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56 DESIGN007 MAGAZINE I AUGUST 2021 the PCB [1] . Secondly, the dangling stub in a through-hole via's layer transition causes deg- radation to the signal transmission [2] due to the inverse proportional relationship between the quarter wave resonance frequency and the via stub length [3] . is article outlines our two-stage study of the impact of through-hole vias, stag- gered microvias, and stacked microvias on multi-gigabit transmission. In the first stage, the three-dimensional models of these via structures were constructed, followed by the extraction of the s-parameter using Keysight EMPro [4] . In the second stage, the s-param- eter files of these via structures are imported to Keysight ADS [5] to analyse the time domain reflectometry (TDR), differential insertion loss (Sdd21), and eye diagram. e analysis and results are explained in the following sec- tion of this article. Analysis and Results Five transmission line (TL) models were constructed with six-layer PCB stack-up listed in Table 1. Each 1-ounce copper layer is insu- lated by low-loss dielectric material. For TL model A (Figure 2a), a 6-inch differ- ential pair with 100-ohm impedance (i.e., trace width 6 mils, spacing of 4.5 mils) on layer 1 is transitioned to a 6-inch pair on layer 3 using a through-hole via. e through-hole via has a drill diameter of 8 mils, pad diameter of 2 mils, a clearance of 28 mils, and a center-to-center separation of 27 mils. is via also comprises a 60-mil dangling stub between layer 3 and 6, highlighted in pink. Model B (Figure 2b) is much like model A, except the via is replaced by a stacked micro- via. is microvia has a drill diameter of 6 mils, pad diameter of 12 mils, clearance of 22 mils, and a center-to-center separation of 20 mils. TL model C (Figure 2c) is similar to model B, except the stacked microvia is replaced by a staggered microvia. is microvia has a drill diameter of 6 mils, pad diameter 12 mils, clear- ance of 22 mils, and center-to-center separa- tion of 20 mils. e short bar connecting the two via barrels has 6-mil width and 10-mil length, highlighted in red. Meanwhile, the TL model D resembles model C, except the short bar linking the two Table 1: A six-layer stack-up. Figure 2a: Cross-sectional view of through-hole via. Figure 2b: Cross-sectional view of stacked microvia.