High density of electrodeposited Sn/Ag bumps for flip chip connection

As peripheral pads in commercial chips have a pitch in the neighbourhood of 40-50 μm, a technique that could deposit solder paste directly in such pitch would be of great interest to reduce the overall cost of flip chip.This paper describes a new technique that can considerably reduce the final pitch. The main new feature of this process is that the bump pads can be built directly onto the peripheral ones. An electroplating process allows solder bump formation with a final pitch goal of 40-50 μm and after an accurate reflow process, eutectic Sn-3.5 wt%Ag solder bumps are obtained. In fact, the typical re-routing process can be eliminated and the process cost considerably reduced.