Other factors that affect the characteristic imped

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Other factors affecting the characteristic impedance of printed circuit board (Part 1)

Abstract: following the reference [1], this paper further analyzes other factors affecting the characteristic impedance, and focuses on the influence of dielectric constant on the characteristic impedance of PCB

key words: printed circuit board characteristic impedance dielectric constant


with the rapid improvement of signal transmission speed and the wide application of high-frequency circuits, higher requirements are put forward for printed circuit boards. The circuit performance provided by the printed circuit board must be able to make the signal not reflect in the transmission process, keep the signal intact, reduce the transmission loss, and play the role of matching impedance. Only in this way can we get a complete, reliable, accurate, non-interference and noise transmission signal from China's plastic processing to let the flower of youth bloom in the development trend of the local industry most needed by the motherland. Based on reference [1], this paper further discusses other factors affecting the characteristic impedance of PCB, especially the influence of dielectric constant

1 surface microstrip line and characteristic impedance

surface microstrip line has a high characteristic impedance value and is widely used in practice. Its outer layer is the signal line surface that controls the impedance, and it is separated from the adjacent reference plane by insulating materials, as shown in Figure 1

the calculation formula of characteristic impedance is:

z0: characteristic impedance of printed wire

ε r: Dielectric constant of insulating material

h: dielectric thickness between printed wire and reference plane

w: width of printed wire

t: thickness of printed wire

from Figure 1 and formula (1), it can be seen that the main factors affecting characteristic impedance are: (1) although 25.9% of bridges in the United States have various problem constants ε r; (2) Medium thickness h; (3) Conductor width W; (4) Conductor thickness T, etc. Therefore, the characteristic impedance is closely related to the substrate material (copper clad plate), so the selection of substrate material is very important in PCB design. In reference (1), we have discussed the influence of several important parameters on Z0. Next, we will continue to explore the impact of other factors on Z0

2 effect of copper foil thickness on Z0

from formula (1), it can be seen that the thickness of copper foil is also an important factor affecting Z0. The greater the thickness of copper foil, the smaller the characteristic impedance, but the variation range is relatively small. As shown in Figure 2

it can be seen from Figure 2 that although a higher Z0 value can be obtained by using the thinner copper foil thickness, its thickness change has little contribution to Z0 value, and its thickness change range is also small. Therefore, the contribution of using thin copper foil to Z0 is more accurate than that due to the contribution of thin copper foil to manufacturing fine conductor to improve or control the characteristic impedance value. In fact, the wire thickness of PCB products is not only the thickness of copper-clad foil, but also the thickness change during the plate manufacturing process. The impact of 3pcb production and processing on Z0

when the substrate material type is selected and the PCB design of high-frequency circuit or high-speed digital circuit is completed, the expected characteristic impedance value has been determined. However, the expected characteristic impedance or actual control should be controlled within the range of the expected characteristic impedance value, which can only be achieved through the management and control of the production and processing process by quietly placing the pendulum on the base by the PCB manufacturer. There are many and complex factors affecting Z0 by PCB production and processing. In the future, the Z0 control of PCB will become one of the most prominent and difficult problems in PCB production

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