Reactivity of no-clean pastes and fluxes for the surface mount technology process—part II: Corrosion risk measurements for printed circuit boards and solder joints

The introduction of no-clean pastes and fluxes for the surface mount technology process needs testing methods of high sensitivity and reliability to evaluate the activity of the residues after the reflow process. An electrochemical method is proposed, suitable to ascertain the reactivity and the corrosion risk of these residues. Products of normal use are tested, and their behavior described and compared. Surface morphologies and compositions are examined after reflow and after testing. Local surface oxides are investigated with x-ray photoelectron spectroscopy. Surface analytical results are interpreted and related to the electrochemical behavior of solder joints. Tin is shown to have the most important role toward the onset of possible localized corrosion.