FORMATION OF LEAD-FREE MICROBUMPS BY ELECTROPLATING FOR FLIP-CHIP AND WLP APPLICATIONS
Authors: R. Kiumi, F. Kuriyama, N. Saito Company: Precision Machinery Co., Ebara Corp. Date Published: 11/1/2006
IWLPC (Wafer-Level Packaging)
Abstract: Lead-free micro-bump soldering is an important step toward the removal of hazardous substances from electronics. The bumping processes for the lead-free soldering are required to be compatible with existing machines and to fabricate lead-free micro-bumps without any defects for advanced packaging applications. In our study, the micro-bump formation of lead free electroplating processes for Sn, Sn-Ag, Sn-Cu and Sn-Ag-Cu interconnects was investigated. In order to have a viable lead-free micro-bumping process, we have studied electroplating of lead-free micro-bumps with a dip-type plating bath. The results announce that (1) electroplating technology has been developed to make with high reliability and void-free for lead-free micro-bumps with existing machines; (2) Sn-Cu micro-bumps was much easy to be formed by plating Sn on Cu with a high reliability and without a whisker issue, comparing with other lead-free solder; (3) the non-uniformities of the lead-free micro-bump height were lower than 5% over the whole wafer; (4) the fracture mode was verified being a ductility fracture only in the micro-bumps for the lead-free bumping interconnects between micro-bump and UBM, (5) electroplating processes are suitable for mass production of bumps well-controlled on the morphology, growth shape, thickness and compositions of alloys.