Short for printed circuit board. Generally, the conductive patterns of printed circuits, printed components or the combination of the two made on insulating materials according to a predetermined design are called printed circuits.
PCB was born in 1936, and this technology was widely used in American military radios in 1943. Since the mid-1950s, PCB technology has been widely used. At present, PCB has become the "mother of electronic products", and its application has penetrated into almost every terminal field of the electronic industry, including computer, communication, consumer electronics, industrial control, medical devices, national defense and military industry, aerospace and many other fields.
1, preliminary preparation
Including preparing component library and schematic diagram. Before PCB design, the schematic diagram SCH component library and PCB component packaging library should be prepared first.
The packaging library of PCB components is best established by engineers according to the standard size data of the selected devices. In principle, the component packaging library of PC should be established first, and then the schematic SCH component library should be established.
The requirements of PCB component packaging library are high, which directly affects the installation of PCB; Schematics SCH component library requirements are relatively loose, but attention should be paid to defining pin attributes and the corresponding relationship with PCB component packaging library.
2.PCB structure design
According to the determined circuit board size and mechanical positioning, the PCB frame is drawn in the PCB design environment, and the required connectors, keys/switches, screw holes and assembly holes are placed according to the positioning requirements.
Give full consideration to determine the wiring area and non-wiring area (such as how many areas around the screw hole belong to non-wiring area).
3.PCB layout design
Layout design is to place the device in the PCB frame according to the design requirements. Generate a network table in the schematic tool (Design → Create
Net table), and then import the net table in PCB software (design → import).
Net table). After the network table is successfully imported, it will exist in the software background. All devices can be called out by placing operation, and there is a flying wire connection between pins. At this time, the device layout can be designed.
The layout design of PCB is the first important process in the whole PCB design process. The more complex the PCB, the better the layout, which directly affects the difficulty of later wiring.
Layout design depends on the basic circuit skills and rich design experience of circuit board designers, which is a high-level requirement for circuit board designers. Junior circuit board designers are inexperienced and suitable for small module layout design or PCB layout design tasks with low overall difficulty.
4.PCB wiring design
PCB wiring design is the most workload process in the whole PCB design, which directly affects the performance of PCB.
In the process of PCB design, there are generally three kinds of wiring boundaries:
The first is Butong, which is the most basic entry requirement of PCB design;
The second is the satisfaction of electrical performance, which is the standard to measure whether a PCB is qualified. After wiring, carefully adjust the wiring to achieve the best electrical performance;
Thirdly, neat and beautiful, messy wiring, even if the electrical performance passes the standard, will bring great inconvenience to the optimization, testing and maintenance of the later board reform. Wiring requirements are unified and cannot be staggered.
5. Wiring optimization and screen printing.
"PCB design is not the best, only better", "PCB design is a flawed art", mainly because PCB design needs to meet all aspects of hardware design, and individual needs may conflict with each other, so you can't have both.
For example, a PCB design project needs to be designed as a 6-layer board after evaluation by the circuit board designer, but the product hardware must be designed as a 4-layer board for cost reasons, so the signal shielding layer can only be sacrificed, which leads to an increase in signal crosstalk between adjacent wiring layers and a decrease in signal quality.
The experience of general design is that the time for optimizing wiring is twice as long as that for initial wiring. After PCB routing optimization is completed, post-processing is needed. The first thing to deal with is the silk-screen logo on the surface of PCB. When designing, the screen printing characters at the bottom need to be mirrored to avoid confusion with the screen printing at the top.
6, network DRC check and structure check
Quality control is an important part of PCB design process. General quality control methods include: design self-inspection, design mutual inspection, expert review meeting, special inspection, etc.
Schematic diagram and structural component diagram are the most basic design requirements. Network DRC check and structural check are to confirm that PCB design meets the two input conditions of schematic diagram network table and structural component diagram respectively.
General circuit board designers will have their own accumulated design quality check list, some of which come from the specifications of the company or department, and the other comes from their own experience summary. Special inspections include Valor inspection and DFM inspection, with emphasis on PCB design and post-processing of optical drawings.
7.PCB manufacturing
Before the formal processing and manufacturing of PCB, the circuit board designer needs to communicate with the PE of PCB supplier and answer the manufacturer's confirmation questions about PCB processing.
Including but not limited to the selection of PCB model, the adjustment of circuit layer line width and line spacing, the adjustment of impedance control, the adjustment of PCB stack thickness, surface treatment technology, aperture tolerance control and delivery standards.