5 PCB Design Mistakes That Could Ruin Your Board

Let's dive in.

1. Improper Trace Width and Spacing

One of the most common mistakes in PCB design is not paying enough attention to trace width and spacing, especially in high-current or high-speed applications. If the trace is meant to carry high currents but it happens to be too narrow, it can result in thermal issues or even a failure of the circuit.

The width of your trace can be determined by things like; how much current it should carry without overheating or causing excessive voltage drops, Impedance control, and sensitivity of the signal running through it.

Flux makes routing high speed signals, such as USB data lines, easier by automatically performing coupled routing of the data lines (D+ and D-) and calculating the impedance of the pair based on the PCB stackup. This helps prevent reflections that can cause signal distortion, timing issues, and data corruption.

Flux Copilot can also help you calculate the appropriate trace width based on the current it needs to carry, while also considering the required impedance for high-speed signals. Just ask something like:

@copilot please recommend trace width for my VBUS.

Then copilot responses:

“For VBUS, typically a 5V supply in USB applications, let's assume a common scenario where you might anticipate a current of up to 1A. Using a temperature rise of 10°C, the general guideline for trace width on a 1 oz/ft² copper PCB is approximately 20-30 mils (0.5-0.8 mm) per amp of current.”

2. Overlooking Via Sizes

Vias are crucial for connecting different layers in a PCB, but choosing the wrong size or type can cause issues in both signal integrity and manufacturing. Blind, buried, and microvias are often used in high-density interconnect (HDI) boards, but these require careful consideration during design. For instance, microvias are perfect for compact designs, but if placed improperly, they can lead to poor layer transitions or increased inductance.

Flux let’s you set up your stackup where you add all the manufacturer capabilities. When you need some more advice on what stackup best suits your design, always feel free to ask copilot for some ideas, you could ask

@copilot in a table format recommend vias sizes that i can use for my VDD3V3, my USB, and the other signal buses?

Then here's the copilot response,

If you're routing a high-speed differential pair, such as USB or PCIe, through multiple layers, via stubs can cause signal reflections that degrade signal quality. A rule of thumb is to ensure via lengths are minimized, or even better, use back-drilling techniques to remove stubs, especially in high-frequency circuits.

Moreover, not all manufacturers support the same via sizes, so checking with your manufacturer early in the design process can avoid headaches later. Make sure to adhere to their capabilities, including the aspect ratio limits (via depth to diameter), to avoid costly redesigns e.g. 20:1 for PCBWay.

3. Ignoring Power and Ground Plane Layouts

The layout of power and ground planes is another common area where mistakes are made. These planes act as the backbone of your circuit's stability, so a poorly designed plane can introduce noise, increase EMI, and degrade power delivery.

By default, Flux starts you off with a solid, contiguous ground plane since it is critical for minimizing noise and providing a low-impedance return path for high-speed signals. It is advisable to avoid creating islands which can cause severe signal integrity.

Example:
Imagine routing a high-speed signal across a split ground plane. The signal may cross the gap, creating a longer return path, which increases inductance and can lead to signal distortion or timing errors in critical circuits like clocks or data buses.

Similarly, power planes should be wide enough to handle the current required by each section of the circuit. For designs with sensitive analog circuits, it’s often a good idea to have separate power planes or split planes for analog and digital sections to avoid cross-talk and noise coupling.

4. Neglecting Design for Manufacturability (DFM)

Designing with manufacturability in mind is essential to ensure that your board can be built without issues. It’s easy to forget that the design rules you use in your ECAD tool may not fully align with your manufacturer’s capabilities, and this can result in delays or additional costs.

Flux provides users with pre-configured templates which align with most of the popular manufacture (e.g. PCBWay, JLCPCB, AISLER, LION Circuits, SEEED Studio and many more) capabilities so that users don’t have to worry about manually configuring things like trace widths, keepout, and other parameters. A good general rule of thumb is to always start new project using Flux manufacturer design rule templates

There are numerous DFM tips but here are some common ones to consider;

• Don’t Place Parts Too Close to the Edge of the Board
  Many designers overlook the fact that most manufacturers require a certain clearance between the edge of the board and components. This clearance is needed for handling, tooling, and depaneling during assembly. If components like connectors or switches are too close to the edge, you risk damaging them during these processes.
• Take into Account Manufacturer Capabilities
  Every manufacturer has specific limitations regarding trace width, spacing, via sizes, and the number of layers they can handle. Sending a design that exceeds these capabilities will either increase costs or lead to a failed production run. For example, your HDI board with 0.1mm microvias might not be feasible for a manufacturer specializing in simpler designs.
• Too Closely Spaced Components
  Placing components too close together can lead to assembly issues, especially for automated pick-and-place machines. Components that are tightly packed can cause soldering problems like bridging, or they may not fit the soldering process at all. Always check for manufacturer’s minimum spacing requirements between components and account for heat sinks or thermal relief pads if necessary.

Using Flux manufacturer design rule templates will alert you when either of the manufacturer capabilities  are violated even before sending your files for manufacturing saving you time.

5. Improper Decoupling Capacitor Placement

Decoupling capacitors are used to filter out noise and provide a stable voltage to ICs, especially in digital circuits where rapid switching causes power fluctuations. However, placing these capacitors too far from the pins of the IC can render them ineffective. It is advisable to place these decoupling capacitors as close as possible to the IC without violating the minimum spacing a manufacturer can work with.

Example:
In a typical microcontroller design, you should place decoupling capacitors (such as 0.1µF and 1µF) as close as possible to the VCC and GND pins. Ideally, the capacitors should be placed on the same layer as the IC to reduce parasitic inductance and ensure faster response times. Failure to do so can cause power integrity issues, leading to glitches or resets in your circuit.

Additionally, use vias sparingly when routing decoupling capacitors. Each via adds inductance to the path, which reduces the capacitor's ability to suppress high-frequency noise.

Final thoughts

Before pressing that button to send your PCB design for manufacturing, it's worth taking a step back and performing a thorough review of your design. These design review steps can be quite a handful but what we have discussed above can be considered as the bare minimum. Flux manufacturer design rules makes it easy to ensure trace widths, appropriate via sizes, and manufacturer capabilities are considered when designing your board.

A thorough PCB design review can be a very daunting task, you might not be sure where to start or what checks to include in the review process. That is one of the reasons Flux’s AI lives in your project. You can use copilot to quickly check decoupling capacitors, power and grounding, ensuring compliance with industry standards, and even creating a stronger supply chain. To learn more about how you can use this tool, Sign up for Flux today.