In-circuit test

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In-circuit test (ICT) 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. [1] It may be performed with a bed of nails type test fixture and specialist test equipment, or with a fixtureless in-circuit test setup.

Printed circuit board Board to support and connect electronic components

A printed circuit board (PCB) mechanically supports and electrically connects electronic components or electrical components using conductive tracks, pads and other features etched from one or more sheet layers of copper laminated onto and/or between sheet layers of a non-conductive substrate. Components are generally soldered onto the PCB to both electrically connect and mechanically fasten them to it.

Contents

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 wires. Named by analogy with a real-world bed of nails, these devices contain an array of small, spring-loaded pogo pins; 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 or a mechanical presser, thus pulling the DUT downwards onto the nails.

Wire single, usually cylindrical, flexible strand or rod of metal

A wire is a single, usually cylindrical, flexible strand or rod of metal. Wires are used to bear mechanical loads or electricity and telecommunications signals. Wire is commonly formed by drawing the metal through a hole in a die or draw plate. Wire gauges come in various standard sizes, as expressed in terms of a gauge number. The term wire is also used more loosely to refer to a bundle of such strands, as in "multistranded wire", which is more correctly termed a wire rope in mechanics, or a cable in electricity.

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. Assuming the nails are numerous enough, the weight is distributed among them so that the pressure exerted by each nail is not enough to puncture the person's skin.

Pogo pin

A Pogo pin or spring-loaded connector is a family of connectors that is used in many modern electronic applications and in the electronics testing industry. Its advantages are its comparably small size as opposed to other spring contacts and the vertical mating, that improves the durability of the connector.

Devices that have been tested on a bed of nails tester may show evidence of this after the process: small dimples (from the sharp tips of the Pogo pins) can often be seen on many of the soldered connections of the PCB.

Bed of nails fixtures require a mechanical assembly to hold the PCB in place. Fixtures can hold the PCB with either a vacuum or pressing down from the top of the PCB. Vacuum fixtures give better signal reading versus the press-down type[ citation needed ]. On the other hand, vacuum fixtures are expensive because of their high manufacturing complexity. Moreover, vacuum fixtures cannot be used on bed-of-nails systems that are used in automated production lines, where the board is automatically loaded to the tester by a handling mechanism. The bed of nails or fixture, as generally termed, is used together with an in-circuit tester. Fixtures with a grid of 0.8 mm for small nails and test point diameter 0.6 mm are theoretically possible without using special constructions. But in mass production, test point diameters of 1.0 mm or higher are normally used to minimise contact failures leading to lower remachining costs.

This technique of testing PCBs 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. Nevertheless ICT is used in mass production to detect failures before doing end-of-line test and producing scrap.

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.

Automated optical inspection (AOI) is an automated visual inspection of printed circuit board (PCB) manufacture where a camera autonomously scans the device under test for both catastrophic failure and quality defects. It is commonly used in the manufacturing process because it is a non-contact test method. It is implemented at many stages through the manufacturing process including bare board inspection, solder paste inspection (SPI), pre-reflow and post-reflow as well as other stages.

A built-in self-test (BIST) or built-in test (BIT) is a mechanism that permits a machine to test itself. Engineers design BISTs to meet requirements such as:

ICT failures & mechanical simulation

In-circuit testing has been known to cause mechanical failures such as capacitor flex cracking and pad cratering. This typically occurs on a bed of nails tester if there is excessive board flexure due to poor support placement or high probe forces. It can be challenging to optimize for ideal support locations and probe forces without spending resources designing and building an ICT fixture. Current methods typically employ strain gaging or similar techniques to monitor board flexure. More recently, some have looked at finite element simulation to proactively design or adjust an ICT fixture to avoid these mechanical failure modes. This approach can be implemented as part of a design for manufacturability methodology to provide rapid feedback on ICT design and reduce costs. [2]

Pad cratering is a mechanically induced fracture in the resin between copper foil and outermost layer of fiberglass of a printed circuit board (PCB). It may be within the resin or at the resin to fiberglass interface.

Strain gauge electronic component

A strain gauge is a device used to measure strain on an object. Invented by Edward E. Simmons and Arthur C. Ruge in 1938, the most common type of strain gauge consists of an insulating flexible backing which supports a metallic foil pattern. The gauge is attached to the object by a suitable adhesive, such as cyanoacrylate. As the object is deformed, the foil is deformed, causing its electrical resistance to change. This resistance change, usually measured using a Wheatstone bridge, is related to the strain by the quantity known as the Gauge factor.

