Basic knowledge of PCB design: detailed explanation of PCB design process
Summary of content: PCB is the abbreviation of Printed Circuit Board (printed circuit board or printed circuit board) in English. Generally, a conductive pattern made of a printed circuit, a printed component, or a combination of the two based on a predetermined design on an insulating material is called a printed circuit.
PCB was born in 1936, and the United States used this technology in 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 applications have penetrated into almost all terminal areas of the electronics industry, including computers, communications, consumer electronics, industrial control, medical instruments, defense industry, aerospace and many other fields.
Having said so much, how is the PCB designed?
Including the preparation of component libraries and schematics. Before designing a PCB, you must first prepare a schematic SCH component library and a PCB component package library.
The PCB component package library is best established by engineers based on the standard size data of the selected device. In principle, the component packaging 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 installation of the PCB; the schematic diagram of the SCH component library requires relatively loose, but pay attention to define the pin properties and the corresponding relationship with the PCB component package library.
Design of PCB structure
According to the determined circuit board size and various mechanical positioning, draw the PCB board frame in the PCB design environment, and place the required connectors, buttons / switches, screw holes, mounting holes, etc. according to the positioning requirements.
Fully consider and determine the wiring area and non-wiring area (such as how much area around the screw hole belongs to the non-wiring area).
3, PCB layout design
The layout design is to place the devices in the PCB board according to the design requirements. Generate the netlist (Design → Create Netlist) in the schematic tool, and then import the netlist (Design → Import Netlist) in the PCB software. After the netlist is successfully imported, it will exist in the software background. All devices can be called out through the Placement operation, and there are flying leads between the pins to connect. At this time, the device can be designed.
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 directly affect the difficulty of the later wiring.
The layout design relies on the basic knowledge of circuit board designers and the rich experience in design, and it is a higher level requirement for circuit board designers. The junior circuit board designer has little experience and is suitable for small module layout design or PCB layout design tasks with low difficulty on the whole board.
4 、 PCB wiring design
PCB wiring design is the process with the largest workload in the entire PCB design, which directly affects the performance of the PCB board.
In the PCB design process, there are generally three realms of wiring:
First of all, it is cloth through, which is the most basic entry requirement for PCB design;
The second is the satisfaction of electrical performance. This is the standard for measuring whether a PCB board is qualified. After wiring, carefully adjust the wiring to achieve the best electrical performance;
Once again, it is neat and beautiful, cluttered wiring, even if the electrical performance is too high, it will bring great inconvenience to the later board optimization and testing and maintenance. The wiring requirements are uniform and can not be crisscrossed without rules.
5.Optimization of wiring and placement of silk screen
"PCB design is not the best, only better", "PCB design is an art of defects", this is mainly because PCB design has to meet the design requirements of various aspects of hardware, and individual requirements may be conflicting. Bear palms do not have both.
For example: a PCB design project needs to be designed as a 6-layer board after the circuit board designer evaluates, but the product hardware must be designed as a 4-layer board due to cost considerations, then the signal shielding ground layer can only 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 that of the initial wiring. After the PCB wiring optimization is completed, post-processing is required. The first thing to deal with is the silk screen logo on the PCB board surface. When designing, the bottom silk screen characters need to be mirrored to avoid confusion with the top silk screen.
6. Network DRC inspection and structure inspection
Quality control is an important part of the PCB design process. General quality control measures include: design self-inspection, design mutual inspection, expert review meetings, and special inspections.
Schematic and structural element diagrams are the most basic design requirements. 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 circuit board designers will have their own accumulated design quality checklists, where entries are partly derived from company or department specifications, and partly from their own experience. The special inspection includes Valor inspection and DFM inspection of the design. These two parts focus on the light drawing files of the PCB design output back-end processing.
7, PCB board
Before the PCB is officially processed, the circuit board designer needs to communicate with the PE of the PCB supplier board manufacturer to answer the manufacturer's confirmation question about the PCB board processing.
These include, but are not limited to, the choice of PCB board model, the adjustment of the line width and spacing of the circuit layer, the adjustment of impedance control, the adjustment of the thickness of the PCB laminate, the surface treatment process, the control of aperture tolerances, and delivery standards.
The above is the entire process of PCB design.