic water soluble flux itself is more likely to oxidize and decompose than a rosin flux because generally the water soluble organic acids are not as heat stable as rosin acids. There are white residue problems with water soluble fluxes and many of the causes not related to the flux compositions are the same as for rosin fluxes. The soldering and cleaning processes involve so many chemicals in the flux, circuit board, components and cleaning agents that a complete understanding of the reactions is very difficult if not impossible. The problem is not limited only to rosin fluxes and solvent cleaning, but also occurs when water soluble fluxes are used and when either flux type is removed with water. The residue remains after cleaning the assembly to remove soldering flux. ![]() These are questions accompanying soldered circuit board assemblies sent to the Kester laboratory for analysis and, hopefully, some answers. What is this white residue on the printed circuit assemblies? Why is the white residue suddenly appearing when it never happened before? What is causing the white residue? Why is this only and intermittent problem? This paper discusses many of the sources of the residues that seem to be an ever-increasing Rosin and water-soluble fluxes, circuit board resins and epoxies, component materials and other contamination all contribute to this complex chemistry. White residue remaining after cleaning circuit board assemblies can be caused by a variety of chemicals and reactions. White Residue: Identification and categorization of white residues often found on cleaned circuit board assemblies.
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