Issue link: https://iconnect007.uberflip.com/i/1233021
APRIL 2020 I DESIGN007 MAGAZINE 23 Circuit Boards), but by using a very fast rise time of 20 ps (20 GHz), as used in the Zmetrix ST808, traces can be tested down to 20 mm in length, allowing the operator to test actual on-board traces—not just test coupons. This is important as test coupons are normally placed outside the board outline on the panel edge, where the impedance is generally higher than those traces in the center due to an increase in resin and may not accurately represent board trace conditions. Let's look at a couple of typical examples of impedance prediction and measurement. 1. 50-ohm Single-ended Impedance The iCD Stackup Planner was used to mod- el a 50-ohm, single-ended impedance for both microstrip (Layer 1) and stripline (Layer 3) on the part stackup in Figure 4. The substrate used Nouya NY2150 dielectric materials. The data from the iCD Stackup Planner was exported to the Zmetrix Zscan software (.zmx format). The results of the Zmetrix ST600 TDR (75 ps rise time, 7 GHz bandwidth) were then correlated to the iCD Stackup Planner imped- ance (Figure 5). The measurements of the 50- ohm impedance test coupons passed for all signal layers. 2. 100-ohm Differential Impedance The iCD Stackup Planner was used to model a 100-ohm differential impedance for microstrip Layers 1 and 6 on the stackup in Figure 6. Figure 4: 50-ohm microstrip and stripline impedance calculation (iCD Stackup Planner). Figure 5: Pass/fail results for the 50-ohm traces (Zmetrix TDR and Zscan software).