PXI system tests MEMS products
Senior engineer Robert Whitehouse of Analog Devices discusses the PXI-based system for testing the MEMS digital microphone product line.
By Richard A. Quinnell, Contributing Technical Editor -- Test & Measurement World, 11/1/2009 1:00:00 AM
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Robert Whitehouse |
Analog Devices recently announced it has developed a PXI-based system for use during production test of the company’s MEMS (microelectromechanical system) digital microphone product line. Senior engineer Robert Whitehouse provided details on this application in an exclusive interview.
Q: What prompted Analog Devices to develop a new test system for the production test of the iMEMS microphone?
A: We needed a tester that could meet the demands of a product test plan with the lowest possible cost and high throughput. Traditional, big-iron ATE (automated test equipment) solutions are far too costly, with too many unnecessary features, to efficiently meet the microphone tester’s modest instrumentation requirements.
Q: Were there any special requirements the tester had to meet?
A: The inputs to MEMS devices are more than just the analog and digital signals that traditional ATE systems generate. To test the microphone, we needed to supply a known acoustic SPL (sound pressure level) at a specified frequency, usually 94 dB at 1 kHz, and have the microphone’s output measured. Other MEMS devices might need acceleration, pressure, or position as inputs, so we needed a tester that was flexible.
Q: Why select PXI as the platform?
A: We chose PXI because of its low cost, small size, and flexible configuration. The low cost helps us avoid large initial capital expenditures as we ramp production. The PXI system’s small size compared to a big-iron ATE tester takes up fewer square feet of expensive factory floor space. Finally, PXI allows us to choose the instrumentation à la carte. The PXI rack has only the instruments we need as opposed to big-iron ATE testers that often have many unused instruments and channels that increase equipment cost without providing any benefit.
Q: What products did you use to build your production test system?
A: We used a variety of National Instruments hardware and software products for this project, including source-measure units, audio-acquisition instruments, high- and low-speed digital I/O, and a timing-control module. We used LabView for all code development, including the test executive and the handler electrical interface. We also created a set of custom virtual instruments for STDF (Standard Test Data Format) output to summarize the test results.
| Read more articles from our November 2009 PXI Test Report. |
Q: How does the new test system compare to your old ATE equipment?
A: Our old system cost about $450,000, required at least 10 kW of power, and took up about 5-by-8 ft of floor space in a 6-ft rack. It also weighed 4000 lb. The PXI tester cost about $40,000, requires 600 W maximum, and is a 60-lb, single-height chassis about 18-by-24 in. We are looking into integrating it with the device-handling equipment to make it a zero-footprint tester. The PXI tester is able to test more units per hour when compared to our previous system.
Q: Any other benefits from the switch to PXI?
A: We intend to install more of these systems for production testing at facilities around the world as production demand grows, which will save us millions in capital costs. Also, the low power means we can avoid costly electrical and cooling systems when installing. The small size, weight, and power also means that we can have a test unit in our development lab that is identical to the production test unit, avoiding correlation issues as new designs move into production.
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