Finite element method Numerical method for solving physical or engineering problems

The finite element method (FEM) is a numerical method for solving problems of engineering and mathematical physics. Typical problem areas of interest include structural analysis, heat transfer, fluid flow, mass transport, and electromagnetic potential. The analytical solution of these problems generally require the solution to boundary value problems for partial differential equations. The finite element method formulation of the problem results in a system of algebraic equations. The method approximates the unknown function over the domain. To solve the problem, it subdivides a large system into smaller, simpler parts that are called finite elements. The simple equations that model these finite elements are then assembled into a larger system of equations that models the entire problem. FEM then uses variational methods from the calculus of variations to approximate a solution by minimizing an associated error function.

Example test sequence

Electrolytic capacitor polarized capacitor whose anode is made of a metal that forms an insulating oxide layer through anodization, acting as the dielectric of the capacitor; a solid, liquid, or gel electrolyte covers the surface of this oxide layer, serving as the cathode

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 electrolyte covers the surface of this oxide layer, serving as the cathode or negative plate of the capacitor. Due to their very thin dielectric oxide layer and enlarged anode surface, electrolytic capacitors have a much higher capacitance-voltage (CV) product per unit volume than ceramic capacitors or film capacitors, and so can have large capacitance values. There are three families of electrolytic capacitor: aluminum electrolytic capacitors, tantalum electrolytic capacitors, and niobium electrolytic capacitors.

EEPROM nonvolatile memory comprising arrays of floating-gate transistors used in computers, microcontrollers &c. to store relatively small amounts of data but allowing individual bytes to be erased/reprogrammed in-circuit through special programming signals

EEPROM (also E2PROM) stands for electrically erasable programmable read-only memory and is a type of non-volatile memory used in computers, integrated in microcontrollers for smart cards and remote keyless systems, and other electronic devices to store relatively small amounts of data but allowing individual bytes to be erased and reprogrammed.

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:

Advantages

In-circuit testing is best suited to stable products with a mature design and higher volumes. [4] It offers the following advantages:

Limitations

While in-circuit test is a very powerful tool for testing PCBs, it has these limitations:

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

Related Research Articles

Multimeter Electronic measuring instrument that combines several measurement functions in one unit

A multimeter or a multitester, also known as a VOM (volt-ohm-milliammeter), is an electronic measuring instrument that combines several measurement functions in one unit. A typical multimeter can measure voltage, current, and resistance. Analog multimeters uses a microammeter with a moving pointer to display readings. Digital multimeters have a numeric display, and may also show a graphical bar representing the measured value. Digital multimeters are now far more common due to their lower cost and greater precision, but analog multimeters are still preferable in some cases, for example when monitoring a rapidly varying value.

Point-to-point construction Method for assembling electrical components

Point-to-point construction is a non-automated method of construction of electronics circuits widely used before the use of printed circuit boards (PCBs) and automated assembly gradually became widespread following their introduction in the 1950s. Circuits using thermionic valves were relatively large, relatively simple, and used large sockets, all of which made the PCB less obviously advantageous than with later complex semiconductor circuits. Point-to-point construction is still widespread in power electronics where components are bulky and serviceability is a consideration, and to construct prototype equipment with few or heavy electronic components. A common practice, especially in older point-to-point construction is to use the leads of components such as resistors and capacitors to bridge as much of the distance between connections as possible, often removing the need to add additional wire between the components.

Surface-mount technology method for producing electronic circuits

Surface-mount technology (SMT) is a method for producing electronic circuits in which the components are mounted or placed directly onto the surface of printed circuit boards (PCBs). An electronic device so made is called a surface-mount device (SMD). In industry, it has largely replaced the through-hole technology construction method of fitting components with wire leads into holes in the circuit board. Both technologies can be used on the same board, with the through-hole technology used for components not suitable for surface mounting such as large transformers and heat-sinked power semiconductors.

Automatic test equipment apparatus used in Hardware testing

Automatic test equipment or automated test equipment (ATE) is any apparatus that performs tests on a device, known as the device under test (DUT), equipment under test (EUT) or unit under test (UUT), using automation to quickly perform measurements and evaluate the test results. An ATE can be a simple computer-controlled digital multimeter, or a complicated system containing dozens of complex test instruments capable of automatically testing and diagnosing faults in sophisticated electronic packaged parts or on wafer testing, including system on chips and integrated circuits.

Electronic component basic discrete device or physical entity in an electronic system used to affect electrons or their associated fields

An electronic component is any basic discrete device or physical entity in an electronic system used to affect electrons or their associated fields. Electronic components are mostly industrial products, available in a singular form and are not to be confused with electrical elements, which are conceptual abstractions representing idealized electronic components.

