The Six Fundamentals of PCB Layout

1) Mechanical Specification

Mechanical constraints must be clearly defined and mutually agreed upon prior to initiating the PCB layout process. These constraints encompass the board outline geometry, overall thickness, mounting hole configurations, and the precise placement of connectors or other mechanical components. Typically, the mechanical design dictates the starting point of the PCB layout, providing the designer with a framework for determining placement flexibility and available routing paths.

2) Component Placement

Component placement is a critical aspect of PCB layout, significantly impacting the overall performance of the final design. Proper isolation of functional areas, such as power, digital, and analogue sections, is crucial to minimizing interference and optimizing circuit performance. In addition to segregation, consistent component orientation is another key factor, as maintaining uniform orientation simplifies inspection processes and accelerates assembly, improving efficiency and reducing the likelihood of errors.

3) Design Constraints

Incorporating design constraints is pivotal in determining the success or failure of a PCB design. A thorough understanding of the design is essential, and any new components or technologies should be carefully studied through datasheets and layout guidelines. A properly configured constraints manager significantly reduces the likelihood of errors. It should encompass both physical and electrical parameters, such as impedance control, matched trace lengths, trace width specifications, spacing rules, and mechanical constraints, among others. A well-defined constraints manager ensures adherence to critical design requirements, streamlining the layout process and improving design integrity.

4) Stack-up

The initial board stack-up requires thorough evaluation at the onset of the PCB layout process, as it can evolve dynamically during the design phase. Nonetheless, the number of layers is a key cost determinant for bare PCB manufacturing. An improperly configured stack-up can have a substantial impact on electromagnetic compatibility (EMC) performance. To mitigate electromagnetic interference (EMI) arising from disrupted return paths and to facilitate controlled trace impedance, it is critical to provide routing layers with uninterrupted reference planes.

5) Design for Manufacture

It is essential to maintain a balance between adhering to layout best practices and optimizing for manufacturability. As previously mentioned, standardizing component orientations enhances manufacturability, but it can also negatively impact board performance by introducing suboptimal trace routing. Other common trade-offs include managing the current-carrying capacity of through-hole connections versus the need for thermal relief to facilitate soldering. Such design trade-offs frequently arise and must be carefully navigated to ensure both performance and manufacturability are not compromised.

6) Grounding

Grounding, arguably the most critical of the six design fundamentals, demands meticulous attention. While some datasheets still recommend splitting ground planes between digital and analogue sections, modern design practices increasingly favour proper component segregation while maintaining continuous, unbroken ground planes to preserve return current paths. Chassis or protective grounding also plays a significant role, particularly when the board is housed in a metal enclosure, as it impacts both safety and EMC performance.

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At HGL Systems, we bring years of expertise in designing and manufacturing PCBs that meet rigorous DO-160 and MIL-STD EMC standards. In addition to complying with stringent electrical requirements, we have extensive experience in producing PCBs that undergo demanding environmental testing, including vibration resistance, explosive atmosphere compliance, fluid susceptibility, and more.