We all know that no matter what you do, there must be a specification, and the same is true in technology. What specifications should be paid attention to when designing PCB?

  1. Layout design specification at design time

　　A. The distance from the board edge during PCB design should be greater than 5mm =197mil

　　B. Place the core components and larger components of the circuit function block first, and then place the surrounding circuit components centered on the core components

　　C. When designing the PCB, place the components closely related to the structure, such as connectors, switches, power sockets, etc.

　　D. The high-power components are placed in a position that is conducive to heat dissipation during PCB design

　　E. When PCB design, the components with high-frequency connections are as close as possible to reduce the distribution of high-frequency signals and electromagnetic interference

　　F. When designing the PCB, keep the input and output components as far away as possible

　　G. During PCB design, components with larger mass should be avoided in the center of the board, and should be placed close to the fixed edge in the chassis

　　H. Thermal components should be kept away from heating components during PCB design

　　I. The layout of adjustable components during PCB design should be easy to adjust

　　J. Place components with high voltages as far as possible out of reach during debugging

　　K. Consider the signal flow direction and arrange the layout reasonably to keep the signal flow direction as consistent as possible

　　L. The layout of PCB design should be uniform, neat and compact

　　M.SMT components should pay attention to the same pad direction as possible to facilitate assembly and soldering and reduce the possibility of bridging

　　N. The decoupling capacitor should be located close to the power input during PCB design

　　O. The component height of the wave soldering surface during PCB design is limited to 4mm

　　P. In PCB design, it is particularly important to add heat sinks to small-sized and high-heat components.High-power components can be used to dissipate heat by using copper, and try not to emit heat-sensitive components around these components.

　　Q. For PCB design with components on both sides, larger and denser ICs, plug-in components are placed on the top of the board, and the bottom layer can only be placed on smaller components and chip components with a small number of pins and loosely arranged.

　　R. During PCB design, the distance from the positioning hole to the nearby pad is not less than 7.62mm (300mil), and the distance from the positioning hole to the edge of the surface mount device is not less than 5.08mm (200mil)

　　S. The high-speed components are as close as possible to the connector during PCB design; the digital circuit and the analog circuit are separated as much as possible, the ground is separated, and the single point is grounded

　　2. PCB design, wiring design specifications

　　A. Adjacent layer signal lines are orthogonal

　　B. The high-frequency signal is as short as possible during PCB design

　　 When designing cPCB, the line should avoid sharp angles, right angles, and forty-five degrees of traces should be used.

　　D. Try to avoid adjacent parallel wiring for input and output signals, and add a ground wire between the wires to prevent feedback coupling

　　E. The digital ground and analog ground should be separated during PCB design

　　F. When designing the PCB, the clock line and high-frequency signal line should consider the line width according to the characteristic impedance requirements to achieve impedance matching

　　G. Double-panel power cord, the direction of the ground wire is consistent with the data flow direction to enhance the anti-noise ability

　　H. During PCB design, the entire circuit board is routed, and the holes should be evenly punched

i. The wiring of the clock should be less perforated, try to avoid running lines with other signal lines, and should be far away from general signal lines to avoid interference with signal lines; at the same time, avoid the power supply part of the board to prevent the power supply and the clock from interfering with each other ; When there are multiple clocks with different frequencies on a circuit board, the two clock lines with different frequencies cannot run side by side; the clock line should be avoided close to the output interface to prevent the high-frequency clock from coupling to the output CABLE line and transmitting; such as a board There is a special clock generation chip on it, and no wires can be routed under it. Copper should be laid under it, and if necessary, it should be specially cut off;

　　J. The distance between the two solder joints is very small, and the solder joints must not be directly connected; the vias drawn from the mounting plate should be as far away from the pad as possible

　　K. Separate power layer and ground layer, power line and ground line should be as short and thick as possible during PCB design, and the loop formed by power supply and ground should be as small as possible

　　L. In PCB design, the pair of differential signal lines are generally routed in parallel, and the holes should be drilled as little as possible. When the holes are punched, the two lines should be punched together to achieve impedance matching