Automatic or automated test equipment (ATE) are a system that performs tests on a device, known as the Device Under Test (DUT), using automation to quickly perform measurements and evaluate the test results. An ATE can be a simple computer controlled digital multimeter, or, more often, a complicated system containing dozens of complex test instruments (real or simulated electronic test equipment) capable of automatically testing and diagnosing faults in complex ICs.The ATE/semiconductor test segment is comprised of six distinct types of testers: • Analog/Linear Test • Mixed Signal Test • RF/Microwave Test • Digital/Logic Test • Memory Test • System-on-Chip (SOC) Test
ATE systems interface with packaged chips through a separate machine called an IC handler. Tested ICs are then “binned” depending on their performance (higher performance devices are sold at a premium). Alternatively, ATE systems can test unpackaged chip directly on the wafer through a wafer prober and probe card designed to touch on the IO/bonding pads of the device. In this way, the cost of packaging bad chips is avoided.
The ATE market is driven by semiconductor chip volumes. As chip volumes steadily increase, the demand for chip testers also grows.
Given the sharp increase in usage of memory devices in end products such as home appliances, cell phones, and automobiles, it’s no surprise that the memory tester sub-segment is the largest in the ATE space.
According to a research report by Radiant Insights, Inc., the global ATE mrket is expected to be valued at $4.48 billion by 2020, as per Increasing design complexity coupled with need for effective testing is expected to drive the global automated test equipment market demand.
Increasing need for optimizing power management in order to ensure longer battery life is likely to favor the growth prospects. However, dependency on semiconductor chips is likely challenge industry participants. Non-memory products were the leading segment, valued at $2,867.5 million in 2013, according to the report. Expansion of consumer electronics, increasing automotive demand and growing number of microcontroller-based applications are factors likely to promote its demand.
Memory products accounted for 21.21% of the overall revenue in 2013, growing at an estimated CAGR of 1.7% from 2014 to 2020. The cyclical variations in growth rates than non-memory semiconductors have resulted in gaining popularity among various applications.
Automatic test or automated test equipment is used extensively within production test to enable the best testing to be achived in the minimum time: there are several different types available.
ATE automatic test equipment is a vital part of the electronics test scene today. Automatic test equipment enables printed circuit board test, and equipment test to be undertaken very swiftly - far faster than if it were done manually. As time of production staff forms a major element of the overall production cost of an item of electronics equipment, it is necessary to reduce the production times as possible. This can be achieved with the use of ATE, automatic test equipment.
Automatic test equipment can be expensive, and therefore it is necessary to ensure that the correct philosophy and the correct type or types automatic test equipment are used. Only by applying the use of automatic test equipment correctly can the maximum benefits be gained.
There is a variety of different approaches that can be used for automatic test equipment. Each type has its own advantages and disadvantages, and can be used to great effect in certain circumstances. When choosing ATE systems it is necessary to understand the different types of systems and to be able to apply them correctly.
Types of ATE automatic test systems
There is a good variety of types of ATE systems that can be used. As they approach electronics test in slightly different ways they are normally suited to different stages in the production test cycle. The most widely used forms of ATE, automatic test equipment used today are listed below:
PCB inspection systems: PCB inspection is a key element in any production process and particularly important where pick and place machines are involved. Manual inspection was used many years ago, but was always unreliable and inconsistent. Now with printed circuit boards that are considerably more complicated manual inspection is not a viable option. Accordingly automated systems are used:
AOI, Automatic Optical Inspection: is widely used in many manufacturing environments. It is essentially a form of inspection, but achieved automatically. This provides a much greater degree of repeatability and speed when compared to manual inspection. AOI, automatic optical inspection it is particularly useful when situated at the end of a line producing soldered boards. Here it can quickly locate production problems including solder defects as well as whether the correct components and fitted and also whether their orientation is correct. As AOI systems are generally located immediately after the PCB solder process, any solder process problems can be resolved quickly and before too many printed circuit boards are affected.
AOI automatic optical inspection takes time to set up and for the test equipment to learn the board. Once set it can process boards very quickly and easily. It is ideal for high volume production. Although the level of manual intervention is low, it takes time to set up correctly, and there is a significant investment in the test system itself.
Automated X-Ray inspection, AXI: Automated X-Ray inspection has many similarities to AOI. However with the advent of BGA packages it was necessary to be able to use a form of inspection that could view items not visible optically. Automated X-Ray inspection, AXI systems can look through IC packages and examine the solder joints underneath the package to evaluate the solder joints.
ICT In circuit test: In-Circuit Test, ICT is a form of ATE that has been in use for many years and is a particularly effective form of printed circuit board test. This test technique not only looks at short circuits, open circuits, component values, but it also checks the operation of ICs.
