Contact angle of 63Sn–37Pb and Pb-free solder on Cu plating

This study investigated the wetting behavior of 63Sn–37Pb and Pb-free solder on different surface roughness Cu plating. The Cu plating roughness was controlled by current density and deposition time. The contact angles were measured to investigate the wetting behavior. The contact angles of DI (de-ionized) water obey Wenzel’s equation and decrease with the increase of surface roughness. Daubing the flux on solder balls as well as on the Cu plating lowers the magnitude of contact angle by 2–23° and the deviation of measured values by 4–6°. The contact angles decrease with the increase of Cu substrate surface roughness in the temperature range of 250–280 °C. The cleaning effect of flux was analyzed by Auger electron spectroscopy. The oxide on the Cu substrate surface was well removed by flux. The carbon residue left behind on the substrate surface after reflow raises both the magnitude and the scattering of contact angle.