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PCB design must know PCB layout design specifications

2020-01-08 10:28:49

We all know that “there is no rule without a square”, the same is true in technology. So, what specifications should we pay attention to when designing a PCB?

I. Layout Design Specifications

 a. The distance the edge of the board should be greater than 5mm = 197mil;

 b. Place components closely related to the structure, such as connectors, switches, power sockets, etc .;

 c. Prioritize the core components larger components of circuit function blocks, then place the surrounding circuit components around the core components;

  d. The high-power components are placed in a position conducive to heat dissipation;

  e. Larger quality components should be avoided in the center of the board, should be placed near the fixed edge in the chassis;

  f. Components with high-frequency connections are as close as possible to reduce the distribution of high-frequency signals electromagnetic interference;

  g. Input output components should be as far away as possible;

  h. Components with high voltage should be placed in hard-to-reach places when debugging;

  i. The thermal element should be far away the heating element;

  j. The layout of adjustable elements should be easy to adjust;

  k. Consider the signal flow direction, arrange the layout reasonably to keep the signal flow direction as consistent as possible;

  l. The layout should be uniform, neat compact;

  m.SMT components should pay attention to the direction of the pads as much as possible to facilitate mounting soldering reduce the possibility of bridging;

  n. The decoupling capacitor should be near the power input end;

  o. The component height of the wave soldering surface is limited to 4mm;

  p. For PCBs with components on both sides, larger denser ICs, plug-in components are placed on the top layer of the board, the bottom layer can only place smaller components loosely arranged patch components;

  q. It is particularly important to add a small size high heat component a heat sink. Copper can be used to dissipate heat under high power components, there should be no heat sensitive components around these components;

  r. High-speed components should be as close to the connector as possible; digital circuits analog circuits should be separated as much as possible. It is recommended to separate the ground ground at a single point;

  s. The distance the positioning hole to the nearby pad is less than 7.62mm (300mil), the distance the positioning hole to the edge of the surface-mount device is less than 5.08mm (200mil).


2. Wiring Design Specifications

 a. The line should avoid sharp angles right angles. Forty-five degrees of line should be used;

 b. The signal lines of adjacent layers are orthogonal;

 c. The high-frequency signal is as short as possible;

 e. The input output signals should be avoided as much as possible in parallel. It is recommended to add a ground wire between the lines to prevent feedback coupling;

 f. The direction of the double-panel power line ground line is recommended to be consistent with the data flow direction to enhance the anti-noise capability;

 g. Digital ground analog ground should be separated;

 h. Clock line high-frequency signal line should consider the line width according to the characteristic impedance requirements to achieve impedance matching;

 i. The whole circuit board is wired, the holes must be uniform;

 j. Separate power ground planes, power lines, ground lines are as short thick as possible, the loop formed by power ground is as small as possible;

k. The clock wiring should be less punched, try to avoid running parallel to other signal lines, keep away general signal lines to avoid interference with signal lines; at the same time, avoid the power part of the board to prevent the power supply clock interfering ; When there are multiple clocks of different frequencies on a circuit board, two clock lines of different frequencies cannot run together; avoid close to the output interface of the clock line, prevent high-frequency clock coupling to the output CABLE line transmitting; such as the board There is a special clock generation chip on it, no traces can be routed underneath, copper should be laid under it, if necessary, it should be specially cut off;

 l. Paired differential signal wires are generally run in parallel, with as few holes as possible. When holes must be punched, two wires should be punched together to achieve impedance matching;

m. The distance between the two solder joints is very small, the solder joints must be directly connected; the vias the patch should be as far away the pads as possible.

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