Although In Circuit Test, ICT is a very powerful tool, it is limited these days by lack of access to boards as a result of the high density of tracks and components in most designs. Pins for contact with the nodes have to be very accurately placed in view of the very fine pitches and may not always make good contact. In view of this and the increasing number of nodes being found on many boards today it is being used less than in previous years, although it is still widely used.
A Manufacturing Defect Analyzer, MDA is another form of printed circuit board test and it is effectively a simplified form of ICT. However this form of printed circuit board test only tests for manufacturing defects looking at short circuits, open circuits and looks at some component values. As a result, the cost of these test systems is much lower than that of a full ICT, but the fault coverage is less.
JTAG Boundary scan testing: Boundary scan is a form of testing that has come to the fore in recent years. Also known as JTAG, Joint Test Action Group, or by its standard IEEE 1149.1, boundary scan offers significant advantages over more traditional forms of testing and as such has become one of the major tools in automatic testing.
The main reason that boundary scan testing was developed was to overcome the problems of lack of access to boards and integrated circuits for testing. Boundary scan overcomes this by having specific boundary scan registers in large integrated circuits. With the board set to a boundary scan mode, serial data registers in the integrated circuits have data passed into them. The response and hence data passing out of the serial data chain enables the tester to detect any failures. As a result of its ability to test boards and even ICs with very limited physical test access, Boundary Scan / JTAG has become very widely used.
Functional testing: Functional test can be considered as any form of electronics testing that exercises the function of a circuit. There are a number of different approaches that can be adopted dependent upon the type of circuit (RF, digital, analogue, etc), the degree of testing required. The main approaches are outlined below:
Functional Automatic Test Equipment, FATE: This term usually refers to the large functional automatic test equipment in a specially designed console. These automatic test equipment systems are generally used for testing digital boards but these days these large testers are not widely used. The increasing speeds at which many boards run these days cannot be accommodated on these testers where leads between the board under test and the tester measurement or stimulus point can result in large capacitances that slow the rate of operation down. In addition to this fixtures are expensive as is the programme development. Despite these drawbacks these testers may still be used in areas where production volumes are high and speeds not particularly high. They are generally used for testing digital boards.
Rack and stack test equipment using GPIB: One way in which boards, or units themselves can be tested is using a stack of remotely controlled test equipment.
Despite its age, many items of rack mounted or bench test equipment still have a GPIB capability. Despite the fact that GPIB is relatively slow and has been in existence for over 30 years it is still widely used as it provides a very flexible method of test. The main drawback of GPIB is its speed and the cost of writing the programmes although test executive packages like LabView can be used to aid programme generation and execution in the test environment. Fixtures or test interfaces can also be expensive.
Chassis or rack based test equipment: One of the major drawbacks of the GPIB rack and stack automatic test equipment approach is that it occupies a large amount of space, and the operating speed is limited by the speed of the GPIB. To overcome these problems a variety of standards for systems contained within a chassis have been developed.
Although there are a variety of ATE, automatic test equipment approaches that can be used, these are some of the more popular systems in use. They can all use test management software such as LabView to assist in the running of the individual tests. This enables facilities such as the ordering of tests, results collection and printout as well as results logging, etc.
Combinational test: No single method of testing is able to provide a complete solution these days. To help overcome this various ATE automatic test equipment systems incorporate a variety of test approaches. These combinational testers are generally used for printed circuit board testing. By doing this, a single electronics test is able to gain a much greater level of access for the printed circuit board test, and the test coverage is much higher. Additionally a combinational tester is able to undertake a variety of different types of test without the need to mover the board from one tester to another. In this way a single suite of tests may include In-circuit testing as well as some functional tests and then some JTAG boundary scan testing.
Each type of automatic test philosophy has its strengths, and accordingly it is necessary to choose the correct type of test approach for the testing that is envisaged.
By utilising all the different test techniques appropriately, it is possible to ATE automatic test equipment to be used to its fullest advantage. This will enable tests to be executed swiftly, while still providing a high level of coverage. Inspection techniques including AOI and X-ray inspection can be used along with In-circuit test, and JTAG boundary scan testing. Functional testing can also be used. While it is possible to use different types of test, it is necessary to ensure that products are not over tested as this wastes time. For example if AOI or X-Ray inspection is used, it may not be appropriate to use In-circuit testing. The place of JTAG boundary scan testing should also be considered. In this way the most effective test strategy can be defined.
Automatic or automated optical inspection, AOI, is a key technique used in the manufacture and test of electronics printed circuit boards, PCBs. Automatic optical inspection, AOI enables fast and accurate inspection of electronics assemblies and in particular PCBs to ensure that the quality of product leaving the production line is high and the items are built correctly and without manufacturing faults.
