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.

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✅ 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.

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🔢 15 Common Mistakes in Prototype PCB Design

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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).

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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.

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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.)

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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.

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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.

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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.

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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.

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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.

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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

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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.

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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.

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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.

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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

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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.

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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.

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🔧 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)

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🧠 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

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📌 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.