The effect of naphthalene-based additives on tin electrodeposition on a gold electrode

Abstract

In this work, we study the adsorption behavior of naphthalene derivatives: naphthalene (NPT), naphthalenesulfonate (NPTS), hydroxynaphthalenesulfonate (HNPTS) and ethoxylated α-napthalenesulfonic acid (ENSA, a commonly used additive in the tin electroplating industry), on gold electrodes and their effect on the tin electrodeposition process, by means of in situ and ex situ surface analysis techniques (cyclic voltammetry, in situ Surface Enhanced Raman Spectroscopy and ex situ Scanning Electron Microscopy). From experiments and density functional theory calculations, we conclude the formation of films of NPT, NPTS, HNPTS and ENSA, where NPT and NPTS lie flat on the gold surface and HNPTS and ENSA undergo oxidative polymerization. The nature and stability of the films are strongly dependent on the surface structure, interaction between the molecules, and applied potential. NPTS is observed to form a denser film than NPT due to attractive interactions between the adsorbed molecules on gold and tin. Tin electrodeposition is strongly affected by the presence of the NPT, NPTS, HNPTS and ENSA films. Tin bulk electrodeposition is inhibited in the presence of NPT and NPTS, but slightly promoted in the presence of HNPTS. Tin deposits grown in the presence of NPT and NTPS have the same morphology, and the characteristic size of the electrodeposited features is smaller than in their absence. The tin deposit grown in the presence of HNPTS exhibits markedly different and smaller features. Some amount of sulfur form is incorporated in the deposit as a result of the reductive desulphonation of NPTS, HNPTS and ENSA on the gold electrode. The effect of ENSA was compared to the results obtained with NPT, NPTS and HNPTS. ENSA exhibits a similar behavior to NPT, NPTS and HNPTS during tin deposition process in terms of the voltammetry of tin deposition, but it severely inhibits the bulk deposition. Naphthalene derivatives and ENSA have an effect on the tin bulk deposition process, but show no or little effect on the formation of AuSn (surface) alloys, which is ascribed to the slow nature of Sn UPD on gold and the SnAu alloying process.