Avoiding Common Mistakes

📘 The Practical Guide to Avoiding Common Mistakes in Prototype PCB Design

Whether you're designing your first board or your fiftieth, prototyping can either be a smooth and satisfying process — or a frustrating one full of avoidable pitfalls. After working on countless prototypes both professionally and personally, I’ve compiled this guide to help you avoid the most common design and testing mistakes.

✅ Quick Philosophy

Prototype PCBs are meant to help you solve problems, not just look production-ready.

Don’t optimize for enclosure fit or aesthetics too early. Optimize for debuggability, testability, and iteration speed.

🔢 15 Common Mistakes in Prototype PCB Design

1. Relying Too Much on Breadboards ("Stale Breadboards")

  • Breadboards are great for early concept validation, but not for long-term prototyping.

  • Loose connections develop over time, leading to untraceable bugs.

  • Use breadboards to test individual subsystems, not whole projects.

  • Transition to PCB as early as possible (within 1–2 weeks of validation).

2. Making DIY "Hardboards" (Perfboards, CNC, Etched)

  • DIY boards often result in:

    • Messy wiring

    • Hidden shorts

    • Difficult-to-debug connections

  • Most modern chips are too small or not breadboard friendly (e.g., QFN, BGA).

  • Use professional PCB services — boards are cheap and arrive within days.

3. Designing for Production Too Early

  • Expect the first PCB to fail or need major changes.

  • Design it with debugging in mind, not enclosure fit.

  • Use bigger boards (e.g., 100mm x 100mm) to give yourself room to test.

  • Focus on function: test all features (power, sensors, UART/I²C, etc.)

4. No Test Points

  • Always add test points for:

    • Power rails (3.3V, 5V, GND)

    • Key communication lines (I²C, UART, SPI)

    • Reset lines, enable lines

  • Use test loops or test pads to easily clip logic probes or scope leads.

  • Saves boards from being scrapped due to one small mistake.

5. No Diagnostic LEDs

  • Add LEDs for:

    • 3.3V, 5V rails

    • Battery charging status

    • MCU "alive" or heartbeat

  • Simple indicators can save hours of debugging.

  • Use a transistor + GPIO for status LEDs if needed.

6. Overcrowding Components

  • Don’t squeeze everything in.

  • Use:

    • Larger passives (e.g., 0805)

    • Extra spacing around ICs and connectors

  • Make room for rework and probing.

  • Shrink later, not during prototyping.

7. Poor Silkscreen Usage

  • Every component should have:

    • Clear label (e.g., “100k”, “MCP23017”)

    • Pin 1 markers for ICs and polarized parts

    • Orientation indicators for diodes and LEDs

  • Use ≥ 2mm text wherever possible.

  • Silkscreen should be visible even when populated.

8. No Isolation Jumpers

  • Add 0Ω resistors or cuttable traces (jumper links) between:

    • Power sections and ICs

    • Communication buses

  • Lets you isolate circuits without desoldering components.

  • Essential for methodical bring-up.

9. Not Breaking Out Unused GPIOs

  • Break out unused MCU pins to:

    • Test pads

    • Small headers

  • Gives you flexibility to:

    • Fix design mistakes

    • Add last-minute features or modules

10. UART Mix-Ups (TX/RX Confusion)

  • Double check UART pin direction:

    • TX → RX

    • RX ← TX

  • Consider swappable jumper pads:

    • Use 0Ω resistors to allow cross/straight selection

  • Can save an entire revision from being scrapped.

11. Locked I²C Addresses

  • Many I²C devices have fixed or semi-fixed addresses.

  • Place two resistors on address pins:

    • One to VCC

    • One to GND

    • Populate only one during assembly

  • Avoid address conflicts without needing a new board.

12. Not Separating Power & Logic Sections

  • Break large boards into:

    • Main (MCU/logic)

    • Power (LDOs, chargers, buck/boost, etc.)

  • Use mouse bites or perforated PCBs for easy separation.

  • Allows you to re-spin the power board independently.

13. Unlabeled SMT Resistors

  • Some manufacturers no longer mark resistor values.

  • For prototyping:

    • Buy labeled SMD resistors (e.g., from Yageo or Panasonic)

    • Makes rework/testing easier and more reliable

14. Using the Wrong Footprints

  • Always verify footprint vs. datasheet dimensions:

    • Pin pitch

    • Pad size

    • Total component size

  • Never trust your EDA software’s built-in libraries blindly.

  • Cross-check with datasheet mechanical drawings.

15. Not Checking Part Availability Before Layout

  • Before you start layout:

    • Make sure parts are actually available

    • Check both stock and lead time

  • Consider pre-ordering key parts (especially PMICs, MCUs, connectors)

  • Prevent “ghost BOM” where your board is ready but parts aren’t.

🔧 Tools & Tips

Recommended EDA Tool:

  • KiCad 7+ (KiCad 8 soon)

    • Free, open source

    • Import Altium files

    • Robust, professional, mature

PCB Fabricators to Use:

  • JLCPCB

  • PCBWay

    • ~$2–5 for 100mm x 100mm 2-layer boards

    • Fast turnaround (3–7 days)

🧠 Bonus Habits for Better Prototyping

  • Log your tests and observations in a project journal.

  • Keep spare PCBs and build partial circuits on each.

  • Use colored wires, labeled bags, and organized bins.

  • Maintain a checklist for every PCB revision:

    • Power check

    • Diode/cap orientation

    • Test pad locations

    • Expected voltages

📌 Final Thought

A prototype PCB is not a final product — it's your lab notebook in physical form. Make it easy to read, edit, and learn from.

If you follow these guidelines, you’ll save time, parts, and headaches — and enjoy the prototyping process a lot more.

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