Conformity Magazine - January 2009 - (Page 20) Challenges in Testing by Michael Hopkins, Amber Precision Instruments Susceptibility Testing of Boards and Semiconductor Devices T © Scott Maxwell | Dreamstime.com here is a disconnect in the EMC world between system manufacturers testing for upset and device manufacturers testing devices for failure. To be fair, the device manufacturers really aren’t trying to perform EMC tests, but the manufacturers of a broad range of products are now asking semiconductor device manufacturers to test devices using system level EMC compliance standards, specifically, IEC 61000-4-2 for ESD (electrostatic discharge). I’m sure the product manufacturers believe that, if devices are qualified to IEC standard(s), finished products will be more likely to pass conformance testing. Unfortunately, there’s a fundamental difference between system level and device level testing. Fortunately, this difference can be bridged using the test methods discussed in this article. Background We all understand that “faster and smaller” is the key to success with modern electronic circuits. But the price we pay is often increased susceptibility to the threats provided by the environment. Static, noise, radiation and transient electrical events of all sorts threaten stable operation of circuits and, in the worst case, cause damage. The problem is not that engineers don’t understand these events. Individual integrated circuits are hardened against potential damage during the handling process, and whole industries exist to provide power line and data line protection at the system level. These efforts successfully protect hardware from most damaging EMC events, but they often fail to prevent system level upset or malfunction. The problem is that upset and malfunction are generally caused by fast, low level events radiated into a circuit bypassing protective devices, or conducted into a circuit at levels below the operating voltage of a protective device.1 An integrated circuit that can withstand a few thousand volts of ESD without damage during handling can often be upset, or even reset, with only a few volts! Pinpointing circuits and devices that are sensitive to low level events is practically impossible using standard EMC test methods, but new methods of susceptibility testing are being used by a few leading edge companies to identify sensitive devices and circuits. These methods can save time and money and, most important, provide consumers with more reliable products. Device Testing—for Immunity? Devices are not really tested for immunity to EMC events. Instead, they’re tested for failure during handling, and it’s 1 Tze Wee Chen, Timothy J. Maloney, Bruce Chou, “Detecting E and H Fields with Microstrip Transmission Lines,” IEEE International Symposium on Electromagnetic Compatibility, Detroit, MI, August 18-22, 2008 20 Conformity JAnUAry 2009 http://www.Dreamstime.com
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