MEETING THE RECENT REQUESTS ORIGINATED BY THE INCOMING EDITION OF EN

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1 BULETINUL INSTITUTULUI POLITEHNIC IAŞI TOMUL LII (LVI), FASC. 5, 2006 ELECTROTEHNICĂ, ENERGETICĂ, ELECTRONICĂ MEETING THE RECENT REQUESTS ORIGINATED BY THE INCOMING EDITION OF EN BY *A. SĂLCEANU, *E. LUNCĂ and *OANA NEACŞU Abstract. In order to receive the C Mark, any electric device or equipment has to meet the EMC requirements of EC Council Directive 89/336/EEC. A distinct and compulsory part of EMC tests is covered by testing the immunity to the personnel electrostatic discharge (ESD), in accordance with the requirements stated by a Basic EMC Standard (first edition published in March 1995), coded EN 61000, Part 4 (testing and measurement techniques)-section 2 (Electrostatic discharge immunity test) with Amendments A1 and A2. The present standard is compulsory to be improved and our paper covers some of the essential reasons and still discussing solutions to update the IEC Keywords: EN , C Mark, EMC Directive. 1. Romania assumes European Norms in the ESD domain The starting point was the standard issued by International Electrotechnical Committee (IEC), adopted with no alterations by CENELEC (European Committee for Electrotechnical Standardization) as European Norm EN , [1]. In our country, ASRO (Romanian Standard Association) translated the French version into Romanian language (published in July 1999), with the purpose of being approved as the Romanian Standard SR EN A1. 2. Reasons for some particular requirements in EN specifications a) The high currents associated with a discharge (which can be of the order of 30A during the test) flow around shields and through conductors, creating voltage drops that can interfere with circuit operation. The response of circuits to such transient currents is non-linear, so it can be possible for significant interference to occur at low ESD voltages but not at high voltages, or with one ESD polarity but not the other. b) There is especially a problem for joints in shielded enclosures. For example, with a current of about 20 Amps with a rise-time of 1 ns, a current in a shield that would have to divert from its ideal (minimum impedance) path by 50 mm to pass through a metal fixing to cross a gap of 0.25 mm, would generate 1075

2 A. SĂLCEANU, E. LUNCĂ, and OANA NEACŞU approximately 1 kv across the gap, enough to cause ionization of the air in the gap and make happen a secondary spark to occur. If the gap is wider, the secondary sparkling did not occur, but secondary magnetic and electric fields near the gap could not be neglected. c) High transitory electric and magnetic fields during a discharge. These can couple to circuits and interfere. The field strengths created by a 5 kv test can be as high as 10 kv/m at 100 mm from the spark and 1 kv/m at one meter distance. This is why EN includes some indirect discharge tests even a totally insulated product that cannot be sparked to during an ESD test can be vulnerable to the fields created by a nearby spark to an unlike object. d) The discharge current measures more than 10 Amperes, but more harmful is the di/dt high value. These high currents could cause damage to the p-n junctions in semiconductors. There energy involved in a personnel ESD event is generally insufficient in order to damage other parts of devices or circuits, but machinery ESD - where large elements of metalwork can be charged to very high voltages, causing ESD events with much larger energies (not to be neglected even the so dangerous lightning produced by the tribocharging of clouds). 3. Attempt to update the ESD immunity tests There is a special group being with IEC, with the identification number IEC TC77b WG-9, working to improve IEC standard by issuing a new edition. In April 2001 IEC elaborated Edition 1.2 of , with Amendment A2, in order to become the controlling ESD document effective December 1, Edition 1.2 of the IEC document consolidates amendment 1 of the 1998 issue and amendment 2 of the 2000 issue. Amendment 1 was made effective by CENELEC January 1, 2001 and amendment 2 is the change that took effect in December 2003, Amendment 1 clarifies ESD testing of ungrounded EUT's such as those using nonconductive grooved holding supports, direct application of the ESD pulse to points only accessible during normal use of the EUT and discharges to the horizontal coupling plane under the EUT (1.6 m x 0.8 m, according to EN ). Additionally, Amendment 2 clarifies the organization of test results and the information to be included in the test report. The IEC committee for ESD issued edition 2 of IEC for vote in April of Edition 2 is very similar to the US ANSI C63.16 (draft version) on ESD Test Methodologies and Criteria for Electronic Equipment. This second edition created much discussion in the EMC testing arena once it was circulated since it meant that users might have to purchase new ESD simulators to meet the new requirements,[2]. Edition 2 addressed the need to reduce differences in test results among the various simulator manufactures. 1076

