New-Tech Europe | Q3 2026 | Digital Edition

Figure 3: The Si-Fly HD Co-Packaged assembly process, from connector attachment on the package substrate through cable installation and integration of the thermal solution. Credit: Samtec

electrical characteristics required for a 224 Gbps PAM4 channel while reducing some of the losses introduced by conventional PCB routing. Density without excessive crosstalk Higher interconnect density creates another challenge: crosstalk. As differential pairs are placed closer together, electromagnetic coupling between neighbouring channels can increase. This becomes particularly significant when dozens of high-speed differential pairs must operate simultaneously within a small package footprint. Si-Fly HD accommodates 64 differential pairs within a 14 × 14 mm footprint. Despite this density, the measurements presented by Samtec show low levels of interference between neighbouring channels. The white paper reports an ICN FEXT result of 0.36 mV rms , remaining well below the target identified for 224 Gbps PAM4 operation. This is important because increasing I/O density cannot come at the expense of channel isolation. The value of a Co-Packaged architecture depends not only on fitting more connections close to the ASIC, but on maintaining acceptable signal integrity when those connections operate simultaneously. When a few picoseconds matter Perhaps one of the clearest illustrations of the challenge at 224 Gbps is skew. At 224 Gbps PAM4, the unit interval is approximately 9 picoseconds . Once the available timing window becomes this small, differences in propagation delay that might

models based on IEEE 802.3 requirements and validated the results through physical measurements. The measured data showed good correlation with the models for both insertion loss and return loss. According to the paper, the insertion-loss response remained smooth across the relevant frequency range, with relatively low variation. Return-loss performance is equally important in this architecture. With the interconnect located directly on the package, reflections occur physically close to the transmitter or receiver, making control of impedance discontinuities particularly important. The measurements therefore provide more than validation of an individual connector. They demonstrate that moving the interconnect onto the package can preserve the

Figure 4: Differential crosstalk measurements for Si-Fly HD show close correlation between measured and modelled performance, with low interference between neighbouring high-speed channels. Credit: Samtec

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