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58 DESIGN007 MAGAZINE I OCTOBER 2024 remove the impurities. e filtering and chemical oxida- tion process reduces the bath to almost purely sulfuric acid and copper sulfate, so the brighteners and levelers must be added back to the solution. Preparing for the Next Phase of Manufacturing Once the plating is com- plete, our boards are freshly coated with copper, dripping sulfuric acid, and copper sul- fate. Next, we rinse them off and put them directly into an electrolytic tin plating pro- cess that is identical to the copper plating process. e result is a layer of tin atop the copper. at tin becomes our etch resist. Aer we add it to the board, we remove the photoresist and expose all the unwanted copper below. e tin pro- tects the copper we want during etching. Now that we have protection over the copper traces, pads, and vias, we are ready for the strip/etch/ strip (SES) process. is will be the subject of my next article. If you are eager to learn more now, listen to episode 9 of On the Line with… where we dis- cuss SES. DESIGN007 Matt Stevenson is vice president and general manager of ASC Sunstone Circuits. To read past columns, click here. NEW: Read Matt's book, The Printed Circuit Designer's Guide to Designing for Reality or listen to his podcast here. flow. Levelers help fill in any small imperfec- tions that may have existed at the start of the plating process. ey do an excellent job of fill- ing in gaps and creating a uniform, level cop- per surface. During the plating process, our components are consumed or broken down at varying rates, jeopardizing our chemical ratios. To ensure that the chemical processes operate at the cor- rect concentrations and ratios, we use analyti- cal chemical processes across all our chemical baths to confirm the concentrations of all the components. Technicians take samples and measure sul- furic acid, copper, chloride, brightener, and leveler content. ey will make additions or dilutions to keep the bath within the optimal operating window. e brighteners and level- ers break down over time and create organic impurities. When they reach the tolerance threshold, the bath will be taken offline and cleaned with a carbon filtering process to