Issue link: https://iconnect007.uberflip.com/i/1383248
54 PCB007 MAGAZINE I JUNE 2021 Although a detailed analysis is beyond the scope of this paper, the impact of eliminating a lossy PTH stub is clearly seen in the compari- son of TRL2 and TRL 3 in Figure 11. Although such a stub could be eliminated by backdrill- ing, the use of TLPS vias to make this inter- connection eliminates the need for this process and preserves routing area in layers 3-8. Nets TRL4, TRL5 and TRL 6 can be seen in cross- section in Figure 12 and the relative signal in- tegrity performance is shown in Table 2. Even when the Z-axis interconnect extends almost through the entire layer count of the coupon, the high frequency performance of the net is improved over the PTH. Finally, the two sets of current-carrying capacity test nets showed no degradation with current levels of 4.5 amps— well in excess of the design margin—for both Figure 11: TLPS paste vias provide high frequency bandwidth capability without the need to backdrill. Figure 12: Comparison of layer 2 to layer 8 interconnection in a 10-layer coupon using: stacked TLPS paste vias, PTH and staggered TLPS paste vias (note: not all TLPS vias are centered in cross-section plane).