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January 2017 • The PCB Magazine 53 ELECTROPLATED COPPER FILLING OF THROUGH-HOLES: INFLUENCE ON HOLE GEOMETRY the mechanism of differential current densities previously discussed. Effects of Hole Size and Substrate Thickness on Through-Hole Fill Results The data of surface copper as a function of through-hole diameter and panel thickness is presented in Table 3. The main effects plots are presented in Figure 10. The total plated surface copper is the sum of the plating thickness from both the bridge and the via fill processes. It is readily observed that hole diameter greatly affects the amount of total plated surface copper that can be expected for the through- hole copper filling process. As the diameter of the through-hole increases, the amount of surface copper that can be expected as a con - sequence of successfully meeting through-hole filling requirements, increases. This is because larger diameter holes require longer periods of time for the copper bridging process to extend across the diameter of the hole to close and form the vias and the longer periods of time to fully fill the resulting larger diameter vias. This can be substantial in the case of extremely wide holes. It is also clear that panel thickness greatly af- fects the amount of total surface copper for sim- Table 3. Total surface copper vs. hole and panel dimensions. Figure 10: Main effects plot for surface copper.