ELECTROPLATING OF LEAD-FREE BUMPS ON 300mm WAFERS FOR WLP APPLICATIONS

Abstract: In lead-free alloy electroplating for Sn-Ag, Sn-Cu or Sn-Ag-Cu solder bumping, composition control is an important subject since the composition ratio is influential to the alloy structures and properties of the solders. The general assumption is that it’s very difficult to control the compositions of plated lead-free alloys in plating production lines because the composition ratio of the alloy element Ag or Cu is small and sensitive to the plating conditions in Sn base eutectic alloys.

Also, when comparing with Sn-Pb solder, the larger electric potential difference between the components of lead-free alloys will make the composition ratio of plated alloys unstable in electroplating. There are a lot of reports on lead-free bumping processes, and then there is little report on research of lead-free bump plating mass-production. This paper describes the control of the compositions in the Sn-Ag alloy plating production line for 300mm wafers.

The composition control of lead-free solder bumping has been primarily experienced on 300mm wafer mass-production conditions for flip chip or wafer level packaging. For fabrication of Sn-1.5-3.5wt%Ag lead-free bumps on 300mm wafers, our study verified over 1000 wafers could be electroplated without adjustment of plating solution by means of UFP-300 plating machine. The results of this study show that an advanced electroplating process can be successfully applied to the fabrication of the Sn-Ag lead-free solder bumps on mass production.

Key Words: Sn-Ag bump, lead-free solder bumping, electroplating, flip chip packaging