Influence of 1,8-naphthalimide derivatives as additives on the electrodeposition of tin from methanesulfonic acid system

A series of 1,8-naphthalimide derivatives containing different quaternary ammonium groups have been synthesized by a two-step method. Electrochemical tests and quantum chemical calculations demonstrated that 1,8-naphthalimide parent conjugate ring adsorbed to the tin surface and occupied active sites, and positive charges on aromatic ring quaternary ammonium group competed with Sn2+ for electrons. Moreover, higher positive charge density and larger conjugate area of the aromatic ring quaternary ammonium group were considered to increase cathodic polarization to inhibit the deposition rate of tin ions and hydrogen evolution. The substituted naphthalimide NI4 which had a current density suppression effect of 90% and negatively shifted tin deposition and hydrogen evolution potential by 20 mV and 0.45 V respectively was deemed to be the best performed one on this basis. In actual tin plating, compared with base electrolyte, the tin layer surface under NI4 electrolyte was smoother at any current density and had no leakage or agglomeration. SEM showed a higher nuclei density with smaller feature size, and XRD demonstrated a shift in the dominant crystalline plane from (420) to (200).