Intermetallic Effects of Electroplated Lead-Free Solder Bumps Using a Novel Single Chamber Electroplating Process for Large Diameter Wafers

In this study solder bumps of various alloys and less than 100 microns in diameter were electroplated using a novel single chamber electroplating process in which the plating baths are exchanged between the different metal plating layers. This equipment is new to the manufacturing arena. The reflow profile and process was then optimized for the various alloys such as SnAg, and electroplated layered SnPb, and PbSn 95/5%, with PbSn 95/5% being the control leaded solder for comparison. Various fluxes were also used during the reflow of these bumps. The solder bumps were reflowed on a conduction reflow oven in a nitrogen environment such that the temperature profile could be carefully controlled. The bumps were analyzed by examining the bump diameter and height uniformity, surface quality, and elemental composition and distribution inside the bumps. These analyses were done by visual inspection by optical microscopy, scanning electron microscopy, and electron dispersive spectroscopy (EDS). The wafers were diced near a row of solder bumps, then podded and polished using a metallographic polishing system to the center of solder bumps. These bump cross-sections were then examined by EDS to perform elemental mapping of the alloy constituents.