What are the wiring skills for circuit board signal integrity?

“In the design and manufacturing process of high-speed PCB circuit boards, engineers need to start with wiring, component settings, etc. to ensure that this PCB board has good signal transmission integrity. In today’s article, we will introduce some wiring skills that are often used in PCB signal integrity design for new engineers, hoping to bring some help to newcomers’ daily study and work.

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In the design and manufacturing process of high-speed PCB circuit boards, engineers need to start with wiring, component settings, etc. to ensure that this PCB board has good signal transmission integrity. In today’s article, we will introduce some wiring skills that are often used in PCB signal integrity design for new engineers, hoping to bring some help to newcomers’ daily study and work.

In the design process of high-speed PCB circuit boards, the cost of the printed circuit of the substrate is proportional to the number of layers and the surface area of ​​the substrate. Therefore, without affecting the function and stability of the system, engineers should use the minimum number of layers to meet the actual design needs as much as possible, resulting in an inevitable increase in the wiring density. In PCB wiring design, the wider the trace width The smaller the interval, the greater the crosstalk between the signals, and the smaller the transmit power. Therefore, the selection of trace size must take various factors into consideration.

What are the wiring skills for circuit board signal integrity?

In the process of PCB layout design, the principles that engineers need to follow are as follows:

First of all, in the process of wiring, the designer should reduce the bending of the leads between the pins of the high-speed circuit device as much as possible, using 45? Folded lines to reduce external reflection and mutual coupling of high-frequency signals.

Secondly, when performing the wiring operation of the PCB board, the designer shortens the leads between the pins of the high-frequency circuit device and the interlayer alternation of the leads between the pins as much as possible. High-frequency digital signal traces should be kept as far away as possible from analog and control circuits.

In addition to the above-mentioned precautions for PCB wiring, engineers also need to be careful when dealing with differential signals. Because the amplitudes and directions of the differential signals are equal, the magnetic fields generated by the two signal lines cancel each other out, thereby effectively reducing EMI. The spacing of the differential lines often leads to changes in the differential impedance. The inconsistency of the differential impedance will seriously affect the signal integrity. Therefore, in the actual differential wiring, the length difference between the two signal lines of the differential signal must be controlled within the signal rising edge time. Within 20% of the electrical length. If conditions permit, differential traces must meet the back-to-back principle and be in the same routing layer. On the line spacing setting of differential wiring, engineers need to ensure that it is at least 1 times or more the line width. The spacing between differential traces and other signal traces should be greater than three times the trace width.