3 BUL. INST. POLIT. IAŞI, TOMUL LII (LVI), FASC. 5 It has been observed that the actual ESD discharge waveform of the human body is flatter and that very little electric field energy is radiated. IEC Edition 2 required to address the test result differences by removing the ringing on the discharge waveform and by reducing the electric field radiation from the ESD simulator. Edition 2 also discusses the ESD target used in the ESD waveform verification in detail as well as providing test set-up guidance for performing the ESD test and pulse verification. 4. The weak points of EN to be reinforced by the new edition The proposed ESD test set-up in order to comply the latest requirements is presented in figure 1. Horizontal coupling plane 1.6 m x 0.8 m Typical position for direct application 220 V / 50 Hz VCP 0.5 m x 0.5 m Typical position for indirect discharge to VCP Yellow-green wire 0.1 m Typical position for indirect discharge to HCP ESD gun HCP to ground Ground reference plane 0.1 m 4 x 470 kω Resistors sheet of plastic (thick 0.5 mm) Wooden supporting table 1.6 m x 0.8 m x 0.8 m Fig. 1.- Strict recommendations for ESD testing tabletop equipment The major differentiations between the existing and the proposed EN/IEC are: The number of discharges must be increased at 50 on each test point. As is usual with EMC test standards, EN requires that equipment be 1077

4 A. SĂLCEANU, E. LUNCĂ, and OANA NEACŞU set-up and functioned as close as possible to its normal action in real life. During the execution of software, the susceptibility of a product to interference is usually much worse at some instants than it is for the rest of the time. These instants are usually not known, making it a problem for a transient test, such as ESD, to be applied at just the right instant (worst moment). This is one of the reasons why there is a proposal to increase the number of discharges applied from 10 to 50 (at each voltage, at each polarity, at each tested location). EN , like all other immunity tests in the EN series, requires all of the normal modes of operation of the EUT to be tested. Because of the number of locations that must be tested to find the most susceptible points this could take a very long time for some types of product. Special exercising software can be run on the product instead of normal software, to save testing time, but it must comprehensively exercise the product. EN helps to save more time during full compliance testing by requiring that the most sensitive mode of operation be determined in advance by preliminary testing, and the product run in that mode during the test. The real problem here is to correctly establish which is really the most sensitive mode of operation for all the selected test points. Here could interfere, as a quite empiric parameter, the experience and competence of the ESD test engineer, which would decide on each couple of test point-most sensitive mode of operation. Unfortunately, this was impossible to be stated in the norm; A clear area around the test site is firmly requested; The ESD simulator has the parameters more obviously expressed; There are supplementary requirements for ESD gun calibration; There are extra constraints on the GRP, HCP, VCP and bleed wires. In the set-up the EUT cables have to be terminated with special EMC Clamps; there is a new set-up for little table-top equipment; the method for ungrounded device is included as per A2 to the first edition. This is one of the weak points of the former EN , being verified that cable layout and termination can make a large difference to the test outcome; all the generally accepted recommendations are too vague and unspecific; The effective test methods are presented in a more detailed manner; For contact discharge, it is not necessary to start from the first level if you are interested in the immunity at the third or fourth level of exposure; contrarily, for air discharge the late procedure is still recommended; It is detailed a gradually increasing methodology for the nominal voltages having to be successively applied to the device, with particular specifications for the difficult to predict malfunctions. As stated above, the ESD waveform is verified only during contact discharge and not air discharge. IEC Edition 1.2 does not cover the air discharge waveform. This issue was discussed 1078

