6-layer circuit board PCB wiring experience sharing
6-layer pcb board has two layers of ground, wiring can be separated from the analog ground and digital ground, for the unified ground or separate ground, involving electromagnetic interference in the signal's minimum return path problem, after drawing the schematic diagram, do not forget to check the error and view the package manager, check the component package.
New PCB file, set the layer structure, after the new, you can import the schematic network table to the PCB file. The next thing to do is the layer structure settings (layer stack manager), add layer is to add the intermediate signal layer, add plane is to add the internal power and internal ground layer. Intermediate signal layer and the top layer, the same as the bottom layer, the placement of signal lines, signal lines on behalf of the copper, no signal lines where the insulation. And the internal power and ground layer, generated by a layer of copper mold, the line used in the division of the internal power layer, representing the corrosion off the copper, that is to say, the dark red on behalf of the corrosion off, other areas on behalf of the copper mold. Another point is that the power supply layer and the main ground layer should be closely coupled, can be taken 5mil (prepreg).
Layout, the main principle of layout is to do a good job of partitioning, that is, the partitioning of analog and digital devices, which can reduce interference, because the interference generated by digital signals is large, anti-interference is also strong, while the interference generated by analog signals is relatively small, but vulnerable to digital signal interference. Another point is to pay attention to the layout of components with different operating voltages, the devices with large pressure differences should be far apart. For some chips decoupling capacitors, the closer to the pins, the better. Other things to pay attention to is the same network of pins close together, pay attention to the layout of the beautiful. In principle, 3 layers of signal layer, 3 layers of power layer, where GND is 2, 5 two layers, 3, 4 intermediate layer for Power and intermediate signal layer. If the intermediate signal layer alignment is less, can be appropriate in the intermediate signal layer for Power to lay copper.
The production of ground plane, because the six-layer board pcb has two layers of ground, AGND and DGND separate, respectively, located in the second and fourth layer, so the operation of the ground network is relatively easy point. The top layer and the ground layer components of the ground network pins, lead with wires, connected to the corresponding ground network can be connected through the hole (consider the production cost, try to use less blind holes, buried holes, with pads instead of through holes). Connection process as little as possible with some pads, because the pads will bring capacitive effect, increasing interference.
The production of the power plane, due to the multilayer board will not have only one working voltage value, so the power supply layer generally need to be divided. The specific steps for splitting are as follows.
1, highlight a voltage network, switch to the inner power supply layer, use line, draw a closed graph, the closed area is the voltage network;
2, the top layer, the ground layer of the pin with a wire lead, through the pad connected to the inner power supply layer;
3, draw the next power supply network, line is the partition line of the two networks, is the part that is eroded away.
Inner power layer should pay attention to: the voltage difference between the region split distance should be wider; not used copper die can be placed plane, in order to make its area corroded off; do not place the pad on the split line, to affect its contact with the inner power layer.