1. Wiring must follow a logical direction: for instance, input/output, AC/DC, strong/weak signals, high frequency/low frequency, high voltage/low voltage, etc. Their paths should be linear (or distinctly separated), avoiding overlap. This is essential to minimize mutual interference. Ideally, the direction should follow a straight line, though this is often difficult to achieve. Circular routing should be avoided. For DC, low signal, and low voltage PCB designs, the requirements can be more relaxed. It’s important to keep the edges of the input and output ends from being parallel to prevent reflection interference. If necessary, a ground wire should be added for isolation, and the wiring on adjacent layers should cross at right angles to reduce parasitic coupling, which tends to occur in parallel arrangements.
2. Select an effective grounding point: Typically, a common ground is necessary, with the digital ground and analog ground connected at the power input capacitor.
3. Position power filter and decoupling capacitors strategically: Place these capacitors as close to the components as possible, as they lose effectiveness if too far away. The decoupling capacitor for the chip should ideally be located on the underside of the device on the opposite side of the board. Power and ground should first pass through the capacitor before entering the chip.
4. Lines should be carefully designed: wide lines should never be reduced to thin if it can be avoided; high-voltage and high-frequency lines should be rounded and smooth, with no sharp angles or corners at 90 degrees. An angle of 135 degrees is generally preferred. The ground wire should be as wide as possible, ideally using a large area of copper to significantly enhance grounding effectiveness. In the design process, minimize the number of vias and reduce the density of parallel lines.
5. Increase the width of power and ground wires as much as possible, with the ground wire being wider than the power wire. The hierarchy is: ground wire > power wire > signal wire.
6. Addressing the common ground for digital and analog circuits: Many PCBs today incorporate a mix of digital and analog circuits rather than just a single functional type. Therefore, it’s crucial to consider the potential mutual interference during PCB wiring, especially noise interference on the ground.
1. The frequency of digital circuits is high, while analog circuits exhibit strong sensitivity. For signal lines, high-frequency lines should be positioned as far away as possible from sensitive analog circuit components. Regarding ground lines, the entire PCB has only one external node, necessitating careful handling of digital and analog common grounds within the PCB. The digital ground and analog ground are effectively separated and not interconnected, except at interfaces (such as connectors) that link the PCB to the external environment, where they are slightly short-circuited.
2. When laying out the signal lines on the ground layer of a multilayer PCB, few wires typically remain unlaid in the signal line layer. Adding more layers can lead to waste and an increase in production workload and costs. To address this issue, consider routing on the ground layer, prioritizing the power layer first and the ground layer second, as preserving the integrity of the formation is crucial.
3. For key signal processing, critical signals such as clock lines should be grounded to minimize interference. Additionally, a solder joint should be made on the side of the crystal oscillator to ground its shell.
4. Design Rule Check (DRC):
Once wiring design is complete, a thorough check must ensure compliance with the designer’s rules, confirming that these rules meet printed board production standards. General inspections should cover:
– The spacing between lines, between lines and component pads, through holes, and among these elements.
– The appropriateness of the power and ground line widths and ensuring tight coupling between them (low wave impedance).
– Opportunities to widen ground wires in the PCB.
– Optimal measures for key signal lines, including minimal length, protective lines, and clear separation of input and output lines.
– Presence of separate ground wires for analog and digital circuits.
– Avoiding graphics (like icons or annotations) that could cause signal short circuits.
– Modifying undesirable linear shapes.
– Ensuring the PCB has a process line and that the solder mask meets production requirements, with appropriate size and positioning to avoid impacting electrical quality.
– Checking that the outer frame edge of the power ground layer in multilayer boards is minimized to prevent exposed copper foil, which could lead to short circuits.
5. Regarding EMC:
A. Opt for devices with slower signal slopes to reduce high-frequency components.
B. Be mindful of the placement of high-frequency components, avoiding proximity to external connectors.
C. Ensure proper impedance matching for high-speed signals, considering the wiring layer and its return current path to mitigate high-frequency reflection and radiation.
