AU-SN SOLDER BUMPS WITH TUNGSTEN SILICIDE BASED BARRIER METALLIZATION SCHEMES

A homogeneous melting eutectic Au/Sn solder bump for flip-chip application has been developed. The underbump metallization consists of a WSi0.4N0.2-layer and a Ni-wetting layer. The solder is deposited as a sequence of alternating Au and Sn layers. The bump can be exposed to multiple fluxless reflow cycles. The reflow of the solder as deposited starts with a phase forming process in the solid state which results in an eutecticlike phase and the near eutectic delta and zeta phases. The Sand zeta phases dissolve during the Liquid state stage of the reflow at temperatures between 300 and 350 degrees C. (C) 1995 American Institute of Physics.