Investigation of the Solder Fluxes Activity by Measuring of the Contact Angle

The aim of this paper was to investigate the activity of ROL0-classified solder fluxes by evaluating their cleaning and wetting performance through contact angle measurements. SAC305 solder balls were reflowed on Cu-clad PCBs (FR4) and DBC substrates (Al<inf xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">2</inf>O<inf xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">3</inf>-based), both with and without cold atmospheric plasma (CAP) surface pre-treatment. Four different ROL0 fluxes, as per IPC-J-STD-004 classification, were compared. The study focused on how flux activity correlates with surface characteristics and the influence of CAP on surface tension and flux activation. The results show that CAP generally enhances wetting on FR4 substrates by reducing the contact angle, but this effect was less pronounced or inconsistent on DBC substrates. Although all tested fluxes share the same ROL0 classification, their performance varied significantly depending on the substrate type, indicating substrate-specific behavior and differences in activation thresholds.