D. Place adequate and suitable decoupling capacitors on the power supply pins of each device to reduce noise on the power and ground planes, ensuring capacitor frequency response and temperature characteristics align with design requirements.
E. The power layer should be positioned 20H away from the ground layer, where H is the distance between these two layers.
2. Select an effective grounding point: Typically, a common ground is necessary, with the digital ground and analog ground connected at the power input capacitor.
3. Position power filter and decoupling capacitors strategically: Place these capacitors as close to the components as possible, as they lose effectiveness if too far away. The decoupling capacitor for the chip should ideally be located on the underside of the device on the opposite side of the board. Power and ground should first pass through the capacitor before entering the chip.
4. Lines should be carefully designed: wide lines should never be reduced to thin if it can be avoided; high-voltage and high-frequency lines should be rounded and smooth, with no sharp angles or corners at 90 degrees. An angle of 135 degrees is generally preferred. The ground wire should be as wide as possible, ideally using a large area of copper to significantly enhance grounding effectiveness. In the design process, minimize the number of vias and reduce the density of parallel lines.
5. Increase the width of power and ground wires as much as possible, with the ground wire being wider than the power wire. The hierarchy is: ground wire > power wire > signal wire.
6. Addressing the common ground for digital and analog circuits: Many PCBs today incorporate a mix of digital and analog circuits rather than just a single functional type. Therefore, it’s crucial to consider the potential mutual interference during PCB wiring, especially noise interference on the ground.
1. The frequency of digital circuits is high, while analog circuits exhibit strong sensitivity. For signal lines, high-frequency lines should be positioned as far away as possible from sensitive analog circuit components. Regarding ground lines, the entire PCB has only one external node, necessitating careful handling of digital and analog common grounds within the PCB. The digital ground and analog ground are effectively separated and not interconnected, except at interfaces (such as connectors) that link the PCB to the external environment, where they are slightly short-circuited.
2. When laying out the signal lines on the ground layer of a multilayer PCB, few wires typically remain unlaid in the signal line layer. Adding more layers can lead to waste and an increase in production workload and costs. To address this issue, consider routing on the ground layer, prioritizing the power layer first and the ground layer second, as preserving the integrity of the formation is crucial.
3. For key signal processing, critical signals such as clock lines should be grounded to minimize interference. Additionally, a solder joint should be made on the side of the crystal oscillator to ground its shell.
4. Design Rule Check (DRC):
Once wiring design is complete, a thorough check must ensure compliance with the designer’s rules, confirming that these rules meet printed board production standards. General inspections should cover:
– The spacing between lines, between lines and component pads, through holes, and among these elements.
– The appropriateness of the power and ground line widths and ensuring tight coupling between them (low wave impedance).
– Opportunities to widen ground wires in the PCB.
– Optimal measures for key signal lines, including minimal length, protective lines, and clear separation of input and output lines.
– Presence of separate ground wires for analog and digital circuits.
– Avoiding graphics (like icons or annotations) that could cause signal short circuits.
– Modifying undesirable linear shapes.
– Ensuring the PCB has a process line and that the solder mask meets production requirements, with appropriate size and positioning to avoid impacting electrical quality.
– Checking that the outer frame edge of the power ground layer in multilayer boards is minimized to prevent exposed copper foil, which could lead to short circuits.
5. Regarding EMC:
A. Opt for devices with slower signal slopes to reduce high-frequency components.
B. Be mindful of the placement of high-frequency components, avoiding proximity to external connectors.
C. Ensure proper impedance matching for high-speed signals, considering the wiring layer and its return current path to mitigate high-frequency reflection and radiation.
D. Place adequate and suitable decoupling capacitors on the power supply pins of each device to reduce noise on the power and ground planes, ensuring capacitor frequency response and temperature characteristics align with design requirements.
E. The power layer should be positioned 20H away from the ground layer, where H is the distance between these two layers.
