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108 SMT Magazine • January 2017 ionic contamination could easily result a disas- trous field failure, so the cleaning process has to be extremely thorough. Normally, boards com- ing out of the wash are periodically tested for ionic contamination, usually using some type of ionograph or omegameter. The detrimental effects of corrosion can even happen in the manufacturing facility if residues are not cleaned off in a timely manner. Below is a photo of water soluble flux corrosion only after sitting for two hours. Another poten- tial failure mode of water soluble residue con- tamination is dendritic growth, which is metal- lic, hair-like growths that can develop between and short adjacent conductor paths. To be clear, the washing systems for water soluble fluxes have proven to be completely ef- fective for decades, but are expensive to operate and take up valuable floor space. However, the aggressive chemistry of water soluble fluxes re- quires corrosive resistant fluxers, and attacks the equipment which is more difficult to keep clean. For these reasons, many do not use, and we do not recommend using water soluble flux, whenever possible. Rosin Flux Full rosin fluxes also provide excellent sol- dering, with an equivalent ability to clean the metals to be soldered and to last throughout the process. But, they do not have the same pro- pensity as water soluble to corrode and dam- age product. In fact, instead, the rosin has the CHOOSING THE CORRECT FLUX —ADVANTAGES/DISADVANTAGES Figure 2: Water soluble corrosion. Figure 3: Dendrites. (Courtesy: Trace Labs) Figure 4: The aggressive chemistry of water soluble fluxes requires corrosive resistant fluxers, and attacks the equipment—which is more difficult to keep clean.