5 BUL. INST. POLIT. IAŞI, TOMUL LII (LVI), FASC. 5 in Edition 2, in a similar manner with that stated in ANSI C For the present moment, due to a number of contentious issues (most of them pecuniary-involving new simulators, not technical in essence), Edition 2 is not adopted, but is a question to be mandatory solved in the very next future. The complexity of the problems to be solved is given by the intrinsic simulation of the actual ESD event with a tester, by the correct verification of the ESD waveform,[3] and by the establishment of a laboratory ESD test set-up that can be used to compare test results among various devices,[4]. We have to notice that starting from the classic human body model (which discharges a 100 pf capacitor through a 15 kω resistor, peak current 2A, rise time 5-20ns) the conditions to be adopted are much tougher: 150 pf discharged through 330 Ω, peak current 30 A, rise time ns. 5. Our experience on manufacturing the Pellegrini target Pellegrini type target is special designed for calibration of ESD-guns. It consists of a 2 Ω resistor across which the pulse is applied and a 48 Ω resistor in series with the connection to the measuring oscilloscope which has an input impedance of 50 Ω. The connection between target and oscilloscope is realized with a coaxial cable. 330 Ω I 48 Ω 150pF 2 Ω U 50 Ω scope input Fig. 2.- Measured voltage (in Volts), equal to the injected current (in Amperes). To truthfully determine the high-slope current from measuring the voltage drop, are necessary transitions built out of a tapered line, which generates a smooth shift from the 18.9 Ω (the characteristic impedance at the injection point of the target) to a N-type connector with a characteristic impedance of 50 Ω. We used 25 identical 0.25 W cylindrical resistors, with nominal value of 51 Ω, parallel mounted on the exterior surface of the disc, the best solution for obtaining a flat reply within ±1 db to 3 GHz. The 48 Ω adapting resistor in figure 2 was obtained by arranging 5 resistors of 240 Ω (also 0.25W) in a parallel pentagonal distribution, the material used for the discs being brass plated with silver, [5]. 1079

6 A. SĂLCEANU, E. LUNCĂ, and OANA NEACŞU 6. Conclusion This paper provides an update on the status of the IEC ESD specification and deals with some compulsory changes to be adopted in order to obtain repeatable test results for ESD experiments. There are presented our approaches in order to manufacture a valuable current transducer adequate for the hard conditions imposed by the ESD European Norm. Acknowledgements This work was financed and developed in the framework of the RTD National Programme CEEX, financed by Romanian Authority for Scientific Research, the grants P-CONFORM CEEX- M4-3885, Laboratory for immunity tests at Electrostatic Discharges and P-INT-VIZ CEEX-M , Support for the integration of Romanian Research in the Field of Electromagnetic Pollution. * Gh. Asachi Technical University, Department of Electrical Measurements and Materials. R E F E R E N C E S 1. IEC , Electromagnetic Compatibility (EMC) - Part 4: Testing and measurement techniques - Section 2: Electrostatic discharge immunity test. Basic EMC Publication (2001). 2. Williams T., Armstrong K., EMC Testing Part 3 - Fast Transient Burst, Surge, Electrostatic Discharge, EMC & Compliance Journal, (2001). 3. Keenan R. K., Rosi L. A., Some fundamental aspects of ESD testing, Proc. of IEEE International Symposium on EMC, (1991). 4. Moyer T., Gensel R., Kunkel H., Update on ESD testing according to IEC , EM Test. 5. Reo UK LTD, The 9-th Handbook on EN ASUPRA UNOR CONDITII SUPLIMENTARE IMPUSE DE VIITOAREA EDIŢIE EN (Rezumat) Acordarea certificării de compatibilitate electromagnetică (sigla C ) pentru orice echipament electric sau electronic (inclusiv din sfera IT) se realizează în prezent pe baza Directivei de Compatibilitate Electromagnetică 89/336/EEC. O parte distinctă şi obligatorie a acestor teste este reprezentată de imunitatea echipamentului respectiv la descărcările electrostatice, stabilită de norma EN elaborată în 1995, completată cu amendamentul A1, elaborat în Experienţa ultimilor 7-8 ani impune elaborarea unor completări şi condiţii suplimentare. Prezenta lucrare este concentrată asupra unor propuneri de soluţii menite să actualizeze, în cadrul unei a doua ediţii, standardul de imunitate la descărcările produse de sarcinile electrostatice generate de activitatea umană. 1080