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PCB factory: the formation principle of circuit board wire impedance interference
2021-08-29
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Author:Aure

PCB factory: the formation principle of circuit board wire impedance interference
 
At present, in the copy board manufacturing of printed circuit boards in PCB factories, the wires are mostly copper wires. The physical properties of copper metal itself determine that there must be a certain impedance in the process of conducting electricity. The inductance components in the wires will affect the voltage signal. Transmission, the resistance component will affect the transmission of the current signal, and the influence of the inductance in the high-frequency line is particularly prominent.

A certain piece of wire on the printed circuit board can be regarded as a very regular rectangular copper strip. Let's take a piece of wire 10cm long, 1.5mm wide, and 50μm thick as an example. The impedance can be seen through calculation.

The wire resistance can be calculated by the formula:

R=ρL/s(Ω)

Where L is the length of the wire (m), s is the cross-sectional area of the wire (square millimeters), and ρ is the resistivity ρ=0.02. The resistance value of the wire is about 0.026Ω through calculation.


PCB factory: the formation principle of circuit board wire impedance interference

When a piece of wire far away from other conductors is much longer than its width, the self-inductance of the wire is 0.8μH/m, then a 10cm-long wire has an inductance of 0.08μH. Then the PCB factory can calculate the inductive reactance presented by the copy board wire from the following formula:

XL=2πfL

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

When f=10KHz, 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 calculation, we can see that the wire resistance is greater than the wire inductance in the low-frequency signal transmission, and the wire inductance is much greater than the wire resistance in the high-frequency signal.

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