Six-layer board design

Many boards now use six-layer board technology, such as memory module PCB design, most of which use six-layer boards (high-capacity memory modules may use 10 layers). The most conventional six-layer board stack is arranged in such a way that it is signal-ground-signal-signal-power-signal. From the point of view of impedance control, this arrangement is reasonable, but because the power supply is far from the ground plane, the radiation effect on the smaller common mode EMI is not very good. If the copper area is changed to 3 and 4 layers, it will cause poor signal impedance control and strong differential mode EMI. There is also a solution for adding a ground plane, the layout is: signal-ground-signal-power-ground-signal, which enables high-speed signal integrity design from both impedance control and EMI reduction. surroundings. However, the disadvantage is that the stacking of the layers is unbalanced. The third layer is the signal routing layer, but the corresponding fourth layer is a large-area copper-clad power supply layer, which may encounter some problems in PCB manufacturing. Copper can be applied to all blank areas of the third layer to achieve an approximately balanced structure.