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Printed circuit boards with impedance requirements require high accuracy.
With the rapid increase of signal transmission speed and the wide application of high-frequency circuits, higher requirements are also proposed for printed circuit boards.
The circuit of the printed circuit board must be able to ensure that the signal in the transmission process has no reflection issues and that the signal remains intact and transport losses are greatly reduced so that complete, reliable, accurate, non-disruptive and noise transmission signals can be obtained. Also, the circuit plays the role of matching impedance.
What is impedance?
The impedance of a printed circuit board results from the interaction of reactance and resistance. It measures the resistance to current when an alternating current is applied to it. As an AC characteristic, impedance is frequency dependent and is expressed in ohms (Ω).
Its transmission is ideal whenever a signal passes through a conductor with the same impedance as another given impedance. The signal is affected if the impedances at the two ends are different.
Impedance control is often required in single-ended microstrip, embedded microstrip, ribbon differential pairs, and planar PCB transmission lines.
How is impedance determined?
Impedance usually ranges from 25 to 125 ohms and depends mainly on the following factors.
Width and thickness of the copper wire
Core thickness or material thickness on both sides of the line
The dielectric constant of the core or material
Distance from the copper plane
Presence of solder resist
Circuit board designers need to realize that their choice of conductors will directly affect the target impedance value. Many advanced tools are available to help with this calculation, which we will discuss later in the article.
Impedance matching is very important in realizing high-frequency design and is closely related to the quality of the signal. The purpose of impedance matching is mainly that all high-frequency microwave signals on the transmission line can reach the load point, and there will be no signal reflecting back to the source point.
From the point of view of PCB manufacturing, the key factors affecting impedance mainly include :
• Line width（w）
• Line spacing（s）
• Line thickness（t）
• Dielectric thickness（h）
• Dielectric Constant （Dk）
Other factors considered in the impedance design:
• Whether the line width can meet the current requirements
• Whether the laminated structure is reasonable
• Mutual interference between signal layers
• Size of the layout density
• Selection of laminates and prepregs
• Whether the thickness of interlayer dielectrics can meet the processing requirements
• Whether the final board thickness can meet customer requirements
Controlled impedance PCBs are used in a variety of fast digital applications including:
• High-quality analog videos
• Signal processing applications
• RF Communications
Impedance control is essential for the design and manufacturing of any printed circuit board (PCB). You can always count on us when your PCB requires impedance control. Over the years, we have gained wide recognition for our high-quality printed circuit boards with controllable impedance.
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