REACTIVITY OF NO-CLEAN PASTES AND FLUXES FOR THE SURFACE-MOUNT TECHNOLOGY PROCESS .2. CORROSION RISK MEASUREMENTS FOR PRINTED-CIRCUIT BOARDS AND SOLDER JOINTS

The introduction of no-clean pastes and fluxes for the surface mount t echnology process needs testing methods of high sensitivity and reliab ility to evaluate the activity of the residues after the reflow proces s. An electrochemical method is proposed, suitable to ascertain the re activity and the corrosion risk of these residues. Products of normal use are tested, and their behavior described and compared. Surface mor phologies and compositions are examined after reflow and after testing . Local surface oxides are investigated with x-ray photoelectron spect roscopy. Surface analytical results are interpreted and related to the electrochemical behavior of solder joints. Tin is shown to have the m ost important role toward the onset of possible localized corrosion.