Highly integrated IC devices like systems-on-a-chip (SoCs) are seeing pin counts balloon, creating untold complexity issues. As a result, it's becoming harder for automatic-test-equipment (ATE) systems to boost performance levels at lower costs per pin tested. Commercial ATE systems have kept pace with these challenges with help from design for test (DFT), built-in self test (BIST), and other methodologies.
But the future looks even more imposing as testing costs rocket upward. Such is the case for both at-speed and functional testing. The volume of test data needed for all kinds of tests rises dramatically as IC line geometries shrink due to process-technology advances and gate counts increase, particularly for "at-speed" and "stuck-at" tests (Fig. 1).
ATE test costs per pin for high-performance circuits have essentially remained flat for some time. Yet new demands for higher speeds, greater accuracy, more timing sets, and increased vector memory have begun to offset many of the reduced costs realized by ATE manufacturers. Some estimates claim that within a decade, it will cost more to test a transistor within an IC than to manufacture it. Capital costs for high-performance ATE systems keep climbing as more pins are added to a system.
Inflaming the challenge is the complexity of testing ICs for an ever-increasing market sector of IC users. Today, ICs are part and parcel of electronics technology in practically every sector of the industry. Each field has its own economic demands that tax the technical capabilities of modern ATE systems. The convergence of audio, video, graphics, and information technology is giving ATE manufacturers more room for thought on how to configure their systems for present and future needs (Fig. 2).
ATE companies rely on more sophisticated scanning chains and boundary-scan techniques to help manage the large number of scan chains in an ATE system's I/O. Another approach uses low-cost benchtop ATE testers that combine in-circuit testing with boundary-scan and functional testing. This method provides a rather high degree of confidence in finding faults with reasonably high testing speeds.
More attention is being paid to flexibility and scalability to control testing costs. ATE manufacturers are developing flexible systems with platforms that can be scaled upward or downward in terms of performance and cost to satisfy a wider range of applications and users.
One trend is a greater reliance on software control. Automatic test generation is helping drive the development of test codes. This allows the reuse of software and compresses the overall automatic-test-program-generation (ATPG) development cycle.
Additionally, ATE manufacturers now use guided probes to make functional pc-board testing more cost-effective. Connected to an ATE system, these probes can be manually applied to different points on the board under program control. They complement the usual "bed of nails" approach, which works fastest for finding faults via the ATE system's I/O.
SYNTHETIC INSTRUMENTATION
Quickly emerging as the standard of choice, synthetic instrumentation (SI) cost-effectively meets today's test demands while preserving future ATE investments. Driven largely by the U.S. Department of Defense (DoD) and its Next Generation Automatic Test Systems (NxTest) program to cost-effectively test military and avionics weapons systems, it promises to revolutionize large-scale testing methods.
Synthetic instruments are implemented purely in software that runs on general-purpose hardware with a high-speed analog-to-digital and a digital-to-analog converter (ADC and DAC) at the core of the measurement system, as well as signal conditioning and upconverters and downconverters. The specific software and generic hardware enable the system to function as a specific piece of test equipment (e.g., a voltmeter, oscilloscope, spectrum analyzer, etc.).
An ATE system based on synthetic instrumentation turns the traditional model of test and measurement literally upside down from a hardware-driven to a software-driven model. As a result, an SI's obsolescence and upgrade capability are limited only to a few hardware blocks and not to the need for a myriad of instruments classes or types.
How well the SI concept will take hold in industry is unclear. Judging from the rising complexity and costs of ATE systems and the DoD's push behind it, though, it may be the one saving grace for propelling the ATE industry forward.
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