How to pre-test your PCB

As a little well known inventor Alexander Graham Bell once said, “Before anything else, preparation is the key to success”. This is also true of your boards. Long before the testing phase, there are steps you should take to pre-test your PCB.

The goal is to catch and fix any manufacturing or design flaws, preventing catastrophic failures on subsequent power-ups. Through much trial and error, we’ve conveniently outlined that process for you and put together a step-by-step guide as well as some handy tips for you to follow.

Let’s get going!

Firstly, gather all your schematics and datasheets. A surprising number of early debugging sessions can be solved by spotting a single mismatched pin name or a power rail assumption not written down.

These documents include:

• Schematic
• PCB layout
• Component placement drawing
• Datasheets for every major component
• Power tree / rail sequencing diagrams
• Known errata for silicon

Next, set up your workspace with the tools you’ll need to pre- test your PCB.

• DMM and oscilloscope
• Thermal camera (great for spotting shorts)
• ESD strap and mat
• Fine-tip probes and needle probes
• Good cables
• Good lighting for inspecting soldering issues

And critically, set the bench supply current limit before anything touches power. A current-limited supply is the first line of defence against accidentally overcooking a regulator or turning a BGA into a heater.

After you’ve got your documents and set up your space, you need to plan your bring-up sequence. It can be very tempting to “wing-it” and just plug it in and see what happens, but if you have a clear plan to follow, you can ensure all those little bugs are worked out before you start your official testing phase.

Make sure to document your plan and stick to it. Only deviate when the evidence tells you to. Write everything down! Remember, boards rarely die from bad design, they die from enthusiastic engineers powering them before checking the fundamentals.

Here is our recommended bring-up sequence:

1. Visual inspection: (under magnification, check for)
   • Solder bridges
   • Misaligned ICs
   • Missing components
   • Tomb stoned passives
   • Solder balls around BGAs
   • Debris or flux residue
   • Incorrect orientation on diodes, ICs, FETs, crystals. (Even high-quality manufacturers occasionally misplace a component)

2. Passive checks:
   • Check every power rail to ground
   • Check across major capacitors
   • Check for unexpected low-ohm paths
   • Validate critical nets aren’t shorted to adjacent nets (a board that reads 0.3Ω to ground on a regulator output needs investigation)

3. Power rail bring-up, one rail at a time:
   • When you’re confident everything is as it should be, start bringing up power one rail at a time.
   • Set current limits aggressively low at first: 20–50 mA, then increase gradually depending on expected consumption. (Overcurrent at this stage is not always a failure, sometimes charging caps or initial inrush. But it must be repeatable and understood).
   • Isolate PSU rails from the rest of the circuitry. (Cut tracks, remove fuses, reposition an output component if necessary).
   • Measure each rail independently
   • Before powering the whole board, power each regulator input manually (if practical) to confirm a) output voltage is correct, b) no excessive heating, and c) startup behaviour matches datasheets
   • If the board uses power sequencing, bring rails up in order and check dependencies. (A rail coming up too early can lead to latch-up or damage).

4. Monitor thermal behaviour: (using an IR cameral, check for)
   • A regulator running at 80°C immediately
   • A shorted capacitor heating at a corner
   • A backwards diode acting as a heater

5. Clocks and Reset behaviour checks:
   • Crystal oscillation
   • Clock frequency
   • Stability and amplitude. An oscilloscope will show whether the MCU’s oscillator has started. If it hasn’t, recheck loading caps and layout.
   • Resets should:
     1. Hold low during power-up
     2. Release cleanly
     3. Not chatter
     4. Not be held by external components. (Incorrect reset behaviour can mimic a dead processor).

6. Connectivity interfaces: (UART, SWD, JTAG)
   • Connect debug interfaces early. UART, SWD, JTAG or similar.
   • If debug isn’t working:
     1. Check pin mappings
     2. Check pull-ups / pull-downs
     3. Confirm the interface isn’t shared with other circuitry
     4. Confirm power and ground integrity

7. Check your peripherals: (with increasing risk level)
   • Storage (flash)
   • Safety-critical circuits
   • Test any high-risk circuits early, for example:
     1. RF front ends
     2. High-speed SERDES
     3. USB-C PD
     4. Motor drivers
     5. Switching power supplies

• Skip low-risk functionality initially, you don’t need:
  1. LED sequences
  2. Simple GPIOs
  3. Display animations

Remember, the goal is to find structural design issues, not verify every corner case (that comes later).

At some point, you’ll ask “have we tested enough?”

Stop when:

1. Power rails are correct and repeatable
2. Clocks run reliably
3. Reset behaves properly
4. The MCU/SoC boots and accepts code
5. High-risk circuits behave within expected margins
6. No unexpected thermal events occur
7. You have a stable platform
   

Then you can move into functional verification, firmware bring-up, and deeper subsystem testing…

Hardware bring-up is part science, part detective work, and part discipline. It isn’t just a step, it’s a skill, and done well, it sets your entire product development up for success. Done poorly, it leads to burnt prototypes, misdiagnosed issues, firmware delays, and unnecessary board spins.

With the right preparation, a systematic approach, and careful testing, bring-up becomes a structured, predictable process. Not a stressful guessing game.

If you’d like support with prototype, bring-up, hardware review, risk assessment or debug, the Ignys team is always here to help.

We hope this guide helps you to pre-test your PCBs and fix any issues before your testing phase. To end as we began, “Concentrate all your thoughts on the task at hand. The sun’s rays do not burn until brought to a focus.” – Alexander Graham Bell