Interfacial reactions of co-electrodeposited eutectic Au-Sn solder bumps on Ni and Cu substrates

Co-electrodeposition is an economic and effective method to prepare Au-Sn solder bumps. Au-Sn solder bumps were prepared in a non-cyanide sulfite-pyrophosphate Au-Sn electroplating bath in the present work. The content of Sn in the deposited Au-Sn solder bumps was precisely controlled to be 30 at.%, i.e., Au-Sn eutectic composition. The interfacial reactions of the co-electrodeposited eutectic Au-30at.%Sn solder bumps on Cu and Ni substrates were investigated. (Ni, Au)₃Sn₂ intermetallic compound (IMC) formed at the Au-30at.%Sn/Ni interface, while two IMC layers, i.e., (Au, Cu)₅Sn close to the solder matrix and AuCu close to the Cu substrate, formed at the Au-30at.%Sn/Cu interface. The co-electrodeposited eutectic Au-30at.%Sn solder bumps exhibited good solderabilities on both Ni and Cu substrates.