Principle of formation of PCB board wire impedance interference

A certain wire on a printed circuit board can be regarded as a regular rectangular copper strip. We take a length of 10cm, a width of 1.5mm, and a thickness of 50μm as an example. The impedance can be seen by calculation. .

The wire resistance can be calculated by the formula:

R=ρL/s (Ω)

026Ω。 The L is the wire length (m), s is the wire cross-sectional area (square mm), ρ is the resistivity ρ = 0.2. By calculation, the wire resistance value is about 0. 026 Ω.

The inductance of the wire is 0. 08μH, and the wire has a self-inductance of 0. 8μH / m, then the wire of 10cm long has an inductance of 0. 08μH. Then we can find the inductive reactance exhibited by the copying wire by the following formula:

XL=2πfL

Where π is a constant, f is the frequency (Hz) of the wire passing signal, and L is the self-inductance (H) of the wire per unit length. In this way we can calculate the inductive reactance of the wire at low and high frequencies:

When f=10MHz, XL=6. 28×10×103×0. 08×10-6≈0. 005Ω

When f=30MHz, XL=6. 28×30×106×0. 08×10-6≈16Ω

From the above formula, we can see that the wire resistance is higher than the wire inductance in the low frequency signal transmission, and the wire inductance is much larger than the wire resistance in the high frequency signal.