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52 I-CONNECT007 MAGAZINE I MARCH 2026 Controlling the copper concentration is essential for a stable operation. This article presents an overview of an ion exchange process that has been fully developed through testing and will soon be made available to the PCB industry as a method for copper control in cupric chloride etching. Testing has established that a copper-phillic medium is a viable alterna- tive to the predominant solvent extraction method used for copper control in cupric etch solutions, also known as liquid-liquid extraction (LLE) sys- tems. Though well-maintained LLE systems are effective, the risks of using a highly flammable sol- vent in a PCB environment are obvious. Cost, foot- print, potential cross-contamination of the etching process, and end-of-life care considerations are significant motivations for doing this differently. Technology and Process Ion exchange is a separation process in which a solid adsorbent captures target ions from solution and releases ions of the same charge to maintain electroneutrality. Ion-exchange resins are com- monly used for metal recovery from waste streams. For cupric etchant treatment, the resin adsorbs copper ions and releases protons into solution. Once saturated, the resin is regenerated using sulfuric acid electrolyte, which desorbs copper and restores the resin to its protonated form. This approach eliminates organic solvents and replaces them with a non-hazardous solid material that is easier to handle and dispose of. To be an equal or better alternative to an LLE system, the ion-exchange resin must be suited to a highly corrosive, acidic environment whilst hav- ing the ability to control the copper concentration within the working parameters. The removal of copper should have a minimal impact on the con- centration of chloride concentration. In short, the removal of copper, or adsorption from the working solution, needs to be evaluated for the ability to be regenerated, or desorbed from the resin. (Air purg- ing is an additional step to remove the stripping solution prior to reengagement for copper control after the regeneration cycle. It is still being evalu- ated for upscaling to achieve a production variant of the tool.) Experiments and Testing As a feasibility evaluation, laboratory-scale adsorp- tion and desorption experiments were conducted. A vertical column with an internal volume of ap- proximately 1.20 L was packed with 0.906 L of Figure 1: Small-scale testing to evaluate initial feasibility.