You just finished your PCB layout. It looks good on screen. DRC passes clean. You're ready to hit "order."
Stop.
DRC only catches geometric violations — traces too close, missing connections, overlaps. It doesn't catch design errors. Things like a decoupling cap on the wrong voltage rail, a UART with TX connected to TX, or a bootloader pin that's floating when it should be pulled high.
I've been making embedded boards for over a decade, and I still use a checklist before sending anything to fab. Because the cost of catching an error in layout is zero dollars and five minutes. The cost of catching it after fabrication is a board spin, two weeks, and $50+ for nothing.
Here's my checklist — 25 items, organized by category. Print it. Use it. Add your own items as you learn what you tend to forget.
Power System (Items 1–6)
1. ✅ Voltage regulator input/output caps match the datasheet
Every LDO and switching regulator has specific capacitor requirements — value, ESR range, and sometimes dielectric type. Don't just sprinkle 100nF everywhere and call it done. The AMS1117-3.3, for example, needs at least 10µF on the output with specific ESR. Check the datasheet, use exactly what it says.
2. ✅ Decoupling caps placed physically near IC power pins
Not just electrically connected — physically close. A decoupling cap two inches away from the IC it's supposed to serve is basically useless at high frequencies. Place it within 5mm if possible.
3. ✅ Power rail voltages verified at every IC
Go through every IC on your schematic and check: does its VCC pin connect to the right rail? A 3.3V sensor on a 5V rail will smoke. A 5V-tolerant input on a 1.8V rail won't work right. Read every single power connection.
4. ✅ Current capacity on all power traces
Use the PCB Trace Width Calculator to verify your power traces can handle the expected current with acceptable temperature rise. A 500mA trace that's 6 mil wide will not end well.
| Current | Min Width (1oz, 10°C rise) |
|---|---|
| 500mA | 10 mil |
| 1A | 25 mil |
| 2A | 50 mil |
5. ✅ Reverse polarity protection on power input
If your board has a barrel jack or terminal block, someone will plug it in backwards. A series diode, a PMOS high-side switch, or a bridge rectifier — pick one. Don't skip this.
6. ✅ Power sequencing if multiple rails exist
Many FPGAs, SoCs, and complex ICs require power rails to come up in a specific order. Check the datasheet's power sequencing section. If rail A must come up before rail B, make sure your design enforces that (using an IC with built-in sequencing, or with a power-good signal).
Clock and Reset (Items 7–10)
7. ✅ Crystal load capacitors calculated correctly
A crystal's load capacitance specification (CL) doesn't mean "put two caps of value CL." The formula is:
CL = (C1 × C2) / (C1 + C2) + Cstray
Where Cstray is typically 3-5pF from PCB traces. If the crystal specifies CL = 12pF and Cstray is 4pF:
C1 = C2 = 2 × (CL - Cstray) = 2 × (12 - 4) = 16pF
Use the value the math gives you, not a generic 22pF.
8. ✅ Reset circuit matches MCU/IC requirements
Is there a pull-up on the reset line? Is it the right value (usually 10kΩ)? Does the reset line have a capacitor for debouncing if it goes to a pushbutton? Check the datasheet for minimum reset pulse width.
9. ✅ Boot configuration pins pulled correctly
Most MCUs and FPGAs have boot mode pins that must be high or low at power-up to select the right boot source. If you're booting from SPI flash, make sure the boot config pins have the right pull-ups/pull-downs. Floating boot pins = random boot behavior.
10. ✅ Watchdog timer enabled (in firmware, but plan for it)
This is firmware, but plan for it in hardware — make sure the MCU you chose has a watchdog, and consider whether you need an external one for safety-critical applications.
Communication Interfaces (Items 11–16)
11. ✅ I2C pull-up resistors sized correctly
The I2C bus needs pull-up resistors, and their value depends on bus capacitance and desired rise time. Too large = slow rise times, communication errors. Too small = excessive current, possible bus contention.
For a 400kHz I2C bus with 200pF total bus capacitance:
Rp(max) = trise / (0.8473 × Cb) = 300ns / (0.8473 × 200pF) = 1.77kΩ
Rp(min) = (Vcc - 0.4V) / (3mA) = (3.3 - 0.4) / 0.003 = 967Ω
Use the I2C Pull-Up Calculator to run the numbers for your specific bus.
12. ✅ UART cross-connected (TX↔RX)
Device A's TX connects to Device B's RX. Not TX to TX. Label them clearly on the schematic and board. This is the #1 communication wiring error.
13. ✅ SPI chip select lines pulled up when idle
If SPI CS lines float, slaves can randomly think they're being addressed. Pull them up to VCC (10kΩ) so they're idle when not driven.
