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 230�C and must be processed at 245� to 260�C.� 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.