Cable tester electronic device used to verify the electrical connections

A cable tester is an electronic device used to verify the electrical connections in a signal cable or other wired assembly. Basic cable testers are continuity testers that verify the existence of a conductive path between ends of the cable, and verify the correct wiring of connectors on the cable. More advanced cable testers can measure the signal transmission properties of the cable such as its resistance, signal attenuation, noise and interference.

A test engineer is a professional who determines how to create a process that would best test a particular product in manufacturing and related disciplines in order to assure that the product meets applicable specifications. Test engineers are also responsible for determining the best way a test can be performed in order to achieve adequate test coverage. Often test engineers also serve as a liaison between manufacturing, design engineering, sales engineering and marketing communities as well.

A device under test (DUT), also known as equipment under test (EUT) and unit under test (UUT), is a manufactured product undergoing testing, either at first manufacture or later during its life cycle as part of ongoing functional testing and calibration checks. This can include a test after repair to establish that the product is performing in accordance with the original product specification.

Test probe

A test probe is a physical device used to connect electronic test equipment to a device under test (DUT). Test probes range from very simple, robust devices to complex probes that are sophisticated, expensive, and fragile. Specific types include test prods, oscilloscope probes and current probes. A test probe is often supplied as a test lead, which includes the probe, cable and terminating connector.

Probe card

A probe card is an interface between an electronic test system and a semiconductor wafer. Typically the probe card is mechanically docked to a prober and electrically connected to a tester. Its purpose is to provide an electrical path between the test system and the circuits on the wafer, thereby permitting the testing and validation of the circuits at the wafer level, usually before they are diced and packaged. It consists, normally, of a printed circuit board (PCB) and some form of contact elements, usually metallic, but possibly of other materials as well.

Semiconductor curve tracer test equipment

A semiconductor curve tracer is a specialised piece of electronic test equipment used to analyze the characteristics of discrete semiconductor devices such as diodes, transistors, and thyristors. Based on an oscilloscope, the device also contains voltage and current sources that can be used to stimulate the device under test (DUT).

SPEA is an Italian company that designs and manufactures Automatic Test Equipment (ATE) for testing MEMS, Sensors, microchips and Printed circuit board.

Bead probe technology

Bead probe technology (BPT) is technique used to provide electrical access to printed circuit board (PCB) circuitry for performing in-circuit testing (ICT). It makes use of small beads of solder placed onto the board's traces to allow measuring and controlling of the signals using a test probe. This permits test access to boards on which standard ICT test pads are not feasible due to space constraints.

In the testing of printed circuit boards, a flying probe test or fixtureless in-circuit test (FICT) system may be used for testing low to mid volume production, prototypes, and boards that present accessibility problems. A traditional "bed of nails" tester for testing a PCB requires a custom fixture to hold the PCBA and the Pogo pins which make contact with the PCBA. In contrast, FICT uses two or more flying probes, which may be moved based on software instruction. The flying probes are electro-mechanically controlled to access components on printed circuit assemblies (PCAs). The probes are moved around the board under test using an automatically operated two-axis system, and one or more test probes contact components of the board or test points on the printed circuit board.

LCR meter

An LCR meter is a type of electronic test equipment used to measure the inductance (L), capacitance (C), and resistance (R) of an electronic component. In the simpler versions of this instrument the impedance was measured internally and converted for display to the corresponding capacitance or inductance value. Readings should be reasonably accurate if the capacitor or inductor device under test does not have a significant resistive component of impedance. More advanced designs measure true inductance or capacitance, as well as the equivalent series resistance of capacitors and the Q factor of inductive components.

Circuit Check

Circuit Check is an American company with about 225 employees and seven direct operations in six countries. Headquartered in Maple Grove, Minnesota, it is one of the largest manufacturers of electronic and mechanical test fixtures in North America, . The company also manufactures Automatic Test Equipment for end-of-line manufacturing test. The company uses either a Microsoft Excel-driven "CCITest" software platform, or the National Instruments LabVIEW software platform.

References

  1. "About Teradyne". Teradyne Corp. Retrieved 28 December 2012.
  2. "Preventing Pad Cratering During ICT Using Sherlock" (PDF). DfR Solutions.
  3. Jun Balangue, “Successful ICT Boundary Scan Implementation,” CIRCUITS ASSEMBLY, September 2010. http://www.circuitsassembly.com/cms/magazine/208-2010-issues/10282-testinspection
  4. "Pick the Best Electronic Test Solution for Your Product". Saline Lectronics. 2016-06-24. Retrieved 2019-02-01.