PCB Layout Design Tutorial Guide for Your Next Electronics Project
A printed circuit board (PCB) serves as a platform for connecting electronic components. Designers are required to adhere to DFM and IPC standards for circuit design to enhance the operational performance of the PCB. Nonetheless, designing a PCB is a complex task that demands extensive knowledge. In this tutorial, FS Technologies aims to provide essential tips and rules for PCB design that are vital for ensuring the functionality and reliability of the final product for your upcoming project.
PCB Layout Guidelines
PCB layout is a critical aspect of the circuit design process as it determines the size, shape, and arrangement of components, as well as the copper traces that connect them. It also involves the placement of vias, connectors, and other mechanical components required for PCB assembly and board mounting. Effective layout design should mitigate issues such as signal noise, crosstalk, and EMI. Typically, it is recommended to keep high traces short and direct and to keep all traces away from noisy components such as power supplies and motors. In this tutorial, we will delve into these issues in greater detail.
Signal Noise
- Shorten wiring paths: The flow of current in a circuit is dependent on wiring. Excessively long wires can increase circuit resistance, decrease signal transmission speed, and lower signal quality.
- Separate digital and analog signals: Digital signals contain high-frequency components and interference. When digital and analog signals are laid out together, the analog signal can be interfered with. It is recommended to separate the ground wires of these signals to prevent backflow interference.
- Ground plan: This involves the deliberate separation of ground layers into distinct areas to ensure adequate ground connections between regions. Separating ground areas can improve thermal performance and reduce signal interference, which is critical to maintaining normal operating temperatures of the components.
- Prevent interference: In addition to wiring and planning, using components such as filters, capacitors, and inductors can prevent mutual interference between signals. These components can reduce electromagnetic radiation and electromagnetic susceptibility in the circuit. If needed, FS Technology can provide comprehensive printed circuit services, including component procurement. We source high-quality components from certified manufacturers for your PCBA project.
- Balanced layout: This is a technique that relies on a more reasonable layout between components and signal lines to improve circuit performance. Factors to consider include power distribution, signal pins, ground planning, power supply capacitance, and impedance matching.
Crosstalk
- Separation of high-speed and low-speed signal lines: High-speed signals change faster, but they also have some disadvantages such as electromagnetic crosstalk, which can affect the stability and reliability of low-speed signal lines due to frequency. Therefore, distributing power and ground wires effectively can reduce the probability of mutual crosstalk.
- Reasonable ground planning: Proper ground planning ensures that all devices on the board are effectively grounded. The following rules should be followed: minimize ground loops, maintain ground planes, avoid thin and long ground lines, and use a large ground area.
- Use shielding: If crosstalk is unavoidable during design, shielding is a good solution. It consists of metal materials placed around the signal line that needs to be shielded from interference. It can effectively isolate the signal line and reduce electromagnetic radiation interference.
- Appropriate PCB layers: While adding more layers increases cost, it is an effective solution. Multilayer PCB provide more signal layers, and the gap between layers can increase surface area, thereby reducing crosstalk problems.
Electromagnetic Interference
- Hierarchical layout: For high-end applications that require a large number of lines on the board, the complexity and crossing of the lines can lead to electromagnetic interference. High frequency PCB is commonly used in such applications, and a layered layout or PCB impedance control technology can help to reduce problems like signal distortion and jitter.
- Appropriate substrate material: Different substrate materials have different effects on PCB performance, which is why it’s important to understand the characteristics of different types of PCB before starting the design process. For example, materials like fiberglass and polyimide can help reduce electromagnetic interference.
- Simulation and analysis: Circuit simulation and analysis prior to design can help designers understand the working principle and performance of the circuit, as well as predict and optimize its anti-interference performance. Tools like the SPICE simulator can perform accurate numerical calculations and simulations of the circuit, helping designers evaluate its performance and determine component parameters. Electromagnetic field simulators can simulate the propagation and interference of electromagnetic fields, aiding in the analysis and resolution of electromagnetic interference problems.
Component Placement Tutorial
As one of the most critical sections on the PCBA board, key components should be placed close to the center of the board during design. This will help minimize the length of signal traces and reduce the possibility of interference. Here are some tutorials for placing components in PCB design:
- Group by function: Different components have various functions and roles. Designers need to understand their characteristics and divide the circuit into different parts according to function. Then, they can place related components together for better control of the signal path and optimization of signal transmission. For example, power components should be placed close to each other, and components belonging to the same signal path should be grouped.
- Assembly and repair: The components designed in the layout are used in the final assembly of the PCBA. If the spacing is too small, it may cause assembly difficulties and failure problems, increasing the project cost. Therefore, considering the possibility of assembly when designing the component layout is a technique to reduce costs. In addition, PCBA failure is inevitable, so it is necessary to consider repairing or desoldering components.
- Thermal characteristics of components: Some components generate more heat when the circuit is running, such as power amplifiers and processors. However, if the components are placed too densely, components with poor thermal performance may be affected and damaged. FS Technology recommends placing heat-generating components in open areas or heat-dissipating areas when designing PCBs to avoid mutual influence between components.
