PCB Design Guidelines 101: Placement and Routing

Welcome to the second article in our PCB design guidelines series. In this article, we will explore the essential PCB design guidelines that are crucial for achieving optimal PCB design performance and functionality. Whether you're an electronics enthusiast, hobbyist, engineer, student, or professional in the field, understanding these guidelines will empower you to create high-quality PCB designs. In this article we will explore foundational principles and best practices in designing printed circuit boards (PCBs). These guidelines help ensure that a PCB functions correctly, is manufacturable, and meets the required performance standards. Let's dive into the details with JLCPCB!

1. Component Placement:

Making Section in PCB Design:

The Digital and Analog section on a PCB is kept separated so that the signals do not interfere with each other. Grouping related components together not only simplifies routing but also enhances signal integrity by minimizing the risk of crosstalk between unrelated circuits. For example in an analog amplifier design the power section is kept away from the main amplifying IC to avoid noise in the signal.

Making Heat Resistance Design:

Heat-generating components like power regulators or high-current devices should be placed in areas with sufficient airflow or near the edges of the PCB to facilitate effective heat dissipation. Proper spacing between components is essential for ease of assembly and maintenance, as well as to ensure that automated soldering processes can be carried out without causing bridging or other defects.

High Speed Design Consideration:

High-speed components, such as processors and memory modules, should be placed close to their associated connectors to minimize trace lengths, which helps reduce signal delay and potential interference. Overall, thoughtful component placement is essential for optimizing the performance and durability of the final PCB design.

2. Trace Routing:

The routing of traces, which are the conductive pathways that connect different components, must be carefully planned to minimize interference, signal loss, and potential issues like crosstalk. Proper trace routing plays a critical role in signal integrity, EMI/EMC compliance, and impedance control.

Basic Routing Techniques:

To maintain signal integrity, it is crucial to minimize signal reflections by following proper trace routing techniques. Signal reflections can occur when there is a sudden change in impedance along the transmission line, leading to a partial reflection of the signal. This can result in signal degradation and timing errors. Additionally, avoiding sharp 90-degree angles in traces helps reduce signal reflection and maintain smoother current flow.

High Speed Design Routing:

High-speed signals require special attention, as they are sensitive to trace length and impedance variations. In high-speed designs, crosstalk is another important consideration. Crosstalk refers to the undesired coupling of signals between adjacent traces, which can result in signal interference and degradation. To mitigate crosstalk, techniques such as spacing the traces adequately, using differential pairs for high-speed signals, and employing shielding techniques can be employed.

Power Track Routing:

Proper routing also involves maintaining adequate spacing between traces to prevent short circuits and ensuring that power and ground traces are sufficiently wide to handle the required current without excessive voltage drops. Additionally, using multiple parallel tracks can help distribute current more evenly and reduce the overall resistance. Power tracks should also be kept as short as possible to reduce voltage drops and ensure stable power delivery to critical components.

Signal and Ground Path Routing:

Ground planes are typically used beneath signal traces to provide a low-impedance return path, which further enhances signal stability. In complex designs, multi-layer routing is often necessary, where signal layers are sandwiched between ground and power planes to minimize noise and interference. Overall, effective trace routing is essential for achieving a PCB design that meets both electrical performance requirements and manufacturing standards.

Antenna Impedance Match Routing:

Impedance control is crucial for maintaining signal integrity, especially in RF design. Impedance mismatches can lead to signal reflections and degraded performance. To ensure impedance control, it is important to use proper trace widths, dielectric materials, and layer stack-up configurations. Design guidelines and simulation tools can be utilized to calculate and verify the impedance values, allowing for efficient signal transmission.

3. Layer Stack-up Strategies:

Layer stack-up in PCB design refers to the arrangement and configuration of different layers within a printed circuit board. Proper stack-up is crucial for optimizing the board’s electrical performance, mechanical stability, and manufacturability.

By choosing the layer stack-up according to the requirements of a design, noise can be reduced to minimum. For instance, if a signal path is positioned over a ground plane, the signal propagates more quickly. And by including a power plane in the stack-up, the number of tracks can be reduced, allowing the use of vias to provide VCC or 5V.

6 layer PCB with EMI/ EMC considerations:

• Signal Layer
• Ground plane
• Signal Layer
• Power Plane
• Ground Plane
• Signal Layer

4 layer PCB with EMI/ EMC consideration for audio applications:

• Signal Layer
• Ground plane
• Ground Plane
• Signal Layer

4 layer PCB designed for embedded solutions:

• Signal Layer
• Ground plane
• Power Plane
• Signal Layer

Design Rules:

Design rules are a set of guidelines that define the minimum requirements for various aspects of PCB layout, ensuring manufacturability and reliability. Design rule checks (DRC) are automated tools that verify if the design adheres to these rules, preventing potential issues during fabrication and assembly.

Minimum Track Spacing and Track Width:

Minimum trace width and spacing are crucial design rules that affect signal integrity, impedance control, and manufacturability. Narrow traces can lead to high resistance and signal loss, while insufficient spacing between traces can result in crosstalk and short circuits. Adhering to proper trace width and spacing requirements minimizes these issues and ensures reliable PCB performance.

Via Drill Hole Size and Annular Ring:

Via design rules specify the size and placement of vias to ensure effective connections between layers and to avoid manufacturing defects. Annular ring size is another important design rule, especially for vias and pads. It defines the copper ring around the drilled hole and affects the mechanical strength and reliability of the connections. Insufficient annular ring size can lead to weak solder joints and potential failures. Designing with appropriate annular ring sizes ensures robust connections and reliable PCB operation.

Solder Mask and Silkscreen:

Solder mask clearance is the distance between the copper features and the solder mask layer. Sufficient clearance is necessary to prevent solder mask encroachment on pads and traces, which can cause soldering issues during assembly. Proper solder mask clearance design rules ensure reliable solderability and avoid solder mask-related defects. Silkscreen design rules ensure the clear and effective placement of markings, text, and symbols on the PCBs surface.

It is important to note that design rules may vary between PCB manufacturers or specific fabrication processes. You can familiarize yourself with the design rules provided by your manufacturer and consider industry standards, such as IPC standards, to ensure compliance and optimize the manufacturability of your PCB designs.

Conclusion:

In this article, we have explored the essential PCB design guidelines for achieving optimal performance. We discussed the significance of component placement, trace routing, and layer stack-up in ensuring signal integrity, EMI/EMC compliance, and thermal management. We also highlighted the importance of design rules and provided insights into key considerations such as trace width and spacing, annular ring size, and solder mask clearance. By following these guidelines, you will be equipped to create high-quality PCB layouts that meet industry standards and ensure the success of your electronic projects. See how PCB are manufactured in the JLCPCB factory.

Visit JLCPCB's website to explore our design tools, tutorials, and services that can help you optimize your PCB layouts and bring your electronic designs to life. Stay tuned for the next article in our PCB Basics series.