PCB Drawing: A Summary of Key Practices from Years of Experience
After years of experience in PCB design, certain best practices have emerged. Here, we outline essential aspects of PCB layout, wiring, copper plating, and more, with a focus on optimizing performance and manufacturability.
1. Layout and Wiring Impact on Electrical Performance
- Separate Digital and Analog Ground: Although challenging, separating these can reduce noise. Understanding IC electrical characteristics and signal paths helps with efficient layout.
- IC Placement: Components prone to electromagnetic radiation should be near the power source, while sensitive signal processing elements should be close to the signal input for a better signal-to-noise ratio.
2. Copper Plating Considerations
- Signal Routing: For high-frequency signals, narrow, short traces are preferred due to skin effect. Wider copper traces are suitable for low-frequency signals but can degrade high-speed data signals.
- Data Synchronization: Consistent trace widths and lengths are crucial for ensuring synchronization in data channels. Use serpentine traces to adjust signal delays and ensure accurate data transmission.
- Shielding: Large-area copper plating is used for electromagnetic shielding, especially on double-sided boards where the ground plane acts as the shielding layer.
3. Multi-Layer PCB Interlayer Layout
- Four-Layer Board Setup: Power planes should be placed centrally between signal layers. Avoid routing signals between power layers to enhance isolation and minimize interference.
- Shielding: Power layers provide natural shielding in multi-layer designs, improving overall board performance and aiding manufacturing yields.
4. Via Design
- Minimize Vias: Vias introduce capacitance and may generate burrs or electromagnetic radiation. Opt for smaller vias (e.g., 0.5mm or 0.8mm) to reduce the risk of burrs while maintaining production efficiency.
- Burr Prevention: Smaller via apertures have a lower likelihood of producing burrs, improving board quality.
5. Software Application
- Familiarity with Tools: The choice of design software (e.g., PADS, PROTEL) is less important than understanding how to use it efficiently.
- Non-Standard Holes: For non-circular holes, create a custom layer to describe them. Use wireframe shapes that are filled in and well-documented to ensure correct interpretation by the manufacturer.
6. Sending the PCB for Manufacturing
When submitting files to a manufacturer, ensure you provide:
- PCB Computer Files: Include all necessary design files.
- Layering Scheme: Provide details on the layer layout (e.g., circuit map, mechanical structure map).
- Manufacturing Process Requirements: Specify board material (e.g., flame-retardant), surface finishes (e.g., gold plating, copper plating), and thickness.
- Sample Quantity: Clearly indicate the number of boards required.
- Contact Information: Include contact details for follow-up.
By following these guidelines—such as optimizing trace width, minimizing via use, and ensuring proper documentation for manufacturing—you can significantly improve the performance, reliability, and manufacturability of your PCB designs.
