Am extended eutectic solder bump for FCOB

An evaporated, extended eutectic (E-3) bump structure has been defined. This positive standoff Pb/Sn solder bump builds on the evaporative structure used to produce C-4 interconnects but utilizes a thicker Sn cap to provide a low temperature, eutectic joining medium for flip chip on board (FCOB) applications. It has been shown that this new structure can be adapted to existing FCOB methodologies without altering the tools or processes being used today. By providing eutectic melting right on the bump itself, direct joining to organic assemblies is achieved without special processing at the board level. This leads directly to cost reductions and improved wirability at assembly. These options are illustrated. The characteristics of the bump have been evaluated and reliability data has demonstrated that this bump performs as well as or better than other solder interconnect structures. Extension of this joining technology to ceramics substrates has also been demonstrated.