Sustainable and cost-effective tin electroplating

Carol Levey

Marketing Manager, Steel Mills, Interconnect Technologies

October 14, 2015


Tin-plating of steel has been a foundational technology for modern food packaging, and turnkey electroplating technologies have been established over the last 70 years to serve the world’s demand for safe food in cans. Now, with the cost of tin (Sn) metal having risen to 20-30 times higher than it was in the 1990s, and with greater concern over environmental release of toxic byproducts, legacy Sn electroplating lines are reconsidering switching to the more efficient and benign methane sulfonic acid (MSA) chemistry branded as Ronastan™. 

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In typical modern tin-plating processes, continuous strips of steel move rapidly (500 m/min) through the following sequential process steps: cleaning, acid activation, electroplating Sn, fluxing, reflow melting to produce a mirror-bright finish and passivation to protect against oxidation. Some sort of fluxing agent is needed to ensure that the tin-hydroxide species left on the surface after tin-plating are soluble after high-temperature reflow melting; failure to do this results in a dull surface. One of the reasons phenol sulfonic acid (PSA/ENSA) legacy chemistries currently represent the largest installed base globally is the ability for “self-fluxing” to occur with dilute electroplating chemistry. 

Ronastan chemistry was initially developed in the 1990s, and the MSA-based technology has been enhanced by Dow over many years to improve its efficiency. Current Ronastan chemistries produce bright conformal Sn coatings at high speed and with minimal sludge formation for over 7 million tons of tin-plate, representing approximately one-third of the world’s current capacity.

However, most of these lines use a Ronastan solution that requires separate fluxing after final rinse. Now, legacy tin-plate lines that are vertically oriented and use PSA/ENSA can be easily converted to use Ronastan chemistries through the use of Stannguard™ AO-FLUX self-fluxing additive. Self-fluxing provides improved electrolyte retention, as no rinse cells need be sacrificed to form a fluxing tank, but instead can all be used for rinsing, which reduces the cost of operation, and eliminates the need for any mechanical modifications to the line in a conversion.

Originally developed as a self-fluxing agent for an alternative sulfuric acid electrolyte base, Stannguard AO-FLUX was also found to confer self-fluxing properties to MSA-based electrolytes including the following properties:

  • Formation of highly soluble stannous compounds,
  • Prevents over-etching of the steel surface,
  • Stability under extended electrolysis with no insoluble byproduct formation, and
  • Antioxidant capabilities with a redox potential in the region of the stannous-stannic couple.

We have a standard process for assisting customers to convert to Ronastan chemistry, starting from a line assessment of costs and capabilities, and including turnkey conversion with staff training and ongoing support. Typically, a tin-plate line only needs to be shut down for one week to be able to move to a new normal of reduced direct costs and improved yield. Our team at Dow Electronic Solutions is proud to be fostering a quiet revolution in tin-plating with a more sustainable and cost-effective chemistry solution.

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