In PCB design, consider signal quality control factors, the general principles of PCB layer stack up should be follow below:
- The second planes adjacent to the component surfaceis ground plane, providing device shielding layer and referenceplane.
- All signal layers are adjacent to the ground plane as much as possible to ensure a complete return channel.
- Try to avoid two signal layer directly adjacent to reduce crosstalk.
- The main power supply is adjacent to ground plane as much as possible to form a planar capacitor to reduce the power level impedance.
- Considering the symmetry of laminated structure, it is beneficial to bow and twist control during PCB making.
Above is the principle of conventional laminated design, in the actual circuit board design, designers can increase the distance between the adjacent wiring layer, reduce the space between wiring layer to the corresponding reference plane, and then control the layer wiring crosstalk ratio under the premise, two signal layer can be directly adjacence.
For more cost oriented consumer products, you can weaken the power and ground plane adjacent to reduce the plane impedance, so minimize the wiring layer and reduce the cost of PCB. Of course, use this method will risk signal design quality.
For the Backplane or midplane stack design, in view of the common backplane is difficult to do the adjacent line perpendicular to each other, inevitably parallel long distance routing. For high-speed backplanes, the general layer stack up principle is as follows:
- Top plane and bottom surface are the complete horizon, and constitute the shielding cavity.
- No adjacent layer parallel wiring is used to reduce crosstalk, or the spacing between adjacent routing layers is great far than the reference plane spacing.
- All signal layers are adjacent to the ground plane as mush as possible to ensure a complete return channel.
In the particular PCB stack up setting, the PCB design should be flexibly applied to the above principles, and reasonable analysis is made according to the requirements of the actual single board.
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