Composition Control of Sn–Bi Deposits: Interactive Effects of Citric Acid, Ethylenediaminetetraacetic Acid, and Poly(ethylene glycol)

Abstract

Interactive effects of complex agents, including citric acid (CA), ethylenediaminetetraacetic acid (EDTA), and poly(ethylene glycol) (PEG) on the electroplating behavior of Sn–Bi deposits from a basic bath containing 0.15 M and 0.05 M with pH 2, were systematically compared by linear sweep voltammetry (LSV) analyses. The onset potential of Bi deposition is obviously shifted to a negative value close to that of Sn deposition by the simultaneous addition of the above three compounds into the basic plating solution. Based on the LSV results, the composition of Sn–Bi deposits with Sn varying from 44 to 96 wt % can be controlled by varying the current density of electroplating and the concentration of EDTA from the basic plating bath containing 0.3 M CA and 0.2 M PEG. This plating bath provides a reliable route to obtain Sn–Bi alloys of high Sn content (e.g., 80Sn–20Bi and 90Sn–10Bi) and the eutectic 42Sn–58Bi deposit. Tin–bismuth deposits plated from the basic bath with different combinations of the above three complex agents were also characterized by scanning electron microscopic and energy-dispersive spectroscopic analyses.