1. If the designed circuit system contains FPGA devices, it is necessary to use Quartus lI software to verify the pin assignment before drawing the schematic diagram. (Some special pins in FPGA cannot be used as ordinary IO)
2. The order from top to bottom of the 4-layer board is: signal plane layer, ground, power supply, and signal plane layer; the order from top to bottom of the 6-layer board is: signal plane layer, ground, signal internal electrical layer, signal internal electrical layer, Power and signal plane layers. For boards with more than 6 layers (advantage: anti-interference radiation), the inner layer wiring is preferred, and the plane layer cannot be left. It is forbidden to route from the ground or power layer (reason: it will split the power layer and produce parasitic effects).
3. Wiring of multi-power supply system: If FPGA+DSP system is made of 6-layer board, generally there will be at least 3.3V+1.2V+1.8V+5V.
3.3V is generally the main power supply. Lay the power layer directly, and it is easy to route the global power network through vias.
5V is generally likely to be a power input, and only needs to lay copper in a small area. And as thick as possible (you asked me how thick it should be - as thick as you can. The thicker the better)
1.2V and 1.8V are the core power supply (if you directly use wire connection, you will encounter great difficulties in the face of BGA devices), try to separate 1.2V and 1.8V during layout, and let 1.2V or 1.8V be connected Components are laid out in a tight area and connected by copper skin. In short, because the power network is spread throughout the PCB, it will be complicated and go around a long way if the wiring method is used. Using the method of laying copper skin is a good choice!
4. The wiring between adjacent layers adopts a crossover method: it can not only reduce the electromagnetic interference between parallel wires (high school learning), but also facilitate wiring.
5. Analo and digital need to be isolated, what is the isolation method? When laying out, the devices used for analo signals are separated from the devices for digital signals, and then one size fits all from the middle of the ad chip! Analo signals are laid with analo ground. Analo ground/analo power and digital power are single-point connected through inductors/magnetic beads.
6. PCB design based on PCB design software can also be done. It is a software development process. Software engineering pays most attention to the idea of "iterative development". I think this idea can also be introduced in PCB design to reduce the probability of PCB errors.
(1) Check the schematic diagram, pay special attention to the power supply and ground of the device (the power supply and ground are the blood vessels of the system, there should be no negligence)
(2) PCB package drawing (confirm whether the pins in the schematic diagram are correct)
(3) After the PCB package size is confirmed one by one. Add a verification tag. Add to this design package library
(4) Import the netlist, and adjust the signal sequence in the schematic diagram while laying out the layout (OrCAD's automatic component numbering function can no longer be used after layout) (5) Manual wiring (check the power supply network while laying out, as mentioned earlier: the power supply network uses Copper laying method, so use less wiring)
In short, the guiding ideology in PCB design is to feedback and correct the schematic diagram while drawing package layout and wiring (considering the correctness of signal connection and the convenience of signal routing).
7. The crystal oscillator should be as close as possible to the chip, and the bottom of the vibration should not be routed as much as possible, and the ground network copper skin should be laid. Clocks used in multiple places are routed using a tree clock tree approach.
8. The layout of the signals on the connector has a great influence on the difficulty of wiring, so the signals on the schematic diagram should be adjusted while wiring (but the components must not be renumbered)
9. Design of multi-board receivers:
(1) Use a cable connection: the upper and lower interfaces are consistent
(2) Live seat: the upper and lower interfaces are mirrored and symmetrical
10. Design of module connection signal:
(1) If two modules are placed on the same side of PCB
(2) If the 2 modules are placed on different sides of the PCB, the serial number of the control is small and then large and then large
Doing this places the signals to cross like the one on the right above. Of course, the above method is not a rule. I always say that everything changes as needed (this can only be understood by yourself), but in many cases, designing in this way is very useful.
11. Design of power ground loop:
The power ground loop area is large. susceptible to electromagnetic interference
Through the improvement - the power supply and the ground wire are close to the wiring, which reduces the loop area and reduces the electromagnetic interference (679/12.8, about 54 times). Therefore, the power supply and ground should be as close as possible to the wiring! And the signal lines should try to avoid parallel wiring to reduce the mutual inductance effect between signals.
