The Effect of Process Variables on Electrotinning in a Methanesulfonic Acid Bath

Abstract

The electrotinning process based on methanesulfonic acid (MSA) has gained acceptance in continuous steel strip plating lines 1-3 after years of applications in the electronics industry. In the reel-to-reel plating of electronics applications, the line speed is about 0.1 m/s, the current density is about 2000 A/m 2 , and the stannous ion concentration is in the range of 420 to 840 mol/m 3 (50 to 100 g/L). 4 In contrast, in a continuous steel strip plating line, the steel strip travels at speeds from 2 to 10 m/s while the current density varies from 1000 to 6500 A/m 2 to encompass the entire product mix of various steel grades and coating weights. Furthermore, the stannous ion concentration is much lower, often in the range of 84 to 168 mol/m 3 to minimize the loss of costly chemicals through leaks and drag-out in a continuous steel strip plating line. Because of the differences in operating conditions, the production experiences from the reel-toreel plating need to be expanded to be used for the continuous strip plating line. Although a guideline on the interactive effects between processing parameters had been established, 5 the basic information on the transport properties of the MSA bath was still lacking. The purpose of this study was to examine how the deposition process is affected by mass transfer under the hydrodynamic conditions created by the fast moving strip. Such an understanding is critical for proper process control. ExperimentalA patented MSA process, Ronastan-TP-HCD from Shipley Ronal, 6 was used in this study. The bath consisted of 50 mL/L stannous methanesulfonate (Ronastan TP Tin Concentrate 300, with 300 g/L stannous ions), 30 mL/L 70% methanesulfonic acid (Ronastan TP acid 70), pH 0.4, 50 mL/L grain refiner (Ronastan TP-HCD primary additive), and 20 mL/L antioxidant (Ronastan TP antioxidant). The grain refiner was nonionic and had a cloud point of 70ЊC. In addition, iron (179 mol/m 3 , or 10 g/L) was added to simulate its buildup due to corrosion of the steel strip by the electrolyte, that is pertinent to a horizontal plating cell where only the bottom side of the steel strip is plated. 7,8 For the 179 mol/m 3 reagent-grade iron powder dissolved, 40 mL/L of methanesulfonic acid was added to maintain the free acid concentration. The ionic composition of the MSA bath tested is listed in Table I. The bath was evaluated at four temperatures: 27, 38, 52, and 60ЊC.A rotating cylinder cathode (RCC) from Lucent Technologies was used because the hydrodynamic conditions and electrical field are well defined. The plating cell consisted of a 2 L Nalgene graduate cylinder cut to 920 mL, 8.1 cm diam ϫ 20 cm tall. The cathode was a steel coupon, 2.86 cm wide and 5.70 cm long, wrapped around the shaft, 1.93 cm in diam, of the RCC. The anode was a cylinder made of platinum mesh, 4.95 cm in diam and 3.02 cm tall. A baffle was placed inside the plating cell so that the rotation speed could reach 3000 revolutions per minute (rpm) without causing a vortex. The shaft of the RCC was driven by a rotator, model AFASR...

Versatile electrochemical coatings and surface layers from aqueous methanesulfonic acid

“…Co-evolution of hydrogen was shown to occur at more positive potentials and the mass transport region became shorter at higher rotation speeds and at a higher concentration of stannous ion. These results are similar to those for deposition of tin from a commercial methanesulfonic acid electrolyte [12]. Voltammetry showed that tin was deposited onto copper over a limited linearity Tafel region.…”

“…The stannous ion concentration is much lower in strip plating often in the range of 0.084 to 0.168 mol dm −3 to minimise the loss of costly chemicals through leaks and drag-out in a continuous steel strip plating line. A recent study [12] using a proprietary MSA bath, Ronastan-TP-HCD (Shipley Ronal) has examined how the deposition process is affected by the hydrodynamic conditions created by the fast moving strip, such an understanding being critical for process control.…”

A review of developments in the electrodeposition of tin

“…The Tafel approximation was realised using pure charge transfer data extracted from the mixed control region Figure 2a). 19 The Tafel slope was approximately 20 mV decade -1 , while Figure 2b) shows a semi-logarithmic plot of stannous ion concentration vs. the half-wave potential of the Sn 2+ /Sn couple. The Tafel slope was obtained from the slope as approximately 18 mV decade -1 , which is similar to literature values.…”

“…These trends are similar to those for deposition of tin from a commercial methanesulfonic acid electrolyte. 19 Figure 1 near here.…”

“…Correlation was found with plating efficiency, electrode rotation speed, current density, temperature and surface morphology. 54 Another example is the study of the surface microstructure of tin deposited from tin chloride and tetrapotassium pyrophosphate as a complexing agent. While the current density affected surface morphology and the solution pH affected the crystal orientation of tin deposits, the current density and pH had no significant effect on the grain size.…”