Need for AOI, automatic optical inspection
Despite the major improvements that have been made, modern circuits are far more complicated than boards were even a few years ago. The introduction of surface mount technology, and the subsequent further reductions in size mean that boards are particularly compact. Even relatively average boards have thousands of soldered joints, and these are where the majority of problems are found.
This increase in the complexity of boards also means that manual inspection is not a viable option these days. Even when it was an accepted approach, it was realised that it was not particularly effective as inspectors soon tired and poor and incorrect construction was easily missed. With the marketplace now requiring high volume, high quality products to be brought to market very quickly very reliable and fast methods are needed to ensure that product quality remains high. AOI, automatic optical inspection is an essential tool in an integrated electronics test strategy that ensure costs are kept as low as possible by detecting faults early in the production line.
One of the solutions to this is to use automated or automatic optical inspection systems. Automated optical inspection systems can be placed into the production line just after the solder process. In this way they can be used to catch problems early in the production process. This has a number of advantages. With faults costing more to fix the further along the production process they are found, this is obviously the optimum place to find faults. Additionally process problems in the solder and assembly area can be seen early in the production process and information used to feedback quickly to earlier stages. In this way a rapid response can ensure that problems are recognised quickly and rectified before too many boards are built with the same problem.
Comparison of the major defect detection capabilities of AOI, AXI and ICT
Defect type
AOI
AXI
ICT
Soldering defects
Open circuits
Y
Y
Y
Solder bridges
Y
Y
Y
Solder shorts
Y
Y
Y
Insufficient solder
Y (not heel of joint)
Y
N
Solder void
N
Y
N
Excess solder
Y
Y
N
Solder quality
N
Y
N
Component defects
Lifted lead
Y
Y
Y
Missing component
Y
Y
Y
Misaligned or misplaced component
Y
Y
Y
Incorrect component value
N
N
Y
Faulty component
N
N
Y
BGA and CSP defects
BGA shorts
N
Y
Y
BGA open circuit connections
N
Y
Y
AOI, automatic optical inspection basics
AOI, automatic optical inspection systems use visual methods to monitor printed circuit boards for defects. They are able to detect a variety of surface feature defects such as nodules, scratches and stains as well as the more familiar dimensional defects such as open circuits, shorts and thinning of the solder. They can also detect incorrect components, missing components and incorrectly placed components. As such they are able to perform all the visual checks performed previously by manual operators, and far more swiftly and accurately.
They achieve this by visually scanning the surface of the board. The board is light by several light sources and one or more high definition cameras are used. In this way the AOI machine is able to build up a picture of the board
The automated optical inspection, AOI system uses the captured image which is processed and then compared with the knowledge the machine has of what the board should look like. Using this comparison the AOI system is able to detect and highlight any defects or suspect areas.
AOI uses a number of techniques to provide the analysis of whether a board is satisfactory or has any defects:
Template matching: Using this form of process the AOI, automated optical inspection system compares the image obtained with the image from a "golden board".
Pattern matching: Using this techniques the AOI system stores information of both good and bad PCB assemblies, matching the obtained image to these.
Statistical pattern matching: This approach is very similar tot hat above, except that it uses a statistically based method of addressing problems. By storing the results of several boards and several types of failure, it is able to accommodate minor acceptable deviations without flagging errors.
In order to build up the database of what the board should be, both known status boards and PCB design information is used as described later.
As technology has improved it has been able for AOI systems to very accurately predict defects and have a small number of no defect found scenarios. As such AOI systems form a very useful element in a sophisticated manufacturing environment.
AOI image capture and analysis
One of the key elements of an AOI, automated optical inspection system is the image capture system. This captures an image of the printed circuit board, PCB assembly which is then analysed by the processing software within the AOI system. There are many variants of image capture system dependent upon the exact application and the complexity / cost of the AOI system.
Imaging systems may comprise a single camera or there may be more than one to provide better imaging and the possibility of a 3D capability. The cameras should also be able to move under software control. This will enable them to move to the optimum position for a given PCB assembly.
In addition to this the type of camera has an impact on performance. Speed against accuracy is a balance that has to be struck and will impact on the camera type used:
Streaming video: One type of camera used for automated optical inspection, AOI, takes streaming video from which complete frames are taken. The captured frame then enables a still image to be generated on which the signal processing is performed. This approach is not as accurate as other still image systems but has the advantage of very high speed.
Still image camera system: This is generally placed relatively close to the target PCB and as a result it requires a good lighting system. It may also be necessary to be able to move the camera under software control.
When analysing an image of a board, the AOI system looks for a variety of specific features: component placement, component size, board fiducials, label patterns (e.g. bar codes), background colour and reflectivity, etc. As an important element of its task the AOI system also inspects the soldered joints to ensure they indicate that the joints are satisfactory.
