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This article shows you how to do a good job in PCB layer design in order to optimize the EMC effect of PCB, the content is concise and easy to understand, absolutely can make you shine, through the detailed introduction of this article I hope you can gain something.

In the EMC design consideration of PCB, the first thing involved is the setting of the layer; the number of layers of the board consists of the number of layers of power supply, ground and signal; in the EMC design of the product, in addition to the selection of components and circuit design, good PCB design is also a very important factor.

The key to PCB EMC design is to minimize the return area and let the return path flow in the direction we designed. The layer design is the basis of PCB, how to do a good job of PCB layer design in order to optimize the EMC effect of PCB?

First, the PCB layer design ideas

The core of PCB stack EMC planning and design idea is to reasonably plan the signal return path, reduce the return area of the signal from the single board mirror layer as much as possible, and make the magnetic flux cancel or minimize.

Single board mirror layer

The mirror layer is a complete copper-plated plane layer (power layer, ground layer) adjacent to the signal layer inside the PCB. It mainly has the following functions:

(1)Reduce return noise: The mirror layer provides a low impedance path for signal layer return, especially when there is a large current flow in the power distribution system.

(2)EMI reduction: The presence of the mirror layer reduces the area of the closed loop formed by the signal and return, reducing EMI;

(3)Reduce crosstalk: help to control the crosstalk between signal traces in high-speed digital circuits, change the height of signal lines from the mirror layer, you can control the crosstalk between signal lines, the smaller the height, the smaller the crosstalk;

(4)Impedance control to prevent signal reflection.

Mirror Layer Selection

(1)Both power and ground planes can be used as reference planes, and have a certain shielding effect on internal wiring;

(2)Relatively speaking, the power plane has a higher characteristic impedance, a larger potential difference with the reference level, and a relatively large high-frequency interference on the power plane;

(3)From the shielding point of view, the ground plane is generally treated as grounding and used as a reference level reference point, and its shielding effect is far better than that of the power plane;

(4)When selecting reference planes, the ground plane should be preferred over the power plane

II. Principle of magnetic flux cancellation

According to Maxwell's equations, all electrical and magnetic interactions between separate charged bodies or currents are transmitted through the intermediate regions between them, whether vacuum or solid matter. In PCB, magnetic flux always propagates in the transmission line. If the RF return path is parallel to its corresponding signal path, the magnetic flux on the return path and the magnetic flux on the signal path are opposite in direction. At this time, they are superimposed on each other, and the effect of flux cancellation is obtained.

III. Nature of magnetic flux cancellation

The essence of flux cancellation is the control of signal return path, and the specific schematic diagram is as follows:

For a six-layer board, preference is given to option 3.

Analysis:

(1) Since the signal layer is adjacent to the return reference plane and S1, S2, S3 are adjacent to the ground plane, there is the best magnetic flux cancellation effect. The wiring layer S2 is preferred, followed by S3, S1.

(2) The power plane is adjacent to the GND plane, and the distance between the planes is small, which has the best magnetic flux cancellation effect and low power plane impedance.

(3) When the main power supply and its corresponding ground distribution are set in layers 4 and 5, increase the spacing between S2-P and reduce the spacing between P-G2 (correspondingly reduce the spacing between G1-S2 layers) to reduce the impedance of the power supply plane and reduce the influence of the power supply on S2.

Option 4 for a six-ply board

Analysis:

In this structure, S1 and S2 are adjacent, S3 and S4 are adjacent, and S3 and S4 are not adjacent to the ground plane, so the magnetic flux cancellation effect is poor.

PCB layer design specific principles:

(1) The component surface and the welding surface are complete ground planes (shielding);

(2) Try to avoid two signal layers directly adjacent to each other;

(3) All signal layers are adjacent to the ground plane as much as possible;

(4) High frequency, high speed, clock and other key signal wiring layers should have an adjacent ground plane.

The above content is how to do a good PCB layer design in order to optimize the EMC effect of PCB, have you learned the knowledge or skills? If you want to learn more skills or enrich your knowledge reserves, please pay attention to the industry information channel.

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