1. SIG GND (PWR) - PWR (GND) - SIG;

2. GND SIG (PWR) - SIG (PWR) - GND;

The potential issue with the above two stacked designs is the traditional 1.6mm (62mil) plate thickness. The interlayer spacing will become large, which is not conducive to controlling impedance, interlayer coupling, and shielding; Especially, the large spacing between the power layers reduces the board capacitance, which is not conducive to filtering out noise.

The first solution is usually applied in situations where there are many chips on the board. This solution can achieve good SI performance, but it is not very good for EMI performance. It mainly needs to be controlled through wiring and other details.

The second solution is usually applied in situations where the chip density on the board is low enough and there is sufficient area around the chip. In this scheme, the outer layer of the PCB is a layer, and the middle two layers are both signal/power layers. From the perspective of EMI control,

This is the best existing 4-layer PCB structure.

Main attention: The spacing between the middle two layers of signal and power mixing layers should be widened, and the wiring direction should be vertical to avoid crosstalk; Properly control the board area to reflect the 20H rule.

Stacking of six layer boards

For designs with high chip density and clock frequency, a 6-layer board design should be considered, and the recommended stacking method is:

SIG GND SIG PWR GND SIG;

This stacking scheme can achieve good signal integrity, with the signal layer adjacent to the ground layer, the power layer paired with the ground layer, and the impedance of each wiring layer well controlled. Both layers can also absorb magnetic field lines well.

2. GND SIG GND PWR SIG GND;

This scheme is only applicable to cases where the device density is not very high. This layer has all the advantages of the upper layer, and the ground planes of the top and bottom layers are relatively complete, which can serve as a good shielding layer

To use. Therefore, EMI performance is better than the first solution.