In-circuit test (ICT)
ICT (in-circuit test) is an electrical test for assembled PCBs that checks individual components and connections. A bed-of-nails fixture contacts test points across the board, and the tester measures for shorts, opens, wrong or missing components, wrong values and incorrect orientation, without needing the board to run its intended function.
In-circuit testing explained
In-circuit testing looks at the board component by component rather than as a working product. The board is pressed onto a fixture fitted with spring-loaded probes, often called a bed of nails, which contacts test points or pads on the nets of the circuit. The tester then applies small signals between probes and measures the response.
A typical ICT program begins with unpowered tests: checking for shorts and opens between nets, and measuring resistors, capacitors, inductors and diodes for correct value and orientation. Guarding techniques are used to isolate the component being measured from the parallel paths around it. Powered tests can then follow, such as basic checks of digital devices, and some systems can also program microcontrollers or memory devices on the board.
Boundary scan, based on IEEE 1149.1 (JTAG), is often combined with ICT. It tests connections to complex devices such as BGAs through the device's own test logic, which helps where physical probe access is limited.
A flying probe tester performs similar measurements without a dedicated fixture, using a few probes that move across the board. It needs no fixture but tests boards much more slowly.
ICT requires access: each net to be tested needs a test point that a probe can reach, ideally on one side of the board, with sufficient spacing and size. The fixture and program are specific to each board design, which makes ICT most efficient for stable designs and larger volumes.
For how ICT compares with other methods, see our guide to PCB testing and inspection methods.
When ICT matters
ICT matters when an assembly must be tested thoroughly at component level and the design is stable enough to justify a dedicated fixture. It is common for medium and high volume production, and for products where faults must be pinpointed quickly for repair.
The key design consideration is test access. Without enough test points, ICT coverage is limited. Test points should be planned during layout, with adequate size and spacing, preferably on one side of the board, and kept away from tall components that obstruct probes.
ICT has limits. It confirms that the right parts are fitted and connected, but not that the product works as a system, so it is often combined with functional testing. Very dense boards with hidden joints and few test points may rely more on X-ray, boundary scan and functional testing. Design changes usually require fixture and program updates, which is why flying probe is often used for prototypes and small batches.
ICT vs flying probe vs functional testing
ICT and flying probe find manufacturing defects such as shorts, opens and wrong parts. Functional testing confirms the board performs its intended function. Many production flows use one of the first two, followed by functional testing.
ICT in your quote request
In your quote request, state whether you need ICT, flying probe, functional testing or a combination, and on how many boards. If you require ICT, include test point locations and any test specification, and say whether you supply the fixture or test program. For functional testing, describe the test procedure and any equipment or firmware involved. Our free DFM check can highlight areas where test access is likely to be limited.
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PCB assembly →FAQ about ICT
What is an ICT test?
An ICT, or in-circuit test, is an electrical test of an assembled PCB that checks each component and connection individually. A fixture with spring-loaded probes contacts test points on the board, and the tester measures for shorts, opens, missing or wrong components, wrong values and reversed polarity. It finds manufacturing defects rather than testing product function.
What is the difference between ICT and FCT?
ICT, the in-circuit test, checks the board at component level: whether the right parts are fitted, soldered and connected. FCT, the functional circuit test, powers the board and checks that it behaves as intended, for example by running firmware or measuring outputs. ICT pinpoints manufacturing faults, while FCT confirms the assembly works as a product.
How is an in-circuit test done?
The assembled board is placed on a bed-of-nails fixture whose probes contact test points on each net. The tester first runs unpowered measurements for shorts, opens and passive component values, then may power the board for basic device checks or programming. The results are compared with expected values, and failures are reported down to the component or net.
Related terms
- Functional testing
Functional testing powers up the assembled PCB and verifies that it performs its intended function, typically using customer-supplied test scripts or fixtures. Unlike ICT, it tests behaviour rather than individual components. Often combined with programming (loading firmware) and calibration as a final assembly step.
- AOI
AOI (Automated Optical Inspection) uses high-resolution cameras to inspect solder joints, component placement, and orientation after assembly. Modern 3D AOI measures joint height and volume volumetrically, catching defects like lifted leads and insufficient solder that 2D systems miss. Limited to visible surfaces — hidden joints under BGAs require X-ray inspection.
- X-ray inspection
X-ray inspection is a non-destructive testing method that penetrates the PCB to reveal hidden solder joints under BGAs, QFNs, and other bottom-terminated packages. It detects voids, head-in-pillow defects, bridging, and missing joints that AOI cannot see. Available in 2D (top-down) and 3D CT (full volumetric) variants.
- PCBA
PCBA (Printed Circuit Board Assembly) is the process of populating a bare PCB with electronic components — resistors, capacitors, ICs, connectors, and other parts — to produce a functional electronic assembly ready for testing or integration into a finished product.
- IPC-A-610
IPC-A-610 is the IPC standard that defines visual acceptance criteria for electronic assemblies. It describes what acceptable and defective solder joints, component placement, cleanliness and damage look like on a populated PCB, using photographs and illustrations, across three product classes. It is the most widely used inspection standard in PCB assembly.