14. ✅ USB data lines have correct impedance (90Ω differential)
If your board has USB, the D+ and D- traces need to be routed as a 90Ω differential pair. This means controlled trace width and spacing, which depends on your stackup. Route them short, avoid vias if possible, and match lengths within 5mm.
15. ✅ CAN bus termination (120Ω at each end)
CAN bus needs 120Ω termination resistors at both physical ends of the bus. Not at every node — just the two ends. If you have a bus with 5 nodes, you need exactly 2 termination resistors.
16. ✅ Level shifting between different voltage domains
If you have a 3.3V MCU talking to a 1.8V sensor, you need level shifters. A direct connection can damage the 1.8V device. Check every signal that crosses voltage domains.
Mechanical and Physical (Items 17–20)
17. ✅ Mounting holes placed and correct size
M3 mounting holes (3.2mm drill on a 5-6mm pad) are standard. Place them with enough clearance from components and traces. A mounting screw shouldn't touch any component.
18. ✅ Board outline matches enclosure
If this board goes in an enclosure, measure twice. Check corner radii, connector cutouts, and any keep-out zones. I export the board outline as DXF and overlay it on the mechanical drawing.
19. ✅ Connector positions aligned with enclosure cutouts
USB ports, Ethernet jacks, barrel connectors — these need to line up with the holes in your enclosure. Getting this wrong means either filing the enclosure or respinning the board.
20. ✅ Component heights checked against enclosure clearance
That tall electrolytic capacitor might not fit under the lid. Check component heights against your enclosure's internal clearance, especially near the edges and any board stacking areas.
Manufacturing and Assembly (Items 21–25)
21. ✅ BOM is complete with exact part numbers and sources
Every component on the schematic should have a manufacturer part number and at least one distributor source (DigiKey, Mouser, LCSC). Don't leave values as generic — specify the exact part.
22. ✅ Footprints verified against datasheets
Don't blindly trust library footprints. Pick 3-5 critical components (especially fine-pitch QFPs, QFNs, and BGAs) and manually verify the pad dimensions against the datasheet's land pattern recommendation. A 0.5mm pitch QFN with the wrong pad size is a rework nightmare.
23. ✅ Polarity markings on all polarized components
Electrolytic caps, diodes, LEDs, tantalum caps — make sure pin 1 / positive terminal is clearly marked in silkscreen. A reversed electrolytic cap can vent spectacularly.
24. ✅ Test points on critical signals
Add test points for:
- Power rails (VCC, 3.3V, 5V, etc.)
- Ground
- Reset line
- Key communication buses (I2C SDA/SCL, UART TX/RX)
- Any signal you might need to probe during debugging
Test points are free. Not having them when you need them is expensive.
25. ✅ Design for manufacturing (DFM) review
Check these minimums against your fab's capabilities:
| Feature | Typical Min | Your Design |
|---|---|---|
| Trace width | 6 mil | ____ |
| Trace spacing | 6 mil | ____ |
| Via drill | 0.3mm | ____ |
| Annular ring | 0.15mm | ____ |
| Silkscreen width | 6 mil | ____ |
| Solder mask clearance | 2 mil | ____ |
If you're pushing the limits on any of these, either redesign with more margin or verify your fab can handle it.
Bonus: The "One More Thing" Review
After you've gone through all 25 items, do this:
Walk through the schematic as if you're the current. Start at the power input. Follow it through the regulator, to the IC power pins. Then follow a signal from the sensor, through level shifters if needed, to the MCU. Then from the MCU out to the actuator or connector.
This mental walkthrough catches things no checklist can — logical errors, missing connections, wrong signal flow directions. It takes 10 minutes and has saved me from more board respins than everything else combined.
Your Pre-Fabrication Checklist Summary
| Category | Items | Key Focus |
|---|---|---|
| Power | 1–6 | Regulators, decoupling, current capacity, protection |
| Clock/Reset | 7–10 | Crystal caps, reset circuit, boot pins |
| Communications | 11–16 | I2C pull-ups, UART crossover, impedance, termination |
| Mechanical | 17–20 | Mounting, enclosure fit, connector alignment |
| Manufacturing | 21–25 | BOM, footprints, polarity, test points, DFM |
That's 25 items. If you check every one before ordering, your chances of a successful first-spin board go up dramatically. Not guaranteed — there's always something — but dramatically better.
Want to knock out items 4 and 11 quickly? Use the PCB Trace Width Calculator for current capacity checks and the I2C Pull-Up Calculator for bus sizing. Both run in your browser with standards-backed formulas and PDF export.
Save this checklist. Use it on every project. Your wallet will thank you.