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88 PCB007 MAGAZINE I JULY 2024 One of the major advantages of HDI, and especially ultra HDI, is the miniature features of the process. Since the microvias and lands are so small, they can be swung around at var- ious angles between the BGA lands, as seen in Figure 2. e angles and distances (Table 1: E, G) will depend on the BGA pitch (Table 1: A) and where the microvia is placed relative to the BGA SMT land (Figure 3). HDI Stackups Chapter 3 of the HDI Handbook 1 shows multiple stackups that pro- vide for distributed capacitance and X-Y routing layer pairs (Figure 4). e finer geometries of UHDI and HDI require thinner dielec- trics to maintain their imped- ances, which can also lower cross- talk and improve signal integrity and PDN impedances. Boulevard Routings e biggest gains from these HDI struc- tures are the additional routings available on inner layers (Figure 5). By concentrating the Table 1 (left): Swing microvias based on BGA pitch and SMT land sizes Figure 2 (right): Swing microvias' geometries. Figure 3: (Near)-via-in-pad techniques can have multiple angles depending on the BGA pitch and land size, the microvia's land size, and where the microvia is placed. These can be a dog-bone, an inset uvia, partially in the microvia and fully in the microvia (but not in the center).