With the development of the electrical age, there are more and more kinds of electromagnetic wave sources in human living environment, such as radio broadcasting, television, microwave communication, household electrical appliances, power frequency electromagnetic field of transmission lines, high frequency electromagnetic field and so on. When the field strength of these electromagnetic fields exceeds a certain limit, the role of time is long enough, it may endanger human health; also interfere with other electronic equipment and communications. In this regard, need to be protected. The development of electronic products, production, use of the process often proposed electromagnetic interference, shielding and other concepts. Electronic products are the core of the normal operation of the PCB board and its installed in the above components, components, etc. between a coordinated work process. It is important to improve the performance of electronic products to reduce the impact of electromagnetic interference.

1, PCB board design

Printed circuit board (PCB) is a support for circuit components and devices in electronic products. It provides electrical connections between circuit components and devices. It is the most basic component of various electronic devices. PCB board performance is directly related to Electronic equipment quality, performance is good or bad. With the development of integrated circuits, SMT technology, micro-assembly technology, high-density, multi-functional electronic products more and more, resulting in PCB board wiring complex, parts, components, installation-intensive, bound to interfere with them More and more serious, so the suppression of electromagnetic interference problem will become an electronic system can work the key. Similarly, with the development of technology, PCB density is getting higher and higher, PCB board design of the circuit interference and anti-interference ability of a great impact. In order to get the best performance of the electronic circuit, in addition to the choice of components and circuit design, a good PCB board design in the electromagnetic compatibility (EMC) is also a very important factor.

1.1 reasonable PCB board design

According to the complexity of the circuit, a reasonable choice of the board of the board can effectively reduce the electromagnetic interference, a substantial reduction in PCB volume and current loop and the length of the branch line, a significant reduction in signal cross-interference. Experiments show that the same material, the four-layer board than the double-board noise 20dB lower, but the higher the number of layers, the more complex manufacturing process, the higher the manufacturing cost. In the multi-layer PCB board wiring, the adjacent layer between the best use of "well" shaped mesh fabric structure, that is, adjacent layers of the direction of their respective vertical lines. For example, the upper side of the PCB board horizontal wiring, the next vertical wiring, and then connected through the hole.

1.2 reasonable PCB board size design

PCB board size is too large, will lead to printed wire growth, increased impedance, anti-noise capacity decreased, the equipment volume increases the cost of a corresponding increase. If the size is too small, the heat is not good, and the adjacent lines are susceptible to interference. In general, the mechanical layer (Mechanical Layer) to determine the physical border that PCB board size, prohibit the wiring layer (Keepout Layer) to determine the layout and wiring of the effective area. Generally according to the number of functional units of the circuit, the overall components of the circuit to the overall, and finally determine the PCB board the best shape and size. Usually use rectangle, aspect ratio of 3: 2. When the board size is greater than 150mm * 200mm, the mechanical strength of the PCB should be taken into account.

2, the layout of the PCB board

In the PCB design, the electronics engineer may focus only on increasing the density, reducing the space occupied, making it simple, or pursuing aesthetically pleasing, uniform layout, ignoring the influence of the line layout on the electromagnetic compatibility (EMC), allowing a large number of signals to radiate into space The formation of mutual interference. A poor PCB layout can lead to more electromagnetic compatibility (EMC) problems than to eliminate these problems.

Electronic devices in the digital circuit, analog circuits and power circuit components of the layout and wiring characteristics are different, they produce interference and suppression of interference methods are not the same. High frequency, low frequency circuit due to different frequencies, the interference and suppression of interference methods are not the same. Therefore, in the component layout, should be digital circuits, analog circuits and power supply circuit were placed, the high-frequency circuit and low-frequency circuit separately. Conditional should make their separate or separate made of a PCB board. The layout should also pay special attention to strong, weak signal device distribution and signal transmission direction and other issues.