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74 PCB007 MAGAZINE I SEPTEMBER 2022 One can easily apply these two entities to develop a model for the electroplating pro- cess. Primary current distribution is deter- mined by voltage drop inside the cell and elec- trode shape and position. Basically, this is gov- erned by the electrical field within the cell itself. Fortunately for the electrodeposition pro- cess, other factors come into play. If only pri- mary current distribution were present, rela- tively uniform plating distribution and good throwing power in high aspect ratio through- holes would be challenging if not nearly unat- tainable. Now, secondary current distribu- tion is influenced by ohmic resistance in the plating cell along with the kinetics of the electrodes. More specifically, organic addition agents and other additives act as high current den- sity inhibitors—suppressing plating in the high current density areas of the board. is allows for improved micro throwing power in the lower current density areas, i.e., areas of higher ohmic resistance. is can be better explained below in Figure 1. Again, if the cell resistance is low, then pri- mary current distribution would dominate. In other words, portions of the part or PC board closest to the anode would receive the most current. us there would be overall poor dis- tribution of plating thickness across the part and in the through-holes (Figure 2). Figure 1: Key factors influencing the plating distribution. Figure 2: Primary current distribution. Low resis- tance in the cell favors thicker deposits in those areas considered as higher current density areas.