When analysing the boards the AOI system must take into account many variations between good boards. Not only do components vary considerably in size between batches, but also the colour and reflectivity. Often there are also differences in the silk screening where ink thickness and colour typeface may change slightly.
AOI light source
Lighting is a key element in the AOI system. By choosing the correct lighting source it is possible to highlight different types of defect more easily. With the advances that have been made in lighting technology in recent years, this has enabled lighting to be used to enhance the images available and in turn this enables defects to be highlighted more easily with a resultant reduction in processing required and an increase in speed and accuracy.
Most AOI systems have a defined lighting set. This will depend upon the operation required and the product types to be tested. These have usually been optimised for the anticipated conditions. However sometimes some customisation may be required, and an understanding of lighting is always of use.
A variety of types of lighting are available:
Fluorescent lighting: Fluorescent lighting is widely used for AOI, automated optical inspection applications as it provides an effective form of lighting for viewing defects on PCBs. The main problem with fluorescent lighting for AOI applications is that the lamps degrade with time. This means that the automated optical inspection system will be subject to a constantly changing levels and quality of light
LED lighting: The development of LED lighting has meant that AOI, automated optical inspection systems are able to adopt a far more stable form of lighting. Although LED lighting does suffer from a reduction in light output from the LEDs over time, this can be compensated for by increasing the current. Using LED lighting, the level of lighting can also be controlled. LEDs are therefore a far more satisfactory form of lighting than fluorescent or incandescent lights that were used years ago
Infra-red or ultra-violet: On some occasions infra-red or ultra-violet lighting may be required to enhance certain defects, or to enable automated optical inspection to be carried out to reveal certain types of defect.
Apart from the form of lighting, the positioning of the lighting for an automatic optical inspection system, AOI, is equally important. The light sources require positioning to not only to ensure that all areas are well light, which is particularly important when certain components may cast shadows, but also to highlight defects. Careful adjustment may be needed for different assemblies.
AOI, automated optical inspection system programming
In order to be able to test a PCB assembly using AOI, automatic optical inspection, the details for an acceptable board must be stored within the system. This programming activity must be carried out correctly if the AOI system is to be able to correctly detect any defects on the PCB assemblies passing through.
there are several methods that can be used to programme an AOI system:
Use of "Golden Board": One method is to provide a known good board as a target for the AOI, automated optical inspection system to use. This is passed through the system so that it can learn the relevant attributes. It will look at the components, the solder profiles of each joint, and many other aspects. In order to provide the system with enough variance data several boards are often required.
Algorithm based programming: PCB data is provided to the system and it then generates its own profile for the board. This scheme will also require real boards, but fewer are generally required.
There are advantages and disadvantages to both systems. It is a balance between set-up time, maintenance, accuracy and the requirements for the particular AOI, automated optical inspection system. Typically the requirements will be largely dependent upon the machine in use.
It is essential that any printed circuit board manufacturing area is able to check the quality of the boards coming off the end of the line. Only in this way are they able to monitor quality and when problems are detected to rectify the process so that further boards are not affected by the same problems. In this way automatic optical inspection and where necessary X-ray inspection are two essential tools for the manufacturing industry.
Automatic optical inspection works very well in electronics manufacturing for printed circuit boards where joints are visible. However many PCBs today are using technologies such as ball grid array, BGA integrated circuits and chip scale packages, CSPs where the solder connections are not visible. This has arisen as a result of the need for greater numbers of interconnections to integrated circuit packages and as a general result of increasing complexity. In these and many other instances it is necessary to carry out checks using automated X-Ray inspection, AXI, equipment that can not only check the solder joints under components, but also reveal many defects in solder joints that may not be visible with ordinary optical inspection equipment.
In recent years, the need for automated X-Ray inspection equipment has grown considerably and as a result, a much wider range of equipment is available. Additionally the techniques used in automated X-Ray inspection equipment has improved and this has enabled far greater levels of detection to be achieved for printed circuit board, PCB manufacture.
As one significant improvement in AXI, automated X-ray inspection, not only are 2D or two dimensional techniques available, but machines utilising 3D technology are available and give significant improvements in performance.
AXI technology features
AXI, automated X-ray inspection systems are able to monitor a variety of aspects of a printed circuit board assembly production. They would normally be placed after the solder process to monitor defects in PCBs after leaving the soldering process. They have the distinct advantage over optical systems that they are able to "see" solder joints that are under packages such as BGAs, CSPs and flip chips where the solder joints are hidden.
SMB BGA package showing top and undersides
AXI, automated X-ray inspection systems are not only able to "see" through the chips, but they are also able to provide an internal view of the solder joints. In this way they are able to detect voiding within a solder joint that may otherwise look perfectly acceptable.
