The recommended way of stacking six-layer board

Some stacking schemes in the 6-layer PCB design are not good enough to shield the electromagnetic field and have little effect on reducing the transient signal of the power busbar. For designs with high chip density and high clock frequency, the creation of a 6-layer board should be considered.

1.1.SIG-GND-SIG-PWR-GND-SIG;

For this scheme, this stack-up scheme can achieve better signal integrity. The signal layer is adjacent to the ground layer, the power layer and the ground layer are paired, the impedance of each trace layer can be well controlled, and the two forms can absorb the magnetic field lines well. And in the case of a complete power supply and ground layer, it can provide a better return path for each signal layer.

1.2. GND-SIG-GND-PWR-SIG -GND;

This kind of scheme is only suitable for the case where the device density is not very high, this kind of stack has all the advantages of the above accumulation, and the ground plane of the top and bottom layers are relatively complete, which can be used as a better shielding layer to use. It should be noted that the power layer should be close to the layer that is not the main component side because the bottom plane will be more complete. Therefore, the EMI performance is better than the first solution.

Summary: For the scheme of the six-layer board, the distance between the power layer and the ground layer should be minimized to obtain good power and ground coupling. However, with a thickness of 62 mils, although the layer spacing has been reduced, it is still not easy to control the gap between the main power supply and the ground layer very small. Comparing the first scheme with the second scheme, the cost of the second scheme is greatly increased. Therefore, we usually choose the first solution when stacking. When designing, follow the 20H rule and the mirror layer rule design.