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PCB & Signal Integrity

microstrip Z₀ · trace current · reflection · decoupling

Microstrip / Stripline Impedance

Hammerstad microstrip & symmetric stripline Z₀.

Critical Length & Reflection

Treat as transmission line if t_r < 2·t_prop; Γ=(Z_L−Z₀)/(Z_L+Z₀).

IPC-2221 Trace Current

I = k·ΔT^0.44·A^0.725 (A in mils²).

Decoupling & Capacitor SRF

C=I·Δt/ΔV; SRF=1/2π√(LC).
Formula reference

Microstrip Z₀=87/√(εr+1.41)·ln(5.98h/(0.8w+t)); stripline Z₀=60/√εr·ln(4b/(0.67π(0.8w+t))).

Prop delay ≈3.33√εr ns/m; critical length where t_r=2·t_prop. Γ=(Z_L−Z₀)/(Z_L+Z₀).

IPC-2221 I=kΔT^0.44A^0.725; R=ρL/A (ρ_Cu=1.72e-8); decoupling C=IΔt/ΔV; SRF=1/2π√(LC).