In-circuit testers are transforming into all-in-one electrical test controllers. The latest ICTs can be used for not only manufacturing defects but also to test functional failures, and even parametric testing
In-circuit testers (ICTs) have become more versatile and efficient as these now come loaded with additional electrical test capabilities and functionalities. The most capable ones have in-circuit test, boundary scan, functional test as well as programming techniques integrated into a single platform.
What drove these changes
The inability of any single test methodology to completely test circuit assemblies is one reason. In addition, the constant drive from circuit assemblers to reduce test costs is driving traditional ICT systems to take the shape of more holistic test systems.
Newer ICT systems can be better described as generic all-in-one electrical test controllers rather than just ICT systems. This is because many of these have different forms of ICT including automated probing, optical inspection and boundary scan combined with functional testing of circuit assemblies.
Let us take a look at the latest changes in ICT systems, and what they deliver to the users.
Small-footprint automated systems moving to ‘zero’ footprint
With the introduction of zero-footprint designs incorporating multi-core test capability combined with automated material handling, the latest inline systems have taken a step forward in reduction in the cost of tests. These systems are a boon to manufacturers that want to increase their capability but do not have the additional real estate to do so.
The industry’s previous solution to this has been use of many discrete automation methods including robotic helps, automatic probes and semi-automatic press for PCB testing along with large automated ICT systems. However, all these systems contribute to an inefficient use of factory space and low machine utilisation due to size of conveyors and speed of travel. Moreover, the additional cost of moving the product from one equipment to another is always a concern.
The newer inline ICT systems introduced last year come with small footprint and there is no manual handling involved. You can integrate your ICT into the assembly line and there is no need of any operator handling.
The small footprints in inline systems are realised by using compact test heads relocated closer to the device under test (DUT). This enables ICT to fit easily within the narrowest automated lines, without the need for any additive storage bay or incremental factory space, thus saving additional cost as well as labour.
Teradyne’s TestStation Multi-Site Inline ICT system uses a novel ‘zero-footprint’ test head design, which fits entirely within the narrowest automations. Teradyne also has offline counterparts with sub 1 m2 footprint and 2560 test-points capability which help PCB manufacturers free up factory space.
Agilent’s i1000D ICT system is another small-footprint design that unifies offline and inline systems onto the same design. Agilent offers easy upgrades to convert offline to inline systems so you can re-use the same system.
Spea’s 3030 system is another true multi-core tester offering up to 4x throughput. The true per pin architecture in this system makes all the analogue and digital resources always available on each system channel.
Multi-core testing and higher throughput
With the increased competition and demanding markets, it is certain that PCB OEMs and the other electronic manufacturing services need to boost their throughput and yield.
“In India, labour costs are increasing day by day and the cost of space has also increased over the last few years. So, if you use one operator, one fixture, one PC, you can save your cost as well as space. And mathematically speaking, previously we were having one tester and one fixture but now we are having two testers or more in one fixture, thus the throughput is increased by at least two times,” says Ravi Richaria, manager sales & service support, Test & Research India Pvt Ltd.
The newer parallel and multi-core testing architectures available from vendors solve this problem. These parallel test architecture ICT systems deliver true multi-core test capabilities to test multiple units concurrently, thereby eliminating test time bottlenecks and increasing your testing productivity as compared to the previous ICT systems. Using the multi-core test systems minimises your system size and cost as these utilise common cooling, power and other infrastructural elements. In addition to system size and density, smaller physical configurations and short signal paths help to deliver high parallel test efficiency.
Integrated test methodologies
Testing of current complex circuit boards requires separate analogue, digital and other test workflows. So each test workflow accounts for individual test systems, multiple test fixtures, and separate operators. As circuit boards become more advanced, the traditional ICT technologies are becoming less effective in achieving reliable test coverage. The advent of SMT IC technologies with IC packages like BGA ball grid array (BGA) has made it difficult to directly access the pins using the traditional ‘bed of nails’ tester.
To solve this, ICT systems now integrate multiple test methods, where some points make contact through bed of nails and the others use edge connectors or JTAG ports or in-circuit emulators, thus using three or four test methods in parallel.
Ganapathy from QmaxTest says, “You should not depend too much on one test methodology or a particular approach. Integrated ICT solutions are a boon. Combinational approach has an advantage of two or more techniques so that yield is more and efficiency is increased.”
TR5001T SII TINY from Test & Research India is the compact version with just 640 test points but it supports extended coverage with boundary scan in a compact and affordable solution. This desktop ICT offers parallel testing using multiple USB-connected units, audio analyser and data acquisition modules.
