Characterizing Soldering Fluxes

For a number of years electronic manufacturers of printed circuit assemblies have used rosin-based soldering fluxes. Post-solder cleaning was accomplished with chlorinated or chlorofluorocarbon (CFC) solvents. With the elimination of these solvent options due to their destructive effect on the stratospheric ozone layer, manufacturers are looking to alternative cleaners for rosin flux or to new flux choices which can be cleaned with water, or left uncleaned. Many of the flux formulations are new and their long-term effect on the performance of product manufactured with them is unknown. Although ionic contamination testers can alert one to the ionic levels remaining on an assembly, the corrosivity of the residues is not directly related to the total ionic level, but only to certain ionic species. Surface insulation resistance testing is used by many in the industry, but the results are complex and often misunderstood. All of these factors have been the driving force to develop a quantitative screening test for soldering flux residues. This test, originally conceived by Dr. David Bono, has been modified and developed at Georgia Tech to provide a quantitative evaluation of flux residue corrosivity. This work, in collaboration with the work being performed by the French standards group, will result in a new international industry standard. This paper reports the latest data on this important test development.