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AUGUST 2021 I PCB007 MAGAZINE 95 bridging are shown in Table 1. e long DC step includes plating at 15 ASF for 13 seconds. e pulse train consists of 50 ms for forward and reverse time with forward-to-reverse cur- rent ratio of 1:3 at 15 ASF. is pulse train is executed for a total time of 1 second. Various factors can affect bridging, which is a critical step in the through-hole fill process and are listed below. Effect of solution flow rate in bridging Plating experiments were carried out using the waveform listed in Table 1 as a function of solution flow-rate. e plating tank is equipped with impingement flow across the panel sur- face. e solution flow-rate was varied from 8 L/minute to 24 L/minute during the bridging step and the cross-section results are shown in Figure 3. Good bridging is seen between 12– 24 L/minute. Very low or high flow resulted in loss of bridging. Function of phase shift degree in bridging Plating was carried out using the waveform listed in Table 1 as a function of phase shi de- gree. e phase shi degree was varied from 25 to 180. As the phase shi was varied from 180 to 50 degrees, the bridging location shied away from the center in the 150 and 250 µm di- ameter through-holes (Figure 4). No bridging is seen in the 250 µm diameter through-holes at lower phase shi degree. Table 1: Phase shift pulse plating parameters for bridging the through-holes. Figure 3: Bridging in 150 and 250 µm diameter through-holes as a function of solution flow rate.