Interconnections based on Bi-coated SnAg solder balls

摘要: To decrease the bonding temperature required for eutectic SnAg solder, solder bumps were chemically coated with a pure Bi layer. During heating, low melting forms between coating and SnAg, enabling at temperatures below points of either or solder. As composition molten changes toward more dilute concentrations, point in joint region increases solidifies. After solidification joints will no longer melt original temperature. Bi-coated balls joined to metallized substrates ranging from 180/spl deg/C 250/spl deg/C. The microstructure interface was characterized by SEM/EDS technique. expected, melted only locally interfacial regions ball substrate so retained their spherical shape during bonding. there lot small precipitates region. At higher temperatures, wetting evidently better, less precipitates, because bismuth. In all cases, formed relatively small, equi-axed instead structure found Sn-Bi joints.