Due to the unique mechanical stimulus requirements for the MEMS sensores the stimulus architecture often does not allow to easily combine them into one and the same test handling machine. In addition the temperature sensitivity of the MEMS often requires temperature test. Therefore the cost of test and calibration of the packages or MEMS modules is significantly increasing. Other trends like constant package size reduction and increasing specification requirements are negatively influencing the test cost as well. While the production cost just slightly increases for multiple integrated MEMS, the test cost is skyrocketing. Therefore the initial invest into final test equipment could become a barrier especial for smaller companies and start ups.
Approaches and concepts how to support multiple MEMS stimulus and even reduce the cost of test for multiple MEMS packages are crucial. The joice of the right test strategy and process is becoming key for success.
In example wafer level electrical or physical stimulus offers one opportunity to shift some of the requirements from final test to front end. But final calibration often requires to also consider the packaging influences to the sensor output reading and therefore restricts to stay at final test with mechnical stimulus at final package level.
Test equipment standardization is for sure the key concept parameter to reduce the test cost. The scalablitiy and modularity of a test platform are the foundation for multi stimulus test within one handler.
The bigger the portfolio of modular stimulus applications for one platform is, the better the return of invest. The Multitest test handlers in example can offer widest portfolio to combine accelerometer, gyroscope, pressure, magnet and microphone test within one platform. As the platforms can support tri-temperture test as a standard, they support test applications of the consumer and automotive MEMS in parallel.
MEMS fusions drives test equipment to enable multiple sensor actuacions in ONE insertion. Equipment suppliers offer set-ups that support up to 9 DOF test. Sensor combinations that physically cannot be tested in one insertion, will benefit from modular approaches.
Parallel test capability of the test handler and the tester is another important parameter for cost of test optimization. Traditionally gravity and pick-and-place MEMS test handlers provide an interface with up to 8 parallel test sites at –55°C to +155°C. The new generation MEMS strip test handler meanwhile provide test interfaces with up to 1200 signal lines at the ambient-hot-cold temperature range. The possible parallel test count is therefore only driven by the lead count of the devices and the tester capability. Due to fact that the MEMS test signals are fairly easy to manage - compared to high end logic or RF applications – the test parallelism can get far above 60 DUTs.
Strip test is of course a test process that provides beside the advantage of high parallel test extremly short index times per DUT compared to pick-and-place or gravity handlers. However, it also has to overcome certain constrains that are not easy to manage. The most critical concern for this test process is the required singulation of the devices after final that might jeopardize the final test results and sort integrity. Nevertheless strip test became a quite popular and well established test process for MEMS calibration especially in the consumer test business due to its excellent cost saving potential.
Test in carriers is a new developped test process that is combining the advantages of singulated test and strip test. The InCarrier™ - a strip like carrier for singulated devices - is mechanically clamping and registering the singulated devices reliably. This way even smallest devices with pitches down to 0.35 mm can get handled very robust with an ‘un-limited’ test parallelism for MEMS test over all temperatures. For calibration and test binning the test results are getting mapped in an electronic map file via the carrier ID. After all tests the devices get sorted according to the map file without any singulation risks unlike at strip test. Also unlike to strip test, the InCarrier™ is supporting retest with one and the same setup.
Test in Carriers – Multitest InCarrier™ enabling highest parallel test for singulated MEMS packages.
To support this new process an InCarrier™ loader and sort-un-loader machine is provided. This tool is available for various loading and unloading types such as tray, tube and bowl / bulk, wafer ring, tape-and-reel. This way it follows the traditional standard material flow of every test floor with its established transport media.
InCarrier™ allows to utilize the test cell at the highest OEE level possible and will provide with its high parallel InMEMS test capability the best COT ratio at 0 ppm quality level.
The main stragic parameters for COT optimization at MEMS test and calibration are:
1. Test platform standardization
2. Rich and modular application portfolio
3. Multiple sensor actuations in ONE insertion to support MEMS fusion
4. High test parallelism up to 1200 signals
5. Test in carriers to combine the advantages of singulated test and strip test
Barbara Loferer received her MBA from the European Business University. After working in the finance sector and the paper industry, she joined Multitest in 2000. In her role as marketing manager she is responsible for branding and marketing communication for the overall Multitest portfolio in all regions.