The present invention provides a means of fabricating a reliable C4 flip-chip structure for low-temperature joining. The electrochemically fabricated C4 interconnection has a barrier layer between the electroplated tin-rich solder bump and the ball-limiting metallurgy that protects the terminal metal in the ball-limiting metallurgy from attack by the Sn in the solder. The barrier layer is electroplated through the same photoresist mask as the solder and thus does not require a separate patterning step. A thin layer of electroplated nickel serves as a reliable barrier layer between a copper-based ball-limiting metallurgy and a tin-lead (Sn--Pb) eutectic C4 ball.
P. Constantin Andricacos, Dr. Madhav Datta, Horkans, W. Jean, Kang, S. Kwon, and Kwietniak, K. Thomas, “Barrier layers for electroplated SnPb eutectic solder joints”, U.S. Patent US 09/057,2051999.