This means that AXI, automated X-ray inspection systems are able to provide additional information over that which could be provided by purely optical systems to ensure that solder joints are being made to the required standard.
AXI, automated optical inspection can inspect the features of solder joints providing information on the way the soldering process is operating. Parameters such as solder thickness, joint sizes and profiles can be undertaken on specific joints on boards. These can then be used to provide data on the solder process and how well it is operating. AXI systems are also able to see the heel of the joint which AOI systems are unable to see as they are masked by the leads from the ICs as shown.
Solder joint geometry for a typical Quad Flat Pack IC
When an automated X-ray inspection system, or an optical system is used within an electronics PCB manufacturing process, the defects and other information detected by the inspection system can be quickly analysed and the process altered to reduce the defects and improve the quality of the process. In this way not only are actual faults detected, but the process can be altered to reduce the fault levels on the boards coming through. Accordingly they ensure that the highest standards are maintained and they are particularly useful when new boards are being set up and the process needs to be optimised.
It should be realised that AXI is only one of the number of tools that can be used within an electronics PCB manufacturing organisation. Two other tools, namely AOI, automatic optical inspection, and ICT, in-circuit test can provide similar information in many areas. The table below provides a comparison of the different types on information that each form of automatic test equipment, ATE can provide. Decisions about which type of types of testing should be used can then be made.
Comparison of the major defect detection capabilities of AOI, AXI and ICT
Defect type
AOI
AXI
ICT
Soldering defects
Open circuits
Y
Y
Y
Solder bridges
Y
Y
Y
Solder shorts
Y
Y
Y
Insufficient solder
Y (not heel of joint)
Y
N
Solder void
N
Y
N
Excess solder
Y
Y
N
Solder quality
N
Y
N
Component defects
Lifted lead
Y
Y
Y
Missing component
Y
Y
Y
Misaligned or misplaced component
Y
Y
Y
Incorrect component value
N
N
Y
Faulty component
N
N
Y
BGA and CSP defects
BGA shorts
N
Y
Y
BGA open circuit connections
N
Y
Y
Automated X-ray inspection, AXI has an important place in many electronics PCB manufacturing organisations. AXI is able to provide a fast and in-depth and accurate inspection of PCBs passing through the production facility and in this way provide real-time feedback that enables the production system to be optimised to enable high quality reliable circuits to be produced. Although more expensive than some other forms of inspection, AXI has many advantages and these need to be carefully balanced against the costs to ensure whatever choice is made, it is correct for the particular production environment.
AOI, automated optical inspection is a particularly successful method for inspecting printed circuit board, PCB assemblies once they have passed through a soldering process. AOI is able to detect defects including solder joint problems and as well as a variety of other problems. In order to be able to detect these defects efficiently and with a minimum number of no problem found instances, it is necessary for the board or assembly to have undergone a design for automated optical inspection or test process.
In order to ensure that the AOI test can be performed efficiently a number of guidelines can be followed in the design and layout of the printed circuit board. This will make the automated optical inspection more effective and less likely indicate problems that do not exist. By implementing these design for test features, testing can be made more effective and this will result in swifter testing, less rework and overall reduced costs.
Design guidelines for AOI testing
There are many steps that can be taken to improve the way in which AOI, automated optical inspection systems may perform. Essentially the success of an AOI system depends upon the way in which the system camera is able to view the board, and the image processing is able to handle images and detect any defects.
The ideas mentioned below are some ideas that can be implemented to improve the AOI performance:
Ensure visible access to all areas of the board: In some instances tall components or other features of the PCB assembly may cause areas of the board to be less visible. When designing the PCB, ensure all areas are easily visible for the AOI system.
Maintain consistent component sizes: Despite the nominal sizes specified for many components including capacitors and resistors, the actual sizes vary slightly between manufacturers.
Use standard component pads: Use standard component pads wherever possible as this means that the AOI processor only needs to sore one profile for a good joint.
Do not use overlapping pads: In some instances it may be convenient to merge two component pads together. If possible this should be avoided as overlapping pads may show a different joint profile and give false defect indications.
Summary
Implementing design for automated optical inspection ideas will improve the reliability of any AOI testing that is undertaken. If design for AOI is not adopted, areas of the board may not be sufficiently inspected and defects may pass this stage of the manufacturing process. If testing and inspection is to be undertaken, it is always better to ensure it can be achieved as effectively as possible. By accommodating the requirements for AOI in the early stages of design will assist in making the manufacturing process as efficient as possible.
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 (real or simulated electronic test equipment) capable of automatically testing and diagnosing faults in sophisticated electronic packaged parts or on wafer testing, including system on chips and integrated circuits.
