PCB Fabrication

The formation of the PCB lead impedance interference principle

by:A-TECH      2020-05-30
Why PCB wire can form impedance interference? R =ρL / s ( Ω) Type of L for the wire length ( M. ) S for the conductor cross-sectional area ( Square millimeters) Rho for resistivity rho = 0. 02. Calculated the conductor resistance is about 0. 026Ω。 When a away from other conductor wire, its length is greater than the width, the self inductance of the wire is 0. Eight mu H/m, 10 cm long wire is 0. 08 mu H inductance. Then we can calculate the copy with the formulas below plate conductor is presented by the impedance: XL = 2 PI PI for constant fL type, for wire through the signal frequency (f Hz) And for the self inductance per unit length of wires (L H) 。 So we can respectively calculate the wire under the low frequency and high frequency impedance: when f = 10 KHZ, XL = 6. 28×10×103×0. 08×10- 6≈0. 005Ω; When f = 30 MHZ, XL = 6. 28×30×106×0. 08×10- June 16 Ω material through the above formula, we can calculate the, in the low frequency signal transmission wire resistance is greater than the line impedance, and in the high frequency signal conductor inductance is far greater than the wire resistance. Because in the manufacture of PCB copy board, the wire is generally for copper wire, copper and the physical properties of metal determines its certain impedance, there must be in the process of conducting wire, inductance components affect the voltage signal transmission, the resistance components will affect the current signal transmission, the influence of high frequency circuit inductance is particularly prominent. On the printed circuit board for a wire can be regarded as very regular rectangular copper bar, we take a long 10 cm wide, 1. 5 mm, thickness of 50 microns wires, for example, can be seen by calculating the size of the impedance.
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