- Data transmission: As mentioned earlier, shortening the signal path is critical. Therefore, communicating components such as microprocessors, memory, and interface chips should be placed close to each other. These components communicate or exchange data with each other, and placing them close to each other can reduce data transfer time.
- Orientation and Alignment: The orientation and alignment of components are related to the signal flow direction, the neatness of the board, and the signal path. Thus, component orientation is an essential aspect of the PCB design guidelines. Here are some tips: resistors should be placed perpendicular to the board’s direction, and capacitors should be placed parallel to the board for easy routing.
- Follow the manufacturer’s suggestions: The design files need to flow to the manufacturer eventually. For PCBA companies like FS Technology, there is an independent design department, whose members are experienced electronics industry practitioners. Thus, referring to the modifications provided by the PCBA company’s opinions is often beneficial rather than harmful to the project.
Trace Width Rules
The width of a trace on a PCB should be based on the current it needs to carry. It should be ensured that the width of the trace is sufficient to prevent it from overheating or burning out due to high current flow.
The formula to calculate the track width of a PCB is as follows:
Track Width (W) = (Temperature Rise × Copper Weight)/(Internal Trace Length × Cross-sectional Area of Copper)
Where,
Temperature Rise Maximum allowable temperature rises for the trace
Copper WeightWeight of copper per unit area of the trace.
Internal Trace Length Length of the trace that runs internally on the PCB.
Cross-sectional Area of Copper Area of the copper trace cross-section. It is calculated by multiplying the trace width by the thickness of the copper
PCB Via Tips
A via is a small hole that passes through different layers of a PCB, connecting them together. It’s important to use vias correctly during PCB design. Vias should be placed in locations that don’t interfere with other components or signal traces, and care should be taken to avoid interference with other vias or components. There are three types of vias based on their position on the PCB:
- Through-hole via: This via passes through the PCB from top to bottom and is easy to drill because there is no need to stop drilling at the desired point. This via is larger than the other types.
- Buried via: Unlike traditional vias that connect the top and bottom layers of a PCB, buried vias are located between inner layers and are not visible from the surface. Efficient use of space on the PCB can help reduce the size and weight of electronic devices.
- Blind via: These vias connect one outer layer to an inner layer of the PCB. They are technically challenging to make as drilling needs to be stopped with precision.
Grounding Guidelines
- Use a solid ground plane: A solid ground plane provides a low-impedance return path for current, reduces noise, and improves the reliability of the circuit. Ideally, the ground plane should cover the entire PCB to ensure the current return path is always the shortest distance possible.
- Keep high-speed signal return currents separate from other ground currents: High-speed signals can create significant current loops that can interfere with other ground currents. To minimize this interference, it’s important to keep high-speed signal return currents separate from other ground currents. This can be achieved by using a separate ground plane or by routing the high-speed signals and their return currents together.
- Minimize ground loop area: Ground loops can create unwanted noise in the circuit. To minimize the ground loop area, keep the ground path as short and direct as possible. Try to avoid routing ground traces in loops or using multiple ground points.
- Separate analog and digital ground: Analog and digital circuits should be kept separate to prevent interference. It’s important to keep the analog and digital ground planes separate and to connect them at a single point to avoid ground loops. Separating analog and digital ground can help reduce crosstalk, noise, and interference.
- Consider grounding for power supplies: Power supplies should be properly grounded to minimize noise and interference. Use a separate ground connection for each power supply and connect them to the main ground at a single point. It’s important to avoid sharing a ground connection between different power supplies as it can create ground loops and introduce noise into the circuit. Proper grounding can improve the performance and reliability of the circuit.
Power supply guidelines
We should use voltage regulators and filters to ensure that the power supply is stable and reliable to operate at its ratings. It’s also important to ensure that the power supply traces are sufficiently wide to handle the current load.
- Minimize voltage drops: Use thick traces or multiple parallel traces to minimize voltage drops between the power supply and the load. Calculate the voltage drop and adjust the trace width accordingly.
- Consider thermal management: power supplies can generate significant heat, especially if they are operating at high current levels. Consider adding heat sinks, fans, or other cooling mechanisms to dissipate heat and ensure reliable operation.
- Power supply bypassing: If your circuit has sensitive analog or digital components, consider adding a bypass capacitor between the power supply and ground. This can help to smooth out any voltage fluctuations and prevent noise.
PCB Testing guidelines
Monitoring the entire PCB test is a crucial aspect of validating the design, and choosing a PCBA prototyping service with a fast turnaround can help you complete testing quickly, allowing problems to be identified and resolved before they become major issues. It is important to test each component and subsystem during the building process and thoroughly test the entire board after assembly is complete. Automated testing tools can assist in the testing process and reduce the chances of human error. Consider using PCB testing tools such as boundary scan, automated optical inspection (AOI), or automated x-ray inspection (AXI). To make ICP testing easier, consider adding a programming connector or pad.
Conclusion
Using well-known PCB layout software in design projects can simplify your design process. These tools enable designers to create, edit and optimize layout designs before PCB manufacturing. Attention to the above-mentioned rules and the use of these techniques, along with sending the design files to FS Technology’s mailbox, are key factors in producing high-quality PCBs or PCBA and gaining the attention of electronics manufacturers.
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