PCBA Quality Control: Flying Probe, AOI, X-Ray, ICT and FCT Explained
A PCBA goes through several checks and tests on its way from bare board to finished assembly. The reason is simple: different problems can only be caught by different methods—whether the traces are connected, whether components are placed correctly, whether the joints hidden under a component are sound, whether the assembled board actually works once powered. No single method covers them all. Once these problems reach final assembly or the customer, the cost of rework and troubleshooting climbs sharply; PCBA quality is built by catching them, layer by layer, during production.
This article covers the five inspection and test methods Fusion commonly uses in PCBA production—flying probe, AOI, X-ray, ICT, and functional test (FCT)—what each one finds, and how together they keep the board you receive reliable.
📋 The five methods at a glance
| Method | What it checks | What it finds |
| Flying probe | Traces on the bare PCB | Opens, shorts, and other trace faults |
| AOI (+ manual inspection) | Component placement and visible joints | Missing parts, offset, wrong polarity, tombstoning, bridging, solder anomalies |
| X-ray | Hidden joints under BGA and similar parts | Voids, bridging, insufficient solder, opens, misalignment |
| ICT | Electrical connections and component values on the assembled board | Opens, shorts, wrong component value or polarity |
| FCT functional test | Actual function under power | Interface, firmware, power, and system-function faults |
Each is introduced below in production order. Which of them a given board goes through depends on its design, its components, and your requirements—not every board runs all five.
📍 Flying probe: verifying the bare board’s traces
Before components go on, the bare board’s traces are checked first. Flying probe uses probes that contact test points one at a time to check the traces for opens and shorts. It needs no custom bed-of-nails fixture, which suits prototypes and mixed, low-volume builds.
📐 AOI: checking component placement and soldering
After placement and reflow, AOI checks component placement and soldering. It captures board images with a camera and flags anomalies against a reference standard—missing parts, offset, reversed polarity, tombstoning, bridging, insufficient solder.
AOI raises inspection speed, and the check also includes manual visual review—the equipment does fast screening, people confirm and fill the gaps, and together they keep assembly quality in check. This step keeps obvious placement and soldering defects out of the following steps. AOI sees the joints on the surface; the ones hidden under a component it cannot see—those go to X-ray.
🛠️ X-ray: checking the joints you can’t see
When the board carries BGA or similar packages, the joints sit under the component, where neither AOI nor the eye can reach. X-ray sees through to the joints and checks for voids, bridging, insufficient solder, opens, or misalignment.
It keeps these hidden-joint problems out of the shipment, so an insufficient or missing joint does not surface later—at final assembly or in the field. This check is used when the board carries such hidden-joint parts.
🛠️ ICT: checking the assembled board’s electrical connections
Unlike flying probe on the bare board, ICT checks the fully assembled board. After assembly, ICT uses a test fixture to contact the board’s test points and check the electrical connections and some component parameters—whether there are opens, shorts, or a wrong component value or polarity.
ICT suits boards with a stable design in repeat production, confirming each board’s electrical connections quickly and consistently across a batch.
🛠️ Functional test (FCT): verifying the board actually works
The methods above confirm that the board is soldered and connected correctly—but correct assembly does not mean the whole unit works. FCT powers the board and verifies interfaces, firmware, and system function against your product’s requirements, keeping functional faults out of delivery and out of the field.
The manufacturer does not know what your product is supposed to do or what counts as a pass, so functional test needs you to provide the test files (a Test Plan)—without them, functional test is not performed by default.
The upside: Fusion offers free 100% functional testing. Upload your test plan on the order page (a Test Plan Example is provided; ZIP/RAR, 20MB max) to use it and verify the whole unit before delivery. If it is not ready, choose “add test plan later” and upload it in the cart.
📐 Common questions
Does every PCBA go through all five checks?
No. The checks applied depend on the board design and production requirements—hidden joints under BGA call for X-ray, and functional test needs a Test Plan from the customer.
After AOI, is functional test still needed?
Yes. AOI checks soldering and placement, not function; interfaces, firmware, and system behavior are confirmed by functional test. The two catch different kinds of problems.
When is X-ray used?
When the board has BGA or similar parts whose joints sit under the component—X-ray checks for voids, bridging, insufficient solder, and opens.
Does functional test cost extra, and what do I do?
Fusion offers free 100% functional testing, provided you upload the test files (Test Plan); without them it is not performed by default. Where a new test program, a dedicated fixture, or a special setup is involved, the team confirms it with you before production.
✅ Want to verify the whole unit? Upload your test plan with the order
From bare-board traces, component placement and soldering, to hidden joints under BGA and full-unit function, these five methods each find different problems and together keep quality issues out of the shipment.
When you submit a project, provide complete Gerber, BOM, and assembly files; mark any special components such as BGA in your files; and if you want functional test, include your Test Plan and related test files.
For functional test or special requirements: upload your test plan on the order page, or send it to [email protected], reply within 2 business days.
Upload your Gerber and BOM for a quote:👉 Fusion PCB/PCBA order page
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