This work presents an approach of design optimization to reduce crosstalk for high-speed signals with lower BGA pitch less than 0.5mm. As data rates goes up, Crosstalk becomes increasingly problematic as signal frequencies rise and as circuits and transmission lines are packed closer together in modern designs. As known, Crosstalk is a phenomenon where an unwanted transfer of energy occurs between adjacent signal paths in a communication or electronic system. It often manifests as noise or interference, degrading the performance of high-speed circuits and communication systems. Hence this work explores the causes, effects and mitigation techniques for crosstalk in electrical systems, providing comprehensive understanding of this critical issue. To minimize crosstalk for high-speed signals with applications having less BGA pitch, following can be practiced • Offset the signal vias if possible, to avoid Pin to Pin and via-via crosstalk which helps to reduce near end crosstalk by reducing the nearby pin and via coupling • If signal nibbles are to be routed in same layer, route spreading signal fan-out near BGA area using short dog bone traces less than 50mil trace and then re-route on inner layers with optimized via. This greatly helps to reduce via-via crosstalk. • Consider routing the adjacent signals at alternate layers to reduce pin-pin coupling as the physical closeness of signal paths exacerbates both capacitive and inductive coupling. Hence, Route the traces in TOP layer for less than 200mils & then reroute in inner layers using via transition. • Consider routing the signals as co-planar waveguide to reduce more coupling between the signals with ground stitching vias placed at 100mil spacing. Vias design also plays important roles in reducing crosstalk coupling. • Providing racetrack at fan-out and fan-in of via transition reduces the inductive effect of signal and improves the impedance of signal. • Via Pitch plays a critical role in Optimization of printed circuit board for case where Nyquist frequency is greater than 60GHz. Reducing the high speed via to ground via helps to increase cut-off frequency of the signal, thereby improving signal integrity. • Placing the unused pad at high speed via, helps to improve the impedance of signal by reducing the inductance. The layer in which the unused pad is placed, helps to increase the cut-off frequency of signal. This idea demonstrates the practical design methodology to minimize crosstalk with various better design optimizations.