ATE is widely used in the electronic manufacturing industry to test electronic components and systems after being fabricated. ATE is also used to test avionics and the electronic modules in automobiles. It is used in military applications like radar and wireless communication.
In the semiconductor industry
Semiconductor ATE, named for testing semiconductor devices, can test a wide range of electronic devices and systems, from simple components (resistors, capacitors, and inductors) to integrated circuits (ICs), printed circuit boards (PCBs), and complex, completely assembled electronic systems. For this purpose, probe cards are used. ATE systems are designed to reduce the amount of test time needed to verify that a particular device works or to quickly find its faults before the part has a chance to be used in a final consumer product. To reduce manufacturing costs and improve yield, semiconductor devices should be tested after being fabricated to prevent defective devices ending up with the consumer.
Components
The semiconductor ATE architecture consists of master controller (usually a computer) that synchronizes one or more source and capture instruments (listed below). Historically, custom-designed controllers or relays were used by ATE systems. The Device Under Test (DUT) is physically connected to the ATE by another robotic machine called a handler or prober and through a customized Interface Test Adapter (ITA) or "fixture" that adapts the ATE's resources to the DUT.
Industrial PC
The industrial PC is nothing but a normal desktop computer packaged in 19-inch rack standards with sufficient PCI / PCIe slots for accommodating the Signal stimulator/sensing cards. This takes up the role of a controller in the ATE. Development of test applications and result storage is managed in this PC. Most modern semiconductor ATEs include multiple computer-controlled instruments to source or measure a wide range of parameters. The instruments may include device power supplies (DPS),[1][2] parametric measurement units (PMU), arbitrary waveform generators (AWG), digitizers, digital IOs, and utility supplies. The instruments perform different measurements on the DUT, and the instruments are synchronized so that they source and measure waveforms at the proper times. Based on the requirement of response-time, real-time systems are also considered for stimulation and signal capturing.
Mass interconnect
The mass interconnect is a connector interface between test instruments (PXI, VXI, LXI, GPIB, SCXI, & PCI) and devices/units under test (D/UUT). This section acts as a nodal point for signals going in/out between ATE and D/UUT.
Example: Simple voltage measurement
For example, to measure a voltage of a particular semiconductor device, the Digital Signal Processing (DSP) instruments in the ATE measure the voltage directly and send the results to a computer for signal processing, where the desired value is computed. This example shows that conventional instruments, like an Ammeter, may not be used in many ATEs due to the limited number of measurements the instrument could make, and the time it would take to use the instruments to make the measurement. One key advantage to using DSP to measure the parameters is time. If we have to calculate the peak voltage of an electrical signal and other parameters of the signal, then we have to employ a peak detector instrument as well as other instruments to test the other parameters. If DSP-based instruments are used, however, then a sample of the signal is made and the other parameters can be computed from the single measurement.
Test parameter requirements vs test time
Not all devices are tested equally. Testing adds costs, so low-cost components are rarely tested completely, whereas medical or high costs components (where reliability is important) are frequently tested.
But testing the device for all parameters may or may not be required depending on the device functionality and end user. For example, if the device finds application in medical or life-saving products then many of its parameters must be tested, and some of the parameters must be guaranteed. But deciding on the parameters to be tested is a complex decision based on cost vs yield. If the device is a complex digital device, with thousands of gates, then test fault coverage has to be calculated. Here again, the decision is complex based on test economics, based on frequency, number and type of I/Os in the device and the end-use application...
Handler or prober and device test adapter
ATE can be used on packaged parts (typical IC 'chip') or directly on the Silicon Wafer. Packaged parts use a handler to place the device on a customized interface board, whereas silicon wafers are tested directly with high precision probes. The ATE systems interact with the handler or prober to test the DUT.
Packaged part ATE with handlers
ATE systems typically interface with an automated placement tool, called a "handler", that physically places the Device Under Test (DUT) on an Interface Test Adapter (ITA) so that it can be measured by the equipment. There may also be an Interface Test Adapter (ITA), a device just making electronic connections between the ATE and the Device Under Test (also called Unit Under Test or UUT), but also it might contain an additional circuitry to adapt signals between the ATE and the DUT and has physical facilities to mount the DUT. Finally, a socket is used to bridge the connection between the ITA and the DUT. A socket must survive the rigorous demands of a production floor, so they are usually replaced frequently.
Simple electrical interface diagram: ATE → ITA → DUT (package) ← Handler
Silicon wafer ATE with probers
Wafer-based ATEs typically use a device called a Prober that moves across a silicon wafer to test the device.
Simple electrical interface diagram: ATE → Prober → Wafer (DUT)
Multi-site
One way to improve test time is to test multiple devices at once. ATE systems can now support having multiple "sites" where the ATE resources are shared by each site. Some resources can be used in parallel, others must be serialized to each DUT.
