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NOVEMBER 2018 I PCB007 MAGAZINE 81 Optimization was performed in terms of en- hancing TH microdistribution, including for thicker panels, up to 1.6 mm (TH ARs up to 6.4:1), via filling (minimal dimple size, void- free filling), while keeping a low surface cop- per thickness. TH microdistribution is given as throwing power (TP) min and TH corner plat- ing is characterized by TP knee [9] . • TP min = Ave. Cu thickness in the TH center / Ave. Cu surface thickness % • TP knee = Ave. Cu thickness at TH corners / Ave. Cu surface thickness % Tests were completed in an 8.5-liter cell (Fig- ure 3) with 200-liter pilot tanks. Insoluble an- odes were used. They allow for higher applica- ble current densities, easy maintenance, and a uniform copper surface distribution. Each bath was made up, dummy-plated for 2 AH/L, ana- lyzed, adjusted to correct additive levels, and then the test panel was plated. Each test panel went through a pre-clean cycle of a two-min- ute acid cleaner, two-minute rinse, two-minute 10% sulfuric acid before the plating in the Pro- cess A bath. Results and Discussion Through-Hole Plating: Effect of Concentration Levels and CD Influence on Throwing Power Results shown are for a basic electrolyte (VMS) containing 250 g/L CuSO 4 ·5H 2 O, 50 g/L sulfuric acid and 45–50 ppm chloride. An in- crease in brightener resulted in an increase in throw power. The wetter and leveler did not show a clear trend. When increasing current density, the throw power decreased in all cas- es. The tests showed that there was a strong interaction between the brightener and leveler concentrations in the electroplating bath. Ex- amples are shown in Figures 4 and 5, TP min as a function of organic additive concentra- tions and current density (CD.) Figure 1: Any layer build. Figure 3: Plating cell (8.5 liters), knife agitation, and eductor spray. Figure 2: PTHs (0.8-mm panel) and filling vias (20 ASF, 60 minutes). Figure 4: Main effect plot for a 0.20-mm diameter TH in a 0.8-mm panel. Figure 5: Interaction plot for a 0.15-mm diameter TH in a 0.8-mm panel (AR = 5.3).