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APRIL 2019 I PCB007 MAGAZINE 91 blind structure with simple panel plating sys- tems under standard, everyday conditions. Figure 3 shows plating results with respect to the slot length and slot depth. Note that for these tests, NextGIn used plating processes at standard parameters and chemistry types. The method of plating was electroless copper followed by a pan - el plate to the required copper thickness in the slot targeting a thickness of 25 µm. The data shows that there will be a limit in terms of the length/width ratio to the depth of the slot in the order of 2 mm deep with a slot length of a minimum of 1 mm and a slot width of 0.5 mm. Longer slots will extend the plating capability of the slot (Figure 4). Note that for application specific process reasons, this work has only addressed copper plating; the plating of the etch-resistant tin is not currently a focus. This choice was made because the applications chosen for this tech- nique at present will fill the slots before finish- ing the external layers. Plating Deep Blind Structures Next is plating deep blind structures. This process accesses the internal layers with- out breaking through the opposite side of the board, which also avoids multiple lamination cycles. This enables new applications and complex structures in design without the man- ufacturing complexity of multiple laminations. In the designs, NextGIn sees this process as contributing to lower board fabrication costs and higher data rates thanks to better-tuned impedance in the vertical connections (imped- ance will be discussed in detail later in this series). Figure 5 shows an example of the density to which components can be placed on two sides of the circuit without interference between the Figure 3: Plating thickness as a function of slot depth and length. Figure 4: Example of a plated slot with a slot width of 0.3 mm. Figure 5: Practical examples of plating deep blind structures with VeCS.