Vector-less testing with JTAG boundary scan. JTAG allows vector-less testing of the PCBs using only the five universal end ports to test these components. So, instead of having the higher number of test points you can test those components with those five points.
Assemblies are getting more complex day by day; you cannot have the test point on each and every point. Moreover, all the complex components in the latest PCBs are boundary-scan enabled. In this context, methods like JTAG boundary scan make it more convenient to access the I/O pins of the JTAG-compliant ICs present on the circuit board.
Even if you have a multiple chain of components that are boundary-scan enabled, these can be tested all together in one chain. This ability to daisy chain all the JTAG-compliant components on the circuit board, reduces the amount of wiring while keeping similar test coverage. Apart from the vector-less testing you can also perform on-board programming of the components using JTAG ports.
High-density channel cards with hybrid test points. But now we have single integrated systems with high-density channel cards, combining various test flows into a single, full-test performance insertion. These can dramatically reduce your production test times, recurring test costs and improve time to market significantly.
The new LX2 system from Teradyne having 128 channel cards can test complex boards which require up to 15,360 hybrid test points in a single insertion. It has full analogue, digital, boundary scan and in-system programming capability. Each 128HD card delivers 512 hybrid test pins, doubling test system pin counts of the existing systems.
Parametric testing. Parametric measurement units (PMUs) are integrated with the latest ICT systems. Usually these come with 4 PMUs, capable of measuring voltage and current with respect to reference current and voltage, respectively. This makes them very useful for analogy testing as well. Since these are integrated in the same digital platform, you are able to effectively test digital, mixed logic, analogue or mixed-signal assemblies.
Integrated intelligence. Integrated intelligence is taking ICT to a whole new level. There are learn and compare features included where the system learns from the golden board and then compares the results. Also, some can learn from past test results and perform a few additional tests, if needed, to produce useful and comprehensive reports.
Increased precision with rotational movement of flying probes
The robotic testers have added a lot of automation. These testers, or the flying probes or the automated probes in ICT systems, can go as close as 20 mils/500 microns between two pins. Complex PCBs sometimes have components that are soldered at certain angles to the PCB plane. So, for high accuracy, the probe should also be able to move at an angle.
Previously probes could move only in x-y direction, but now systems include range expansion rotational movement where you can rotate the probe at different angles, thereby allowing you to go very close to the adjacent pins and increasing the testing accuracy.
QTouch 1248 Flying Prober from QmaxTest is based on the technology of hands-free probing which can probe both sides of the board due to its vertical design. It provides scalability from one to eight probes with a maximum of four probes on each side of the board. Apart from X, Y and Z axes, probes can move in theta direction up to an angle of 36 degrees.
Acculogic’s Flying Scorpion FLS980Dxi offers programmable probe angles of +6º to -6º with ±0.1 micron resolution for testing.
With the latest software tools, application engineer’s job has been totally reduced. With graphical user interface (GUI), you perform all the tests in a graphical way. There is no need to write codes for complex circuits. The GUI provides flexibility to the system and assists test environments for different production cycles.
You can also define your own test program by creating different steps that can be sequenced in an automated sequence. You can give your own conditions and put conditional jumping between different steps. For example, if a particular test is passed then jump to a specific step, otherwise to the other one.
Also, you can protect your test conditions with passwords and ensure another user cannot change them; he can only run the test. You can maintain a record of how many boards were tested and how many failed, and have all the relevant reports of yield rate or efficiency.
For quick debugging and diagnostics, where you want to quickly test any particular area of the PCB, software allows you to perform these localised tests without writing any test sequence. So, if you want to test any particular IC or a few ICs or any other component, you can just make interface for the device under test using interactive GUIs and perform the required tests.
Drawback. The only drawback of the ICT software tools is that they are unique and proprietary for each system. Ganapathy of QmaxTest says, “Every tester has its own driver and capabilities, and so every tester should be directly sequenced with a set of instructions. If someone is thinking of developing a software, they can see the software function and develop one but, however, when you buy any ICT system, the proprietary software only will work.”
Life of an ICT system
Testing at component level will remain for years, but with technological advancements these components are getting smaller and making the circuits more and more complex. These advancements have caused older techniques to fail, and will continue to do so with the coming systems as well. Is there a solution?
Ganapathy explains, “An important consideration while selecting any solution should be the number of test points and the associated scalability. A manufacturer should first analyse how many board types are to be tested, and how many maximum test points are required, and then, finally, what scalability is available with the solution.”
He adds, “Today you might not require a certain number of test points, but at least the equipment should have the capability to add more in future when there is a requirement. For these reasons there are more of open architecture systems coming up, so that as the requirement increases you are able to increase the channel capacity or add new test methodologies as well.”
The author is a technical correspondent at EFY