PCB design process
PCB rule settings
The design unit follows the unit set in canvas properties, where the unit is mil. Wire width is 10mil； minimum; The minimum distance between different network elements is 8 mil; The external diameter of the hole is 24mil, and the internal diameter of the hole is 12mil；. Line length is not set; In the process of PCB design, the functions of “real-time rule detection”, “detecting the distance between elements and copper clad” and “displaying DRC safety boundary during wiring” should be turned on.
Layout principle
Generally, the layout should follow the following principles:
(1) principle of shortest wiring. For example, the decoupling capacitors of integrated circuits (IC) should be placed at the corresponding VCC and GND as much as possible.
Pins, and be as close to the IC as possible, so that the loop formed between it and VCC and GND is the shortest.
(2) The principle of centralizing the same functional modules. That is, the components in the related circuit modules that realize the same function are centrally distributed nearby.
Bureau.
(3) Abide by the principle of “first big and then small, first difficult and then easy”, that is, the layout of important unit circuits and core components should be given priority.
(4) The layout should refer to the schematic diagram, and arrange the main components according to the flow law of the main signal of the circuit.
(5) The arrangement of components should be convenient for debugging and maintenance, that is, large components should not be placed around small components, and there should be enough space around the components to be debugged.
(6) Plug-in components of the same type should be placed in one direction in X or Y direction. The same type of polarized discrete components should be consistent in the X or Y direction as far as possible, which is convenient for production and inspection.
(7) During layout, the components located at the edge of the circuit board should generally be no less than 2mm away from the edge of the circuit board. If space permits, it is recommended to keep the distance at 5mm.
(8) When the crystal oscillator is laid out, it should be as close to IC as possible, and the capacitor connected to the crystal oscillator should be close to the crystal oscillator.
Wiring precautions
Pay attention to the following matters when wiring:
(1) In principle, the main power supply line should be bold (especially the power input/output line of the circuit board).
(2)PCB wiring should not be too close to the positioning hole and the circuit board frame, otherwise, when drilling the PCB, the wires will be easily cut off or even cut off.
(3) 90 corner wiring is forbidden in the same layer, but 90 wiring of vias between different layers is allowed. Moreover, wiring should follow the principle of one layer of horizontal wiring and the other layer of vertical wiring as much as possible.
(4) The wiring of high-frequency signal lines, such as the crystal oscillator circuit on the STM32 core board, should not be bold. It is recommended that the line width should be 10mil, and the wiring should be on the same layer as much as possible.