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96 PCB007 MAGAZINE I AUGUST 2021 Function of current density in bridging Plating experiments were carried out at 10, 15, 20 and 25 ASF to see the impact on bridge formation (Figure 5). Plating at 15 and 20 ASF gave good bridging in the 150 and 200 µm di- ameter through-holes. Plating at the lower cur- rent density of 10 ASF showed no bridging in the through-holes while plating at the higher current density of 25 ASF showed pinching at different points leading to void formation. Filling Copper in Mechanically Drilled Through-holes e through-hole fill process of bridging and filling the through-holes was applied to a wide range of panel thicknesses and hole diameters. Mechanically drilled panels with electroless seed layer were used for evaluation. 250 µm thick core with 150 and 200 µm diameter through-holes Mechanically drilled panels 250 µm thick by 150 and 200µm diameter were used for evalu- ation. For 150 µm diameter through-holes, the plating was carried out for a total time of 182 minutes, while the bridging was carried out for 38 minutes and fill was done for 144 min- utes. e bridging was performed for 9 µm and fill was carried out for 34 µm for a total surface copper thickness of 43 µm. e 200 µm diame- ter through-holes were filled for a total surface Figure 4: Bridging in 150 and 250 µm diameter through-holes as a function of phase shift degree. Figure 5: Bridging in 150 and 250 µm diameter through-holes as a function of current density.