First: prepare in advance. This includes preparing component libraries and schematic diagrams. "If you want to do a good job, you must sharpen your tools first." To make a good board, we should not only design the principle well, but also draw it well. Before PCB design, the schematic diagram SCH and PCB component library should be prepared first. The component library can use peotel's own library, but in general, it is difficult to find a suitable one. It is best to make your own component library according to the standard size data of the selected devices. In principle, do the component library of PCB first, and then do the component library of SCH. The component library of PCB has high requirements, which directly affects the installation of the board; The requirements of SCH's component library are relatively loose, as long as the pin attributes and the corresponding relationship with PCB components are defined. PS: pay attention to the hidden pins in the standard library. After that, the schematic diagram is designed, and then the PCB design is ready to start.
Second: PCB structure design. In this step, according to the determined circuit board size and mechanical positioning, the PCB surface is drawn in the PCB design environment, and the required connectors, keys/switches, screw holes, assembly holes, etc. are placed according to the positioning requirements. And fully consider and determine the wiring area and the non-wiring area (such as how many areas around the screw hole belong to the non-wiring area).
Third: PCB layout. To put it bluntly, the layout is to put the device on the board. At this time, if the preparatory work mentioned above is done, you can generate a network table (Design->; CreateNetlist), and then import the network table (design->; Load-bearing net). I saw a whole pile of devices rushing up, and there was a flying wire connection between the pins. Then you can arrange the equipment. The general layout shall follow the following principles:
① According to electrical performance, it can be divided into digital circuit area (that is, fear of interference and interference), analog circuit area (fear of interference) and power drive area (interference source); (2) The circuits that perform the same function should be placed as close as possible, and the components should be adjusted to ensure the simplest connection; At the same time, adjust the relative position between functional blocks to make the connection between functional blocks simplest; (3). For components with large mass, the installation position and strength should be considered; Heating elements should be placed separately from temperature sensitive elements, and thermal convection measures should be considered when necessary; ④ The I/O driver should be as close to the edge of the printed board as possible and close to the lead-out connector; ⑤. The clock generator (such as crystal oscillator or clock oscillator) should be as close as possible to the equipment using the clock; ⑥. A decoupling capacitor (usually a monolithic capacitor with good high frequency performance) should be added between the power input pin of each integrated circuit and the ground; When the circuit board space is dense, a tantalum capacitor can also be added around several integrated circuits. ⑦. Add a discharge diode at the relay coil (1n 4148); ⑧ The layout should be balanced, dense and orderly, not top-heavy.
-Pay special attention to the actual size (occupied area and height) and relative position of components when placing components, so as to ensure the electrical performance of the circuit board and the feasibility and convenience of production and installation, and at the same time ensure the above principles.
Under this premise, the arrangement of equipment should be modified appropriately to make it neat and beautiful. For example, the same equipment should be placed neatly and in the same direction, and it should not be "misplaced". This step is related to the overall image of the circuit board and the difficulty of wiring in the next step, which requires great effort to consider. In the layout, you can make preliminary wiring for those places that are not sure and give full consideration.