1. From Schematic to PCB Design Process
Establish component parameters → input principle netlist → design parameter settings → manual placement → manual routing → design verification → review → CAM output
2. Parameter Settings
The spacing between adjacent traces must meet electrical safety standards, and to facilitate assembly and production, the spacing should be as wide as possible. The minimum spacing must be sufficient for the voltage rating. When trace density is low, signal line spacing can be increased. For signal lines with large voltage differences, the spacing should be minimized, but the gap should be increased for critical signals. Typically, trace spacing is set to 8 mils. The distance between the inner hole of the PCB pad and the edge of the board should be no less than 1 mm to avoid pad defects during manufacturing. When connecting thin traces to pads, the design should use a tapered connection. This shape helps prevent pad delamination and ensures that traces and pads remain securely bonded.
3. PCB Component Layout
1. **Introduction**
Practice has shown that even if the circuit schematic design is correct, improper design of the printed circuit board (PCB) can negatively impact the reliability of electronic equipment.
For instance, if two thin parallel traces on the PCB are placed too closely, this can cause signal waveform delays and generate reflection noise at the transmission line’s termination. Similarly, improper power and ground plane design can degrade product performance. Therefore, it is essential to use the correct methods when designing the PCB.
2. **Current Loops in Switching Power Supplies**
Every switching power supply contains four current loops:
– Power switch AC circuit
– Output rectifier AC circuit
– Input signal source current loop
– Output load current loop
The input capacitor is charged by an approximate DC current, and its primary function is broadband energy storage. Similarly, the output filter capacitor stores high-frequency energy from the output rectifier while also eliminating DC energy in the output load loop.
Thus, the terminals of both input and output filter capacitors are crucial. The current loops must be connected to the power supply terminals of these capacitors, and not directly to the power switch or rectifier loop. If the input/output loops are directly linked to these components, the AC energy will radiate into the environment via the input or output filter capacitors.
3. **Power Switch and Rectifier AC Circuits**
The AC circuits of both the power switch and the rectifier involve high-amplitude trapezoidal currents, with substantial harmonic components. These high-frequency components can be many times greater than the switch’s fundamental frequency, and the peak amplitude can reach up to five times the amplitude of the continuous input/output DC current. The transition time is typically about 50ns.
These two loops are particularly susceptible to electromagnetic interference, which is why their AC loops should be routed before other power supply traces. The three primary components in each loop—filter capacitors, power switches or rectifiers, and inductors or transformers—should be placed close to each other. The positions should be adjusted to minimize the length of the current paths between them.
4. **Designing the Switching Power Supply Layout**
The optimal switching power supply layout should mirror the electrical design. The recommended design sequence is as follows:
1. Place the transformer
2. Design the power switch current loop
3. Design the output rectifier current loop
4. Connect the control circuit to the AC power circuit
5. Perform PCB routing
Switching power supplies operate at high frequencies, and any PCB trace can act as an antenna. The trace length and width directly influence impedance and inductance, which in turn affect frequency response. Even traces carrying DC signals can couple with RF signals from nearby traces, leading to interference or even radiated emissions.
To mitigate this, all AC-carrying traces should be as short and wide as possible. Components connected to these traces should be placed close together.
5. **Minimizing Impedance and Inductance**
The length of a trace is proportional to its inductance and impedance, while width is inversely related. Longer traces have lower frequencies at which they can send or receive electromagnetic waves and are more prone to radiating RF energy. To reduce loop resistance, power traces should be made wider, and the direction of the power trace and ground trace should align with the current flow. This configuration enhances noise immunity.
6. **Grounding Considerations**
Grounding plays a critical role as the common reference point for all current loops in a switching power supply and is key to controlling interference. Proper grounding placement is essential to avoid mixing different ground types, which can lead to unstable power supply operation.
7. **Design Review**
After the PCB routing is complete, it is important to carefully review the design to ensure that it adheres to the rules established by the designer. Additionally, it should be verified that these design rules comply with the requirements of the PCB manufacturing process.
Key checks include:
– Adequate spacing between traces and pads
– Proper clearance between traces and vias
– Reasonable distances between component pads and vias
– Appropriate trace widths for power and ground lines
– Presence of ground planes in sufficient areas of the PCB
8. **Exporting Design Files**
When exporting Gerber files, the following layers need to be output:
– Routing layer (bottom layer)
– Silk screen layer (top and bottom)
– Solder mask (bottom solder mask)
– Drilling layer (bottom layer)
– NC Drill files
For the silk screen layers, avoid selecting “Part Type.” Instead, select the top (or bottom) layer along with the Outline, Text, and Line from the silk screen layer. Ensure that each layer is correctly set to “Board Outline” when configuring the Layer settings.
