Abstract
This paper presents the suitability of solders for solder-coating of surface mount wiring boards. We found that the degradation of solderability is due to the growth of Cu-Sn intermetallic compounds and subsequent oxidation of the Cu. Adding Cu to the solder-coating inhibits the growth of Cu-Sn compounds by reducing Cu diffusion. Adding Ge or In prevents the oxidation of Cu by forming a Ge- or In-rich layer on the surface. Solder-coatings with Sn-Pb solder containing these elements have good solderability.
