Investigation of a Low-Cost Sequential Plating Based Process for Pb-free Bumping

摘要

In this paper, a low-cost bumping process is proposed, achieved and characterized. The proposed approach is based on a sequential plating of Sn and Ag instead of the conventional alloy plating. Our objective, therefore, focusses on the understanding of the metallurgical aspects of repeatable sequential plating processes for lead-free Sn-Ag-Cu (SAC) bumping. To this end, different plating sequences with varying Sn-Ag layers configuration are established and the fabrication processes for 95 μm diameter bumps on a 100mm wafer are demonstrated. Characterization results, obtained through cross-sectional energy dispersive spectroscopy (EDS) local analysis and SEM observation, are described and discussed for the various plating sequences and resultant structures, in particular, Ag diffusion behavior and intermetallic formation.