Conformity Magazine - October 2007 - (Page 33)

The IEC waveform has a very fast, large amplitude current spike at the beginning of the waveform. The circuit diagram shown in Figure 6, as it is presented in the IEC standard, can not create the waveform that the standard calls for. A superficial examination of the IEC and HBM circuit diagrams often leads people to expect the waveforms to be similar. The movement of the relay from one side of the resistor to the other, and the presence of parasitic capacitance, results in a significant change in the waveform. A more realistic circuit diagram is shown in Figure 9. (Pommerenke and Aidam give a more detailed circuit diagram useful for waveform simulation [1]) The placement of the relay on the device under test side of the resistor means that any parasitic capacitance on the device side of the resistor will be charged before the relay closes. When the relay closes, the capacitance C2 will discharge into the device under test with only parasitic inductance and resistance to limit the current. This produces the large initial current spike in the IEC waveform. The presence of the spike in the required IEC waveform requires the parasitic capacitor C2. In contrast, HBM parasitic capacitance on the device under test side of the 1500Ω resistor will not be charged before the relay closure and no initial current spike is produced. The dominance of the “parasitic” capacitor C2 on the initial current pulse is easily illustrated if the IEC 61000-4-2 waveform is compared with the waveforms for the automotive system level test ISO 10605. The ISO test uses the same type of ESD gun as the IEC test but the resistor R1 is changed from 330Ω to 2000Ω, while the 150pF C1 capacitor is either left at 150pF or changed to 330pF, depending on the system being tested. Waveforms from the same ESD gun with the different R1 and C1 values at 4000V are shown in Figure 10. The initial peak is identical because it is dominated by C2 and I2; but, after the first 5 to 10 ns, the waveform starts to depend on C1 and R2. The difference between the two ISO waveforms only becomes obvious at longer times, such as in Figure 11 for stress at 8000V. System and Device Waveform Comparison The difference between system and device level stress becomes obvious when the current waveforms are displayed on the same plot as they are in Figure 12, and with an expanded time scale in Figure 13. 500V CDM and 2000V HBM are the most common target levels for product acceptance for ESD tests on integrated circuits, and it is often hard to obtain these levels of robustness especially on Figure 8: Waveform from an IEC compliant ESD gun at 4000V Figure 9: More realistic IEC 61000-4-2 schematic october 2007 conformity 33 http://www.ddbunlimited.com http://www.ddbunlimited.com

Table of Contents Feed for the Digital Edition of Conformity Magazine - October 2007

Contents Editor’s Note Commission Proposes Changes for 57-64 GHz Spectrum Rules FCC Continues Actions Against Jamming Device Distributors Radio Operator Fined for Failing to Make Equipment Available for Inspection Commission Fines Unsolicited Fax Advertisers Firm Offering Quality Standards Training Also Fined Breaking New Ground with Lithium-Battery Generic Requirements for Use in Telecommunications Facilities ESD Open Forum EMC UK 2007 Conference Set Staying Abreast of U.S. E-Waste Legislation EU Commission Establishes RFID Expert Group Update on China's CCC Compliance Program System Level ESD Testing: The Waveforms An Alternative Approach to Surge Suppression Testing Equipment Buyer's Guide EU Scientific Committee Releases Updated Data on EMF Risks Updated Standards List For The EU’s EMC Directive Updated Standards List For The EU’s Directives on Measuring Instruments Call for Presentations for 2008 International ESD Workshop Announced CPSC Actions In The News IEC Standards Update Product Reviews UL Standards Update New Products From Our “You Can’t Make This Stuff Up” Department Looking Back: Items from Past Issues of Conformity Upcoming Events Advertisers

Conformity Magazine - October 2007

For optimal viewing of this digital publication, please enable JavaScript and then refresh the page. If you would like to try to load the digital publication without using Flash Player detection, please click here.