PCB Tech - Technology expansion PCB circuit board wiring and layout

Prevent signal lines from forming self-loops between different layers, which will cause radiation interference.

PCB layout and layout

Short-line rule: The wiring should be as short as possible, especially for important signal lines, such as clock lines, the oscillator must be placed very close to the device.

PCB layout and layout

Chamfering rules: In the PCB design, sharp and right angles should be avoided, and unnecessary radiation should be avoided. At the same time, the process performance is not good. The angle between all lines should be greater than 135 degrees

PCB layout and layout

The wire from the filter capacitor pad to the connection pad should be connected with a thick 0.3mm wire, and the interconnection length should be ≤ 1.27mm.

PCB layout and layout

Generally, the high frequency part is set in the interface part to reduce the wiring length. At the same time, the division of the high/low frequency part of the ground plane must be taken into consideration. Usually, the two grounds are divided and then connected at a single point at the interface.

PCB layout and layout

For areas with dense vias, attention should be paid to avoid connecting the power supply and the hollowed-out area of the ground layer to form a division of the plane layer, thereby destroying the integrity of the plane layer and causing the signal line to increase the loop area of the ground layer.

PCB layout and layout

Guidelines for non-overlapping power supply layer projection: For PCBs with more than two layers (including), different power supply layers should avoid overlapping in space, mainly to reduce interference between different power supplies, especially between power supplies with large voltage differences, The overlapping problem of the power plane must try to avoid, if it is unavoidable, consider the intermediate ground layer.

PCB layout and layout

3W rule: In order to reduce the interference between lines, ensure that the line spacing is large enough. When the line center distance is not less than 3 times the line width, 70% of the electric field can be maintained without mutual interference, if it is necessary to achieve 98% of the electric field without mutual interference, The 10W rule can be used.

PCB layout and layout

20H criterion: Taking a H (the thickness of the medium between the power supply and the ground) as a unit, if the shrinkage is 20H, 70% of the electric field can be limited within the grounding edge, and if the shrinkage is 1000H, 98% of the electric field can be limited.

PCB layout and layout

Five-five criteria: the selection rule of the number of layers of the printed board, that is, the clock frequency is 5MHZ or the pulse rise time is less than 5ns, then the PCB board must be a multilayer board. If a double-layer board is used, it is best to use one side of the printed board as one Complete ground plane

PCB layout and layout

Mixed-signal PCB partitioning criteria: 1 partition the PCB into independent analog and digital parts; 2 place the A/D converter across partitions; 3 do not divide the ground, set a unified ground under the analog and digital parts of the circuit board ; 4 In all layers of the circuit board, the digital signal can only be wired in the digital part of the circuit board, and the analog signal can only be wired in the analog part of the circuit board; 5 realize the division of analog power and digital power; 6 wiring cannot cross the divided power plane 7 The signal line that must cross the gap between the divided power supplies should be located on the wiring layer close to the large area ground; 8 Analyze the path and method of the return ground current actually flow;

PCB layout and layout

Multilayer board is a better design measure for board-level EMC protection, and it is recommended and optimized.

PCB layout and layout

The signal circuit and the power circuit have separate ground wires, and finally a common ground at one point. It is not advisable to have a common ground wire between the two.

PCB layout and layout

The signal return ground wire uses an independent low-impedance ground loop, and the chassis or structural frame parts cannot be used as a loop.

PCB layout and layout

When the equipment working in medium and short wave is connected to the earth, the grounding wire is less than 1/4λ; if the requirements cannot be met, the grounding wire cannot be an odd multiple of 1/4λ.

PCB layout and layout

The ground wires of the strong signal and the weak signal should be arranged separately and connected to the ground network at only one point.

PCB layout and layout

In general equipment, there must be at least three separate ground wires: one is the low-level circuit ground wire (called signal ground wire), and the other is the relay, motor and high-level circuit ground wire (called interference ground wire or noise ground wire). ); The other is when the equipment uses AC power, the safety ground wire of the power supply should be connected to the chassis ground wire, and the chassis and the subbox are insulated, but the two are the same at one point. Finally, all ground wires should be grounded at one point. . The breaker circuit is grounded at a single point at the point of maximum current. When f<1mhz, ground="" at="" one="" when="" f="">10MHz, ground at multiple points; when 1MHz