Six-Layer PCB Stackup
The PCB stackup arrangement is the basis of the entire PCB design system. Any deficiencies in the stackup design will ultimately affect the overall EMC performance.
In general, EPCB thinks that the design of the PCB stackup mainly comply with two rules:
1.Each alignment must have an adjacent reference layer (power or ground);
2.Keep the minimum spacing between adjacent main power and ground so as to provide a larger coupling capacitance.
When design a 6-layer PCB board with large chip density and high clock frequency, recommended stackup method are as follows:
SIG- GND- SIG- PWR- GND- SIG: This kind of stackup method can obtain better signal integrity, the signal layer and the ground layer are adjacent, the power layer and the ground layer are paired, the impedance of each wiring layer can be well controlled, and both ground layers can well absorb magnetic field lines.
GND- SIG- GND- PWR- SIG- GND: This kind of stackup method is only suitable for PCB with less density components. This way has all the advantages of the above method, and the top and bottom of the ground plane is relatively complete so that it can be used as a better shield layer. It should be noted that the power layer should be close to the layer with non-primary components, that’s because the underlying plane can be more complete. Therefore, EMI performance here is better than the first solution.
Summary: For the six-layer PCB board, the spacing between the power plane and the ground plane should be minimized so as to achieve good power and ground coupling. However, the board thickness of 62mil, although the layer spacing is reduced, it is not easy to control the small spacing between the main power and the formation. Compared two methods, the cost of the second one will greatly increase, therefore, we usually choose the first option.