Electroplating of Sn-2.5Ag solders as 20 μm pitch micro-bumps

A Cu/Ni UBM and Sn-2.5Ag lead-free solder for 20 μm pitch micro-bump was successfully fabricated via consecutive electroplatings of Cu, Ni, and binary SnAg. Materials characterizations such as Scanning Electron Microscopy (SEM), X-ray Diffraction (XRD), Electron Probe Micro-analyzer (EPMA), and X-ay Photoelectron Spectroscopy (XPS) were carried out to obtain relevant materials properties. We observed a strong effect of the plating current density on the resulting bump morphologies. After reflow, the solder revealed a spherical shape with a composition variation within 0.2 wt%.