PCB News - Printed circuit board PCB layout specification reference

One: layout design principles

1: The distance from the edge of the PCB board should be greater than 5mm =197mil

2: First place the components closely related to the structure, such as connectors, switches, power sockets, etc.

3: 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
4: The high-power components are placed in a position that is conducive to heat dissipation

5: The components with larger mass should be avoided to be placed in the center of the board, and should be placed close to the fixed edge in the chassis

6: The components with high-frequency connections are as close as possible to reduce the distribution of high-frequency signals and electromagnetic interference

7: Keep input and output components as far away as possible

8: The components with high voltage should be placed as far as possible out of hand during debugging

9: Thermal components should be far away from heating components
10: The layout of adjustable components should be easy to adjust

11: Consider the signal flow direction and arrange the layout reasonably to keep the signal flow direction as consistent as possible

12: The layout should be even, neat and compact
13: SMT components should pay attention to the same pad direction as possible to facilitate assembly and soldering and reduce the possibility of bridging

14: Decoupling capacitor should be near the power input end
15: The component height of the wave soldering surface is limited to 4mm

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

17: It is especially 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.
18: The high-speed components should be as close as possible to the connector; the digital circuit and the analog circuit should be separated as much as possible, preferably separated by ground, and then grounded at a single point

19: 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)

Two: wiring design principles

1: The line should avoid sharp angles, right angles, and forty-five degrees should be used for routing

2: The signal lines of adjacent layers are orthogonal

3: The high-frequency signal is as short as possible

4: Try to avoid adjacent parallel wiring for input and output signals, and it is best to add a ground wire between the wires to prevent feedback coupling

5: Double-panel power cord, the direction of the ground wire is best to be consistent with the data flow direction to enhance the anti-noise ability
6: Separate digital ground and analog ground

7: Clock lines and high-frequency signal lines should consider the line width according to the characteristic impedance requirements to achieve impedance matching

8: The entire circuit board is wired, and the holes should be evenly punched
9: Separate power layer and ground layer, power line, ground line as short and thick as possible, power and ground loop as small as possible

10: 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;
11: The pair of differential signal lines are generally routed in parallel, and as few holes are punched as possible. When holes must be punched, the two lines should be punched together to achieve impedance matching

12: 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

The above is an introduction to the PCB layout specifications of printed circuit boards. Ipcb is also provided to PCB manufacturers and PCB manufacturing technology.