If you have any PCB manufacturing needs, please do not hesitate to contact me.Contact me
Establish component parameters → input principle netlist → design parameter settings → manual placement → manual routing → design verification → review → CAM output
2. Parameter Settings
The spacing between adjacent traces must meet electrical safety standards, and to facilitate assembly and production, the spacing should be as wide as possible. The minimum spacing must be sufficient for the voltage rating. When trace density is low, signal line spacing can be increased. For signal lines with large voltage differences, the spacing should be minimized, but the gap should be increased for critical signals. Typically, trace spacing is set to 8 mils. The distance between the inner hole of the PCB pad and the edge of the board should be no less than 1 mm to avoid pad defects during manufacturing. When connecting thin traces to pads, the design should use a tapered connection. This shape helps prevent pad delamination and ensures that traces and pads remain securely bonded.
3. PCB Component Layout
1. **Introduction**
Practice has shown that even if the circuit schematic design is correct, improper design of the printed circuit board (PCB) can negatively impact the reliability of electronic equipment.
For instance, if two thin parallel traces on the PCB are placed too closely, this can cause signal waveform delays and generate reflection noise at the transmission line’s termination. Similarly, improper power and ground plane design can degrade product performance. Therefore, it is essential to use the correct methods when designing the PCB.
2. **Current Loops in Switching Power Supplies**
Every switching power supply contains four current loops:
– Power switch AC circuit
– Output rectifier AC circuit
– Input signal source current loop
– Output load current loop
The input capacitor is charged by an approximate DC current, and its primary function is broadband energy storage. Similarly, the output filter capacitor stores high-frequency energy from the output rectifier while also eliminating DC energy in the output load loop.
Thus, the terminals of both input and output filter capacitors are crucial. The current loops must be connected to the power supply terminals of these capacitors, and not directly to the power switch or rectifier loop. If the input/output loops are directly linked to these components, the AC energy will radiate into the environment via the input or output filter capacitors.
3. **Power Switch and Rectifier AC Circuits**
The AC circuits of both the power switch and the rectifier involve high-amplitude trapezoidal currents, with substantial harmonic components. These high-frequency components can be many times greater than the switch’s fundamental frequency, and the peak amplitude can reach up to five times the amplitude of the continuous input/output DC current. The transition time is typically about 50ns.
These two loops are particularly susceptible to electromagnetic interference, which is why their AC loops should be routed before other power supply traces. The three primary components in each loop—filter capacitors, power switches or rectifiers, and inductors or transformers—should be placed close to each other. The positions should be adjusted to minimize the length of the current paths between them.
4. **Designing the Switching Power Supply Layout**
The optimal switching power supply layout should mirror the electrical design. The recommended design sequence is as follows:
1. Place the transformer
2. Design the power switch current loop
3. Design the output rectifier current loop
4. Connect the control circuit to the AC power circuit
5. Perform PCB routing
Switching power supplies operate at high frequencies, and any PCB trace can act as an antenna. The trace length and width directly influence impedance and inductance, which in turn affect frequency response. Even traces carrying DC signals can couple with RF signals from nearby traces, leading to interference or even radiated emissions.
To mitigate this, all AC-carrying traces should be as short and wide as possible. Components connected to these traces should be placed close together.
5. **Minimizing Impedance and Inductance**
The length of a trace is proportional to its inductance and impedance, while width is inversely related. Longer traces have lower frequencies at which they can send or receive electromagnetic waves and are more prone to radiating RF energy. To reduce loop resistance, power traces should be made wider, and the direction of the power trace and ground trace should align with the current flow. This configuration enhances noise immunity.
6. **Grounding Considerations**
Grounding plays a critical role as the common reference point for all current loops in a switching power supply and is key to controlling interference. Proper grounding placement is essential to avoid mixing different ground types, which can lead to unstable power supply operation.
7. **Design Review**
After the PCB routing is complete, it is important to carefully review the design to ensure that it adheres to the rules established by the designer. Additionally, it should be verified that these design rules comply with the requirements of the PCB manufacturing process.
Key checks include:
– Adequate spacing between traces and pads
– Proper clearance between traces and vias
– Reasonable distances between component pads and vias
– Appropriate trace widths for power and ground lines
– Presence of ground planes in sufficient areas of the PCB
8. **Exporting Design Files**
When exporting Gerber files, the following layers need to be output:
– Routing layer (bottom layer)
– Silk screen layer (top and bottom)
– Solder mask (bottom solder mask)
– Drilling layer (bottom layer)
– NC Drill files
For the silk screen layers, avoid selecting “Part Type.” Instead, select the top (or bottom) layer along with the Outline, Text, and Line from the silk screen layer. Ensure that each layer is correctly set to “Board Outline” when configuring the Layer settings.
If you have any PCB manufacturing needs, please do not hesitate to contact me.Contact me