Many ATE platforms used in the semiconductor industry output data using Standard Test Data Format (STDF)
Diagnostics
Automatic test equipment diagnostics is the part of an ATE test that determines the faulty components. ATE tests perform two basic functions. The first is to test whether or not the Device Under Test is working correctly. The second is when the DUT is not working correctly, to diagnose the reason. The diagnostic portion can be the most difficult and costly portion of the test. It is typical for ATE to reduce a failure to a cluster or ambiguity group of components. One method to help reduce these ambiguity groups is the addition of analog signature analysis testing to the ATE system. Diagnostics are often aided by the use of flying probe testing.
Test equipment switching
The addition of a high-speed switching system to a test system's configuration allows for faster, more cost-effective testing of multiple devices, and is designed to reduce both test errors and costs. Designing a test system's switching configuration requires an understanding of the signals to be switched and the tests to be performed, as well as the switching hardware form factors available.
Test equipment platforms
Several modular electronic instrumentation platforms are currently in common use for configuring automated electronic test and measurement systems. These systems are widely employed for incoming inspection, quality assurance, and production testing of electronic devices and subassemblies. Industry-standard communication interfaces link signal sources with measurement instruments in "rack-and-stack" or chassis-/mainframe-based systems, often under the control of a custom software application running on an external PC.
GPIB/IEEE-488
The General Purpose Interface Bus (GPIB) is an IEEE-488 (a standard created by the Institute of Electrical and Electronics Engineers) standard parallel interface used for attaching sensors and programmable instruments to a computer. GPIB is a digital 8-bit parallel communications interface capable of achieving data transfers of more than 8 Mbytes/s. It allows daisy-chaining up to 14 instruments to a system controller using a 24-pin connector. It is one of the most common I/O interfaces present in instruments and is designed specifically for instrument control applications. The IEEE-488 specifications standardized this bus and defined its electrical, mechanical, and functional specifications, while also defining its basic software communication rules. GPIB works best for applications in industrial settings that require a rugged connection for instrument control.
The original GPIB standard was developed in the late 1960s by Hewlett-Packard to connect and control the programmable instruments the company manufactured. The introduction of digital controllers and programmable test equipment created a need for a standard, high-speed interface for communication between instruments and controllers from various vendors. In 1975, the IEEE published ANSI/IEEE Standard 488-1975, IEEE Standard Digital Interface for Programmable Instrumentation, which contained the electrical, mechanical, and functional specifications of an interfacing system. This standard was subsequently revised in 1978 (IEEE-488.1) and 1990 (IEEE-488.2). The IEEE 488.2 specification includes the Standard Commands for Programmable Instrumentation (SCPI), which define specific commands that each instrument class must obey. SCPI ensures compatibility and configurability among these instruments.
The IEEE-488 bus has long been popular because it is simple to use and takes advantage of a large selection of programmable instruments and stimuli. Large systems, however, have the following limitations:
Driver fanout capacity limits the system to 14 devices plus a controller.
Cable length limits the controller-device distance to two meters per device or 20 meters total, whichever is less. This imposes transmission problems on systems spread out in a room or on systems that require remote measurements.
Primary addresses limit the system to 30 devices with primary addresses. Modern instruments rarely use secondary addresses so this puts a 30-device limit on system size.[4]
LAN eXtensions for Instrumentation (LXI)
The LXI Standard defines the communication protocols for instrumentation and data acquisition systems using Ethernet. These systems are based on small, modular instruments, using low-cost, open-standard LAN (Ethernet). LXI-compliant instruments offer the size and integration advantages of modular instruments without the cost and form factor constraints of card-cage architectures. Through the use of Ethernet communications, the LXI Standard allows for flexible packaging, high-speed I/O, and standardized use of LAN connectivity in a broad range of commercial, industrial, aerospace, and military applications. Every LXI-compliant instrument includes an Interchangeable Virtual Instrument (IVI) driver to simplify communication with non-LXI instruments, so LXI-compliant devices can communicate with devices that are not themselves LXI compliant (i.e., instruments that employ GPIB, VXI, PXI, etc.). This simplifies building and operating hybrid configurations of instruments.
LXI instruments sometimes employ scripting using embedded test script processors for configuring test and measurement applications. Script-based instruments provide architectural flexibility, improved performance, and lower cost for many applications. Scripting enhances the benefits of LXI instruments, and LXI offers features that both enable and enhance scripting. Although the current LXI standards for instrumentation do not require that instruments be programmable or implement scripting, several features in the LXI specification anticipate programmable instruments and provide useful functionality that enhances scripting's capabilities on LXI-compliant instruments.[5]
VME eXtensions for Instrumentation (VXI)
The VXI bus architecture is an open standard platform for automated test based on the VMEbus. Introduced in 1987, VXI uses all Eurocard form factors and adds trigger lines, a local bus, and other functions suited for measurement applications. VXI systems are based on a mainframe or chassis with up to 13 slots into which various VXI instrument modules can be installed.[6] The chassis also provides all the power supply and cooling requirements for the chassis and the instruments it contains. VXI bus modules are typically 6U in height.
