Abstract
Cu/electroless Ni/immersion Au metallization is usually used as bonding pad on the substrate side of flip chip solder joints. Sn-Ag-Cu solder is one of the promising candidates to replace the conventional Sn-Pb solder. Isothermal interfacial reaction in Sn-3.0Ag-(0.5 or 1.5)Cu solder joints with electroless Ni/immersion Au surface finish after aging at 150°C was investigated in this study. Intermetallic compounds (IMC) of (Cu 1-y ,Ni y ) 6 Sn 5 , (Ni 1-x ,Cu x )Sn 4 and P-rich layer formed between the solder and the EN layer in both Sn-Ag-Cu joints during aging. For the Sn-3.0Ag-0.5Cu joints after more than 2000 h aging, (Ni 1-x ,Cu x ) 3 Sn 4 IMC gradually grew. Through the investigation of cross-sectional microstructural observation and quantitative analysis, the interfacial microstructure and the elemental distribution between the solder and bonding pad could be clearly revealed. It was demonstrated that Cu content in the solders near the solder/IMC interface played an important role in the growth of (Ni 1-x ,Cu x ) 3 Sn 4 and (Cu 1-y ,Ni y ) 6 Sn 5 . © 2006 IEEE.