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88 PCB007 MAGAZINE I NOVEMBER 2018 proper conditions for an accelerated filling pro- cess and a suppressed deposit growth onto the substrate surface. The most common thicknesses of the plat- ed boards vary from 60–200 μm and the TH di- ameters are 45–100 microns. The holes are me- chanically or laser drilled, resulting in different hole shapes with different requirements for the filling process. Laser-drilled through-via-holes usually have an X shape since a laser beam is applied from both sides of the substrate. This makes filling easier because the closure of the hole in the middle is easily achieved. In this study, laser-drilled X-through-via- holes in boards up to 0.150 mm and diameter at the hole opening of 85−90 μm were used. Filling capability in terms of dimple size, void formation within the filled hole, and metal dis- tribution on the cathode surface are used as measures to describe the capabilities and effec- tiveness of the technology. Tests were run to determine the conditions for the best plating process performance. A high- copper, low sulfuric acid, low chloride concen- tration electrolyte was the most favorable for hole filling. Voids during X-plating occur easier for smaller TH diameter and higher board thick- ness. The shape and the drilling quality signifi- cantly affect the void occurrence as well. In ad- dition, depending on designs, different pitches on one board increase the difficulty to achieve an acceptable plating uniformity. Using eductor nozzles, fluid impingement, "knife" cathode movement, low CDs and cur- rent, and/or flow ramping resulted in a uni- form plating and reduction or complete elimi- nation of the voids within the holes. Examples of void-free performance are shown in Figure 18 (dimple 0 or <5 μm). Figure 19 shows plating results for a sub- strate thickness = 80 μm, diameter = 60 μm, surface thickness = 18−19 μm, and dimple <10 μm with no voids. For pattern plate, electroplating uniformity becomes critical. While panel uniformity can be controlled by mechanical parameters like solution flow, usage of insoluble anodes, etc., in pattern plating, the uniformity is mainly de- termined by usage of proper organic additives that have a significant influence on the surface current distribution. Figure 20 shows pattern TH filling in the innovative copper bath (VCP), 100-μm substrate, through-via-hole diameter of 88 μm at the entrance and51 μm at the hole center, dimple <2 μm, no voids, and surface copper thickness 20−21 μm with uniform and mirror bright surface appearance. Figure 18: TH fill, thickness 158 μm, diameter at the open- ing 86−90 μm, middle 52 μm. Figure 20: Pattern X-via fill, vertical plating application, 15 ASF, 68 minutes, flow rate = 1 bar/23 min. + 0.2 bar/45 min. Figure 19: TH fill (30 ASF for 40 minutes).