1. Incorrect PCB Traces (Routing Issues)
Trace routing is one of the most visible indicators of design quality. Well-routed traces show attention to detail and understanding of signal integrity principles.
- Avoid 90° sharp angles — Use 45° or curved bends. Sharp corners cause acid traps during manufacturing and impedance discontinuities.
- High-current traces — Must be sufficiently wide to handle current without overheating.
- Critical analog traces — Do NOT run parallel to digital or fast-switching traces to prevent noise coupling.
Note: If you see sharp 90° angles, it often means the designer didn't configure their CAD tools correctly.
2. Incorrectly Placed Decoupling Capacitors
Missing or poorly placed capacitors is a major red flag. This is the #1 indicator of amateur or bad design. Decoupling capacitors filter high-frequency noise from power supplies and must be strategically placed.
Every IC power pin needs proper decoupling. The effectiveness of a decoupling capacitor decreases exponentially with distance due to parasitic inductance in the traces.
Requirements Checklist
- Every IC power pin needs at least one decoupling capacitor (typically 0.1 µF ceramic + 10 µF bulk electrolytic)
- Capacitors MUST be placed within 5mm of the power pin (closer is better)
- Via-in-pad or adjacent vias to ground plane are essential for low inductance
- Multiple capacitor values provide filtering across different frequency ranges
If an outsourced designer does this wrong — consider it a serious red flag for the entire design.
3. No Length Matching on High-Speed Signals
Signal propagation delay is approximately 6 inches per nanosecond in FR-4. For multi-gigabit interfaces, even millimeter-level mismatches cause timing skew that leads to data corruption.
This is critically important for:
- DDR memory interfaces (DDR3/DDR4/DDR5)
- Differential pairs (USB 3.0, PCIe, HDMI, DisplayPort)
- Clock distribution networks
- Parallel data buses above 50 MHz
- Look for serpentine traces (controlled meandering) to add precise delay
- All signals in the same timing group must have matched lengths (within ±5 mils typically)
- Equal number of vias per signal (each via adds ~50-100 ps delay)
- Differential pair traces should be tightly coupled and length-matched within the pair
4. Improper RF Feed Lines
For any wireless or RF design, the antenna feed line is mission-critical. Impedance mismatches cause standing waves, signal reflections, and power loss—directly reducing transmission range and reception sensitivity.
At RF frequencies (above 100 MHz), traces behave as transmission lines and must maintain consistent characteristic impedance to prevent reflections.
5. Non-Optimized Component Placement
Component placement affects thermal management, signal integrity, and manufacturing yield.
Inductors
Separate them to avoid magnetic coupling. If they must be close, orient them perpendicular (90°) to each other.
Heat Management
Keep hot components (regulators, power resistors) away from temperature-sensitive parts like crystals, TCXOs, or sensors.
Switching Regulators
Group switching components tightly together. Keep them isolated from sensitive analog circuits to reduce noise coupling.
6. Poor Grounding
A solid ground plane is preferred for most designs. For 2-layer boards, use a star ground topology. Never daisy-chain grounds.
Poor grounding causes voltage drops and signal noise. Ground traces have resistance — current causes voltage drops — distant ICs see a shifted/bouncing ground reference.
Best Practices
- 4-layer boards: Use solid ground and power planes
- Mixed analog/digital: Split ground planes, connect at one point (power supply)
- 2-layer boards: Each IC/subcircuit gets its own ground return trace → star topology back to power supply GND
Summary Checklist
| Check Item | Target | Notes |
|---|---|---|
| Trace Angles | No 90° bends | Use 45° or curves |
| Decoupling Caps | Close to Pins | Biggest giveaway of bad design |
| High-Speed Traces | Length Matched | Check for serpentines |
| RF Lines | 50 Ω Impedance | Specific width required |
| Inductors | Spaced & Perpendicular | Avoid magnetic coupling |
| Grounding | Solid / Star | Never daisy-chain |
Use this checklist to quickly spot major design errors on any PCB — even if you're not an expert, you can identify serious problems in minutes on Gerbers or manufactured boards!