PCB design is often seen as a manual task by many. However, in my experience, I’ve always taken a hands-on approach during the early stages of a design. I personally handle the placement and routing of components, and only after making necessary adjustments do I hand the design over to my colleagues, providing a detailed explanation of why certain routing choices were made. I regularly review my colleagues’ PCB designs, offering constructive feedback on areas that need improvement, which significantly helps them enhance their own design skills.
For example, about a year ago, a colleague was tasked with designing a stepper motor driver board. While the board was functional, its performance didn’t meet the specifications outlined in the documentation. Although it could operate, the board had issues like power loss at high currents, poor performance at high speeds, and subpar waveforms. After a thorough analysis, we discovered that the design violated several fundamental PCB routing principles. Once we made the necessary revisions, the performance improved significantly, demonstrating the importance of proper PCB design techniques. This experience reinforced for me the critical role that PCB routing plays, especially when designing high-power supplies and sensors, where precise routing is crucial to meeting strict performance standards.
Recently, the msOS group has been buzzing with discussions around PCB wiring, particularly concerning issues related to stepper motors. From my experience with PCB layout design, I believe it’s crucial to approach this topic in a way that’s understandable to everyone, regardless of their technical background. Let’s break down the PCB wiring concept clearly, avoiding jargon, and gaining a better understanding of how it works in practice.
### What is PCB Wiring?
PCB wiring is essentially the process of creating paths (or traces) on a printed circuit board to connect various components, allowing electrical signals to flow between them. This is similar to constructing a network of roads to connect different cities. Just as roads are built to guide vehicles, PCB traces guide electrical signals, ensuring they reach the correct destinations.
When designing these paths, there are two key considerations: avoiding circuit loops and minimizing electromagnetic interference.
### Low-Frequency vs. High-Speed Circuits
For low-frequency circuits, the signal paths form simple loops. However, in high-speed circuits, such as those dealing with electromagnetic fields, the signal paths are treated as transmission lines, which are more complex and require careful consideration of their impedance and behavior. A common example of such high-speed circuits is differential signaling, which is widely used in protocols like USB or Ethernet.
Differential signal lines are often considered the ideal way to transmit data between devices because they provide high signal integrity. However, when dealing with complex PCBs that have many components, arranging all traces as differential lines can become impractical. The PCB size would increase dramatically, and routing the necessary traces would be much more challenging.
### The Role of Multilayer PCBs
To solve this problem, multilayer PCBs are introduced. A typical multilayer PCB design may use a two-sided board, with one layer dedicated to a reference ground. This simplifies routing, as you can use fewer signal traces—typically, just N+1 lines, where N is the number of differential pairs.
A “reference ground” is often used in the industry, especially for digital signals, as it helps to maintain signal quality by reducing noise and minimizing the effects of electromagnetic interference (EMI). This is particularly beneficial in embedded systems, where time and space constraints are critical. The reference ground helps shrink the PCB size and improves overall signal quality by shortening the length of the signal traces.
### Design Considerations for Ground Layers
When designing a double-sided PCB, one common challenge is dealing with crossover signals—where traces need to pass over one another. This is where the reference ground comes in, allowing traces to be routed over the ground layer. However, it’s essential that the jumpers connecting the traces to the ground are kept short. If they are too long, the ground reference may be disrupted, leading to degraded signal quality—especially for high-speed signals. In such cases, it’s better to use a more complex, multilayer PCB design.
The ground layer helps maintain signal integrity by providing a stable reference point. However, the reference ground should not be divided or disrupted, as this would undermine its effectiveness.
### Signal Trace Spacing and High-Frequency Considerations
When routing signal traces, especially high-speed ones, it’s important to maintain a reasonable distance between them. For instance, when trains are on parallel tracks, the proximity can cause interference, much like how closely spaced signal traces can affect each other. This is particularly true for high-frequency circuits, where signal integrity is more susceptible to interference.
If signal traces are placed too close to each other, crosstalk can occur, leading to signal degradation. It’s essential to maintain adequate spacing, and ensure the ground layer remains continuous beneath the traces to minimize the risk of interference.
### High-Current Circuits and Signal Integrity
In designs that involve high-current or high-voltage, such as power supply circuits, it’s critical to separate power and signal traces. High-current paths can easily induce noise or affect nearby signal traces. For example, the drive signal for a MOSFET can be affected by nearby power traces carrying high current. In such cases, keeping power and signal traces separated is crucial to avoid interference.
This principle was similarly relevant in the analog audio era, where high gain amplifiers could lead to self-excitation if the layout wasn’t carefully designed. In both cases—whether dealing with MOSFETs or audio amplifiers—the key is to minimize the risk of interference between high-power and low-power signals.
### Design Guidelines for PCB Trace Layout
For typical PCB designs, the reference ground should be placed about 1mm from the edge of the board, with signal traces also placed approximately 1mm away from the reference ground. This creates a controlled environment where signals are confined within the PCB, helping to reduce electromagnetic emissions (EMC) and improve overall performance.