PCI eXtensions for Instrumentation (PXI)
PXI is a peripheral bus specialized for data acquisition and real-time control systems. Introduced in 1997, PXI uses the CompactPCI 3U and 6U form factors and adds trigger lines, a local bus, and other functions suited for measurement applications. PXI hardware and software specifications are developed and maintained by the PXI Systems Alliance.[7] More than 50 manufacturers around the world produce PXI hardware.[8]
Universal Serial Bus (USB)
The USB connects peripheral devices, such as keyboards and mice, to PCs. The USB is a Plug and Play bus that can handle up to 127 devices on one port, and has a theoretical maximum throughput of 480 Mbit/s (high-speed USB defined by the USB 2.0 specification). Because USB ports are standard features of PCs, they are a natural evolution of conventional serial port technology. However, it is not widely used in building industrial test and measurement systems for a number of reasons; for example, USB cables are not industrial grade, are noise sensitive, can accidentally become detached, and the maximum distance between the controller and the device is 30 m. Like RS-232, USB is useful for applications in a laboratory setting that do not require a rugged bus connection.
RS-232
RS-232 is a specification for serial communication that is popular in analytical and scientific instruments, as well for controlling peripherals such as printers. Unlike GPIB, with the RS-232 interface, it is possible to connect and control only one device at a time. RS-232 is also a relatively slow interface with typical data rates of less than 20 kbytes/s. RS-232 is best suited for laboratory applications compatible with a slower, less rugged connection. It works on a ±24 Volts supply
JTAG/Boundary-scan IEEE Std 1149.1
JTAG/Boundary-scan can be implemented as a PCB-level or system-level interface bus for the purpose of controlling the pins of an IC and facilitating continuity (interconnection) tests on a test target (UUT) and also functional cluster tests on logic devices or groups of devices. It can also be used as a controlling interface for other instrumentation that can be embedded into the ICs themselves (see IEEE 1687) or instruments that are part of an external controllable test system.
Test script processors and a channel expansion bus
One of the most recently developed test system platforms employs instrumentation equipped with onboard test script processors combined with a high-speed bus. In this approach, one "master" instrument runs a test script (a small program) that controls the operation of the various "slave" instruments in the test system, to which it is linked via a high-speed LAN-based trigger synchronization and inter-unit communication bus. Scripting is writing programs in a scripting language to coordinate a sequence of actions.
This approach is optimized for small message transfers that are characteristic of test and measurement applications. With very little network overhead and a 100Mbit/sec data rate, it is significantly faster than GPIB and 100BaseT Ethernet in real applications.
The advantage of this platform is that all connected instruments behave as one tightly integrated multi-channel system, so users can scale their test system to fit their required channel counts cost-effectively. A system configured on this type of platform can stand alone as a complete measurement and automation solution, with the master unit controlling sourcing, measuring, pass/fail decisions, test sequence flow control, binning, and the component handler or prober. Support for dedicated trigger lines means that synchronous operations between multiple instruments equipped with onboard Test Script Processors that are linked by this high speed bus can be achieved without the need for additional trigger connections.[9]
A bipolar junction transistor (BJT) is a type of transistor that uses both electrons and electron holes as charge carriers. In contrast, a unipolar transistor, such as a field-effect transistor, uses only one kind of charge carrier. A bipolar transistor allows a small current injected at one of its terminals to control a much larger current flowing between two other terminals, making the device capable of amplification or switching.
BJTs use two junctions between two semiconductor types, n-type and p-type, which are regions in a single crystal of material. The junctions can be made in several different ways, such as changing the doping of the semiconductor material as it is grown, by depositing metal pellets to form alloy junctions, or by such methods as diffusion of n-type and p-type doping substances into the crystal. The superior predictability and performance of junction transistors soon displaced the original point-contact transistor. Diffused transistors, along with other components, are elements of integrated circuits for analog and digital functions. Hundreds of bipolar junction transistors can be made in one circuit at very low cost.
Bipolar transistor integrated circuits were the main active devices of a generation of mainframe and mini computers, but most computer systems now use integrated circuits relying on field effect transistors. Bipolar transistors are still used for amplification of signals, switching, and in digital circuits. Specialized types are used for high voltage switches, for radio-frequency amplifiers, or for switching heavy currents
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