Conformity Magazine - September 2008 - (Page 36)

was so much smaller that the 10MΩ input impedance of the oscilloscope probes that had been used had to be augmented with 100MΩ resistors, so that the PPV could be easily observed. The simulated BGA packages were not suitable for determining a quantitative measurement of the PPV as a function of pin size. A second set of simulated packages was developed with a variety of pin sizes made from wires of various diameters, as well as a flat surface control and a pin made out of thin sheet metal. The measured results are shown in Figure 8. Figure 6: Schematic of simulated integrated circuit The measurements show that, for a flat surface, the PPV was enough to raise the voltage all the way to the breakdown voltage of the Zener diode. At smaller geometries, similar to those in modern high pin count packages, the PPV was well below a volt. PPV and HBM Standards The measurement on simulated packages showed the PPV not to be as serious a problem in a real world situation as was originally feared. It is only for unusual geometries, very high impedance, and low capacitance situations where PPV is likely to result in the failure of dynamically triggered circuits to function. For this reason, the JEDEC HBM standard [5] was modified to allow as low as a 10kΩ resistor to be placed across the pulse source during HBM stress. This resistance allows the charge to bleed off of the integrated circuit pin being stressed, but will not carry any significant current during the actual HBM current pulse. The Electrostatic Discharge Association (ESDA) is taking a more cautious approach on their HBM standard [6]. An appendix has been added, showing how to measure the PPV, but they have not gone so far as to allow the PPV to be entirely removed from the HBM simulator. Conclusion The PPV has been shown to be a cause for failure of dynamically triggered ESD protection circuits in HBM simulators, but measurements on specially designed simulated integrated circuit packages have shown that it is not a severe a problem in real world situations. For this reason, the JEDEC HBM standard has been modified to allow HBM simulators to remove the PPV with a bleed resistor. There are, however, many HBM simulators still in use throughout the world that do not have this modification in place. There can also Figure 7: Photos of simulated integrated circuit 3 Conformity September 2008 http://www.spira-emi.com

Table of Contents Feed for the Digital Edition of Conformity Magazine - September 2008

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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