Printed circuit board {PCB circuit board}, also known as printed circuit board, is a provider of electrical connections for electronic components. It has a history of more than 100 years; Its design is mainly layout design; The main advantage of using circuit boards is to greatly reduce wiring and assembly errors, improve the level of automation and production labor rate.
Because the printed circuit board is not a general terminal product, so the definition of the name is slightly confused, for example: the mother board used in personal computers, called the motherboard, and can not be directly called the circuit board, although there is a circuit board in the host board, but not the same, so the evaluation of the industry when the two are related but can not be said to be the same. Another example: because there are integrated circuit parts loaded on the circuit board, the news media calls it an IC board, but in essence, it is not equivalent to a printed circuit board. The printed circuit board we usually say refers to the bare board - that is, the circuit board without the components on it.
PCB circuit boards have developed from single-sided to double-sided, multi-layer, flexible and flexible, and still maintain their respective development trends. Due to the continuous development to the direction of high precision, high density and high reliability, and the continuous reduction of size, reduction of cost and improvement of performance, the printed board still maintains a strong vitality in the future development of electronic equipment engineering.
So how is the PCB designed? Follow these seven steps to understand.
1. Preliminary preparation
This includes preparing components and schematics. Before the PCB design, it is necessary to prepare the schematic SCH components and PCB component package library.
The PCB component package library is best established by the engineer according to the standard size data of the selected device. In principle, the PC component package library is established first, and then the schematic SCH component library is established.
PCB component package library has high requirements, which directly affects the installation of PCB; Schematic SCH component library requirements are relatively loose, but care should be taken to define the pin properties and the corresponding relationship with the PCB component package library.
2. PCB structure design
According to the determined PCB board size and mechanical positioning, draw the PCB board frame in the PCB design environment, and place the required connectors, keys/switches, positioning holes, assembly holes, etc., according to the positioning requirements.
Fully consider and determine the wired area and unwired area (such as how much of the area around the positioning hole belongs to the unwired area).
3. PCB layout design
The layout design is to place the device in the PCB board frame according to the design requirements. Generate the 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 be stored in the software background. All devices can be pulled out through the Placement operation, and there is a flying line connection between the pins. Then the device layout can be designed.
PCB layout design is the first important process in the entire design process of PCB, the more complex PCB board, the better or worse the layout can directly affect the difficulty of the realization of later wiring.
The layout design depends on the circuit foundation and design experience of the PCB circuit board designer, which belongs to the higher level of requirements for the PCB circuit board designer. The experience of junior circuit board designers is still shallow, suitable for small module layout design or PCB layout design tasks with low difficulty of the whole board.
4. PCB layout design
PCB layout design is the most workload process in the entire PCB design, which directly affects the performance of the PCB board.
In the design process of PCB, there are generally three levels of wiring:
The first is the layout, which is the most basic entry requirements of PCB design;
The second is the satisfaction of electrical performance, which is a measure of whether a PCB board is qualified, after the line layout, carefully adjust the wiring, so that it can achieve the best electrical performance;
Once again, neat and beautiful, disorderly wiring, even if the electrical performance passes, it will bring great inconvenience to the later optimization and testing and maintenance of the board, the wiring requirements are neat and uniform, and can not be criss-crossed without any rules.
5. wiring optimization and silk-screen placement
"PCB design is not the best, only better", "PCB design is a defective art", mainly because PCB design to achieve all aspects of hardware design needs, and individual needs may be conflicting, can not have both.
6. Network DRC inspection and structure inspection
Quality control is an important part of the PCB design process, the general quality control means include: design self-check, design mutual check, expert review meeting, special inspection, etc.
Schematic diagram and structural element diagram are the most basic design requirements, and the network DRC inspection and structural inspection are to confirm that the PCB design meets the two input conditions of schematic diagram and structural element diagram respectively.
Generally, circuit board designers have their own accumulated design quality Checklist, in which the entries are partly derived from company or department specifications and partly from their own experience. The special inspection includes the Valor inspection of the design and the DFM inspection, which focus on the PCB design output back-end processing light drawing file.
7. PCB board
Before the PCB is officially processed into a board, the PCB designer needs to communicate with the PCB supplier's PE to answer the manufacturer's confirmation questions about the PCB board processing.
This includes, but is not limited to, the selection of PCB sheet type, the adjustment of line width and line distance of the line layer, the adjustment of impedance control, the adjustment of PCB stacking thickness, the surface treatment processing technology, the aperture tolerance control and delivery standards.
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