Electronic Design - Solve EMI and PCB proofing in 4-layer PCB design

There are several potential problems with 4-layer PCB design. First of all, the traditional four-layer board with a thickness of 62 mils, even if the signal layer is on the outer layer, and the power and ground layers are on the inner layer, the distance between the power layer and the ground layer is still too large.

4-layer PCB

If the cost requirement is first, you can consider the following two traditional 4-layer board alternatives. Both of these solutions can improve the performance of EMI suppression, but they are only suitable for applications where the component density on the board is low enough and there is enough area around the components (place the required power supply copper layer).

The first is the preferred solution. The outer layers of the PCB are ground layers, and the middle two layers are signal/power layers. The power supply on the signal layer is routed with a wide line, which can make the path impedance of the power supply current low, and the impedance of the signal microstrip path is also low. From the perspective of EMI control, this is the best 4-layer PCB structure available. In the second scheme, the outer layer uses power and ground, and the middle two layers use signals. Compared with the traditional 4-layer board, the improvement is smaller, and the interlayer impedance is as poor as the traditional 4-layer board.

If you want to control the trace impedance, the above stacking scheme must be very careful to arrange the traces under the power and ground copper islands. In addition, the copper islands on the power supply or ground layer should be interconnected as much as possible to ensure DC and low-frequency connectivity.
PCB proofing

PCB proofing is to determine whether there is a problem with the produced circuit board and whether it can achieve the required functions before mass production. To avoid problems in the later stage, resulting in scrap and increasing costs, so PCB circuit board proofing is very important.
Precautions:
1. As a group of engineers, the precautions for PCB circuit board proofing are as follows:

1. It is necessary to select a reasonable number of samples according to different situations to reduce costs.

2. Specially confirm the device packaging to avoid proofing failure due to packaging errors.

3. Conduct a comprehensive electrical inspection on the PCB circuit board to improve the electrical performance of the circuit board.

4. Do a good job of signal integrity layout, reduce noise, and improve the stability of the circuit board.

2. As a manufacturer, PCB proofing needs ideas:

1. Carefully check the relevant PCB files to avoid data problems.

2. Complete process approval and process configuration with its own manufacturers.

3. Conduct in-depth communication with customers, understand customer requirements and precautions in detail, and prevent mistakes.

Three, PCB circuit board proofing process attention

1. Layout and routing of components

The layout and wiring of the components have a great impact on the life, stability, and electromagnetic compatibility of the product, so special attention should be paid. Need to pay attention to the placement order of the components, usually first place the components in a fixed position related to the structure, and place other components from the largest to the smallest. In addition, the component layout needs to pay attention to the heat dissipation problem. The heating components should be distributed and not concentrated in one place.

2. Adjust and perfect

After the PCB circuit board wiring is completed, some adjustments to the text, individual components, wiring, and copper are required for production, debugging, and maintenance.

3. Use simulation function for PCB circuit board proofing

In order to ensure that the PCB circuit board can be proofed correctly, software can be used for simulation. Especially for high-frequency digital circuits, some problems can be found in advance and the workload of later debugging can be reduced.