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OCTOBER 2024 I DESIGN007 MAGAZINE 57 some incredibly tight tolerances and many opportunities for variation. Several elements create variations in the copper tanks. Variations in the Copper Tanks First, there is the makeup of the chemistry bath itself. ere are at least five chemical com- ponents that make up a copper bath, and it's imperative to have them in the correct ratio for the intended output of the plating cell. Depending on the setup of the chemical ratio, the bath can perform differently: higher throw = slower plating times, lower throw = faster plating times, high current density plating, low current density plating, etc. Copper plating is not simply about the cop- per concentration and the sulfuric acid (elec- trolyte) concentration. We need to consider other components in the bath, including pro- prietary levelers and brighteners. Brighten- ers, as their name sounds, brighten the copper deposit. e copper from electroless and foil is matte and pinkish. Once it's plated, the result is the shiny copper deposit we all expect—one with a grain structure that optimizes current the panel into a tank of sulfuric acid (~10%). is concentration is like the plating bath and helps eliminate dilution due to the drag-out of water coming into the copper bath. Adhering Copper to the Board e panels go into the copper bath using a conductive flight bar to hold them. e flight bar is screwed onto the copper cathode bars in the plating cell for a tight electrical con- nection. e copper anodes on the outer edge receive a negative charge. When we turn on the juice, the copper anodes begin to dissolve in the solution, and the positive copper ions are attracted to the panel's surface where they undergo a reduction-oxidation (redox) reac- tion, reducing it to copper metal and giving off hydrogen gas. e copper metal adheres to the board where the electricity initiates the redox reaction. Elements of this process are visible to the human eye. You can see the color of the copper change on the panel's surface and the hydrogen in the form of bubbles created by the chemi- cal reaction. We blow air over both sides of the panels to sweep away the hydrogen. is helps avoid leaving microbubbles on the surfaces we are trying to plate. e goal is to get copper into the holes. We refer to this as "throw." In a perfect world, we want to plate as much copper at the center of the hole as at the edge or knee of the hole, or even more. en there's reality. It is a lot easier for a free-floating copper ion to slam into the horizontal surface of the board than to dive into a via-hole. To encour- age the ions to go where we want them, we must sway the panels and encourage solution in and out of the holes, sweeping them back and forth in the solution. is creates more surface tension to push the solution into and out of the holes. If our only concern during plating was whether the panels were swaying (agitating), it would be a straightforward process. However, our work happens on a very small scale with " Copper plating is not simply about the copper concentration and the sulfuric acid (electrolyte) concentration. "