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Types of Flux
Attempting to divide flux materials into corrosive and non-corrosive categories is a misleading and inaccurate method of classification. Every material used as a fluxing agent is corrosive to some degree. It is this corrosiveness that chemically cleans a metal's tarnished surface creating an environment where solder can flow and bond. A more accurate method of classification is to first classify the available fluxes as rosin based or watersoluble and then either organic or inorganic and then determine the various sub-groups or categories of each of these classifications.
Rosin Based fluxes
Organic Materials (Rosin Based):
These fluxes are made from rosin, (the purified product is known as water-white rosin) which is extracted from pinesap. A wide variety of compounds may be added in order to increase the flux's cleaning and deoxidizing abilities. Therefore this classification can be subdivided into three separate groups, as follows:
R (rosin only). This type of flux is the least active and is generally recommended for use on surfaces that are all ready very clean. It is intended for this type of flux to leave virtually no residue behind.
RMA (rosin mildly activated) This type of flux contains activators that have been added in order to enhance its cleaning and deoxidizing abilities. It will leave a minimal amount of inert residue behind. That residue should be non-corrosive, tack free and be substantially free from ionic contamination after cleaning.
RA (rosin activated) This type of flux also contains activators that have been added and is the most aggressive of the rosin-based fluxes. Although it leaves the most residues behind, these residues can be easily removed by using the appropriate type of flux cleaners.
These flux groups are the only ones specified for mil spec work (ANSI/IPC-SF-818 Class 3 or Mil-F-14256E) in electronic applications.
Water Soluble Fluxes (The flux itself is not water soluble, but the residue that remains after soldering usually is.)...
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