In-circuit testing (ICT) is an example of

white box testing White-box testing (also known as clear box testing, glass box testing, transparent box testing, and structural testing) is a method of software testing that tests internal structures or workings of an application, as opposed to its functionality ...

where an electrical probe tests a populated

printed circuit board A printed circuit board (PCB; also printed wiring board or PWB) is a medium used in Electrical engineering, electrical and electronic engineering to connect electronic components to one another in a controlled manner. It takes the form of a L ...

(PCB), checking for shorts, opens, resistance, capacitance, and other basic quantities which will show whether the assembly was correctly fabricated. It may be performed with a "bed of nails" test fixture and specialist test equipment, or with a fixtureless in-circuit test setup.

Fixtures for in-circuit testing

A common form of in-circuit testing uses a bed-of-nails tester. This is a fixture that uses an array of spring-loaded pins known as "pogo pins". When a printed circuit board is aligned with and pressed down onto the bed-of-nails tester, the pins make electrical contact with locations on the circuit board, allowing them to be used as test points for in-circuit testing. Bed-of-nails testers have the advantage that many tests may be performed at a time, but have the disadvantage of placing substantial strain on the PCB. An alternative is the use of

flying probe In the manufacture of electronic printed circuit boards, flying probes are used for testing both bare circuit boards and boards loaded with components. Flying probes were introduced in the late 1980’s. Flying probes can be found in many manufactur ...

s, which place less mechanical strain on the boards being tested. Their advantages and disadvantages are the opposite of bed-of-nails testers: the flying probes must be moved between tests, but they place much less strain on the PCB.

Example test sequence

* Discharging capacitors and especially

electrolytic capacitor An electrolytic capacitor is a polarized capacitor whose anode or positive plate is made of a metal that forms an insulating oxide layer through anodization. This oxide layer acts as the dielectric of the capacitor. A solid, liquid, or gel el ...

s (for safety and measurement stability, this test sequence must be done first before testing any other items) * Contact Test (To verify the test system is connected to the Unit Under Test (UUT) * Shorts testing (Test for solder shorts and opens) * Analog tests (Test all analog components for placement and correct value) * Test for defective open pins on devices * Test for capacitor orientation defects * Power up UUT * Powered analog (Test for correct operation of analog components such as regulators and opamps) * Powered digital (Test the operation of digital components and Boundary scan devices) *

JTAG JTAG (named after the Joint Test Action Group which codified it) is an Technical standard, industry standard for verifying designs and testing printed circuit boards after manufacture. JTAG implements standards for on-chip instrumentation in ele ...

boundary-scan tests Jun Balangue, “Successful ICT Boundary Scan Implementation,” CIRCUITS ASSEMBLY, September 2010. http://www.circuitsassembly.com/cms/magazine/208-2010-issues/10282-testinspection *

Flash Memory Flash memory is an electronic non-volatile computer memory storage medium that can be electrically erased and reprogrammed. The two main types of flash memory, NOR flash and NAND flash, are named for the NOR and NAND logic gates. Both us ...

EEPROM EEPROM (also called E2PROM) stands for electrically erasable programmable read-only memory and is a type of non-volatile memory used in computers, usually integrated in microcontrollers such as smart cards and remote keyless systems, or as a ...

, and other device programming * Discharging capacitors as UUT is powered down While in-circuit testers are typically limited to testing the above devices, it is possible to add additional hardware to the test fixture to allow different solutions to be implemented. Such additional hardware includes: * Cameras to test for presence and correct orientation of components *

Photodetector Photodetectors, also called photosensors, are sensors of light or other electromagnetic radiation. There is a wide variety of photodetectors which may be classified by mechanism of detection, such as Photoelectric effect, photoelectric or photoc ...

s to test for

LED A light-emitting diode (LED) is a semiconductor Electronics, device that Light#Light sources, emits light when Electric current, current flows through it. Electrons in the semiconductor recombine with electron holes, releasing energy i ...

color and intensity * External timer counter modules to test very high frequencies (over 50 MHz) crystals and oscillators * Signal waveform analysis, e.g. slew rate measurement, envelope curve etc. * External equipment can be used for hi-voltage measurement (more than 100Vdc due to limitation of voltage that is provided) or AC equipment Source those have interface to PC as the ICT Controller *

Bead probe technology A bead is a small, decorative object that is formed in a variety of shapes and sizes of a material such as stone, bone, shell, glass, plastic, wood, or pearl and with a small hole for threading or stringing. Beads range in size from under ...

to access small traces that cannot be accessed by traditional means

Limitations

While in-circuit test is a very powerful tool for testing PCBs, it has these limitations: * Parallel components can often only be tested as one component if the components are of the same type (i.e. two resistors); though different components in parallel may be testable using a sequence of different tests - e.g. a DC voltage measurement versus a measurement of AC injection current at a node. * Electrolytic components can be tested for polarity only in specific configurations (e.g. if not parallel connected to power rails) or with a specific sensor * The quality of electrical contacts can not be tested unless extra test points and/or a dedicated extra cable harness are provided. * It is only as good as the design of the PCB. If no test access has been provided by the PCB designer then some tests will not be possible. See

Design For Test Design for testing or design for testability (DFT) consists of IC design techniques that add testability features to a hardware product design. The added features make it easier to develop and apply manufacturing tests to the designed hardware. Th ...

guidelines.

Related technologies

The following are related technologies and are also used in electronic production to test for the correct operation of Electronics Printed Circuit boards: *

PCB electrical test A printed circuit board (PCB; also printed wiring board or PWB) is a medium used in electrical and electronic engineering to connect electronic components to one another in a controlled manner. It takes the form of a laminated sandwich struc ...

of bare PCBs * AXI

Automated x-ray inspection Automated inspection (AXI) is a technology based on the same principles as automated optical inspection (AOI). It uses as its source, instead of visible light, to automatically inspect features, which are typically hidden from view. Automated ...

* JTAG

Joint Test Action Group JTAG (named after the Joint Test Action Group which codified it) is an industry standard for verifying designs and testing printed circuit boards after manufacture. JTAG implements standards for on-chip instrumentation in electronic design auto ...

(

Boundary Scan Boundary scan is a method for testing interconnects (wire lines) on printed circuit boards or sub-blocks inside an integrated circuit. Boundary scan is also widely used as a debugging method to watch integrated circuit pin states, measure voltage ...

Technology) * AOI

automated optical inspection Automated optical inspection (AOI) is an automated visual inspection Visual inspection is a common method of quality control, data acquisition, and data analysis. Visual Inspection, used in maintenance of facilities, mean inspection of equipment a ...

* Functional testing (see

Acceptance testing In engineering and its various subdisciplines, acceptance testing is a test conducted to determine if the requirements of a specification or contract are met. It may involve chemical tests, physical tests, or performance tests. In systems en ...

and FCT)

References

External links

In-Circuit Test Tutorial
{{DEFAULTSORT:In-Circuit Test Printed circuit board manufacturing Hardware testing Electronic test equipment