Table of Contents
The PCB routing is an important part of the PCB schematic. Proper PCB routing should ensure a reliable Power Distribution Network, adhere to Voltage DRC, and yield good performance for high-speed signals.
This blog delves into key PCB routing aspects, including trace layout, vias, auto-routing, area routing, and escape routing, to help manufacturers develop high-quality PCBs that meet the stringent design and performance requirements.
Principles of PCB Routing
- Key signal traces first: power supply, simulation of small signals, high-speed signals, clock signals, synchronisation signals, and other key signals.
- Routing density priority principle: routing should begin in the densest area of the single board connection. Start wiring from the device with the most complex connection relationships on the single board.
- Key signal processing considerations: provide a special wiring layer for clock signals, high-frequency signals, sensitive signals and other key signals to ensure the minimum circuit area. Methods such as shielding and increasing safety spacing should be employed where necessary.
Arrange networks with impedance control requirements on the impedance control layer and avoid their signals across the split.
PCB Routing Types
Auto-Routing & Area Routing
Many of the modern PCB design tools offer auto-routing. These algorithms are optimized for trace paths to minimize designer work. Still, it’s always good to see auto-routing adhere to specific rules.
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Review and Refine: One always needs to review an auto-routed layout to detect potential violations or inefficiencies.
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Route critical nets first: The routing of critical high-speed or high-current nets is to be done manually and the remaining can be allowed for auto-routing.
Escape Routing
Escape routing is a process of connecting very tightly packed component pins (example Ball Grid Arrays) to reachable routing channels. The major strategies are:
- Via-in-Pad: Put vias directly in pads for space-saving, which enhances routing flexibility.
- Fan-out techniques: Use short traces to disperse signals from densely-packed pins into open routing regions.
- Layer transition: Employ extra layers if a clean and efficient exit can be achieved through transitions of layer.
PCB Routing Design Practices
in Routed Systems
PCB routing is the process of creating and layering the traces that join the PCB’s components. PCB Routing Design must consider the requirements of the IPC-2221 standard.
The proper width of the trace should be selected when routing. The trace’s thickness and width should be minimised to avoid overheating the board, while ensuring compatibility with current standards. If there is enough space, it is recommended that a width greater than the minimum is used to improve thermal management and reliability. Besides, some of the best practices of PCB routing designs includes:
Voltage DRC Compliance
Voltage design rule checks ensure that voltage across traces, pads, and via fall within specified tolerances set by designs. Maintaining voltage DRC should ensure the following:
- No Shorts and Open Circuits: The spacing and clearances are maintained to avoid potential failures.
- No Crosstalk: Trace separation reduces electromagnetic interference between signals.
- Signal Integrity: Proper trace width and spacing reduce power losses and signal distortion.
Voltage PDN
Another important aspect of the Power Distribution Networks in the routing of PCBs is a good PDN that routes power effectively from the source to all components around the board.
Some of the key things to consider, but not limited to, are:
- Trace Width and Copper Thickness: The trace should be able to carry the needed current without excessive voltage drops.
- Decoupling Capacitors: Properly placed capacitors reduce noise, thus stabilize power delivery.
- Ground Planes: The availability of proper, dedicated ground planes in a PCB increases the signal integrity and reduces EMI.
Trace Layout Optimization
Trace layout is very basic in PCB Routing. Each trace routed in PCB routing acts like a conduit for the electrical signals flowing through it, and its design significantly affects the entire board’s performance. Some of the best practices in trace laying include:
- Right Angle vs. Curves:
At high frequencies, sharp and right-angled curves can creat discontinuities that compromise signal integrity due to increased crosstalk, radiation and reflections. To minimize impedance discontinuities, avoid sharp 90-degree angles.
As shown below, the right angle corner is replaced by two forty-five degree angles.
- Alternating alignment directions: When wiring, connections between components should be as short and straight as possible. If most of the traces in a layer follow a certain direction like horizontal, giving preference to perpendicular alignments like vertical can reduce crosstalk between tracks.
- Controlled Impedance: Keep traces of uniform width and employ differential pairs for high-speed signals.
- Clearance: Keep trace spacing adequate to avoid arcing and crosstalk.
Logo & Silkscreen Integration
- Size & Proportion: According to the overall size of the PCB and functional areas to determine the size and proportion of the logo, to maintain coordination with other signs.
- Line Clarity: Ensure that the logo lines are clear and coherent, and plan the main outline wiring for complex logos first.
- Avoid Circuit Interference: Avoid logo wiring and signal lines, power lines, cross shorting, pay attention to the distance from the hole, pads.
- Color Conversion: When converting bmp to gerber file, make sure the color information is converted accurately.
- Gerber File Requirements: Familiar with the format specification, check the preview before transfer to ensure that the logo information is complete.
Via Design Considerations
Vias are critical in multi-layer PCB designs, offering vertical connectivity between layers. With vertical connectivity, designers can optimize the PCB routing paths and effectively manage the signal integrity issue. Poorly designed vias can increase noise, signal integrity issues and mismatched impedances.
Types of Vias
The most common vias types includes:
- Through-hole Vias
- Blind Vias
- Buried Vias
Note:
- Avoid via clusters under BGA components.
- Use via-in-pad for space-constrained designs.
- Match via size to current requirements.
The selection of via type and size is crucial. Microvias reduce parasitic capacitance and inductance, thus ideal for high-frequency designs. Proper placement of vias also minimizes PDN impedance and signal integrity issues.
Check this out to know the general knowledge of PCB vias!
People often use these softwares for robust simulation capabilities and an extensive library of them. For hobbyists and beginners, open-source tools such as KiCAD, and EasyEDA are available.
Want to learn more about PCB E-Routing tools? Check out this blog by ELEPCB!
Conclusion
By understanding and applying principles such as voltage DRC compliance, PDN optimization, thoughtful trace layout, efficient via usage, and advanced routing techniques, manufacturers can produce reliable, high-performance PCBs. Spending time on proper routing not only enhances the functionality of the board but also reduces production costs and time-to-market.
Want to find a reliable PCB manufacturer? Check out ELEPCB! You can contact us to get precision PCBs!
FAQs
A1: The DRC of voltage makes sure that all traces and vias meet the desired clearances and electrical tolerances, avoiding short circuits, and hence, guaranteeing reliable operation.
A2: PDN guarantees stable power supply to all components on a PCB. This decreases the noise level and hence ensures overall circuit reliability.
A3: Auto-routing is appropriate for less critical or simple designs. Manual routing is advised for high-speed or high-current nets.
A4: Escape routing routes densely packed component pins to wider routing channels, thereby ensuring proper connectivity in complex designs.
A5: 5 PCB routing mistakes include:
- Improper Trace Width
- Incorrect Via Placement
- Poor grounding
- Signal integrity issues
- Wrong trace spacing
References
- H. Johnson, “High-Speed Digital Design: A Handbook of Black Magic,” Pearson, 1st ed., Apr. 8, 1993.
- IPC-2221 Standard, “Generic Standard material on Printed Board Design,” IPC, Feb. 1998, Superseded by IPC-2221A, [https://www.ipc.org/TOC/IPC-2221A.pdf].
- EMA-EDA, “PCB Design Tutorials and Guides,” [https://www.ema-eda.com/ema-academy/how-to/], 2019 – 2024.
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