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COTS system slashes MEMS test costs

04 October 2011

Using COTS equipment for its MEMS testing platform has enabled Analog Devices to achieve an eleven-fold reduction in capital equipment costs, not to mention a 16-fold reduction in power consumption, compared with that of a full-blown bespoke automated test equipment installation.

Analog Devices Inc. (ADI) provides analogue, mixed-signal and digital signal processing integrated circuits that convert, condition, or otherwise process light, sound, temperature, motion, or pressure into electrical signals for use in electronic equipment. They are to be found almost everywhere, in automobiles, cameras, televisions, mobile handsets, medical imaging devices and industrial automation equipment.

Over the past two decades, the company has made a significant investment in microelectromechanical systems (MEMS) based inertial sensing technology, producing the industry’s first fully integrated iMEMS (integrated MEMS) accelerometers and gyroscopes, helping electronic designers incorporate acceleration, tilt, shock, vibration, rotation, and multiple degrees-of-freedom motion into their product designs.

MEMS testing
MEMS testing poses a number of challenges for the production test process. ADI needed an automated test equipment (ATE) system that met its test plan demands at lowest possible cost without compromising product quality. Traditional 'big iron' ATE proved far too costly, too highly featured, and physically too large to meet the company's requirements for a dedicated MEMS tester. What it really needed was a subset of the measurement capability of a big-iron ATE system.

A number of alternative options to its traditional production ATE platform were evaluated. In particular, ADI sought to exploit as much commercial off-the-shelf (COTS) technology as possible, in order to reduce its overheads. But the test platform had to be flexible enough to accommodate custom MEMS test requirements while not sacrificing instrumentation speed or performance.

The PXI platform from National Instruments (NI) offered the test instrumentation capability needed to meet these challenges, providing a high level of flexibility and modularity to develop a targeted MEMS test system, that could be reconfigured for various test needs.
Indeed, for multi-site testing, test resources are simply duplicated by plugging in additional modules without changing any of the software, allowing the test equipment to be scaled as a factor of throughput.

The software had to be easy to use and offer the ability to create operator, program, and data interfaces to existing tools to ease the process of integration into ADI’s production environment. NI LabVIEW software - already widely used in the company’s characterisation and design labs - met these challenges and was chosen in preference to ANSI C or C++. The company’s new production test system was duly built, based solely on PXI and LabVIEW.

The flexibility of the PXI system combined with the ease of use of LabVIEW enabled ADI engineers to make rapid progress in terms of system design and prototyping.

The benefits of COTS
Test times with the new system are comparable or even better than those of the previous ATE system but, more significantly, the company achieved a dramatic reduction in capital equipment expenditures, footprint, weight, and power requirements for its MEMS production testing using the PXI/LabVIEW system. The previous ATE system actually cost more for its basic configuration than the new PXI system’s total all-inclusive cost. It also takes up very little space; in fact, the entire system is now physically small enough to wheel around on a cart.

This has a positive impact on shipping costs. Now, if any problems arise, the company can simply switch out PXI instruments onsite using local spares, or even ship the entire test system back from the production line to the development labs with very little overhead (the shipping container for the previous ATE system alone would have cost as much as the entire new PXI test system).

The new system has also led to improvements in the overall quality of ADI’s testing procedures. Because the test system was designed in-house, there is an assurance that every tester shipped to branch facilities features exactly the same hardware and runs exactly the same programming and code sequences. Furthermore, with LabVIEW controlling the system, the programmed test code is both modular and reusable.

This flexibility and ease-of-use has encouraged the test development teams to use the same system in other product development phases outside of production testing, including design, characterisation, and metrology. ADI now uses the same ATE equipment in all environments without incurring an impact on cost, reducing time-to-market and improving product quality.

Using PXI and LabVIEW, ADI was able to develop an application-specific MEMS test platform that could scale from production to lab characterisation with minimal cost implications.

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