The characteristic impedance value of the surface microstrip line of the impedance circuit board is relatively high and is widely used in practice. Its outer layer is the signal line surface for impedance control, and it is separated from the adjacent reference surface with an insulating material.
The calculation formula of characteristic impedance is: Z0=87/SQRT(εr+1.41)×ln[(5.98h)/(0.8w+t)]:
Z0: characteristic impedance of printed wire
εr: the dielectric constant of the insulating material
h: The thickness of the medium between the printed wire and the reference surface
w: the width of the printed wire
t: the thickness of the printed wire
It can be seen from the formula that the main factors affecting the characteristic impedance are (1) dielectric constant εr; (2) dielectric thickness h; (3) wire width w; (4) wire thickness t, etc. Therefore, it can be seen that the relationship between the characteristic impedance circuit board and the substrate material (copper-clad plate) is very close, so the choice of substrate material is very important in PCB design.
In actual production, slight changes in the width and thickness of the wire, the dielectric constant of the insulating material and the thickness of the insulating medium will cause the characteristic impedance to change. In addition, the characteristic impedance will also be related to other production factors, so in order to control the characteristics impedance circuit board, the producer must understand the factors that affect the characteristic impedance value change, master the actual production conditions, and adjust the various process parameters according to the requirements of the designer to make the change within the allowable tolerance range to obtain the desired impedance value.
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