Three lead-free solder alloys were studied for BGA interconnect applications. These alloys are Sn/3.5Ag, Sn/3.0Ag/0.5Cu and Sn/4.0 Ag/0.5Cu. These were compared to eutectic Sn/Pb. The behavior and reliability of these solders were compared in a BGA bump configuration using Cu and Ni pad metallurgies. The solder microstructure and intermetallic reaction products and kinetics were determined. The Sn/Pb eutectic solder has a relatively large grain structure, whereas the Sn/3.0Ag/0.5Cu, Sn/4.0/0.5Cu and the Sn/3.5Ag exhibit finer dual phase structures of Sn and Ag_3Sn in lamellar configurations. Post reflow intermetallics were generally similar for all the non-Pb solders. Cu_6Sn_5 Cu_3Sn were formed over Cu, whereas on Ni substrates, Ni_3Sn_4 was primarily formed. The growth rate for intermetallic formation during reflow was faster for all non-Pb alloys when assessed in comparison to Sn63/Pb37. Following solidification and recrystallization however, intermetallic growth was faster in the Sn/Pb solder than in the non-Pb solders.
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