What PCB engineers need to pay attention to
Many PCB engineers often draw computer motherboards and are very proficient with excellent tools such as allegro. However, it is a pity that they rarely know how to control impedance and how to use tools for signal integrity analysis. For the IBIS model, I think the real PCB master should be a signal integrity expert, not just staying at connecting wires and vias. It is easy to lay out a board, but it is difficult to lay a good one.
After determining the number of power, ground and signal layers, the relative arrangement of them is a topic that every PCB engineer cannot avoid;
The general principle of the arrangement of the veneer layers:
The bottom of the component surface (the second layer) is the ground plane, which provides the device shielding layer and the reference plane for the top layer wiring;
All signal layers are as close as possible to the ground plane;
Try to avoid two signal layers directly adjacent;
The main power source is as close as possible to it correspondingly;
takes into account the symmetry of the laminated structure.
For the layer layout of the motherboard, it is difficult for the existing motherboard to control parallel long-distance wiring. For the board-level operating frequency above 50MHZ (refer to the case below 50MHZ, please relax appropriately), it is recommended to arrange the principle:
The component surface and the welding surface are a complete ground plane (shield);
No adjacent parallel wiring layers;'
All signal layers are as close as possible to the ground plane;
The key signal is adjacent to the ground and does not cross the partition.
Note: When setting up the specific PCB layers, the above principles should be flexibly mastered. Based on the understanding of the above principles, according to the actual requirements of the single board, such as: whether a key wiring layer, power supply, ground plane division is required, etc., Determine the arrangement of the layers, and don't just copy it bluntly, or hold on to it.
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