In theory, there are three options.
Option One
1 power layer, 1 ground layer and 2 signal layers are arranged in this way: TOP (signal layer), L2 (ground layer), L3 (power layer), BOT (signal layer).
Option II
1 power layer, 1 ground layer and 2 signal layers are arranged in this way: TOP (power layer), L2 (signal layer), L3 (signal layer), BOT (ground layer).
third solution
1 power layer, 1 ground layer and 2 signal layers are arranged in this way: TOP (signal layer), L2 (power layer), L3 (ground layer), BOT (signal layer).
What are the advantages and disadvantages of these three options?
Option One
The main stack-up design of the four-layer PCB of this scheme has a ground plane under the component surface, and the key signal is preferably placed on the TOP layer; as for the layer thickness setting, there are the following suggestions: The impedance control core board (GND to POWER) should not be too thick, In order to reduce the distributed impedance of the power supply and ground plane; ensure the decoupling effect of the power supply plane.
Option II
These schemes are mainly to achieve a certain shielding effect, and the power and ground planes are placed on the TOP and BOTTOM layers. However, in order to achieve an ideal shielding effect, this scheme has at least the following defects:
1. The power supply and ground are too far apart, and the impedance of the power supply plane is large.
2. The power and ground planes are extremely incomplete due to the influence of the component pads. Because the reference plane is incomplete, the signal impedance is discontinuous. In fact, due to the large number of surface mount devices, the power supply and ground of this solution can hardly be used as a complete reference plane when the devices are getting denser and denser, and the expected shielding effect is very high. difficult to achieve;
Scheme 2 has a limited scope of use. However, among individual boards, scheme 2 is still the best layer setting scheme.
third solution
This scheme is similar to scheme 1, and is suitable for the case where the main device is placed in the BOTTOM layout or the bottom layer of the key signal is routed.
