4-Layer Board:

Traditional 4-layer board designs may face challenges such as large distances between power and ground layers. Two possible alternatives include:

1. Preferred Solution: Outer layer as ground, middle layers for signal/power. Wide traces for power supply on signal layer help reduce path impedance and signal microstrip path impedance, offering improved EMI control.
2. Lesser Preferred Solution: Outer layer for power and ground, middle layers for signal. While offering some improvement over traditional 4-layer boards, careful routing of traces is required to control impedance.
   6-Layer Board:
   When component density is high, a 6-layer board is advisable. Consider the following stacking schemes:
3. Example 1: Power on 2nd, ground on 5th layer; suitable for signal impedance control but unfavorable for common-mode EMI radiation.
4. Example 2: Power on 3rd, ground on 4th layer; mitigates power supply impedance issues, but may increase differential mode EMI. Effective mitigation requires minimal signal traces on outer layers.
   General High-performance 6-Layer Board Design:
   Typically, 1st and 6th layers are ground, and 3rd and 4th layers for power and ground. EMI suppression is excellent due to centered dual microstrip signal line layers. Alternatively, the Signal, Ground, Signal, Power, Ground, Signal layout offers advanced signal integrity but may pose processing challenges.