Pb-free Solder Interconnects for Flip Chip and Area Array Interconnects

D. R. Frear, J.-K. Lin

Motorola

Semiconductor Products Sector

Final Manufacturing Technology Center

Tempe, AZ USA

 

This presentation will discuss the issues involved with the development of a system level packaging solution for flip chip and area array interconnects. This includes the metallurgy of the solder alloys and under bump metallization (UBM) structures for flip interconnects and ball grid array (BGA) structures. A variety of Pb-free solder alloys have been proposed for use as interconnects including Sn-Ag, Sn-Cu, Sn-Ag-Cu, Sn-Ag-Bi, and Sn-Sb, among others. A review of the physical (melting, wetting, intermetallic formation, etc.) and mechanical (strength, creep, thermomechanical fatigue, etc.) behavior of promising Pb-free solder alloys will be presented. Recommendations will be given for optimal alloy composition as a function of performance requirements. Electronic packaging process modifications are also required to accommodate Pb-free solders. The most promising Pb-free alloys melt at temperatures between 217 and 230C and must be processed at 245 to 260C. Therefore, components joined with Pb-free solder must be able to withstand the higher processing temperatures and avoid packaging materials degradations such as delamination and popcorning effects. The materials and process trends of Pb-free packaging are summarized with optimal conditions identified.