Top PCB Routing Techniques to Know

In the forum, I saw a lot of PCB wiring problems raised by netizens. I felt the problems caused by the stepping motor wiring before. I understand this PCB wiring with common sense, which is easy to understand, avoids circuit loops, electromagnetic field transmission lines, etc. Complicated things that become more and more difficult to explain, fundamentally let everyone understand what is going on, and are not bound by some professional terms, and have won the approval of most netizens. Today qihe smt pick and place machine sharing some PCB Routing Techniques to Know .

PCB wiring is the laying of roads for energized signals to connect various devices. This is like building roads and connecting cities to cars. It is exactly the same thing.
Road construction requires two lines to go and one to go back. The same is true for PCB wiring. A two-line loop needs to be formed. For low-frequency circuits, it is a loop. For high-speed electromagnetic fields, it is a transmission line. The most common such as differential signals Wire. Such as USB, network cable, etc. For the impedance characteristics of the transmission line, etc., this article will not give further explanation.
It can be said that the differential signal line is an ideal model for connecting device signals. The higher the signal requirements, the closer to the differential signal line.

Double-sided PCB boards use the bottom layer as a common reference loop
When there are many components on a board, if they are all laid out according to differential lines, one is that the PCB area is too large, and the other is that 2N lines need to be laid out. The most typical concept is the double-sided PCB board. The bottom layer is used as a common reference loop, so that only N+1 wiring is required, and the PCB layout is greatly reduced.

The public reference loop, also known as the reference ground, for most embedded industries, the signal quality requirements are not very high after digitalization, so the use of the entire layer of reference ground can reduce the size of the board and improve efficiency , which greatly saves time and is deeply loved by everyone. In fact, reducing the board area means shortening the length of the signal line, which can also partially offset the signal quality degradation caused by the reference ground. Therefore, in practice, the PCB layout effect of introducing the reference ground is basically close to the ideal model of the differential line. Today, we are all accustomed to this method. It seems that PCB wiring requires a layer of reference ground. There is no reason.

In the double-panel design, because there are often crossed wires, it is necessary to jumper the wire to the ground for cross wire exchange. This needs to be pointed out that the jumper should not be too long. If it is too long, it is easy to split the reference ground, especially for some For lines with high signal quality requirements, the reference ground at the bottom cannot be divided. Otherwise, the circuit of the signal is completely destroyed, and the reference ground loses its meaning. So generally speaking, the reference ground layer is only suitable for short jumpers of signal lines, and the signal lines should be placed on the top layer as much as possible, or more layers of PCB boards should be introduced.

If the road is too close to the road, it will easily be affected. For example, when you take the high-speed rail, you can feel the impact of the train coming from the opposite side on the train you are taking. The same is true for the signal lines, not too close. If the signal lines are parallel to each other, a certain distance must be kept. This is subject to the experiment, and there must be a good reference ground at the bottom. Under low-frequency small signals, the general impact is not very great, and high-frequency strong signals need attention.

For PCB wiring with high frequency and high current, such as switching power supply, the most taboo is that the driving signal is interfered by the output of strong current and strong voltage. The drive signal of the MOS tube is easily affected by the strong output current, so keep a certain distance between them and don’t get too close. In the era of analog audio, if the magnification of the op amp is too high, the self-excitation effect will appear, the reason is the same as that of the MOS tube.

The carrier of PCB wiring is the PCB board. Generally, the reference ground is about 1mm away from the edge of the PCB board, and the signal line is about 1mm away from the edge of the reference ground. In this way, all signals are confined within the PCB board, which can reduce EMC radiation.
When you have no concept of PCB design, just think about our daily roads, the two are exactly the same.

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