The Study on the Interaction of Interfacial Reactions between UBM/Solder and Solder/Pad in Miniature Joints

This stud} investigated the interaction of interfacial reactions between Cu/Sn3.5Ag and Sn3.5Ag/AuNi diffusion couples with different stand-off heights (SOH) in immature solder joints. After reflowing. many (Cu_x,Ni_1-x)6Sn5 IMCs were found to surround the original IMCs at both interfaces of the solder joint, which were attributed to Cu and Ni atoms diffusion throughout the w hole solder. This phenomenon was defined as the interaction of two interfacial reactions in miniature solder joints. The concentrations of Ni and Cu in (Cu_x,Ni_1-x)₆Sn₅ ternary IMC at each side depended on the diffusion rates to Ni and Sn. the height of the solder joint and the experimental conditions. At Sn3.5Ag/AuNi interface, the concentrations of Ni and Cu decreased and increased in (Cu_x,Ni_1-x)6Sn5 ternary IMCs with SOH decreasing, respectively. At Cu/Sn3.5Ag interface, the concentrations of Ni and Cu changed in opposite rules. Cu had a faster diffusion rate in molten Sn to generate a higher concentration in (Cu_x,Ni_1-x)6Sn5. which also took a sharp slope of the percentage of IMC thickness/SOH with SOH increasing at Sn3.5Ag/AuNi interface.