PCB News - Circuit board wiring rules in PCB design

PCB layout rules, there are many points to pay attention to, but basically notice the following rules, LAYOUT PCB board should be better, whether it is a high-speed or low-frequency circuit, it is basically the same.

1. General rules

1.1 Pre-divided digital, analog, and DAA signal wiring areas on the PCB board.

1.2 Digital and analog components and corresponding wiring should be separated as much as possible and placed in their respective wiring areas.

1.3 The digital circuit is placed near the parallel bus/serial DTE interface, and the DAA circuit is placed near the telephone line interface.

1.4 DGND, AGND, and ground are separated.

1.5 Reasonable distribution of power and ground.

1.6 The high-speed digital signal trace should be as short as possible.

1.7 The traces of sensitive analog signals should be as short as possible.

1.8 Use wide cables for power supply and critical signal traces.

2. Component placement

2.1 In the system circuit schematic diagram:

a) Divide digital, analog, DAA circuits and related circuits;

b) Divide digital, analog, and mixed digital/analog components in each circuit;

c) Pay attention to the positioning of the power and signal pins of each IC chip.

2.2 Preliminarily divide the wiring area of the digital, analog, and DAA circuits on the PCB board (general ratio 2/1/1), and keep the digital and analog components and their corresponding wiring as far away as possible and confine them in their respective wiring areas.

Note: When the DAA circuit takes up a large proportion, there will be more control/status signal traces crossing its wiring area, which can be adjusted according to local regulations, such as component spacing, high voltage suppression, current limitation, etc.

2.3 After the preliminary division, start placing components from Connector and Jack:

a) Leave the plug-in position around Connector and Jack;

b) Leave space for power and ground wiring around the components;

c) Leave the corresponding plug-in position around the Socket.

2.4 First place mixed components (such as Modem devices, A/D, D/A conversion chips, etc.):

a) Determine the placement direction of the components and try to make the digital signal and analog signal pins face their respective wiring areas;

b) Place the components at the junction of the digital and analog signal wiring areas.

2.5 Place all analog devices:

a) Place analog circuit components, including DAA circuits;

b) The analog devices are close to each other and placed on the side of the PCB containing the TXA1, TXA2, RIN, VC, and VREF signal traces;

c) Avoid placing high-noise components around TXA1, TXA2, RIN, VC, and VREF signal traces;

d) For serial DTE modules, DTE EIA/TIA-232-E

The receiver/driver of the series interface signal should be as close as possible to the Connector and far away from the high-frequency clock signal traces to reduce/avoid the noise suppression devices added to each line, such as chokes and capacitors.

2.6 Place digital components and decoupling capacitors:

a) Digital components are placed centrally to reduce the length of traces;

b) Place a 0.1uF decoupling capacitor between the power supply and ground of the IC, and the connection traces should be as short as possible to reduce EMI;

c) For parallel bus modules, the components are placed close to the edge of the Connector to comply with the application bus interface standard, such as the ISA bus line length is limited to 2.5in;

d) For serial DTE modules, the interface circuit is close to the Connector;

e) The crystal oscillator circuit is as close as possible to its driving device.

2.7 The ground wires of each area are usually connected at one or more points with 0 Ohm resistors or beads.

3. Signal routing

3.1 In the modem signal wiring, the signal wires that are prone to noise and the signal wires that are susceptible to interference should be kept as far away as possible. If it is unavoidable, use a neutral signal line to isolate.

3.2 The digital signal wiring should be placed in the digital signal wiring area as far as possible;

Place the analog signal wiring as far as possible in the analog signal wiring area; (isolated wiring can be placed in advance to limit it to prevent the wiring from being laid out of the wiring area)

Digital signal traces and analog signal traces are perpendicular to reduce cross-coupling.

3.3 Use isolated traces (usually ground) to confine the analog signal traces to the analog signal wiring area.

a) The isolated ground traces in the analog area surround the analog signal wiring area on both sides of the PCB with a line width of 50-100 mils;

b) The isolated ground traces of the digital area surround the digital signal wiring area on both sides of the PCB with a line width of 50-100 mils, and one side of the PCB should be 200 mils wide.

3.4 Parallel bus interface signal line width>10mil (usually 12-15mil), such as /HCS, /HRD, /HWT, /RESET.

3.5 Analog signal trace line width>10mil (usually 12-15mil), such as MICM, MIMV, SPKV, VC, VREF, TXA1, TXA2, RXA, TELIN, TELOUT.

3.6 All other signal traces should be as wide as possible, the line width is >5mil (usually 10mil), and the traces between components should be as short as possible (pre-consider when placing components).

3.7 The width of the trace from the bypass capacitor to the corresponding IC>25mil, and try to avoid using vias.

3.8 Signal wires passing through different areas (such as typical low-speed control/status signals) should pass through the isolated ground wire at one point (preferred) or two points. If the trace is located on only one side, the isolated ground trace can be routed to the other side of the PCB board to skip the signal trace and keep it continuous.

3.9 Avoid 90-degree bends for high-frequency signal routing, and use smooth arcs or 45-degree angles.

3.10 High-frequency signal wiring should reduce the use of via connections.

3.11 Keep all signal wires away from the crystal oscillator circuit.

3.12 For high-frequency signal wiring, a single continuous wiring should be used to avoid the situation where several sections of wiring extend from one point.

3.13 In the DAA circuit, leave a space of at least 60 mils around the perforation (all layers).

3.14 Clear the ground loop to prevent unexpected current feedback from affecting the power supply.

The above is the introduction of circuit board wiring rules in PCB design. Ipcb is also provided to PCB manufacturers and PCB manufacturing technology.