The circuit board stacking arrangement is the basis for the overall system design of the PCB. Laminated design, if defective, will ultimately affect the overall EMC performance. In general, the stack design is mainly to comply with two rules:
1. Each alignment layer must have an adjacent reference layer (power or formation);
2. The adjacent mains and layers must be kept at a minimum distance to provide a larger coupling capacitance;
The following lists the stacks from single-layer to eight-layer boards:
For the Two Layer Board, due to the small number of layers, there is no problem with the stack. Control EMI radiation mainly from the wiring and layout to consider;
Single-layer and double-board electromagnetic compatibility issues more and more prominent. The main reason for this phenomenon is because the signal loop area is too large, not only produced a strong electromagnetic radiation, and the circuit is sensitive to external interference. To improve the electromagnetic compatibility of the line, the easiest way is to reduce the critical signal loop area.
Key signal: from the perspective of electromagnetic compatibility, the key signal mainly refers to the strong radiation generated signals and sensitive signals to the outside world. Signals that produce strong radiation are typically periodic signals, such as clock or low-order signals. Sensitive signals that are sensitive to interference are those of lower level analog signals.
Single and Two Layer Board is usually used in less than 10KHz low frequency analog design:
1 in the same layer of the power line to the radial alignment, and to minimize the sum of the length of the line;
2 take the power, ground, close to each other; in the key signal line cloth on a ground, the ground should be close to the signal line. This results in a smaller loop area that reduces the sensitivity of differential mode radiation to external disturbances. When the signal line next to add a ground, it formed a minimum area of the loop, the signal current will certainly take this circuit, rather than other ground path.
3 If it is a double-layer circuit board, you can in the circuit board on the other side, close to the signal line below, along the signal line cloth a ground line, the line as wide as possible. The circuit area thus formed is equal to the thickness of the pcb circuit board multiplied by the length of the signal line.
Recommended stacking method:
2.1 SIG-GND (PWR) -PWR (GND) -SIG;
2.2 GND-SIG (PWR) -SIG (PWR) -GND;
For the above Two Layer Board stack designs, the potential problem is for the traditional 1.6mm (62mil) plate thickness. Layer spacing will become very large, not only is not conducive to control the impedance, interlayer coupling and shielding; especially the power between the formation of a large gap between the board capacitance is reduced, is not conducive to filter out noise.
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