Synergistic Regulation of Sn-Ag Bump Electrodeposition Using Ternary Additives for Enhanced Flatness and Coplanarity

A ternary additive system (morin, cinnamaldehyde, and cuminaldehyde) was developed to fabricate Sn-Ag bumps with high flatness (<5%) and coplanarity (<5%) under high-current-density electrodeposition (8 ASD). Cyclic voltammetry revealed distinct potential-dependent adsorption behavior: morin preferentially adsorbed at relative positive potentials (-0.44 to -0.60 V), inducing -160 mV shift in onset electrodeposition potential (-0.60 V) compared to that without additives (-0.44 V), which enhanced nucleation site density and promoted grain refinement. In contrast, cinnamaldehyde and cuminaldehyde adsorbed predominantly at more negative potentials (-0.50 to -0.80 V and -0.55 to -0.80 V, respectively). This enabled their adsorption at the edge and tip of bumps, thereby achieving leveling effects by selectively suppressing deposition at protrusions. Convective diffusion amplified the cinnamaldehyde adsorption at the edge and tip while suppressing cuminaldehyde adsorption. Chronopotentiometric analyses further elucidated the synergistic regulation mechanism. At 8 ASD, the adsorption of morin shifted the electrodeposition potential negatively, enabling subsequent adsorption of cinnamaldehyde and cuminaldehyde. Consequently, electrodeposition at relative negative potentials and rapid diffusion regions was suppressed, yielding fine-grained structures alongside superior flatness and coplanarity.