Conformity - November 2008 - (Page 33) device. Figure 12 shows the comparison of the simulated and measured induced voltage inside the hand held device. The measurement is able to predict the main noise pulses with moderate accuracy. Also a stronger ringing is visible in the simulation result. We believe that this ringing is suppressed in the measurement data by many ferrites that are placed on the outside of the coax cable used to probe the voltage. It is difficult to simulate the ferrites in a time domain analyzer, especially as they might saturate at the current levels injected by the ESD generator. However, one has to consider that this is a demanding test case. Limits We are researching methodology for predicting the ESD softerror response of systems. This requires a combination of ESD [4] generator model, correctly simplified DUT model and IC response model. The present article has analyzed the ESD generator and coupling into the DUT. We see the following challenges: • The ESD generator model yet does not match some [5] of the fine structure of the discharge current pulse, especially the 300-800MHz ringing after the initial peak. This might not be of concern to the modeling accuracy. • On comparing ESD generators from different manufacturers, different transient fields will be measured. Thus, the numerical model must model the specifics of the ESD generator used in system level testing. • The falling edge of the current (e.g., at 30 ns) in the cable attached to the hand held device is not well modeled, since we substitute the ground strap in the actual measurement by either a short ground strap or a short ground strap and an inductor. Our primary objective to do this was to reduce the domain size. During testing, we did not observe any soft errors being caused by the tail current and hence do not consider this an important limitation. • The modeling of the DUT may have to include finer details of the PCB, IC and bond wire structure. This will clearly lead to a very large computational problem. The selection of the correct simplifications will be based on experience in the analysis of ESD problems on previous products. • The IC input response model is not included in the simulation yet. However, based on experience, we can estimate if a current or voltage might cause a problem. We consider the last two aspects to be the most difficult challenges on the path to a complete ESD soft error response simulation. Conclusions An improved ESD generator model has been introduced. Its usefulness has been shown on simple and more demanding test cases, including ESD current, voltage induced in a small loop, and voltage induced inside a small product. Cai Qing, Jayong Koo, Argha Nandy, and David Pommerenke are members of the Electrical and Computer Engineering Department at the Missouri University of Science and Technology (formerly the University of Missouri at Rolla). Jong Sung Lee and Byong Su Seol are with the Manufacturing Technology R&D Center at Samsung Electronics in Suwon, Korea. Inquiries to the authors can be sent to David Pommerenke at davidjp@mst.edu. References 1. 77B/378/CDV, “IEC 61000-4-2: EMC-Part 4-2: Testing and Measurement Techniques - ESD Immunity Test,” 2003-04-11. H. Tanaka, O. Fujiwara, Y. Yamanaka, “A Circuit Approach to Simulate Discharge Current Injected in Contact with an ESD Gun,” 2002 3rd Int. Symp. Electromagnetic Compatibility, pp. 486 – 489, 21-24 May 2002. K. Wang, D. Pommerenke, R. Chundru, T. Van Doren, J. Drewniak, A.Shashindranath, “Numerical Modeling of Electrostatic Discharge Generators“, IEEE Trans. on EMC, vol. 45, no. 2, May 2003. F. Centola, D. Pommerenke, K. Wang, T. V. Doren and S. Caniggia, “ESD excitation model for susceptibility study,” IEEE Int. Symp. Electromagnetic Compatibility, vol.1, pp.58 – 63. 18-22 Aug. 2003. S. Caniggia, F. Maradei, “Circuital and Numerical Modeling of Electrostatic Discharge Generators,” Industry Applications Conference, 2005, Vol. 2, pp. 1119-1123, Oct. 2005. 2. 3. 4. 5. FAST Link www.conformity.com/2340 Figure 12: Comparison of simulated and measured induced voltage november 2008 Conformity 33 http://www.conformity.com/2340
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