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Electronic manufacturing industry PCB/PCBA knowledge
Why can’t PCB traces be too long?

PCB (Printed Circuit Board) is an important part of electronic equipment and is used to connect and support electronic components. Routing is the process of connecting circuits between electronic components. In PCB design, excessively long traces in PCB routing may cause some problems, including the following:

Signal attenuation: Signals in the circuit will be attenuated during transmission. Excessively long traces will increase the possibility of signal attenuation that can lead to signal distortion, increased noise, and communication errors. Especially for high-frequency signals and fast signal transmission, excessively long traces will cause problems more obviously.

Signal delay: It takes a certain amount of time for signals to propagate in a circuit. Excessively long traces will increase the delay of signal propagation. In some applications, such as high-speed communications and timing-sensitive circuits, signal delays may cause system performance degradation or functional failure.

Crosstalk interference: Excessively long traces will increase the possibility of crosstalk interference between circuits. Crosstalk interference refers to the interference caused by signals on one signal line to other signal lines. When traces are too long, electromagnetic interactions between signal lines may cause crosstalk of signals, thereby introducing errors or interference.

Difficulties in PCB layout: Excessively long traces may cause layout difficulties. When laying out the PCB, factors such as the signal path, the distribution of power and ground wires, and the arrangement of components need to be considered. If the traces are too long, it may increase the complexity of the layout and make the design more difficult.

Therefore, in PCB design, it is usually necessary to control the length of traces as much as possible to ensure reliable signal transmission and system performance. This can be achieved through reasonable circuit layout, signal line path planning, and the use of appropriate inter-layer connections.

If the PCB trace is too long, the combined parasitic capacitance will eventually increase.

According to the definition of capacitance, we know that the larger the area of two planes with the same distance, the greater the capacitance value. Therefore, the longer the trace, the more comprehensive ground capacitance will continue to increase. The larger the capacitance value, it is equivalent to a low-pass filter and will attenuate high-frequency components.

When the PCB trace is too long, the parasitic capacitance will become larger. This is because increased trace length increases the physical distance between circuit components, which in turn results in increased capacitance. Here are a few major factors that lead to increased parasitic capacitance:

Increased trace length: Trace length is a key factor in capacitor value. According to the definition of capacitance, the capacitance value is proportional to the strength of the electric field in the electric field and the distance between the objects. When the length of the trace increases, the distance between objects increases, causing the capacitance value to increase.

Trace Width and Thickness: Trace width and thickness also have an impact on parasitic capacitance. Typically, the larger the trace width, the smaller the electric field strength between the traces, thus reducing the capacitance value. The increase in the thickness of the trace will cause the capacitance value to increase, because the increase in the thickness of the trace will increase the surface area of the trace, thereby increasing the effect of the capacitance.

Surrounding environment and adjacent traces: The size of the parasitic capacitance is also related to the surrounding environment and the location of adjacent traces. When traces are too long, they may become closer to other traces, which causes increased capacitance between adjacent traces. In addition, other conductors or ground planes in the surrounding environment can also affect the capacitance between traces.

It is important to note that the increase in parasitic capacitance may have a negative impact on the performance of the circuit. It can affect the transmission speed of signals and introduce problems such as interference and crosstalk. Therefore, in PCB design, it is necessary to reasonably plan the trace length and layout to control the size of parasitic capacitance and ensure the reliability and performance of the circuit.

the PCB and tracparasitic inductance
the PCB and tracparasitic inductance

If the PCB trace is too long, the combined parasitic inductance will eventually increase.

When the PCB trace is too long, the parasitic inductance will become larger. This is because increased trace length increases the physical distance between circuit components, resulting in increased inductance. Here are a few major factors that lead to increased parasitic inductance:

Increased trace length: According to the definition of inductance, the inductance value is proportional to the length of the coil (trace) in the circuit. When the length of the trace increases, the length of the coil also increases, causing the inductance value to increase.

Trace width and thickness: Trace width and thickness also have a certain impact on parasitic inductance. Wider traces and thicker traces reduce the inductance value of the trace because they provide more conductor surface area and cross-sectional area, thereby reducing the length of the coil.

Trace shape and layout: Trace shape and layout also affect parasitic inductance. For example, trace shapes that are meandering, coiled, or wrapped increase the inductance of the trace. In addition, the parasitic inductance of the trace can also be increased if the trace is in close proximity or coupled to other traces or conductors.

Increased parasitic inductance can have a negative impact on the circuit. It can cause problems such as slowing down signal transmission, introducing crosstalk, and reducing the bandwidth of the circuit. Therefore, in PCB design, it is necessary to rationally plan the trace length, width and layout to control the size of parasitic inductance and ensure the reliability and performance of the circuit.

Optimize trace length through layout
Optimize PCB trace

Optimize trace length through layout

In design, layout is an important link. The quality of the layout results will directly affect the wiring effect, so it can be considered that reasonable layout is the first step to successful PCB design. To simply understand, PCB layout is to arrange all components according to functional structure, modularity, meet the requirements of DXF, and meet the principles of smooth layout and wiring.

Considering the overall beauty, whether a product is successful or not, one must pay attention to the internal quality, and the other is to take into account the overall beauty. Only when both are perfect can the product be considered successful. On a PCB board, the layout of components must be balanced, dense and orderly.

Reasonable layout can optimize the shortest routing path. Improper layout will lead to unnecessary trace lengths.

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