In-circuit test
Encyclopedia
In-circuit test is an example of white box testing
where an electrical probe tests a populated printed circuit board
(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 type test fixture and specialist test equipment, or with a fixtureless in-circuit test
setup.
There are many different test platforms for performing in-circuit test; for instance, Aeroflex
4220, 4230, 4250, Agilent
3070, i5000, i3070 Series 5, and i1000, Genrad
(now part of Teradyne) TestStation, TS8x, 228x, Stinger, Teradyne
, Spectrum 88xx, Z18xx, SPEA
, Qmax Systems like QT200, QT8200, V200, V250, V2200, Digitaltest, SEICA, and Test Research Inc. TR5000 and TR8000 Series.
s. Named by analogy with a real-world bed of nails
, these devices contain an array of small, spring-loaded pogo pin
s; each pogo pin makes contact with one node in the circuitry of the DUT (device under test)
. By pressing the DUT down against the bed of nails, reliable contact can be quickly and simultaneously made with hundreds or even thousands of individual test points within the circuitry of the DUT. The hold-down force may be provided manually or by means of a vacuum
, thus pulling the DUT downwards onto the nails.
Devices that have been tested on a bed of nails tester may show evidence of this after the fact: small dimples (from the sharp tips of the Pogo pins) can often be seen on many of the soldered connections of the PCB.
Typically, four to six weeks are needed for the manufacture and programming of such a fixture. Fixtures can either be vacuum or press-down. Vacuum fixtures give better signal reading versus the press-down type. On the other hand, vacuum fixtures are expensive because of their high manufacturing complexity. The bed of nails or fixture as generally termed is used together with a in-circuit tester.
This technique of testing PCB's is being slowly superseded by boundary scan
techniques (silicon test nails), automated optical inspection
, and built-in self-test
, due to shrinking product sizes and lack of space on PCB's for test pads.
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:
White box testing
White-box testing is a method of testing software that tests internal structures or workings of an application, as opposed to its functionality...
where an electrical probe tests a populated printed circuit board
Printed circuit board
A printed circuit board, or PCB, is used to mechanically support and electrically connect electronic components using conductive pathways, tracks or signal traces etched from copper sheets laminated onto a non-conductive substrate. It is also referred to as printed wiring board or etched wiring...
(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 type test fixture and specialist test equipment, or with a fixtureless in-circuit test
Fixtureless In-Circuit Test
Fixtureless in-circuit test is a cost-effective alternative to a "bed of nails" tester for in-circuit testing of low to medium volumes of printed circuit board assemblies. It relies on a computerized optical inspection of the circuit assembly and positionable test probes...
setup.
There are many different test platforms for performing in-circuit test; for instance, Aeroflex
Aeroflex
Aeroflex Inc. is an American company which produces and markets RF and microwave integrated circuits, components, and systems used for wireless communications. Aeroflex consists of Aeroflex Microelectronic Solutions , a fabless manufacturer of rad-hard and hi-rel semiconductor devices and...
4220, 4230, 4250, Agilent
Agilent Technologies
Agilent Technologies , or Agilent, is a company that designs and manufactures electronic and bio-analytical measurement instruments and equipment for measurement and evaluation...
3070, i5000, i3070 Series 5, and i1000, Genrad
General Radio
General Radio Company was a broad-line manufacturer of electronic test equipment. Started in Cambridge, Massachusetts in 1915, the company moved to West Concord in the 1950s. There, it became a major player in the automatic test equipment business, manufacturing a line of testers for assembled...
(now part of Teradyne) TestStation, TS8x, 228x, Stinger, Teradyne
Teradyne
Teradyne , a US company, is a supplier of automatic test equipment . The company's divisions Semiconductor Test and Systems Test Group, are organized by the products they develop and deliver.-History:...
, Spectrum 88xx, Z18xx, SPEA
SPEA
SPEA is an Italian company that designs and manufactures Automatic Test Equipment for testing microchips and electronic boards.The Company, founded in 1976 by Luciano Bonaria, who still is its President, today employs about 450 people, distributed among the Italian headquarters in Volpiano and 24...
, Qmax Systems like QT200, QT8200, V200, V250, V2200, Digitaltest, SEICA, and Test Research Inc. TR5000 and TR8000 Series.
Bed of nails tester
A bed of nails tester is a traditional electronic test fixture which has numerous pins inserted into holes in an Epoxy phenolic glass cloth laminated sheet (G-10) which are aligned using tooling pins to make contact with test points on a printed circuit board and are also connected to a measuring unit by wireWire
A wire is a single, usually cylindrical, flexible strand or rod of metal. Wires are used to bear mechanical loads and to carry electricity and telecommunications signals. Wire is commonly formed by drawing the metal through a hole in a die or draw plate. Standard sizes are determined by various...
s. Named by analogy with a real-world bed of nails
Bed of nails
A bed of nails is an oblong piece of wood the size of a bed with nails pointing upwards out of it. It appears to the spectator that anyone lying on this "bed" would be injured by the nails, but this is not so...
