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68 PCB007 MAGAZINE I MARCH 2025 attraction, forms a layer on the copper surface where it enters—together with CI—in the one- electron transfers: Cu ++ →Cu + →Cu 0 . Brightener "masks" preferential growth sites on the planes. Even with the brightener, the growth of the plated copper shows little directional prefer- ence. e grain structure of the copper is semi- amorphous microcrystalline. is is why a car- rier-type molecule is needed. Carrier is class of organic materials is a high molecular weight compound. ese materi- als, such as polyvinyl alcohols and polyeth- ylene glycols (PEGs), are designed to exert a strong plating suppression effect on the high current density areas of the cathode. ese carriers aid in preventing overplating in the high current density areas. ese high molec- ular weight polymers form a diffusion barrier along the cathode surface. The Leveling Agents Typical leveling agents indicated here are based on polyamine compounds. ese are very low molecular weight. Leveling agents exert an influence over non-uniform areas within the via and on the surface. Working in synergistic fashion with the carrier, the level- ing agent carries a positive charge and thus is able to migrate to the most negatively charged areas of the cathode—the highest current den- sity areas. ese higher current density areas, if unmitigated, will see more current than lower current density areas. ese higher current areas are the edges of the circuit board, protru- sions, and surfaces of the vias versus the holes. e leveling agent selectively slows down the deposition of copper and helps to shi some of the plating away from the high current areas to the lower current density areas. So many people I have worked with over the years considered plating chemistr y as black magic or foo-foo dust. e workings of plating chemistr y are not magic, but based on science. PCB007 Michael Carano brings over 40 years of electronics industry experience with special expertise in manufac- turing, performance chem- icals, metals, semiconduc- tors, medical devices, and advanced packaging. To read past columns, click here.