What functional tests should require as part of PCB delivery?

If you’ve ever unboxed a “finished” PCB delivery, plugged it in, and watched nothing happen, you already know the problem: a board can “pass inspection” and still fail your product. That’s why smart OEMs, EMS teams, and design houses don’t just ask for “testing.” They ask for the right tests, plus the proof that those tests actually ran.

This guide fits China B2B buyers who do custom builds, wholesale batches, and OEM/ODM. It also works for NPI ramps (EVT/DVT/PVT) and steady mass production.

PCB delivery vs PCBA delivery

Start here, or you’ll argue in circles later.

• PCB (bare board) delivery means copper and laminate. You can’t run real “functional tests” because there are no parts to power up.
• PCBA (assembled board) delivery means components are mounted. Now you can require functional test (FCT) that powers the board and checks behavior.

If your PO says “PCB” but you expect “board boots firmware,” you’re setting up a field-fail surprise.

You can see the service split clearly on our site: PCB Fabrication vs PCB Assembly.

Functional test (FCT)

FCT answers one question: Does this board work like it will in real life? Not “are the nets connected,” but “does the product do the job.”

What FCT should cover

A practical FCT plan usually checks:

• Power-up sequence: inrush, rails stable, brownout behavior, reset timing
• Boot and firmware: bootloader, version readback, watchdog, basic self-test
• I/O and interfaces: USB, UART, CAN, Ethernet, RS232, GPIO, ADC/DAC
• Output behavior under load: relays, motors, LEDs, speakers, heaters
• Safety trip points: overcurrent/overtemp flags, shutdown, fault latching
• Golden unit comparison: compare key measurements against a “golden board” baseline

Here’s the part buyers forget: FCT needs a test spec. If you don’t define stimulus + expected result, the factory can only give you a vague “PASS.”

FCT deliverables you should request

Ask for more than pass/fail:

• Test procedure (steps + setup)
• Test limits (thresholds, tolerances, timing windows)
• Unit log (serial number + result)
• Failure record (what failed, where, and how it was confirmed)

That bundle makes your dock-to-stock smoother and makes RMAs less painful.

AOI and X-ray inspection

FCT is not your first line of defense. You want to catch dumb mistakes before you power anything.

• AOI (Automated Optical Inspection) catches wrong part, missing part, polarity flips, tombstoning, solder bridges—your classic SMT headaches.
• X-ray inspection matters when joints hide under the part (BGA/QFN). If you ship without X-ray on those packages, you’re betting your schedule on luck.

In real builds, AOI/X-ray protects your yield. FCT protects your customer experience. You need both when the design is dense or the volume is high.

If your build involves fine pitch, HDI, or tight layouts, it’s worth aligning early with the factory’s Capabilities page so your test approach matches the process window.

ICT and flying probe test

This is the “manufacturing truth serum.”

• ICT (In-Circuit Test) uses a bed-of-nails fixture to test components and nets fast. Great for stable, repeat runs.
• Flying probe test avoids custom fixtures and works well in prototypes and low-to-mid volumes. It’s slower, but it gets you coverage without tooling delays.

A clean strategy looks like this:

• Prototype / NPI: flying probe + a lighter FCT (focus on core functions)
• Mass production: ICT (or boundary scan/JTAG where it fits) + full FCT

FCT does not replace AOI/ICT

This point saves a lot of teams.

If you only run FCT, you can still ship boards with:

• marginal solder joints that “work today”
• swapped passives that slip through a light functional check
• intermittent opens that appear after vibration or thermal cycling

AOI/ICT/Flying probe catch manufacturing defects. FCT validates system behavior. Put them together and you stop playing whack-a-mole.

Design for test (DFT)

If you want reliable testing, your layout has to cooperate.

DFT means you plan for:

• test points on critical nets (power rails, resets, key buses)
• access for bed-of-nails probes
• programming headers or pads (SWD/JTAG/UART)
• clear reference points for automated measurement
• built-in self-test hooks in firmware (simple command set = faster FCT)

A board with zero test access forces the factory into hand probing and “best effort.” That’s how schedules slip.

Acceptance criteria and test reports

Buyers often say “send a test report,” but they don’t define what that means. Here’s a clean way to write acceptance:

• For PCB (bare board): require electrical test (opens/shorts) + dimensional checks + any impedance verification you specified in the build notes.
• For PCBA: require AOI (and X-ray where needed) + ICT or flying probe (when appropriate) + FCT with documented limits and logs.

If you want a single place to route these requirements internally, link your team to Quality so purchasing, engineering, and your supplier all speak the same language.

Functional tests to require as part of PCB delivery

Below is a buyer-friendly table you can copy into a PO or SOW. It avoids fluff and tells the factory exactly what “done” looks like.

Test / deliverable	PCB (bare board)	PCBA (assembled board)	What it protects you from	Evidence you should request
Electrical test (opens/shorts)	√	√ (as part of ICT/flying probe coverage)	dead nets, shorts, hidden scrap	test summary + lot trace
Dimensional checks	√	√	fit issues, connector misalignment	measurement record
AOI	—	√	wrong/missing parts, polarity, solder bridges	AOI result + defect images
X-ray inspection	—	√ (BGA/QFN)	voids, head-in-pillow, hidden solder fails	X-ray images + checklist
Flying probe test	(common in prototype)	√(low-mid volume)	early build escapes without fixtures	coverage statement + results
ICT (bed-of-nails)	—	(repeat volume)	systematic assembly faults	coverage + yield trend
Functional test (FCT)	—	(required for “works in product”)	“passes inspection but doesn’t work”	limits + serial logs + failure record
Firmware programming & ID	—	(if firmware applies)	wrong build, wrong version in field	version readback + SN mapping

Typical functional test scenarios

Here are a few real-world FCT “must-haves” that match common buyer pain:

• Motor control board (industrial / robotics): spin test, current sensing sanity, fault injection, safe stop. If you’re building a control panel style board, a related product example lives here: multilayer motor control PCB.
• High-frequency / RF board: impedance-critical checks plus a basic RF path sanity check (at minimum, power rails + interface + config). See: Rogers 4003 RF PCB.
• Automotive-oriented control assemblies: traceability, tighter process discipline, and test logs that map serial numbers to results. A relevant internal page: IATF16949 control PCB assembly.
• Fast prototype builds: keep FCT lean—power + boot + key I/O—then expand coverage as you move from EVT to DVT. For quick-turn prototypes, this page is a good anchor: PCB prototype manufacturing service.

A simple buyer checklist

Before you place the order, make sure your team can answer these:

1. Is this PCB or PCBA delivery?
2. What does “works” mean in one sentence (boot, communicate, drive load, measure sensor)?
3. Which tests run 100% and which run by sampling?
4. What proof do you need per unit (logs) vs per lot (summary)?
5. Who owns the FCT fixture, firmware, and golden unit?

If you want an easy next step, point new buyers to our homepage to route them to fabrication, assembly, and quality expectations in one place.