Barrier layers for electroplated SnPb eutectic solder joints

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.