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PCB design basics: detailed PCB design process

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Published by: Keyou September 30,2019

PCB is the abbreviation of Printed Circuit Board. A conductive pattern which is formed on a conductive material in a predetermined design as a printed circuit, a printed component, or a combination of both is generally referred to as a printed circuit.

1. Preparation in advance

    Includes preparation of component libraries and schematics. 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 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, wiring generally has three realms:

    The first is Butong, which is the most basic entry requirement for PCB design;

    Secondly, the electrical performance is satisfied. This is a standard for measuring whether a PCB board is qualified. After the wiring is completed, the wiring is carefully adjusted to achieve the best electrical performance.

    Once again, it is neat and beautiful, chaotic and uncluttered wiring, even if the electrical performance is passed, it will bring great inconvenience to the later reforming and testing and maintenance. The wiring requirements are neat and uniform, and there is no rule in the vertical and horizontal.

    5, wiring optimization and silk screen placement

    “PCB design is not the best, only better”, “PCB design is the art of a defect”, mainly because PCB design has to meet the design needs of all aspects of hardware, and individual needs may be conflicting, fish and The bear's paw can't 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

    Before the PCB is formally processed, the board designer needs to communicate with the PE of the PCB supplier board 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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