What is PCB design, detailed PCB design process
PCB Design - The printed circuit board design is based on the circuit schematic and implements the functions required by the circuit designer. Printed circuit board design mainly refers to layout design, which needs to consider the layout of external connections. Optimized layout of internal electronic components. Optimized layout of metal wiring and vias. Electromagnetic protection. Various factors such as heat dissipation. Excellent layout design can save production costs and achieve good circuit performance and heat dissipation.
The PCB design process is outlined as follows:
- Preparation in advance
Prepare PCB design software and component libraries and schematics on your computer. Before proceeding with PCB design, first prepare the schematic SCH component library and PCB component package library. The PCB component package library is preferably built by the engineer based on the standard size data of the selected device. In principle, the component package library of the PC is first established, and then the schematic SCH component library is established. The PCB component package library has higher requirements, which directly affects the PCB installation; the schematic SCH component library requirements are relatively loose, but care should be taken to define the pin attributes and the correspondence with the PCB component package library.
2, PCB structure design
According to the determined board size and various mechanical positioning, draw the PCB frame in the PCB design environment, and place the required connectors, buttons/switches, screw holes, assembly holes, etc. according to the positioning requirements. Fully consider and determine the wiring area and non-wiring area (such as the extent of the screw hole is a non-wiring area).
3, PCB layout design
The layout design is to place the device in the PCB frame according to the design requirements. Generate a network table (Design→Create Netlist) in the schematic tool, and then import the network table (Design→Import Netlist) in the PCB software. After the network table is successfully imported, it will exist in the software background. Through the Placement operation, all devices can be called out, and there is a flying line prompt connection between each pin. At this time, the device can be laid out. PCB layout design is the first important process in the entire PCB design process. The more complicated the PCB board, the better the layout can affect the ease of implementation of the post-wiring. Layout design relies on the circuit board designer's circuit foundation and design experience, which is a high level requirement for circuit board designers. The primary circuit board designer has a light experience, suitable for small module layout design or PCB layout design tasks with low board difficulty.
4, PCB layout design
PCB layout design is the most labor-intensive process in the overall PCB design, directly affecting the performance of the PCB. In the PCB design process, the wiring generally has three realms: First, the cloth pass, which is the most basic entry requirement for PCB design; the second is the satisfaction of electrical performance, which is a standard for measuring whether a PCB board is qualified, in the line cloth After the pass, carefully adjust the wiring to achieve the best electrical performance; again neat and beautiful, messy wiring, even if the electrical performance is passed, it will bring great inconvenience to the later reformation and test and maintenance, and the wiring requirements are neat. Uniform, can not be criss-crossed without rules.
5, wiring optimization and silk screen placement
PCB design is not the best, only better, "PCB design is a flaw in the art", mainly because PCB design to achieve all aspects of hardware design needs, and individual needs may be conflicting, fish and bear's paw Can not have both. For example, a PCB design project needs to be designed into a 6-layer board after evaluation by the board designer. However, due to cost considerations and the requirement that the product hardware must be designed as a 4-layer board, only the signal shielding ground layer can be sacrificed, resulting in adjacent wiring. Signal crosstalk between layers increases and signal quality decreases. The general design experience is that the time to optimize the wiring is twice the time of the initial wiring. After the PCB layout optimization is completed, post-processing is required. The first thing to deal with is the silk screen mark on the PCB board surface. The bottom screen silk screen characters need to be mirrored during design to avoid confusion with the top screen printing.
6, network DRC inspection and structural inspection
Quality control is an important part of the PCB design process. The general quality control methods include: design self-inspection, design mutual inspection, expert review meeting, special inspection, etc. The schematic and structural element diagrams are the most basic design requirements. The network DRC inspection and structural inspection are to confirm that the PCB design meets the two input conditions of the schematic netlist and the structural element diagram. General board designers will have their own accumulated design quality checklists, some of which are derived from the specifications of the company or department, and others from their own experience. Special inspections include Valor inspection and DFM inspection of the design. These two parts focus on the PCB design output back-end processing lithography files.
7, PCB board proofing board
Before the PCB is formally processed, the board designer needs to communicate with the PE of the PCB factory to answer the manufacturer's confirmation of the PCB board processing. These include, but are not limited to, PCB board model selection, line layer line width adjustment, impedance control adjustment, PCB laminate thickness adjustment, surface treatment process, aperture tolerance control and delivery standards.
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