The 10 most common mistakes to avoid in PCB design

In the domain of electronic circuits, the printed circuit board (PCB) stands as a crucial element. It facilitates electrical connections among numerous components, bridging the entire device with external environments. Thus, even the tiniest mistake in design can cascade into substantial delays, extra costs, or even total circuit failure. Despite the progressive design technologies that have streamlined production costs for PCB manufacturers, errors in the PCB design phase can lead to unanticipated financial implications. It is worth noting that mistakes can occur, even among seasoned PCB designers. Thus, we present ten prevalent design mistakes to avoid, along with guidelines to steer clear of them.

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1. Incorrect Trace Geometries

The geometry of PCB traces is paramount since they carry electrical signals between various circuit elements, adhering to speed, current strength, and frequency constraints. This makes it essential to properly define the width and thickness of each trace. For traces carrying a current greater than 0.5 A, they are classified as power transmission lines, requiring specific dimensions that deviate from low-power designs. Designers can utilize tools based on the IPC standard for calculations regarding internal (stripline) and external (microstrip) traces. External PCB traces can typically handle higher currents due to superior airflow and heat dissipation properties. Additionally, proper thickness selection is crucial, as many manufacturers offer copper thickness options ranging from 0.5 oz/ft2 to 2.5 oz/ft2 or more. It is vital to choose a thickness that minimizes resistance and enhances thermal management, often requiring thicknesses of 2 or 3 ounces for high-power applications.

2. Subpar Layout Decisions

As the trend toward miniature printed circuit boards persistently intensifies, the use of smaller components and reduced spacing becomes more prevalent. An inefficient layout can lead to connection issues and non-compliance, particularly with miniaturized components featuring higher pin counts. To guarantee optimal performance and future-proof designs, selecting a layout strategy that closely aligns with the specific circuit requirements is essential. Additionally, allocating adequate space for potential future components is advisable, allowing for flexibility in the design.

3. Misplaced Decoupling Capacitors

Decoupling capacitors are imperative for stabilizing power supply lines, ensuring voltage consistency across PCB components. Proper connection in parallel with the power supply—positioned as close as possible to the relevant pins—is necessary for functionality. Power lines should route directly to the decoupling capacitor before reaching the targeted pin; otherwise, feedback circuits could become unstable.

4. Errors in Landing Patterns

Landing patterns, significantly distinct from footprints, pertain specifically to the pad sizes required for components. Each landing pattern must exceed the footprint dimensions slightly to accommodate proper soldering. Even minor measurement discrepancies, as little as half a millimeter, can lead to misalignments during the manufacturing process. Modern PCB CAD tools come outfitted with libraries containing both symbols and landing patterns. However, inaccuracies can arise when integrating non-standard components, necessitating manual creation of pads and corresponding symbols. For example, if two pads are spaced less than one millimeter apart, soldering becomes virtually impossible due to misalignment issues.

5. Overdependence on Automatic Routing Features

While automatic routing is available in most PCB design software, excessive reliance can lead to undesired routing layouts. This can increase the overall PCB area used and result in larger via holes than would typically be required with manual routing. Both the volume of PCB traces and via holes directly influence manufacturing costs.

6. Use of Blind or Buried Vias

Vias can be invaluable for enhancing PCB routing and thermal performance. However, care must be exercised while considering their implementation. Blind vias link external layers with internal ones, while buried vias connect internal layers together. Through-hole vias are intended for external layer connections, or to potentially link internal layers. Each via's size, tolerances, and specifications must be meticulously defined, and while useful, blind and buried vias often come with increased production costs.

7. Excessively Long Traces

Traces designed to carry high-speed signals should prioritize minimal dimensions. Extended trace lengths can introduce significant issues such as signal reflection, increased susceptibility to electromagnetic interference (EMI), and elevated manufacturing costs. If a trace exceeds one-tenth of the wavelength of the signal it carries, it must undergo impedance calculations to maintain signal efficacy.

8. Insufficient Management of EMI

Electromagnetic interference can often be a byproduct of inadequate PCB design practices. To mitigate EMI, it is advisable to organize components by their functional groupings, including separating analog and digital circuits, as well as power and low-speed sections from high-speed sections. Additionally, integrating shielding materials and eliminating right-angle traces on the PCB can further mitigate interference.

9. Flawed Antenna Layout

For PCBs incorporating antennas for wireless applications, attention must be paid to layout precision to ensure optimal power transfer. The transmission line connecting the transceiver and antenna should maintain an impedance of 50 ohms. Employing a matching circuit, such as a Pi (LC) tuner filter, is helpful in achieving accurate impedance matching.

10. Neglecting to Review Designs Thoroughly

Often given inadequate attention, the review process is pivotal in the PCB design lifecycle. Conducting periodic reviews ensures alignment with overarching project requirements, functionality standards, and accurate interconnections among circuits. Peer reviews from team members can unearth errors that a designer may overlook, significantly improving the quality of the end product.

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