Comparison of Methods for Characterising Soldering Fluxes and their Interactions with Substrates and Metallisation

The 1980s and 1990s have seen the development of new and interesting soldering flux formulations. Many of these fluxes exhibit improved soldering performance or are favoured because of their reduced environmental impact. In order to further the understanding of these new fluxes and their interaction with the metallisation on the printed wiring board, as well as the substrate itself, one needs to examine test methods carefully and begin to correlate the data among the existing test methods. At Georgia Tech a variety of data have been collected on a number of fluxes including water soluble, low solids and activated rosin fluxes. Test methods for flux characterisation include surface insulation resistance testing,corrosion test measurements and recently impedance spectroscopy at low frequencies. This paper will review the variety of fluxes available, report on results of testing these fluxes using the techniques mentioned above and will define the important information related to soldering flux interactions which each test method uncovers.