Definition

Insertion loss measures the reduction in signal power as it travels through a PCB transmission line, expressed in dB per unit length (typically dB/inch). It results from conductor loss (resistance of copper traces) and dielectric loss (energy absorbed by laminate material). Insertion loss increases with frequency, trace length, and narrow trace width. For high-speed signals (>10 Gbps), low-loss materials with lower Df are essential to maintain signal quality over longer trace lengths. Eye diagram closure is a visible effect of excessive insertion loss.