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34 I-CONNECT007 MAGAZINE I JANUARY 2026 PCBs as Electromagnetic Structures At modern data rates, PCB traces can no longer be treated as simple connections. With rise times in the tens of picoseconds and frequencies extend- ing well into the multi-gigahertz range, nearly all interconnects behave as transmission lines. The PCB must be analyzed as a distributed electromag- netic system rather than a lumped circuit. Key SI challenges include: • Impedance discontinuities from vias, pads, connectors, and layer transitions • Reflections and eye-diagram closure caused by poor impedance control • Crosstalk due to tight trace spacing and shared return paths • Dielectric and conductor losses that attenu- ate high-frequency content Simultaneously, PI challenges arise as supply voltages decrease and transient current demands increase. Modern ICs operate at very low volt- ages (often <1 V) but draw large transient currents with extremely fast di/dt. The PCB power delivery network (PDN) must supply these currents without allowing voltage droop or noise beyond millivolt- level tolerances. The PDN—comprising VRMs, power and ground planes, vias, interconnects, and bulk, ceramic, and on-die decoupling capacitors—must maintain extremely low impedance across a wide frequency spectrum. Failure to do so results in voltage droop, ground bounce, timing margin loss, intermittent logic errors, and EMI issues. Failures in PDN design often manifest into problems that are notoriously difficult to debug. These issues ensure that SI/ PI remains the most challenging problem in PCB design and will likely continue to be so for the fore- seeable future. There are no technological trends that ease these underlying physics: • Edge rates continue to increase even as clock frequencies plateau • Voltage rails continue to drop below one volt • Interconnect density increases due to finer- pitch packages and higher integration Emerging standards such as PCIe Gen 6/7, CXL, DDR5/DDR6, and 112G+ SerDes operate with single-digit millivolt noise margins. In these systems, the PCB is often the limiting factor in achieving target performance and reliability. While SI/PI remains foundational, the most diffi- cult challenge in future PCB design broadens into system-level convergence: the need to design boards that behave predictably across multiple interacting domains. Heterogeneous Integration and Advanced Packaging As Moore's Law slows, performance gains are increasingly being driven by advanced packaging approaches such as chiplets and multi-die architec- tures, 2.5D interposers and advanced substrates, fan-out wafer-level packaging (FOWLP), and the embedding of die and passive components. These technologies blur the boundary between IC package and PCB. Designers must manage ultra- fine pitch escapes, hybrid interconnect models, and new reliability risks at package–board interfaces. The PCB becomes part of a larger interconnect ecosystem, rather than a standalone entity. Thermal–Electrical–Mechanical Coupling Rising power densities make thermal behavior inseparable from electrical performance. Tempera- ture affects copper resistance, dielectric properties, timing skew, and long-term reliability. At the same time, thermal cycling induces mechanical stress that can cause via fatigue, solder joint cracking, and delamination. Future PCB challenges require co-optimization, not sequential analysis, of SI, PI, heat spreading and dissi- pation, and mechanical stress and material aging. Materials and Stackup as Design Variables Traditional FR-4 materials are increasingly insuffi- cient for high-speed and RF designs due to dielec- tric loss and variability. Low-loss laminates improve performance but introduce higher costs and tighter fabrication constraints. Stackup design has become an electrical design task in its own right, directly affecting controlled impedance accuracy, return path continuity, cross- talk behavior, and plane capacitance and PDN impedance. Poor stackup decisions can negate even the most careful routing strategies.