Conformity Magazine - September 2008 - (Page 53)

Are IEC 61000-4-2 Based Standards and Simulators the Only Ones in Use Today? Certainly not. Although IEC 61000-4-2 and standards harmonized with it are dominant worldwide for testing consumer, medical and information technology products, there are others that are applicable in special circumstances. As an example, there are ESD standards in the automotive industry, where there exists not only a general ISO standard, but also corporate standards from most automotive manufacturers. Each of these standards still requires a unique set of capacitor and resistor values for the simulators. Another example is MIL-STD 883, which requires a different network and specifies a discharge current waveform identical to that used for testing individual ICs for ESD in the production and handling phases. Two new standards are being developed by the Electrostatic Discharge Association (ESDA) that have interesting characteristics, dealing with HMM (human metal model) and CDE (cable discharge events). Although each has a basis in the IEC 61000-4-2 standard, they diverge from it in order to deal with unique applications and characteristics of the required tests. HMM - Human Metal Model – Is a New Kind of ESD Simulator for ESD in the Wings? Manufacturers who are required to test their products to IEC 610004-2 for ESD have, in turn, been placing that requirement on the suppliers of sub-assemblies, and more recently on the suppliers of integrated circuits – specifically those ICs that will interface directly with the outside world, such as drivers for USB ports or Ethernet cables. IEC 61000-4-2 is a test standard describing a simulator and procedures for testing finished products, procedures that simply cannot be used for testing ICs. This leaves device manufacturers in a quandary, since IEC 61000-4-2 was never intended for testing ICs. So how does one test a single IC pin using a simulator designed to replicate a human touching devices such as video displays, computer keyboards, telephones and ATM machines? Because no standard exists, IC manufacturers are all using different test methods. Some have an IC laying on a table dead-bug fashion and attempt to make discharges to pins. Others put devices in sockets. Some use ground planes while others don’t. In other words, there is no consistency and no reason to believe any of these tests are valid, since they are certainly far from being repeatable or reproducible. In order to give some guidance to IC manufacturers, Working Group 5.6 within the ESDA is developing a standard that will define ways to use the IEC 61000-4-2 stimulus to perform ESD tests on a device installed in a socket mounted on PC board. IC pins are connected via track on the board to pads that will allow using an IEC compliant simulator to zap pins individually. Although not perfect, the standard will define the test conditions and environment, and will help to put everyone on a level playing field. Because IEC 61000-4-2 simulators were never designed for testing ICs, alternative simulators are being investigated that are based on commercially available transmission line pulse (TLP) testers currently in use by many semiconductor manufacturers for investigating ESD protection structures on devices. It seems like a natural progression, but there are problems getting the IEC 61000-4-2 current waveform as specified. CDE – Cable Discharge Events – A Mix of Simulators For some time, manufacturers of telecom equipment have experienced problems with cable discharge events (CDE), particularly concerning Ethernet cable ports.6 7 8 During installation of an Ethernet cable network in a building, the cable is pulled through walls and across overhead structures, resulting in triboelectric charging of the cable itself. When this now charged Ethernet cable is plugged into a piece of electronic equipment, a discharge occurs to the Ethernet input port and the electronics behind that port. Conversely, let’s assume that the Ethernet cable is already installed in a building, not moving and uncharged. A laptop user is leaving a meeting and headed back for an office or cubicle where they will likely reconnect their laptop to the network via an Ethernet cable connection. As this person moves through the facility, the person and their laptop will accumulate charge – nothing too significant, maybe a couple of thousand volts – too low to be felt as a discharge by the user. When the Ethernet cable is connected, the charges on the laptop and person holding it will equalize with the cable, and ESD currents will flow as a result. The only difference between this event and the case above where the cable has the initial charge is polarity. It’s still a cable discharge event. The resulting currents from a cable discharge are complex. Initially there is a very fast spike similar to an ESD event from a person, followed by a ringing discharge the frequency of which is dependant on the length of the cable. One might expect the discharge from a charged cable to be the classic square wave, but this is not the case. Reflections along the cable length produce the characteristic ringing. Working Group 14 of the ESDA is in the process of developing a standard practice that will make recommendations about how to test for the effects of CDE. And, in order to get a test that is representative of a real CDE, more than one kind of simulator is required. Although some manufacturers have set up racks with very long cables (hundreds of meters) which are charged via high voltage power supplies and then discharged through relays into the equipment being tested, this is cumbersome and difficult t September 2008 Conformity 53

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Conformity Magazine - September 2008 Contents Editor’s Note Commission Adopts Regulations for Internet-Based TRS Services Another Company Fined for Non-Compliance with HAC Requirements FCC Extends “Do-Not-Call” Registry Compliance Requirements Marketing Company Gets $1.4 Million Fine for Junk Faxes EU Commission Codifies Directive on TTE Market Competition EU Commission Releases Updated Standards List for the R&TTE Directive Updated Standards List for the “New” Low Voltage Directive Released New Standards List Released for the EU’s Machinery Directive The ESD Association: Voluntary Standards in Action ESD Open Forum Medical EMC Standards: Towards the 4th Edition of IEC 60601-1-2 iNARTE Informer Pre-Pulse Voltage in the HBM ESD Model Digital Interfaces and EMC Performance ESD Design Buyer’s Guide Product News Commission Publishes Updated Standards List for the EU’s Personal Protective Equipment Directive FDA Links “Human Factors” to Adverse Events with Medical Devices CPSC Actions in the News IEC Standards Update UL Standards Update Product Reviews Telcordia Standards Update From Our “You Can’t Make This Stuff Up” Department Looking Back: Items from Past Issues of Conformity Advertisers

Conformity Magazine - September 2008

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