, these devices contain an array of small, spring-loaded pogo pin
Pogo pin
A Pogo pin is a device used in electronics to establish a connection between two printed circuit boards. Named by analogy with the pogo stick toy, the pogo pin usually takes the form of a slender cylinder containing two sharp, spring-loaded pins...
s; each pogo pin makes contact with one node in the circuitry of the DUT (device under test)
Device under test
Device under test , also known as unit under test , is a term commonly used to refer to a manufactured product undergoing testing.-In semiconductor testing:...
. By pressing the DUT down against the bed of nails, reliable contact can be quickly and simultaneously made with hundreds or even thousands of individual test points within the circuitry of the DUT. The hold-down force may be provided manually or by means of a vacuum
Vacuum
In everyday usage, vacuum is a volume of space that is essentially empty of matter, such that its gaseous pressure is much less than atmospheric pressure. The word comes from the Latin term for "empty". A perfect vacuum would be one with no particles in it at all, which is impossible to achieve in...
, thus pulling the DUT downwards onto the nails.
Devices that have been tested on a bed of nails tester may show evidence of this after the fact: small dimples (from the sharp tips of the Pogo pins) can often be seen on many of the soldered connections of the PCB.
Typically, four to six weeks are needed for the manufacture and programming of such a fixture. Fixtures can either be vacuum or press-down. Vacuum fixtures give better signal reading versus the press-down type. On the other hand, vacuum fixtures are expensive because of their high manufacturing complexity. The bed of nails or fixture as generally termed is used together with a in-circuit tester.
This technique of testing PCB's is being slowly superseded by boundary scan
Boundary scan
Boundary scan is a method for testing interconnects 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, or analyze sub-blocks inside an integrated circuit.The Joint...
techniques (silicon test nails), automated optical inspection
Automated optical inspection
Automated optical inspection is an automated visual inspection of a wide range of products, such as printed circuit boards , LCDs, transistors, automotive parts, lids and labels on product packages or agricultural products...
, and built-in self-test
Built-in self-test
A built-in self-test or built-in test is a mechanism that permits a machine to test itself. Engineers design BISTs to meet requirements such as:*high reliability*lower repair cycle timesor constraints such as:...
, due to shrinking product sizes and lack of space on PCB's for test pads.
Example test sequence
- Discharging capacitors and especially electrolytic capacitorElectrolytic capacitorAn electrolytic capacitor is a type of capacitor that uses an electrolyte, an ionic conducting liquid, as one of its plates, to achieve a larger capacitance per unit volume than other types. They are often referred to in electronics usage simply as "electrolytics"...
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)
- Testjet (Agilent), FrameScan (Genrad/Teradyne) or ElectroScan (SPEA) (Test for defective open pins on devices)
- 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 Boundary scan tests
- Flash,ISP and other device programming
- Agilent Medalist Beadprobe - Bead probe technologyBead probe technologyBead probe technology is technique used to provide electrical access to printed circuit board circuitry for performing in-circuit testing ....
- Agilent/Teradyne Powered Vectorless Test Solution – VTEP v2.0/Powered FrameScan
- 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
- PhotodetectorPhotodetectorPhotosensors or photodetectors are sensors of light or other electromagnetic energy. There are several varieties:*Active pixel sensors are image sensors consisting of an integrated circuit that contains an array of pixel sensors, each pixel containing a both a light sensor and an active amplifier...
s to test for LEDLEdLEd is a TeX/LaTeX editing software working under Microsoft Windows. It is a freeware product....
color and intensity - External timer counter modules to test very high frequencies (over 50 MHz) crystals and oscillators
- 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
Limitations
While in-circuit test is a very powerful tool for testing PCBs, it has these limitations:- Parallel components can only be tested as one component if the component is same, but different component in parallel connection sometimes can be tested for each component in different testing method
- Electrolytic components can be tested for polarity only on specific configuration (e.g. if not parallel connected to power rails) or with specific sensor
- The quality of electrical contacts can not be tested
- 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 TestDesign For TestDesign for Test is a name for design techniques that add certain testability features to a microelectronic hardware product design. The premise of the added features is that they make it easier to develop and apply manufacturing tests for the designed hardware...
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- AXI Automated x-ray inspectionAutomated x-ray inspectionAutomated inspection is a technology based on the same principles as automated optical inspection . It uses as its source, instead of visible light, to automatically inspect features, which are typically hidden from view....
- JTAG Joint Test Action Group (Boundary ScanBoundary scanBoundary scan is a method for testing interconnects 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, or analyze sub-blocks inside an integrated circuit.The Joint...
Technology) - AOI automated optical inspectionAutomated optical inspectionAutomated optical inspection is an automated visual inspection of a wide range of products, such as printed circuit boards , LCDs, transistors, automotive parts, lids and labels on product packages or agricultural products...
- Functional testing (see Acceptance testing and FCTFCT (test)FCT refers to functional test. The functional test is typically performed in the last phase of the production line of a product, as a final quality control. FCT are performed to ensure that the device under test fulfills its functional specifications....
)