Ag Diffusion Control Through Sn on a Sequential Plating-Based Bumping Process

In this paper, we present our investigations on sequential plating for a low-cost bumping process. Following the demonstration of this process for low Ag concentration (1.4 wt%), we aimed this study on increase Ag concentration to 3 wt% and investigate its impact on Ag diffusion and intermetallics compound formation. Moreover, we created a Ag concentration gradient within the same bump in order to benefit from both favorable effects of low and high Ag concentration on the solder. To this end, we plated different metal sequences to form bumps with 90 μm and 75 μm of diameter and height respectively. The fabricated bumps were characterized, after a cross-sectional preparation, through SEM and EDS analysis to reveal the effects of the reflow profile and the use of a barrier on the Ag diffusion, as well as, the IMC formation.