Electrochemically deposited tin-silver-copper ternary solder alloys

A study on film properties of electrochemically deposited tin-silver-copper (SnAgCu) alloys was performed with an alkaline bath. This research focused on the bath and process development for dendrite-free, near-eutectic SnAgCu alloy deposition through the investigation of cathodic polarization, morphological transition, and film composition. Effects of process parameters on surface morphology, film composition, and diffusion-limited current density (LCD) were also examined. Ternary alloys were obtained only when the current density was driven beyond the mass-transfer limitation of noble metals (silver and copper), which seemed to cause the transition of surface morphology and film composition with increasing current density. The morphological transition occurred through four stages (dendrites, suppression of dendrites, nodules, and columns/dendrites), and the content of noble metals in the film tended to drop with increasing current density. With increasing the concentration of noble metals, bath temperature, and agitation, the morphology at low current densities became increasingly dendrite-dominated and the content of noble metals in the film was enhanced at a fixed current density. The morphology of stage four was influenced by the ratio of the applied current density to the LCD, where the LCD was significantly influenced by the metal concentration, bath temperature, and agitation. © 2002 The Electrochemical Society. All rights reserved.