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Why converting tin electroplating lines makes sense

Carol Levey
Marketing Manager, Steel Mills, Interconnect Technologies

Legacy tin electroplating processes based on phenol sulfonic acid (PSA/ENSA) are the most common processes for tin-plated steel, but increasing concerns about toxicity and materials waste pose compelling reasons to switch to a chemistry that avoids these problems. Dow’s Ronastan™ family of electrolytes based on methane sulfonic acid (MSA) provides a nontoxic alternative for high speed tin electroplating. 

Converting an existing PSA/ENSA plating line to MSA provides benefits in cost, quality and environmental safety. We outline various comparisons to PSA/ENSA to illustrate the advantages of this solution.

Cost savings: overall reduction in cost of operation

  • Requires less than half the amount of tin in solution for operation. This translates to less tin lost to dragout or leaks, and up to 90% reduction in sludge production.
  • Ronastan MSA-based electrolytes are 25 to 40% more conductive than PSA/ENSA, allowing systems to run at a lower voltage, saving electricity costs.
  • The need for waste treatment is drastically reduced or even eliminated (depending on local legislation), reducing disposal costs.
  • The all-liquid chemistry enables auto-dosing of electrolyte additives, requiring fewer personnel to operate and reducing overhead costs.

Quality of tin plating

  • Deposits are consistently brighter, even at high current density.
  • The drawn and wall ironing process produces less dust.
  • Deposits exhibit more consistent thickness, with less dogboning (thicker deposits at edges).
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Figure 1: Tin deposits produced by PSA/ENSA and Ronastan™ at various current densities.

Environment: lower toxicity

  • The Ronastan electrolyte is nontoxic and phenol-free, and the low amount of sludge produced is nonhazardous.
  • MSA is part of nature’s sulfur cycle, and the electrolyte additives are phosphate-free. It is therefore able to biodegrade quickly.
  • MSA is REACH-compliant, creating a safer environment for workers.
  • Chemical oxygen demand is up to 90% lower. Under standard operation, the electrolyte should not require periodic discharge to keep components in balance.

When converting a tin electroplating line, the fluxing process needs to be taken into consideration. Lines may use either integrated fluxing (self-fluxing) or isolated fluxing. The self-fluxing property of PSA/ENSA has been one of its key advantages. Integrated fluxing lines can maintain low chemical costs over a wide range of line speeds and distillate capacity.

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Figure 2: Chemical cost for vertical line with integrated fluxing

Chemical costs for lines with integrated fluxing bottom out at $1.50 per ton. Isolated fluxing can enable even lower chemical costs in lines with sufficient rinse water availability. Line speed and rinse water requirements need to be balanced for optimal cost of operation.

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Figure 3: Chemical cost for vertical line with isolated fluxing and 2 rinse tanks

Dow’s Ronastan MSA-based electrolyte has been around since 1989, during which time we have continued to refine and improve it. Ronastan is compatible with both integrated and isolated fluxing processes and state-of-the-art, high-speed plating lines running at up to 750 m/min. Dow recently introduced StannGuard AO-Flux, an additive that conveys both self-fluxing and antioxidant properties and extends the range of applications to integrated fluxing lines.

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Figure 4: Schematic of integrated fluxing line

The conversion process from PSA/ENSA to Ronastan is simple, requiring no line modifications. For an integrated fluxing line, the fluxing agent is added into the second rinse tank. Process simulation software is useful for modeling the electroplating process, demonstrating the effect of conversion from PSA/ENSA to MSA from both a process control and a financial viewpoint. Inputting the line configuration, dosing rates and materials costs allows engineers to create a model that is specific to that line and optimizes plating quality, efficiency and cost of operation.

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Figure 5: Example screen from process simulation of Integrated fluxing line

Results from actual Ronastan plating lines demonstrate that a “greener” solution that generates less waste is also less expensive, despite using an electrolyte that may cost more per liter than PSA/ENSA when stannous content is not taken into consideration. Conversion costs are minimal, meaning that the savings from lower tin loss and reduced waste disposal overcome upfront costs very quickly.

MSA-based electrolytes for tin electroplating have provided a nontoxic alternative to PSA/ENSA for over 25 years. Electroplating suppliers are converting their lines now because the latest materials combine this benefit with integrated fluxing and compatibility with high line speeds for an efficient, reliable, low-cost process that meets stringent environmental regulations and creates minimal waste.

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