December 09, 2020
In PCB multilayer board design, four-layer boards are generally used more. So, do you know the design rules of PCB four-layer board?
1. Design form of four-layer board:
(1) Uniform spacing: The biggest advantage is that the distance between the power supply and the ground is very small, which can greatly reduce the impedance of the power supply and improve the stability of the power supply. The disadvantage is that the impedance of the two signal layers is relatively high, and because the distance between the signal layer and the reference plane is large, the signal reflow area is increased, and the EMI is relatively strong.
(2) Non-uniform spacing: The design of non-uniform spacing can better control the impedance. The signal close to the reference plane is also beneficial to improve the quality of the signal and reduce EMI. The disadvantage is that the distance between the power supply and the ground is too large, which can weaken the coupling between the power supply and the ground and increase the impedance, but it can be improved by adding a bypass capacitor.
2. The structure of the four-layer board:
(1) Scheme 1: The first layer is the signal layer, the second layer is the ground layer, the third layer is the power layer, and the fourth layer is the signal layer. The setup of scheme 1 is the main scheme for the four-layer board setup. The ground plane is under the components, and the key signals are arranged on the top layer.
(2) Scheme 2: The first layer is the ground layer, the second layer is the signal layer, the third layer is the signal layer, and the fourth layer is the power layer. Solution 2 is suitable for the plane without power supply on the whole board, only the GND plane. The wiring of the whole board is simple, but the radiation area of the wiring of the interface filter board must be paid attention to. The SMD components of the board are relatively few, and most of them are plug-ins.
(3) Scheme 3: One layer is the signal layer, the second layer is the power layer, the third layer is the ground layer, and the fourth layer is the signal layer. Scheme 3 is similar to scheme 1, which is suitable for the main components in the BOTTOM layout or the bottom wiring of key signals. Generally, this scheme is not used.