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article influence of via stub length and antipad size on the insertion loss profile continues Figure 4: Stackup of the test vehicle. Figure 5: Design features. ers was identical on L2, L4, L5 and L7, but they were modified between 50 mil and 90 mil in diameter for the various coupons. The primary drill (plated through-hole) was backdrilled from the bottom side of the test vehicle to different depths, resulting in nominal stub lengths between around 100 mil down 46 The PCB Design Magazine • January 2014 to practically no stub at all (Figure 5). Some of these stub lengths can be seen in Figure 6. An overview of the test panel with the various backdrill and insertion loss coupons is given in Figure 7 and an example of one of the coupons populated with the flange mount connectors is shown in Figure 8.