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52 I-CONNECT007 MAGAZINE I JANUARY 2026 solution of micro-etch without copper in the bath, it won't etch. Adding copper starts the chemical reaction. So, etch rates can vary day to day, even shift to shift, depending on how much of the chem- icals are used. There are many variables in this process: the chemical behavior, aggressiveness in etch, and changes in temperature or humidity on the production floor. The etch rate coupon helps manufacturers ensure they are removing copper within the appropriate window. Painting a Picture of the Plating Floor The size and layout of plating operations vary by manufacturer. Our plating floor has six tanks that range from 200 to 500 gallons of blue copper sul- fate plating solution. The tanks contain copper bars (cathodes) running down the middle of the tank where the manufacturing panels connect, and bas- kets filled with copper balls (anodes) on the out- side of the cell. The anodes and cathodes connect to a rectifier, the electricity source that creates the electrolytic plating cell. In the last step before the copper bath, we dip the panel into a tank of 10% sulfuric acid solution. This concentration resembles the plating bath and helps eliminate dilution due to drag-in of water coming into the copper bath. Adhering Copper to the Board The panels go into the copper bath using a con- ductive flight bar, which is screwed onto the cop- per cathode bars in the plating cell for a tight elec- trical connection. The copper anode on the outer edge receives a negative charge. When we turn on the juice, the copper anodes slowly dissolve into the solution, and the positive copper ions are drawn to the panel's surface, where they undergo a reduction-oxidation (redox) reaction, reducing it to copper metal and giving off hydrogen gas. The copper metal adheres to the board where the elec- tricity initiates the redox reaction. You can see the copper's color change on the surface of the panel, and the hydrogen gas bubbles up in the solution. We blow air across both sides of the panels to sweep away the hydrogen gas during plating. This helps avoid leaving micro bubbles on the surfaces we are trying to plate. The goal is to get plated copper all the way into the holes, which we refer to as throw. In a perfect world, we want to plate as much copper at the center of the hole as at the edge or even more. Then there's reality. It's easier for a free-float- ing copper ion to slam into the board's horizontal surface than dive into a via hole. For the ions to go where we want them to, we have to sway (agitate) the panels to encourage solution in and out of the holes, sweeping them back and forth. This creates less surface tension to push the solution into and out of the holes. If our only concern during plating were sway- ing (agitating) panels, it would be a straightforward process; however, our work occurs on a very small scale with incredibly tight tolerances and numer- ous opportunities for variation. There are several elements creating variation in the copper tanks. Variations in the Copper Tanks First is the composition of the chemical bath. There C O N N ECT T H E D OT S