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38 I-CONNECT007 MAGAZINE I OCTOBER 2026 via, the loop area increases and so does inductance. Inductance slows the flow of energy, and in digital logic, timing is noth- ing more than the speed at which energy can be delivered to and from charge and discharge nodes. When inductance increases, several timing- critical effects appear, including delayed edge transitions, propagation delay, and mode conversion. Signals do not propagate along traces; they propagate through EM fields, and if the return current must detour around a split or void, the loop area increases, then inductance increases, causing the elec- tromagnetic wave to slow down. The conse- quences are severe: • Channel-to-channel skew • Reflections and jitter • Mode conversion in differential pairs • Increased common-mode radiation • In modern buses running at tens of gigabits, even small RPDs create measurable skew and channel-to- channel noise. Designing for Low Inductance Across both SI and PI, the same principles apply: • Separate signal traces to reduce mutual inductance and crosstalk. • Couple signals tightly to reference planes to minimize loop area. • Maintain continuous return paths— no splits, voids, or detours. • Use low-inductance capacitor mounting (via-in-pad or dual-via). • Place decoupling capacitors on the same side as the BGA to reduce loop area. • Tightly couple power and ground planes to create high-frequency capacitance. These practices are not optional in modern designs. They are foundational. Inductance is the common thread linking SI and PI. It shapes crosstalk, return-path behavior, PDN impedance, capacitor effectiveness, and electro- magnetic emissions. By treating inductance as a first-order design parameter (not an afterthought), designers can build boards that are quieter, faster, more stable, and far more predictable. The curse of the high-speed board is not complexity; it is ignoring the physics that govern it. Master inductance, and you master both SI and PI. B E YO N D D ES I G N Figure 2: A capacitor has series capacitance, resistance, and inductance.