In summary, the principles of PCB design are much like road construction—just as roads need to be carefully planned to avoid traffic jams and ensure smooth travel, PCB traces need to be carefully laid out to ensure optimal signal integrity and minimal interference. By considering factors like ground layers, signal trace spacing, and trace routing, we can effectively manage high-speed signals and create efficient PCB designs.
For example, about a year ago, a colleague was tasked with designing a stepper motor driver board. While the board was functional, its performance didn’t meet the specifications outlined in the documentation. Although it could operate, the board had issues like power loss at high currents, poor performance at high speeds, and subpar waveforms. After a thorough analysis, we discovered that the design violated several fundamental PCB routing principles. Once we made the necessary revisions, the performance improved significantly, demonstrating the importance of proper PCB design techniques. This experience reinforced for me the critical role that PCB routing plays, especially when designing high-power supplies and sensors, where precise routing is crucial to meeting strict performance standards.
Recently, the msOS group has been buzzing with discussions around PCB wiring, particularly concerning issues related to stepper motors. From my experience with PCB layout design, I believe it’s crucial to approach this topic in a way that’s understandable to everyone, regardless of their technical background. Let’s break down the PCB wiring concept clearly, avoiding jargon, and gaining a better understanding of how it works in practice.
### What is PCB Wiring?
PCB wiring is essentially the process of creating paths (or traces) on a printed circuit board to connect various components, allowing electrical signals to flow between them. This is similar to constructing a network of roads to connect different cities. Just as roads are built to guide vehicles, PCB traces guide electrical signals, ensuring they reach the correct destinations.
When designing these paths, there are two key considerations: avoiding circuit loops and minimizing electromagnetic interference.
### Low-Frequency vs. High-Speed Circuits
For low-frequency circuits, the signal paths form simple loops. However, in high-speed circuits, such as those dealing with electromagnetic fields, the signal paths are treated as transmission lines, which are more complex and require careful consideration of their impedance and behavior. A common example of such high-speed circuits is differential signaling, which is widely used in protocols like USB or Ethernet.
Differential signal lines are often considered the ideal way to transmit data between devices because they provide high signal integrity. However, when dealing with complex PCBs that have many components, arranging all traces as differential lines can become impractical. The PCB size would increase dramatically, and routing the necessary traces would be much more challenging.
### The Role of Multilayer PCBs
To solve this problem, multilayer PCBs are introduced. A typical multilayer PCB design may use a two-sided board, with one layer dedicated to a reference ground. This simplifies routing, as you can use fewer signal traces—typically, just N+1 lines, where N is the number of differential pairs.
A “reference ground” is often used in the industry, especially for digital signals, as it helps to maintain signal quality by reducing noise and minimizing the effects of electromagnetic interference (EMI). This is particularly beneficial in embedded systems, where time and space constraints are critical. The reference ground helps shrink the PCB size and improves overall signal quality by shortening the length of the signal traces.
### Design Considerations for Ground Layers
When designing a double-sided PCB, one common challenge is dealing with crossover signals—where traces need to pass over one another. This is where the reference ground comes in, allowing traces to be routed over the ground layer. However, it’s essential that the jumpers connecting the traces to the ground are kept short. If they are too long, the ground reference may be disrupted, leading to degraded signal quality—especially for high-speed signals. In such cases, it’s better to use a more complex, multilayer PCB design.
The ground layer helps maintain signal integrity by providing a stable reference point. However, the reference ground should not be divided or disrupted, as this would undermine its effectiveness.
### Signal Trace Spacing and High-Frequency Considerations
When routing signal traces, especially high-speed ones, it’s important to maintain a reasonable distance between them. For instance, when trains are on parallel tracks, the proximity can cause interference, much like how closely spaced signal traces can affect each other. This is particularly true for high-frequency circuits, where signal integrity is more susceptible to interference.
If signal traces are placed too close to each other, crosstalk can occur, leading to signal degradation. It’s essential to maintain adequate spacing, and ensure the ground layer remains continuous beneath the traces to minimize the risk of interference.
### High-Current Circuits and Signal Integrity
In designs that involve high-current or high-voltage, such as power supply circuits, it’s critical to separate power and signal traces. High-current paths can easily induce noise or affect nearby signal traces. For example, the drive signal for a MOSFET can be affected by nearby power traces carrying high current. In such cases, keeping power and signal traces separated is crucial to avoid interference.
This principle was similarly relevant in the analog audio era, where high gain amplifiers could lead to self-excitation if the layout wasn’t carefully designed. In both cases—whether dealing with MOSFETs or audio amplifiers—the key is to minimize the risk of interference between high-power and low-power signals.
### Design Guidelines for PCB Trace Layout
For typical PCB designs, the reference ground should be placed about 1mm from the edge of the board, with signal traces also placed approximately 1mm away from the reference ground. This creates a controlled environment where signals are confined within the PCB, helping to reduce electromagnetic emissions (EMC) and improve overall performance.
In summary, the principles of PCB design are much like road construction—just as roads need to be carefully planned to avoid traffic jams and ensure smooth travel, PCB traces need to be carefully laid out to ensure optimal signal integrity and minimal interference. By considering factors like ground layers, signal trace spacing, and trace routing, we can effectively manage high-speed signals and create efficient PCB designs.
