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JULY 2022 I PCB007 MAGAZINE 101 e degree of difficulty for plating through- holes depends on board thickness as well as hole diameter. For example, given a choice of two holes, both 10:1 in aspect ratio, one pre- fers a design with a 100-mil thick panel and a via with a 10-mil diameter, vs. a 200-mil thick panel with 20-mil diameter holes. Both designs are of the same aspect ratio. Figure 2 underscores the difficulty in main- taining throwing power as the aspect ratio and board thickness increase. It illustrates that the IR drop (or the electrical resistance through the via) increases as a squared factor, while via diameter only affects the resistance (or throw- ing power) in a linear fashion. In my next column, I will continue to explore the electrodeposition process and the science behind the technology. PCB007 Michael Carano is VP of quality at Averatek. To read past columns, click here. of the deposit. Current density across the plat- ing surface depends on the rectifier capacity, related anode and cathode sizes and spacing, shielding, cell efficiency, and solution conduc- tivity. Current density distribution across the plating surface depends on some of the before- mentioned parameters and, in pattern plating, also on the circuit pattern. Current density in the through-hole depends on the following additional variables: • rough-hole diameter and aspect ratio • Replenishment efficiency (in the holes) of plating solution (agitation) • rowing power of the bath, which is largely determined by the acid/copper ratio, the organic plating additives, and the level of impurities (leachants) that inter- fere with the organic plating additives. In Figure 1, throwing power is defined for purposes of this and subsequent columns. e actual mechanics of the electrodeposition pro- cess and the influence of process parameters will be discussed in future columns. Figure 2: Left hand column represents board thickness, and right-hand column represents hole diameter.